A study of the kinetics of the oxidation of maleic hydrazide by ferricyanide in basic aqueous solution
by Robert Baxter Miller
A thesis submitted to the Graduate Faculty in partial fulfillment of the requirements for the degree of
MASTER OF SCIENCE in Chemistry
Montana State University
© Copyright by Robert Baxter Miller (1969)
Abstract:
Ferricyanide oxidizes maleic hydrazide in aqueous basic solution. The reaction was followed
spectrophotometrically by monitoring the disappearance of ferricyanide from the solution. Attempts to
study this oxidation without ferrocyanide initially present were unsuccessful due to the speed of the
reaction, but when excess ferrocyanide is initially present this reaction follows the following. rate law:
[Formula not captured by OCR] This kinetic expression suggests several possible mechanisms which
are discussed.
In p r e s e n tin g th is t h e s i s in p a r tia l fu lfillm e n t o f th e re q u ire m e n ts
for a n a d v a n c e d d e g re e a t M o n ta n a S ta te U n iv e rs ity , I a g re e th a t th e
L ib rary s h a ll m ake i t f r e e ly a v a ila b le fo r in s p e c tio n . I fu rth e r a g re e
th a t p e rm is s io n fo r e x te n s iv e c o p y in g o f th is t h e s i s fo r s c h o la rly
p u rp o s e s m ay be g ra n te d by my m ajo r p r o f e s s o r , o r, in h is a b s e n c e , by
The D ire c to r o f L i b r a r ie s . It is u n d e rs to o d th a t an y c o p y in g o r p u b lic a ­
tio n o f th is t h e s i s for f in a n c ia l g a in s h a ll n o t be a llo w e d w ith o u t my
w ritte n p e r m is s io n .
S ig n a tu r e _
D a te
x7S
J
/3 .
L
s
/9 ^ 9
A STUDY OF THE KINETICS OF THE OXIDATION OF MALEIC HYDRAZIDE
BY FERRICYANIDE IN BASIC AQUEOUS SOLUTION
by
ROBERT BAXTER MILLER
A t h e s is subm itted to the Graduate F acu lty in partial
fu lfillm en t o f the requirem ents for the d egree
of
MASTER OF SCIENCE
in
C hem istry
Approved
'6
H ea d , Major D epartm ent
Chairm an, Exam ining C om m ittee
D ean ^/Graduate D iv is io r ^
MONTANA STATE UNIVERSITY
B ozem an, M ontana
D ecem b er, 1969
. i ii
A cknow ledgm ent
I
w ish to e x p r e s s my a p p recia tio n to the fa c u lty o f the Departm ent
o f C hem istry for th eir u n stin tin g help and for th eir fin a n c ia l support
-through te a c h in g a s s is t a n t s h ip s .
To Dr. R. G eer I exten d my thanks for g u id a n ce and en cou ragem en t.
To my parents for th eir fin a n c ia l and. moral su p p ort, w ith out w h ich
th is t h e s is w ould not be p o s s i b l e , my d eep g r a titu d e .
TABLE OF CONTENTS
PAGE
VITA. ...........................................................
ACKNOWLEDGMENT
...
....................
TABLE OF CONTENTS ........................................
• LIST OF T A B L E S....................................... . . .
-LIST OF FIGURES
. . . . . . . . . . . . . . .
.
ii
. iii
.
iv
. vi
. v ii
ABSTRACT . .................... .................. ..................
.
ix
INTRODUCTION ........................................
.
I
A Partial H istory o f M a le ic H ydrazide
.
I
The F erri/F errocyanide System . . . . .
.
5
7
M eth od ology . . . . . . . . . . . . . . . .
.
10
■■Equipment ..................................... • . . . . ; .
.
10
M ethods . . . . . . . . . . . . . . . . . . .
.
14
C h em icals . . . . . . . . . . . . . . . . . .
.
18
RESULTS . . . . . . . . . . . . . . . . . . . . . .
.
20
.
20
Io n iz a b ility o f M a le ic H ydrazide . . .
.
21
Prelim inary R e a ctio n D ata . . . . . . . .
.
25
In itia l K inetic E x p e r im e n t s ................ .
.
25
P h o to ly sis Experim ent . . . . . . . . . .
.
32
EXPERIMENTAL....................
S p ectral Work
. . . . . . . . . . . . . . .
Q u a lita tiv e S a lt E ffects
. . . . . . . . .
32
LIST. OF TABLES
TABLE
I.
PAGE
A T yp ical R eaction W ithout Ferrocyanide Being
In itia lly P resen t . .............................. . . . . . . .
II.
.................... ...
26
A T yp ical R eaction W here a T en-Fold. E x c e ss o f
Ferrocyanide is O rigin a lly P resen t .................................................... .31
III.
. H ydroxide C oncentration V s . ke x p ............. ...
36
IV.
M aleic. H ydrazide M onoanion C oncentration V s . Ice x p .................. .38
• V.
Ferrocyanide C oncentration Vs... Square Root o f-th e
In v erse o f kexp
. . . . .
. . . .
. . . .
.. .. .. .. . . . .
AL
LIST OF FIGURES
PAGE
FIGURE
I . The V is ib le Spectra o f Ferricyanide and Ferrocyanide
.
8
2
.
11
Stopped. F low R e a c to r .............................. ................................ ..
3 . E le c tr ic a l C ircuitry o f Stopped Flow- Reactor . . . . . .
.. 13
4.. B eer's Law P lot o f F erricyanide . . . . . . . . . . . . . .
. 22
5 . Titration o f M a le ic H y d r a z id e ............. ...
. 23
6 . N atural Log o f F erricyanide V s. Time
. 27
.......................... .
7.. In verse F erricyanide V s . Time . ................................. . . <
.. 29
8 . In v erse F erricyanide V s . T im e, w ith Ferrocyanide
P resen t I n itia lly ........................................................... . . .
. 30
9 . kexp . V s .. H ydroxide . . . . . . . . . . . . . . . . . . . . . .
. 35
1 0. Icexp V s . M a le ic H ydrazide M onoanion . . . . . . . . .
. 40
11. In v erse Square Root O fk exp-V s . Ferrocyanide . . . .
. 42
1 2 . T ypical Stopped Flow R esu lts
...........................................
. 45
1 3 . keXp V s. M a le ic H ydrazide D i a n i o n ....................... ... .
. 49
1 4. M a le ic H ydrazide Tim es In verse ^exp - V s .
. In v erse M a leic. H ydrazide ...........................................
.■
. 5 1
v iii
FIGURE
: 15..
PAGE
H ydroxide Tim es
In verse ^exp-
V s. In v erse H ydroxide . . . . . . . . 52
1 6.
Evaluation, o f
= 0.0048 M .............................................
55
, 1 7.
E valuation o f
= 0.0028 M
56
..............................................................
1 8. T est for P o s s ib le F irst Order Ferrocyanide D e p e n d e n c e ............. . 57
19. E xploration o f P o s s ib le S a lt C orrection in V ariable
F errocyanide D ata .............................. ...................... ...
58
i%
■
A bstract
F erricyanide o x id iz e s m a le ic hydrazide. in a q u eou s b a s ic s o lu tio n .
The r e a c tio n .w a s fo llo w e d sp ectro p h d to m etrica lly by m onitoring the d i s ­
app earance o f ferricyan id e from, the s o lu tio n . Attem pts to stu d y th is
o x id a tio n w ith ou t ferrocyan id e in it ia lly p resen t w ere u n s u c c e s s fu l due
to the sp eed , o f th e r e a c tio n , but w hen e x c e s s ferrocyanid e is in itia lly
p r e se n t th is r ea ctio n fo llo w s the fo llo w in g , rate law:
d[F e(C N lg j]
dt
0.42 [ m h “] 2 [ o H^]2 [F e(C N )2 "]2
[O.OI + [MH"][OH~]] [F e(C N )4 ~ ]2
This k in e tic e x p r e s s io n s u g g e s ts several, p o s s ib le m echanism s, w hich are
d is c u s s e d .
INTRODUCTION
A Partial H istory o f M a le ic H ydrazide
M a le ic hyd razide (1,2-d ih y d r o -3 ,6 -p y r id a z in e d io n e) (I) has been
i
known s in c e 1875 . It fir st becam e o f com m ercial im portance when in
1949 S ch oen e and Hoffman noted th at it a lm o st c o m p le te ly in h ib ited
2
p lan t p lan t growth in tom atoes . It w a s la te r found th at alth ough it
stop p ed g r a s s e s from, grow in g, it did not a ffe c t certa in .o th er plan ts
su ch a s c o tto n . This m akes it an e ffe c t iv e herb icid e in. m ech an ized
farm ing.
B ec a u se o f m a le ic h y d ra zid e's com m ercial im p ortan ce, it has fr e 3
q u en tly b een in v e s tig a te d in a b io lo g ic a l environm ent . L ight, o x id a n ts ,
and m icroorganism s in the s o il are- a ll known to degrade m a le ic hydraz id e . The o b je c t o f th e p r e se n t k in e tic stud y o f the r ea c tio n b etw een
fe r r ic y a n id e , a o n e -e le c tr o n a b str a c to r ^ arid m a leic hyd razide w as to
help e lu c id a te th e m echanism or m ech an ism s by w h ich m a le ic hydrazide
i s o x id iz e d .
There are three p o s s ib le tautom eric forms o f m a le ic hydrazide ( la ,
Ib , I c ). In 1939 Arndt s u g g e ste d that the m a le ic h yd razide m o lecu le e x ­
i s t s prim arily in the e n o l form (Ib)^. This v ie w w as supported by M iller and
5 6
W h ite's ' com parative polarographic a n d .u ltr a v io le t stu d y o f v a r io u sly
7
su b stitu te d d e r iv a tiv e s o f m a le ic h y d r a z id e , and by O h a s h i1s and
K atritsky's
3
n u clea r m agn etic reso n a n ce s t u d ie s .
2
C lem en t^ '^ and Kealy^1 have both in v e s tig a te d the o x id a tio n o f
m a le ic h y d ra z id e . C lem ent o b serv ed that lea d te tr a a ce ta te o x id ize d
m a le ic hyd razide in a c e to n e at 0 ° C . He reported that th e rea ctio n m ix­
ture turns a s lig h t y e llo w -g r e e n tin t and g iv e s o ff n itro g en . When the
rea ctio n w as performed w ith an e x c e s s o f bu tadiene in m eth ylen e
ch lorid e a 76% y ie ld o f the D ie ls-A ld e r adduct (III) w a s reco v ered .
C lem ent co n clu d ed from h is exp erim en ts that the d ia zo q u in o n e o f m a le ic
hydrazide (II) is formed and that it is an e x c e lle n t d ie n o p h ile .
O -H
O
I
Ib
Pb(OAc)4 ^
II
Kealy** u sed th e m onoanion o f m a le ic hydrazide in h is w ork. The
p o ta ssiu m s a lt o f m a le ic hydrazide (IV) w as o x id iz e d by V-butyl hypo­
c h lo rite in a c e to n e at - 5 0 ° to - 7 7 ° C . Kealy found that th e em erald
3
green d iazoq u in on e w a s s ta b le at -7 7 ° C In s o lu tio n , but dim erized upon
warming to form 1,4 ,6 ,9 -te tr a k e to p y r id a z in o -(l,2 -a )-p y r id a z in e (V) (43%
y ield ) at 3 0 ° C . In b o ilin g w ater th is product d e c o m p o se s to m a leic
hydrazide and m a le ic a cid (VI).
o-
O
A
V
o
IV
ii
I
V -butylhypochlorite
N
- 7 6 ° to -5 0 ° C
>
warm to
O
N -H
IOO0 C
O -H
O
VI
V
He found that con ju gated d ie n e s (b u ta d ie n e , 2 ,3 -d im e th y lb u ta d ie n e , c y c lo p e n ta d ie n e , c y c lo h e x a d ie n e , and co u m a lic a cid ) react very
rapidly w ith th e d iazoq u in on e at -7 7 ° C in is o la b le y ie ld s o f approxi­
m ately 50%. About 6% o f the product from a ll o f the d ia zo q u in o n e r e a c ­
tio n s w as due to the attack o f w a ter, w hich is p resen t in reagen t grade
a c e t o n e , to g iv e m a le ic anhydride (VIII) and a dimer (VII).
4
Feurer and R ubinstein
12
tried to s y n th e s iz e " b ic y c lic
dim aleich yd razid e" (V) by treating m a le ic hydrazide w ith d ie th y l m aleate
anhydride in variou s s o lv e n ts and under variou s co n d itio n s but fa iled to
to g e t the d e sire d product. Attempts to brominate or ch lo rin a te the
carb on-carbon double bond o f m a leic hyd razide w ere u n s u c c e s s fu l.
They attribute the in a b ility o f th e se r ea c tio n s to p roceed to reso n a n ce
s ta b iliz a tio n in m a le ic h yd razid e.
S t e o s s l ^ ' ^ has reported that m a le ic hydrazide is p h o to -la b ile .
Aqueous neutral m a le ic hydrazide so lu tio n s w ere irradiated by an 8 5 w att H anovia lamp at 40°C through a Pyrex filter w h ich cu ts o ff a ll lig h t
b elo w 300 mp. W hen the reactio n so lu tio n w as stirred by a ir , w h ile
b ein g irradiated for 48 h o u rs, n itric a c id (12.5%), formic a c id (7.5%),
s u c c in ic a cid (11.8%), m a le ic a cid (8.3%), and fumaric a c id (22.6%) w ere
is o la te d ; w hen stirred by o x y g e n -fr e e n itro g en , the o n ly a c id ic product
w as s u c c in ic a cid in 26% y ie ld after 96 hou rs. H o w ev er, S t o e s s l re­
ported the p h o to ly s is o f the m onoanion to be im m easurably s lo w .
5
In ad d ition to. M ille r 's work con cern in g the correct tautom eric
form o f m a le ic h y d r a z id e , h e ^ a ls o stu d ied ,the polargraphic reduction
o f m a le ic h y d ra zid e. He found th a t, in s o lu tio n s w ith a pH o f less.-th an
tw o , he ob tain ed a tw o -e le c tr o n ch an ge a s e x p e c t e d , but ab ove p H 3.5
a o n e -e le c tr o n ch an ge w as o b se r v e d . In con ju n ction w ith th e above
work he found by an u ltra v io let stu d y and by d irect titra tio n a first
io n iza tio n , co n sta n t (pKg = 5.65), but w a s unable to find, a se c o n d io n iz a tio n c o n sta n t up to a pH o f 12. E p ste in , Hubbard, and Anson
I fi
, w h ile
working on the polargraphic oxid a tio n o f m a le ic hydrazide at a platinum
e le c tr o d e in 1.0 F sodium hydroxide so lu tio n ,(pH= 14), a ls o found .no
e v id e n c e for a d ia n io n .
The F erri-ferrocyan id e System
F erricyanide w a s c h o se n a s the o x id a n t s in c e it is ty p ic a lly a
o n e -e le c tr o n a b stra ctin g a g en t
17
. Its o x id iz in g p o ten tia l is not a ffec te d
by a ch an ge in the hydroxide co n cen tra tio n above a pH o f 7
18
, i t is
r ea d ily a v a ila b le , it h as b een u sed in many other o x id a tio n s tu d ie s ,
and it le n d s i t s e l f r ea d ily to sp ectrop h otom etric te c h n iq u e s s in c e it
o b e y s B eer's la w
19
.
F erricyanide is a fairly pow erful oxid an t w ith a h a lf c e ll p o ten tia l
o f -3 7 0 mV. S in ce very, lit t le rearrangem ent o f the lig a n d s is n e c e s s a r y
Fe(CN)g"
—>
Fe(CN) g~ + e
. g = -3 7 0 mV
6
to go from the reduced, to th e o x id iz e d ’s ta te ,, the e lec tr o n ex ch a n g e r e ­
action. b etw een the two can be very f a s t .. The rate, c o n sta n t for the
reaction , is 9 x m o l e
* sec ^ at 3 2 °C ^ .
In s o lu tio n s more b a s ic than pH 7 n eith er ferricy a n id e nor Jierrocyan id e. i s protonated
. Ibers h a s found th at although, both, ferricyanid e
and ferrocyan id e form, com p lexes, w ith ferric and ferrous io n , th ey w ill
not form an a p p recia b le amount o f com p lex b e tw e e n ,th e m s e lv e s , and
th ey w ill o b e y B eer's la w a s the sum o f th e ab sorb an ce o f e a c h in d e ­
pend en t s p e c ie ^ .
F erricyanide h a s .a d is s o c ia t io n c o n sta n t o f 10
w h ile ferrocyanid e has a c o n sta n t o f IOi ^
Fe(CN)
36
4Fa(CN) 6g
#
-
F e3+ + 6 CN
K = 10 31
F e2+ + 6 CN"
K = IO"24
F erricyanide can o x id iz e a compound; in se v e r a l d ifferen t w ays
.
It can sim p ly a b stra ct an e le c tr o n , it can a c c e p t a hydrogen rad ical (H ”),
or in a fe w c a s e s it can. donate a cy a n id e rad ical (CN*):.
F e(C N )3 - +
Ie
*
F e(C N )4 -
F e(C N )3 " + H*
H Fe(C N )3 -
F e(C N )3 "
F e(C N )3 - ■
Thyagarajan
17
*
m ain tains that in th e c a s e o f p h e n o ls , the s o lv e n t
a b str a c ts a proton, and ferricyan id e rem oves an e lec tr o n from -the m o le­
c u le . S in ce th ey are sim ila r m o le c u le s , m a le ic hydrazide m ight rea ct by
7
the sam e m ech a n ism .a s a p h en o l. This m echanism w a s s e le c t e d over
the other tw o s in c e there is norm ally a pH d ep en d en ce on th e in itia l
sp e e d o f the r e a c tio n .. If a hydrogen, ra d ica l w ere a b str a c ted by the
ferricyan id e there w ould not be a pH d ep en d en ce sin c e, the deprotonation
o f th e ferricyan id e w ould not be the rate determ ining s t e p . The donation
o f the c y a n id e ra d ica l has o n ly b een p o stu la te d w ith fiv e coordinate
rea cta n ts
18
.
H ow ever,.1it is thought th at a bridging cation, m ight f a c ili-
ta te the transfer o f an. e lec tr o n
20
.
F erricyanide forms a bright y ello w , s o lu tio n , w h ile ferrocyanide
forms a p a le y ello w , so lu tio n a t the sam e co n cen tra tio n . Their sp ectra
(F ig . I) sh o w a- Xmax at 420 mp w ith e = 1.04x10^ ji m ole *cm 1 for ferri­
cy a n id e and. a Xmax a t 320 mu w ith e = 2.90. jl m ole *cm 1 for ferro cy a nid e
.
This d iffe re n c e in .e x tin c tio n c o e f fic ie n t at 420 mp. a llo w s the
d isa p p ea ra n ce o f ferricyan id e to be fo llo w e d sp e ctro p h o to m e tr ic a lly .
M eth od ology
The p seu d o order tech n iq u e w a s c h o s e n .to stu d y the k in e tic s of.
the o x id a tio n o f m a le ic hydrazide by fe r r ic y a n id e . This, tech n iq u e is to
hold a ll co n cen tra tio n s o f rea cta n ts e x c e p t one in la rg e e x c e s s o f the
sto ic h io m e tr ic amount w h ich e ff e c t iv e ly h old s c o n sta n t the co n cen tra ­
tion, o f a ll the rea cta n ts e x c e p t th at one . Since, it is the d isa p p ea ra n ce
o f ferricyan id e w h ich is fo llo w ed sp ectro p h o to m etrica lly , the ferricya­
nid e concentration, is. the one. w h ich is a llo w e d to v a r y w ith tim e.. The
.
8
FIGURE I
THE VISIBLE SPECTRA OF FERRICYANIDE AND FERROCYANIDE
M = 5.0 xlO 4, |i = 0 .6 5 , I cm c e ll s
9
m a le ic hyd razide is kept at 2 5 0 -fo ld e x c e s s , and the hydroxide is kept
a t a 2 5 0 -fo ld e x c e s s in the c o n c en tr a tio n .r a tio s w h ich are u s e d .in .a
ty p ic a l r ea c tio n .
EXPERIMENTAL
Equipment
The in itia l u lt r a v io le t -v is ib le sp ectra w ere o b tain ed .with a
Beckman. DK-2 ratio recording spectrop hotom eter (m odel #129.02) and a
pair o f Beckman, m atched 1-cm s ilic a c e l l s (se r ia l # 4 6 0 2 0 ). Later v is ib le
sp ectra w ere ob tain ed w ith a Cary recording spectrop hotom eter (m odel 14)
u sin g B eckm an.1-cm Pyrex c e ll s (m odel # 7 5 1 5 2 ).
The r e la tiv e ly s lo w k in e tic exp erim en ts (data recorded, for periods
greater than. 2 m inutes) w ere carried, out in a. Gilford 2000 v i s i b l e /
u ltr a v io le t m u ltiple sam p le ab sorb an ce recorder at a fix e d w ave len g th
o f 410 m|a. The tem perature o f the c e ll compartment w a s h eld co n sta n t at
25.0°C by a Bronwill S c ie n tific In d u stries w ater b ath, e le c tr ic h ea ter,
and e le c tr ic pump com b in ation . Four m atched P y ro cell Pyrex c e lls
(m odel #102 6) w ith a 1-cm path, le n g th and a 5 -mm path w idth w ere u sed
in .th e in itia l exp erim en ts w ith th e Gilford. 2 0 0 0 . Due to th e c e lls '
narrow w id th , ad eq u ate m ixing w as not obtained; th er e fo re , a ll o f the
q u an titative, r e s u lts w ere ob tain ed u sin g four m atched Beckman, (m odel
#75152 Pyrex c e ll s w ith I cm x I cm. c r o s s s e c t io n s .
The fa ste r k in e tic experim en ts w ere carried out u sin g a stopped.
27
flow reactor o f o rig in a l d e s ig n but fo llo w in g the p r in c ip les o f C hance . .
The reactor (F ig . 2) i s m e c h a n ic a lly c o n n e c te d to a.Beckm an. DU quartz
sp ectrop h otom eter. The tu n g sten lig h t s o u r c e , a GE 23 -3 1 b u lb, is
A, b a c k f ill s y rin g e
B, r e a c ta n t r e s e r v o ir
C , m ix in g c h a m b e r
D , o p tic a l c e ll
E, s to p c o c k
F z h y d ra u lic p lu n g e r
G z c o n s ta n t te m p e ra tu re w a te r
.
r e s e r v o ir
FIGURE 2
STOPPED FLOW REACTOR
12
pow ered by an 85 am p-hour 6 v o lt tractor battery w hich i s trick le
charged w hen not in u s e . The m onochrom atic lig h t from the Beckm an DU
p a s s e s , through the r e a c t io n .c e ll, and str ik e s the. p h otocath od e o f a RCA
931A p h otom u ltip lier tu b e . The s ig n a l from the p h otom u ltip lier is a m p li­
fied by a Philbrick EP55AU op era tio n a l am p lifier and is fed to a
T ektronix type 561A o s c i l l o s c o p e . The a s s o c ia te d , e le c tr o n ic c ircu ity is
show n in F ig. 3 . The o s c illo s c o p e , is triggered by a 3KHz square w ave
from a H eathkit IG -82 s in e -s q u a r e w a v e g en era to r. A .m icrosw itch a q ti- •
v a ted by the handle o f th e hydraulic s y ste m sta rts and. sto p s the tr a c e .
The tra ce is recorded by a Tektronix 016-231 camera u sin g P olaroid .type
3000 film . • W ater from, a co n sta n t tem perature bath flo w s around the
c e l l and syrin ge; th is sy ste m is pow ered by a 95 w att cen trifu g a l pum p.
The tem perature o f the sy ste m is co n tro lled by a P h ila d elp h ia S c ie n tific
G la s s Company m odel SW-912 mercury c o n ta c t therm om eter w hich a c t i­
v a t e s .a S c ie n tific Kit Company s o lid s ta te r ela y (m odel 300) w hich in
turn co n tro ls a 250 w att W estin g h o u se Brooder-Lite. h eat lam p. The
w ater in the main bath is a g ita ted by an. e le c tr ic motor driven p rop eller.
A Beckman m odel 72 pH m eter w ith Sargent (3 0070-10) lo w s a lt
e ffe c t g la s s e le c tr o d e s w as u sed for pH m ea su rem en ts.
67K
I----- 'AWv
.02 Uf
S o u rce
j
R eaction
V o ltag e
oscilloscope
O ffs e t
C ham ber
C am era
P h o to m u ltip lie r
H y d ra u lic A c tu a to r
S w eep
T rig g er
FIGURE 3
ELECTRICAL CIRCUITRY OF STOPPED FLOW REACTOR
14
' M ethods
In. the titra tio n s a m easured amount o f eith er sodium hydroxide or
hydrochloric a c id in e x c e ss: to the sto ic h io m e tr ic amount w a s added to a
w eigh ed .am ou n t o f m a le ic hydrazide . The sto ich io m etry w a s b a sed on
the assu m p tion that m a le ic hydrazide is am photeric and co u ld beh ave a s
eith er a d ia c id or a m on obase w ith in th e range o f a c id or b a s e c o n c e n ­
tration, e x p e rim e n ta lly -a v a ila b le . This so lu tio n .w a s m a g n e tic a lly stirred
, and titrated w ith the o p p o site sta n d a rd ized rea g en t. The pH o f the s o ­
lu tio n w as m onitored w ith a Beckman pH m eter.
M ost ab sorp tion sp ectra w ere ob tain ed on the: Beckman D K -2. The
instrum ent w a s turned on one hour b efore u s e . The s e n s it iv it y control
w a s s e t a t about 50 and th e time, c o n sta n t a t 0 .2 . The c h e m ic a ls w ere
w e ig h e d to the n e a r e st m illigram on a M ettler s in g le pan b a la n ce and
. d is s o lv e d q u a n tita tiv ely , in volu m etric f la s k s . The Beckman. I cm
2
c e ll s
e a ch required about 3 ml o f so lu tio n to fill them . The sp ectra o f s o lu ­
tio n s o f p o ta ssiu m ferricyan id e a n d .p o ta ssiu m ferrocyahide w ere taken
by fillin g , the sam p le c e ll w ith a s o lu tio n .o f known m olarity o f the
c h e m ic a l. The in itia l q u a lita tiv e k in e tic sp ectra w ere tak en by m ixing
; 1.0 ml o f 0.30 M sodium hydroxide w ith 1.0 ml o f 0.03 M m a le ic hydrazide
and then adding 1.00 ml o f 0.003 M ferricyan id e to th is s o lu tio n . The
so lu tio n s, w ere scan n ed , from 700 m|_i to 400 mfl., M a le ic hyd razide a b ­
sorb s so stro n g ly b e lo w 400 mp. th a t, e x c e p t for v ery lo w co n cen tra tio n s,
s o lu tio n s are v ir tu a lly opaque to- u ltr a v io le t lig h t . The instrum ent w as
15
a llo w e d to s c a n .fa ir ly q u ick ly (900 m n/m in) to w here ferricyan id e's. a b ­
sorb an ce sta rts (470 mu) and then th e scan, rate w a s s lo w e d down
(200 m |j/m in) for the r e s t o f the s c a n . The blank w as e ith e r d is tille d
w ater or, in som e c a s e s , th e products o f rea ctio n w h ich had the sam e
in itia l c o n d itio n s .
The ea rly spec.trop ho tome trie work w a s rep ea ted .o n a Cary 14 r e ­
cording u lt r a v io le t -v is ib le sp ectrop h otom eter. The Cary 14 w a s operated
w ith the sc a n sp e e d at X20 (60 m p/m in) and the sc a n d irectio n a lw a y s
toward shorter w ave le n g th . In the Cary 14 experim en ts the io n ic
stren gth o f the sa m p les w as kept c o n sta n t at y.= 0.65 by the add ition o f
sodium c h lo r id e .
The G ilford 2000 w as u se d to m onitor the m ajority o f the k in e tic
e x p e r im e n ts. The m achine w as turned on for an hour and a llo w ed to
reach thermal eq u ilib riu m . It w as then, a d ju sted to read fu ll s c a le on
it s recorder for th e d e sir e d range in a b so rb en cy u n it s , u s u a lly 0.00 to
I. OOau. This required th at the s l i t width, be s e t from 0.06 to 0.08 mm. A
blank w as o b serv ed a t variou s tim es throughout the exp erim en ts to
c h e ck th e drift o f the instrum en t. It proved to be v ery s t a b le . In the
ea rly exp erim en ts w ith the I cm x 0.5 cm c e l l s , 0.50 ml o f b a se w as added
to the sam e amount o f m a le ic hydrazide so lu tio n w ith H am ilton 1.5 ml
and 500 pi s y r in g e s . T h ese sy rin g es sh ou ld d e liv e r reproducibly to at
l e a s t + 0.01ml an d , in p r a c tic e , w ere good to about 1%. The m a leic
hyd razide r ea ctio n so lu tio n w a s a llo w e d to s it for about 15 m inutes in
16
order to approach .thermal equilibrium w ith the c e ll cham ber. The cham ­
ber w as kept at a c o n sta n t tem perature by c irc u la tin g w ater from a w ater
bath a t 2 5 .0 °C . At th is tim e 0.50 ml o f ferro /ferricy a n id e so lu tio n w as
th en in je c te d into the c e l l . O rig in a lly it w a s thought that the. a g ita tio n
c a u se d by the fo rcefu l a d d itio n .o f th is so lu tio n , w ould g iv e adequate
m ix in g , but unfortun ately str a tific a tio n w a s o b serv ed in a few c a s e s ,
w h ich w as probably a c ce n tu a te d by the d iffe r e n c e s in d e n s itie s o f the
s o lu tio n s . Due to th is la y e r in g , the tech n iq u e w a s ch an ged s lig h tly .
Larger c e l l s (I cm x I cm) w ere u s e d , w hich required an in c r e a s e in the
volum e o f e a c h reactan t so that the to ta l volum e w a s 3 m l. The sodium
ch lorid e w a s added to th e rea ctio n so lu tio n o f som e o f th e experim ents
in order to keep the io n ic stren gth co n sta n t (p = 0 .65). U s u a lly the c o n ­
d itio n s w ere su c h th at 2.25 ml o f so lu tio n w hich co n ta in ed sodium
c h lo r id e , m aleic, h y d r a z id e , and sodium hydroxide w a s a llo w e d to reach
therm al equilibrium . (15 m inutes) and th en the fe r ric/ferro cy a n id e s o lu ­
tion w a s in j e c t e d . The so lu tio n w a s.th e n rapidly stirred w ith a sm all
Teflon "putter-shaped" stirrer about 3 in c h e s long before: the reaction
w as o b serv ed sp e c tr o p h o to m e tr ic a lly . The stirring op eration u su a lly
took under 15 s e c o n d s from the tim e o f in je c tio n ; Each r ea ctio n w as run
in tr ip lic a t e , s in c e there w as about a 3% random error in the r e s u lt s .
The m u ltip le sam p le handling feature o f th e Gilford 2000. w a s u sed to
record three exp erim en ts s im u lta n e o u sly , w hen the slo w e r rea ctio n s
w ere o b se r v e d .
17
The stop p ed flo w reactor w a s u se d for a ll o f the f a s t rea ctio n
w ork. The large c a p a c ity 6 -v o lt sto ra g e battery w a s a llo w e d to d i s ­
charge through the tu n g sten sou rce b u lb , and the b a ttery 's tr ic k le charger w a s rem oved . The square w a v e generator w a s turned to about
8 v o lts and about 3 KHz. The o s c illo s c o p e w a s turned on and a d ju sted
so .th a t the m icro sw itch stop p ed and sta rted the tr a c e . The sw e e p w as
s e t for 0.50 c m / s e c . The s c r e e n .Ium ination con trols o f the o s c illo s c o p e
w ere ad ju sted so th at a good pictu re w a s o b ta in e d . The op eration al
a m p lifier, the high v o lta g e su p p ly to the p h o to c e ll, and the w ater c irc u ­
la tin g pumps w ere turned o n . The s y ste m w as a llo w e d to com e to ther­
mal and e le c tr ic a l equilibrium for an hour. The gain o f th e o s c illo s c o p e
and zero v o lta g e o f f s e t w ere.th en a d ju sted so that a ground lin e ( i . e .
o s c illo s c o p e input shorted) w ould be 5 cm ab ove the lin e formed by a
zero p ercen t tr a n sm issio n sam p le and 5 cm. b elo w the lin e w hich repre­
sen te d a 100% tr a n s m is sio n . The 100% lin e u su a lly in v o lv e d a s lit
w idth o f about 0.38m m . The b a c k -fillin g sy rin g es w ere flu sh ed se v e r a l
tim es w ith r ea cta n ts w h ich w ere kept in a th er m o sta tic a lly controlled
(25.0°C ) w ater b ath . These, rea cta n ts had approxim ately eq u a l io n ic
stren gth s (|J = 0 .6 5 ). The sy r in g e s'w e r e fille d .with rea c ta n ts until the
plu ngers w ere snug a g a in s t the hyd rau lic driver. The o u tle t sto p co ck
w a s o p e n e d , the dark s lid e p u lled out o f the ca m era , and. the lig h t path
to the p h otom u ltip lier b lo c k e d . The cam era shutter w a s op en ed and the
o s c illo s c o p e w as triggered for one s w e e p . The lig h t path w as o p en ed .
f
18
the o s c illo s c o p e w a s tr ig g e r e d , and the hydraulic pump handle w as d e ­
p r e s s e d . After about fiv e tr a c es a c r o s s th e o s c il lo s c o p e , the sw e e p s
w ere sto p p e d , the sh u tter w as c lp s e d , and the dark s lid e w a s r e p la c e d .
The P olaroid picture w as d e v e lo p e d , c o a te d , and c a ta lo g u e d .
C h em icals
All rea c tio n s o lu tio n s w ere made w ith at le a s t d is t ille d w a te r ,
and m ost w ere made w ith dou bly d is t ille d w a ter. All c h e m ic a ls u sed
w ere o f reagen t grade q u a lity .
S in ce the sodium s a lt w as not rea d ily a v a ila b le , p o ta ssiu m ferricy a n id e w as u se d for a ll r e a c tio n s requiring ferric y a n id e . T hese
potassium , io n s w ere a ssu m ed to not a p p recia b ly a ffe c t th e rea ctio n rate
s in c e the p o ta ssiu m con cen tratio n w a s a lw a y s lo w com pared to the
sodium c o n c en tr a tio n . B and A1s te c h n ic a l grade p o ta ssiu m ferricyanide
w a s r e c r y sta lliz e d three tim es from w ater and air dried b efore u sin g .
The sodium ferrocyanid e w a s M a th e so n , C olem an, and B e ll's reagent
g r a d e . Sodium ch lorid e w a s M a llin ck ro d t1s a n a ly tic a l rea g en t grade .
The sodium hydroxide w as ob tained from se v e r a l d ifferen t s o u r c e s . The
prelim inary experim en ts u sed A c cu lu te ® so d iu m hydroxide w hich w as
d ilu ted to the d e sire d m olarity. In further e x p e rim en ts,. F ish er S c ie n ­
tif ic C o .'s certified , sodium hydroxide w a s u s e d , eith er from an 0.800 M
P o ly -P a c ® or from 1.00 M g a llo n p la s t ic f l a s k s . In the sto p p ed flow
19
exp erim en ts 1.00 M sodium hydroxide so lu tio n s w ere prepared from B&A
reagen t grade sodium hydroxide p e l l e t s .
The m a le ic hydrazide w as ob ta in ed from se v e r a l d ifferen t s o u r c e s .
Some w a s the product o f th e rea ctio n o f m a le ic anhydride w ith hydrazine
s u lfa t e .. This w a s r ec r y sta lliz e d , three tim es from w a ter. The r e st w as
eith er p u rch ased from C ity C hem ical Company o f N e w Y ork-(techn ical
grade) and r e c r y s ta lliz e d three tim es or it w as p u rch ased from Sigma
C hem ical Company (a n a ly tic a l grade) and r e c r y s ta lliz e d t w i c e . •
RESULTS
S p ectral Work
. . .
The v is ib le spectrum o f a 5 .0 0 x 1 0
^
M aqu eou s so lu tio n o f p o ta s ­
sium fe r r ic y a n id e , recorded by a Beckman DK-2 sp ectrop h otom eter,
3
*”1 “1
sh ow ed a Xmax at 408 mp w ith an e o f 1 .0 5 x 1 0 % m ole cm
The a c ­
cep ted v a lu e has a Xmax a t 420 m|J w ith an e o f 1.04 x 10^ j?, m ole ^cm
The spectrum o f a 5 .0 0 x 1 0
-4
M aq u eou s so lu tio n o f p o ta ssiu m ferroc y a ­
nid e sh ow ed an e =10 a t 400 mp.. W hen p o ta ssiu m ferricyan id e so lu tio n
w as made 0.1 M in sodium hydroxide n eith er the Xmax nor the absorption
c o e ffic ie n t w as ch anged compared to th e o rig in a l sp ectru m . A spectrum
_3
o f 1 .00x1 0 M p o ta ssiu m ferricyan id e so lu tio n v e r su s 1 .0 0 x 1 0 M
p o ta ssiu m ferrocyanid e so lu tio n sh o w ed a maximum at 410 mp,. At a la ter
d ate th e s e data w ere check ed , on a Cary 14 sp ectro p h o to m eter. It w as
found that the p o ta ssiu m ferricyan id e so lu tio n a c tu a lly a b sorb s m ost
stro n g ly a t 420 mp w ith an e = 1.02 XlO0J^ m ole
sec
(F ig . I ) . The
ferrocyanid e spectrum and the ferricyan id e v e rsu s ferrocyan id e sp ectra
sh ow ed sim ilar d iffe r e n c e s . T h ese d iffe r e n c e s are a sc r ib e d .to an error
in the ca lib ra tio n o f the Beckman D K -2 . All o f the exp erim en tal data
w ere c o lle c te d a t 410 mp. This w as c lo s e enough to the optimum point
th at good r e s u lts w ere o b ta in e d .
In. order to determ ine the a p p lic a b ility o f Beer1s la w to ferricya­
nid e at 410 mp and to make sure th at the G ilford 2000 spectrop hotom eter
i s lin ea r at th at w a v e le n g th , a B eer1s la w stu d y w as made o f p o ta sssiu m
21
ferricyan id e at 410 mp. u sin g the m ethod o f R e ille y and Saw yer
23
. The
gain ratio o f the G ilford 2 0 0 0 , th e instrum ent in w h ich m ost o f the
k in e tic exp erim en ts w ere carried o u t, w a s varied d epend ing on the c o n ­
cen tration o f potassium , fe r ric y a n id e, w h ich varied from 4 .0 0 x 1 0 ^ M to
1.50x10
-5
M , in order to m inim ize the error in reading the graph and
m axim ize th e p o s s ib le instrum ent e rro r.. The io n ic stren gth w as kept
co n sta n t (p, = 0.2 5 M) w ith sodium ch lo rid e and the tem perature o f the
w ater bath w as s e t at 25.0 °C . W ithin experim en tal error, there w as a
lin ea r r ela tio n sh ip at 410 mu (s e e F ig . 4 ).
Io n iz a b ility o f M a le ic H ydrazide
S in ce a ch an ge in. the pH ab ove pH 7 should not a ffe c t the o x id a ­
tio n p o ten tia l o f the ferri/ferro cy a n id e sy ste m as lo n g a s a ll o f the
lig a n d s rem ain com p lexed to the iro n , the o n ly rea cta n t in the sy stem
w h ich cou ld be pH d ep en d en t is m a le ic h y d ra z id e . A stu d y o f the
io n iz a b ility o f m a le ic hyd razide w a s therefore undertaken. M a leic
hydrazide w as titrated w ith a c id in the p r e se n c e o f e x c e s s b a se (F ig . 5)
and w ith b a s e in th e p r e se n c e o f e x c e s s a c id . M a le ic hydrazide in. its
neutral s ta te is o n ly s lig h tly so lu b le in w ater at room, tem perature. It
w ill d is s o lv e a p p recia b ly in eith er strong a c id (4 to 8 M HC1) or in b a s e ,
M a leic hyd razide w ill q u ite e a s ily g iv e up one proton (pKa = 5.63) and,
s in c e it d is s o lv e s in strong a c id , w ill probably a c c e p t a p roton . There
is a p o s s ib ilit y th at m a le ic hydrazide w ill a ls o g iv e up a sec o n d proton .
22
o
FIGURE 4
BEER'S LAW PLOT OF FERRICYANIDE
0.020 m o le s o f N aO H
0.01842 m o les o f m a le ic h y d ra z id e in
0.040 m o les o f HaOH
5
10
ml o f 1.0 M HCl
FIGURE 5
TITRATION OF MALEIC HYDRAZIDE
24
M ille r 's v alu e^ for the m onoanion pKa o f 5.65 a g rees q u ite c lo s e ly w ith
. the exp erim en tal v a lu e from th is work o f 5.63. M iller w a s not a b le , by
u ltra v io let s p e c t r o s c o p y > p olarograp h y, or a c id b a se titr a tio n s , to find
e v id e n c e o f the m a le ic hydrazide d ia n io n up to a pH o f 12.5.
in order to determ ine if a s e c o n d io n iz a tio n w as occurring in the
exp erim en tal range o f hydroxide co n cen tra tio n s w h ich w ere u sed for the
k in d e t ic s , a spectrop h otom etric in d ica to r stu d y w as tried u sin g the
m ethod o f R e ille y and Saw yer
24
. The. in d ica to rs in v e s tig a te d and their
pH ran ges w ere 1,3,5-trin itro b en zen e (12 to 14), C layton y e llo w (12.1 to
13.2), and 4 -a m in o -l-n a p h th a le n e s o lfo n ic a c id (12 to 14). The la s t com ­
pound, h o w ev er, is a flu o r e sc e n t in d ica to r and cou ld o n ly be u sed w ith
a sp e ctro flu o r im e ter . U n fortu n ately, one w a s not a v a ila b le . C layton
y e llo w 's co lo r ch an ge i s due to a co m p lex change in both w a v elen g th
and e x tin c tio n c o e f f ic ie n t s , and it probably in v o lv e s more than ju st tw o
s p e c i e s . This elim in a ted a ll o f th o se tried e x c e p t 1,3,5-trin itro b en zen e
( T . N . B . ) a s a p o s s ib le u se fu l in d ica to r. The literature confirm ed that
the spectrum o f T . N . B.. v a r ie s sm oothly up to 0.6 M hydroxide c o n c e n tration
25
. H o w ev er/ w hen e x c e s s -m a le ic hydrazide and T . N . B . were
m ixed togeth er in a b a s ic aqu eou s s o lu tio n , the Xmax w a s sh ifted to a
lon ger w a v elen g th and th e so lu tio n absorbed more lig h t than-the s ta n ­
dard d id . This, in d ic a te d that a c o m p le x -b e tw e e n ,T .N .B . and m aleic
hydrazide i s form ed. T herefore, a s e c o n d io n iz a tio n c o n s ta n t, if it
e x i s t s , cou ld not be found w ith th e s e in d ic a to r s. Another m ethod.
25
w h ich u s e s n u clear m agn etic r eso n a n ce (NMR), w a s ruled out b e c a u se
the protons ex ch a n g e too rapidly^'
Prelim inary R eaction D ata
C u rvettes co n ta in in g a so lu tio n w h ich w a s 1.0 x10
-3'
M in fe r ric y a -
n id e , 0.10 M in hydroxide and 0.010 M in m a le ic hyd razide w ere p la ced in
a Beckman D K -2 . The instrum ent sca n n ed the ab sorp tion o f the so lu tio n
from SOOmp to 350 mp at se v e r a l p r e -s e le c te d tim e in te r v a ls . Examina­
tion o f th e s e sp ectra confirm ed that the reaction, cou ld be fo llo w ed at
410 mp. The r ea ctio n rate w as s lo w at th e s e c o n c e n tr a tio n s , requiring
20 hours to becom e 90% c o m p le te . W hen a sm a ll amount o f 0.1 M sodium
hydroxide w a s a d d e d , th e rea ctio n rate in c r e a se d co n sid e ra b ly so that
the r ea ctio n w as 97% co m p lete a fter 4 hours . '
In itia l K inetic Experim ents
_3
A rea ctio n mixture w h ich w as in itia lly 1.00x10
LO-OxlO
__2
.
M in fe r r ic y a h id e ,
M .in m onoanion o f m a le ic h y d ra z id e , and 0.2 50 M in sodium
hydroxide Was m onitored at 410 mp and the absorbance v e r su s tim e w as
recorded by a G ilford 2000 (s e e Table I ) . If pseu d o fir st order k in e tic s
are fo llo w e d by th is r e a c tio n , a p lo t o f ln(At - A j v e r su s tim e should be
lin ea r s in c e the ab sorb an ce is a ssu m ed to be proportional to .th e ferric y a n id e co n cen tra tio n . (Here A^ is a b sorb an ce at tim e t and A00 is
26
TABLE I.
■A TYPICAL REACTION WITHOUT FERROCYANIDE BEING INITIALLY PRESENT
Time
A bsorbency
,Ferricyanide
(s e c o n d s)
( A ,- A J
M x lO 4
7.5
0.690
7.45
9.0
. 0.670
7.24
12.0
0.620
6.70
18.0
0.550
5.95
24.0
0.500
30,0
0.468
5.06
42.0
0.414
4.48
54.0
0.378
4.08
66.0.
0.352
3.81
.78,0
0.330
3.56
96.0
0.301
3:2 6
120.0
0.174
2.96
156.0
0.242
2.62
192.0
0.222
2.40
240.0
0.199
2.15
,
.
Sodium H ydroxide
. 5.40
= 0.2 50 M
M onosodium m a le ic hyd razide = 0.00330 M
P otassiu m Ferricyanide
= 0.00100 M
ab sorb an ce at end o f r e a c tio n .) H o w ev er, a graph.of this, nature did not
g iv e a good stra ig h t lin e fit for the experim en tal data (F ig . 6 ).
■S in ce th e recording o f the o rig in a l data w as roughly sim ilar in form
to a hyperbola and sin c e, the oxidation, o f m a leic hydrazide should require
27
-7.2
-7.4
co to
\
o
-7 .6
- I
CU
S
-7.8
-
8.0
-
8. 2 -
-8.4
60
120
180
.240
T im e, s e c .
FIGURE 6
NATURAL LOG OF FERRI CYAN IDE VERSUS TIME
N aO H = 0.250 M , M a le ic H ydrazide = 0.033 M , KgFe(CN)^= 0.00100 M,
T= 2 5.0°C
28
a minimum o f a tw o -e le c tr o n o x id a tio n , a p seu d o s e c o n d order p lo t o f the
data w as m a d e. That i s , the recip ro ca l o f (At -A oo) w a s p lo tted v e r su s
tim e (F ig . 7 ).
This p lo t w as curved during th e fir st part o f th e rea ctio n but b e ­
cam e a sy m p to tic to a stra ig h t lin e a s th e rea ctio n neared, co m p letio n .
This r e su lt s u g g e s ts th at som e rate lim itin g factor o f the rea ctio n
c h a n g e s a s the rea ctio n p ro ceed s and th at th e .r e a c tio n approaches
p seu d o seco n d .o rd er in ferricyanide. w hen it nears c o m p letio n .
S in ce the o n ly c h em ica l co n cen tra tio n s w hich w ere e ffe c t iv e ly
ch an gin g in the reactin g mixture w ere th e co n cen tra tio n s o f ferricyanide
and th e p r o d u c ts, i . e . ferrocyanid e and th e o x id a tio n products o f m a le ic
h y d ra zid e, it w as a ssu m ed that the ch an ge in the co n cen tra tio n o f one or
more o f th e s e w as a ffe c tin g the r ea ctio n r a te . If ferrocyan id e is in v o lv ed
in a r ev e r sib le s te p (s) prior to the k in etic , s lo w s te p , then the rea ctio n
w ould be an in v e r se order in ferro cy a n id e. T herefore, th e.r e a ctio n m ix -2
ture w a s made 1 .00x10 M in ferrocyanid e (in ad d ition to the origin al
reactan t c o n cen tra tio n s) and w as fo llo w e d sp e ctro p h o to m e tr ic a lly „ W hen
the data o f th is rea ctio n (Table II) w ere p lo tted a s a p se u d o seco n d order
r e a c tio n , an e x c e lle n t straigh t lin e fit w as o b ta in e d .(F ig . 8 ).
29
T im e, s e c .
FIGURE 7
INVERSE FERRICYANIDE VERSUS TIME
N aO H = 0.250 M , M a le ic H ydrazide= 0.033 M , K^Fe(CN)fi= 0.00100 M 1
T = 2 5.00 C
30
slo p e
T im e, s e c .
FIGURE 8
INVERSE FERRICYANIDE VS. TIME, WITH
FERROCYANIDE PRESENT INITIALLY
NaOH = 0.25 M , M a leic H ydrazide = 0.05 M
F e ( C N ) = 0.0100 M , Fe(CN)J?" = 0.00100 M , T = 25.0°C
31
TABLE II.
A TYPICAL REACTION WHERE A TEN-FOLD EXCESS OF FERRO CYANIDE
IS ORIGINALLY PRESENT
Time
A bsorbency
F erricyanide
(s e c o n d s)
(At - A j
M x lO 4
15
0.810
8.75
30
0.660
7.14
45
0.585
6.32
60
0.530
5.73
75
0.475
5.14
90
0.430
4.66
0.400 .
4.32
120
0.370
4.00
135
0.345
3.73
150
.0.320
• 3.46
165
0.305
3.30
180
0.290
3.14
210
0.260
2.81
240
0.235
2.54
. 105
Sodium H ydroxide
.
= 0.2 50 M
M onosodium M a leic H ydrazide = 0.050 M ■
Sodium Ferrocyanide
= 0.0100 M
P o tassiu m Ferricyanide
= 0.00100 M
32
P h o to ly sis Experim ent
In th e literatu re it has b een show n th at under certain, c o n d itio n s'.
m a le ic hyd razide un dergoes p h o t o l y s i s ^ ' T o c h e ck th e p o s s ib ilit y
that lig h t m ight be a ffe c tin g the rea ctio n r a te , three id e n tic a l rea ctio n
s o lu tio n s w ere a llo w e d to p roceed tow ards •eq u ilib riu m . under differin g
lig h t c o n d itio n s . The f ir s t , a c o n tr o l, w a s allow ed, to proceed, i n the
dark; the s e c o n d w as in the normal op erating environm ent o f co n sta n t
m onochrom atic lig h t o f 410 m|i; and th e third w a s e x p o se d to u ltra v io let
lig h t at the fu ll s l i t w idth o f the G ilford a t 300 mu, w here m a leic hydra*-.'
z id e is known to ab sorb .
All three o f th e rea ctio n ra tes w ere w ith in exp erim en tal error o f
e a c h oth er. This im p lie s that under the rea ctio n c o n d itio n s, u sed for the
k in e tic e x p e r im e n ts, 410 mu lig h t cloe's not a ffe c t the. rea ctio n r a te , and
th at probably lig h t in gen eral doe's not a ffe c t th e .r a te . S t o e s s l a ls o
found that the m on oanion, in co n tra st to neutral m a le ic hydrazide ,. d o e s
not a p p recia b ly p h o to ly z e
13
.
.
Q u a lita tiv e S alt E ffects
••
-.
S in ce the reaction appeared to in v o lv e the rea ctio n b etw een n e g a t iv e ly charged s p e c i e s , it w as e x p e c te d that s a lt e f f e c t s m ight be
9c
a p p recia b le . A few q u a lita tiv e exp erim en ts sh ow ed th at a s the io n ic
stren gth in c r e a se d so did the r a te . U n fortu n ately, e v e n th e v a ria tio n s on
th e D e b y e -H u c k e l la w becom e in a ccu ra te at high io n ic stren gth (> 0 .1 ).
.
33
For m u lticharged s p e c ie s th e situ a tio n is e v en more c o m p lic a te d . There­
fo r e , to sim p lify m a tte r s, a c o n sta n t io n ic stren gth (^ = 0.65) w as m ain­
ta in ed ,throughout m ost o f the rem ainder o f th e exp erim en ts by the
ad d ition o f sodium c h lo r id e . In the v a ria b le ferrocyanid e experim en ts the
io n ic stren gth w as unfortunately a llo w e d to vary from 0.60 M to 1.00 M .
. U n ex p ected A bsorbances
It w as n o tic e d th at at the sta rt o f the rea ctio n the ab so rb a n ce o f
the r ea ctio n m ixture a t 410 mp was greater by up to 10% than the sum o f th e
a b so rb a n ces o f the r ea c ta n ts a lo n e . L ik e w is e , the a b sorb an ce o f a com ­
p le te d r ea ctio n mixture w a s greater than the e x p e c te d v a lu e , assu m in g
a ll fe r r ic y a n id e .is con verted to ferro cy a n id e. There are se v e r a l p o s s ib le
ex p la n a tio n s w h ich cou ld a cco u n t for e ith e r o f th e se o b s e r v a tio n s . The
r ea cta n ts cou ld form a com p lex to g eth er w h ich absorbs, in th is r e g io n , a
.reaction, in term ed iate (su c h a s the d ia zo q u in o n e w h ich is known to be
h ig h ly colored) co u ld be ab so rb in g , a rea ctio n product .(Dr, R. G eer has
is o la te d from a sim ila r rea ctio n mixture a dimer w h ich is y e llo w in b a s ic
so lu tio n ) cou ld be a b so r b in g , or (s in c e m a le ic hyd razide ca n .b e reduced
a s w e ll a s o x id iz e d and s in c e ferrocyanid e is p re se n t in e x c e s s ) m a leic
hyd razide m ight o x id iz e ferrocyanid e to fe r r ic y a n id e . This la s t p o s s i ­
b ility w a s te s te d by m onitoring a reaction .m ixtu re w h ich w a s standard
e x c e p t that th e ferricyan id e w as o m itted . T he.absorb ancy o f th is s o lu ­
tion at 410 mp. did not ch an ge w ith tim e and w as equal to the sum. o f the
34
a b so rb a n ces o f th e c o n stitu e n ts, o f th e s o lu tio n . This e f f e c t iv e ly ruled
out the p o s s ib ilit y o f m a le ic hydrazide b ein g red uced by ferrocyanid e in
b ase.
K inetic D ependence, on H ydroxide
-
In order to a sce r ta in , if a r e la tiv e ly high co n cen tra tio n o f hydroxide
is n eed ed for th e r ea c tio n to proceed, or if the m a leic h y d fa zid e bein g in
th e m onoanion is the o n ly p rereq u isite > a rea ctio n w a s ,.tried w ith the s o ­
lu tion buffered a t a p H .of 9.00. After a p e r io d .o f 12 h o u r s, there w a s no
d e c r e a s e in th e ab sorb an cy at 410 m u. This in d ic a te d that a very b a s ic
so lu tio n is n eed ed in. order for the rea c tio n to proceed;- At pH = 9 , more
th a n .99.9% o f the m a le ic hydrazide is in th e mono'ariion form .
S in ce it w as o b se rv e d in th e prelim inary work th at the hydroxide
co n cen tra tio n stro n g ly a ffe c te d the r ea ctio n r a te , ex p erim en ts w ere c o n ­
d u cted a t variou s hydroxide, co n cen tra tio n s ranging from 0.500 M to
0.0500 M (M = 0.65) ( s e e Table III). W h en .hydroxi.de w a s p lo tted a s a
p seu d o fir st order c o n s titu e n t a g a in s t the observed, rate c o n sta n t
([O H ■] v s keXp) (F ig . 9), the rea ctio n .o rd er w a s show n to. be fir st order
in hydroxide at higher c o n cen tra tio n s and a higher order,, probably s e c ­
o n d , a t low er c o n c e n tr a tio n s. There i s a p o s s ib ilit y th a t th e rea ctio n .
order d e c r e a s e s a t very high hydroxide c o n c e n tr a tio n s. The curvature o f
the graph cou ld be due to a d e c r e a s e in th e m a leic h yd razide m onoanion
p op u lation a t high hydroxide co n c en tr a tio n .
sec
35
[o H ~ ], Mx l O2
FIGURE 9
kexp.VERSUS HYDROXIDE
[Fe(CN)^"] = 0.0010 M , ^m aleic hyd razide m oncanionj - 0.050 M,
[F e(C N )^ " ]= 0.010 M , U= 0.65, T = 2 5 .0 °C
36
TABLE III.
HYDROXIDE CONCENTRATION VS. Kexp
^exp
-I
-I
X m ole s e c
[O H - ] , M
[OH ] , M .
^exp
-I ' -I
X m ole s e c
63.2
63.0
64.3
0.2167
0.450
57.7
60.5
58.1
0.1833
19.6
20.4
19.4
0.400
51.2
52.8
0.1500
0.350
42.7
46.1
44.4
14.2
14.0
14.6 ;
0.1167
,36.7
37.8
37.2
9.64 ■
9.44
9.60 '
0.0833
■4.50 •
■5.23
5.32
0.500
0.300
30.2
30.0
29.4
29.1
30.3
32.2
0.250
25.2
2 5.4
23.7
2.22
.2.11
2.08
0.0500
,
M onosodium m a le ic hydrazide
=' 0.500
P o ta ssiu m fe r r ic y a n id e
•= 0.00100
Sodium Ferrocyanide
= 0.0100
Sum o f sodium hydroxide and the
sodium chlorid e co n cen tra tio n
= 0.500
■
.
. K inetic D ep en d en ce on M a le ic H ydrazide C oncentration
A s e r ie s o f r e a c tio n s a t d ifferen t m a le ic hydrazide co n cen tra tio n s
ranging from 7 .5 0 x 1 0 ^ M to 5.0 x 1 0 0 M w ere run ( s e e T able IV). When
th e s e r e s u lts w ere p lo tte d , [MH ] v s ke x p , the r ea ctio n w a s found to be
fir st order in m a le ic hydrazide a t high m a le ic hydrazide con cen tration
and a higher order, p o s s ib ly s e c o n d , a t lo w m a le ic hyd razide co n cen tra ­
tion (F ig . 10). This stro n g ly in d ic a te s that th e rate lim itin g step c h a n g e s
w ith a ch an ge in e ith e r hydroxide or m a le ic .hydrazide c o n c e n tr a tio n . The
sim ila r ity b etw een the e ffe c t s o f the tw o r ea cta n ts s u g g e s t s that there
m ight be a rela tio n b etw een the tw o .
. K inetic D ep en d en ce on Ferrocyanide C oncentration
The la s t r ea ctio n v a ria b le in v e s tig a te d w as the ferrocyanid e de-r
p e n d e n c e . A s e r ie s o f s o lu tio n s w ith d ifferen t ferrocyan id e con cen tra —3
-2
tio n s ranging from 5 .0 x 1 0 0 M to 4 .5 x 1 0 M w ere a llo w e d to rea ct (s e e
T able V). W hen the ferrocyan id e co n cen tra tio n w a s p lo tte d v e r su s the
square root o f the in v e r se o f the exp erim en tal rate c o n s ta n t, a fairly
stra ig h t lin e fit w as ob tain ed at lo w c o n c e n tr a tio n s , but th e ferrocyanide
seem ed not to retard th e rate o f the r ea c tio n so stro n g ly at higher c o n centra t io n s . This la tte r e ffe c t (F ig . 11) cou ld eith er be due to a real
ch an ge in m echanism or it c o u ld .b e due to the ch an ge in io n ic strength
w h ich w a s not a d ju sted to the ch an gin g ferrocyanid e c o n c e n tr a tio n . The
io n ic stren gth varied from 0.60 to 1.00.
38
TABLE IV.
MALEIC HYDRAZIDE MONOANION CONCENTRATION VS. k _
[M H ~ ], M
exp
n
-I
-I
X m ole s e c
[M H " ], M
exp
. t m ole ^ sec ^
0.00750
1.33
1.51
1.32
0.0500
28.0
27.2
27.9
0.0150
4.23
4.59
4.77
0.0525
34.5
30.8
31.4-
0.01750
5.67
5.57
5.54
0.0550
32.0
31.2
0.0575
0.0225
8.88
8.05
35.7 •
36.5
36.0
0.0600
34.2
35.4
36.2
34.8
34.8 '
0.0275
12.1
12.1
11.7
0.0325
15.4
15.4
18.9
0.625
18.6
19.9
19.0
33.7
34.4
35.5
0.0650
20.9
20.6
21.1
37.8
37.9
0.0675
21.6
22.3
22.0
41.0
41.3
41.6
0.0700
0.0375
0.040
0.425
0.0450
25.2
23.8
23.6
41.7
41.7
43.3
45.9
46.2
■
39
TABLE IV (continued)
Ir
Kexp
M H "], M
0.0475
& m ole ^ sec *
26.2
27.0
28.2
Sodium hydroxide
=
Sodium ch lorid e
=
P otassiu m ferricyan id e . =
S o d iu m ferro cy a n id e
=
pxp
[m h ' L m
0.0750
0.250 M
0.250 M
0.00100 M
0.0100 M
I m ole ^sec
46.4
44.4
. 45.9
44.5
43.4
[Fe(C N )g ”] = 0.0010 M
[Fe(CN) g“] = 0.010 M
I
[NaOn] = 0.25 M
IJ = 0.65
T = 2 5.0°C
A.
O
4
5
[m a leic hydrazide monoanion] x IO2, M
FIGURE 10
kexp VERSUS MALEIC HYDRAZIDE MONOANION
7
41
. TABLE V.
FERROCYANIDE CONCENTRATION VS. SQUARE ROOT OF THE
INVERSE OF k
;■
■
. :
• ■ ^exp
[Fe(CN)Q - ] , M
£ m o l e 1s e c 1 0.0050
. 63.0
82.5
73.0
0.0075
35.3
41.6
40.0
. 21.0
21.1
22.2
0.0100
.
.0.0150
10.9
10.5 •
10.9
■
5.00
4.65
4.77 . . .
0.0225
3.2 6
3.13
3.10 '
0.0300
0.0375
. 2.37
2.34
0.0450
M onosodium m a le ic hyd razide
Sodium hydroxide
P o ta ssiu m fe r r ic y a n id e
Sodium ch lo rid e
.
. :.
=
=
=
=
' 2.13
2.11
. 2.20
0.0500 M
0.2500 M
0.00100 M
0.250 M
.
••
■
0.70h
0.60
'
; 0.40
fo q.0.30
[Fe(CN) g_] x IO2, M
FIGURE 11
INVERSE SQUARE ROOT OF kexp VERSUS FERROCYANIDE
43
Stopped F low R eactor
Prelim inary in itia l rate s tu d ie s w ith out ferrocyanid e in itia lly p r e s­
en t w ere tr ie d . T h ese exp erim en ts turned out to be a lm o st to ta lly
, irrep ro d u cib le. This w a s due to s e v e r a l d e fic ie n c ie s in .th e stop p ed flo w
reactor w h ich w a s u s e d .to fo llo w the fa s t in itia l r a te s . One o f the minor
d if fic u lt ie s w a s that a s u b s t a n c e p o s s i b l y ferric h y d ro x id e , kept c lo u d ­
ing th e w ind ow s o f th e o p tic a l c e l l . This cou ld be p a r tia lly clea red by
running 0.1 M hyd rochloric acid ,th rou gh the c e l l . The fo g g in g led to e a c h
s e r ie s o f runs requiring a w ider monochrom ator s l i t w idth than the pre­
c e d in g s e r ie s to maintain, th e sam e s ig n a l strength a t 100% tr a n sm issio n .
S e c o n d ly , there w a s a great d e a l o f s tr e s s on .b o th the sy rin g es .
an d .th e w in d ow s o f th e o p tic a l c e l l .. This c a u se d a sy rin g e to crack in
one c a s e and the c e ll w ind ow s to break lo o s e on s e v e r a l o c c a s io n s . The
c e l l w indow problem w as c a u se d by the fa c t th at the o rig in a l ep oxy c e ­
m e n ts, w h ich w ere u se d to s e a l the w ind ow s to the c e l l , w ere p a rtia lly
perm eable to w ater and w ould s w e ll, w eak en in g the b on d. T hus, any
e x c e s s p ressu re on the w ind ow s cou ld break the s e a l .
The third problem w a s that it w a s very d iffic u lt to keep the tw o
r ea cta n ts se g r e g a te d in th eir r e s p e c tiv e sy rin g es and tubing w h ile pre­
paring, for a run.
S in ce there w a s approxim ately a 2 0 0 -fo ld e x c e s s , o f m a le ic hydraz id e over the fe r fic y a n id e , ev en a s lig h t amount o f eith e r reactan t g e t ­
tin g into the o th er's se c tio n , w ould in v a lid a te .th e data from th at run.
44
S to p co ck s b etw een the r ea ctio n c e ll and the tw o s e t s o f reactants, w ould
have a lle v ia te d th is d iffic u lty .
The fourth problem w a s that the sto p p ed flo w reactor did not u se a
p o s itiv e stop s y s t e m . This le t th e r ea c ta n ts s lo w ly s e e p into the r e a c ­
tion c e ll after the flo w o f both sh o u ld .h a v e sto p p ed . This Would e f f e c t ­
iv e ly ruin the k in e tic data, from th at exp erim en t.
T h ese d if fic u lt ie s did not a llo w reproducible data to be taken w ith
th e stop p ed flo w r e a c to r . (S ee F ig . 12 for ty p ic a l r u n s.)
45
A= 0% tr a n sm issi on lin e
B = a b so rb a n ce o f reaction
mixture
% T ransm ission
C = co n tin u a n ce o f B
in itia l [Fe(CN)g™] = 7 .5 x 1 0 4 M
A= 0% tr a n sm issio n lin e
B= a b sorb an ce o f rea ctio n
mixture
% T ran sm ission
C = co n tin u a tio n o f B
D = conti nuation o f C
Tim e, s e c .
in itia l [F e(C N )g '] = 3.3 x 1 0 4 M
FIGURE 12
TYPICAL STOPPED FLOW RESULTS
M a leic H ydrazide M onoanion = 0.05 M , N aO H = 0.25 M ,
N aC l = 0.25 M , T = 25.0°C
DISCUSSION
Summary o f Experim ental R esu lts
At the co n cen tra tio n s (m a leic h yd razide m onoanion = 5 x 1 0
-2
M,
-3
-2
ferricyan id e = 10 M , ferrocyanid e = 10 M , hydroxide = 0.25 M , sodium
:
■
ch lorid e = 0.25 M , and |a= 0.65) a t w h ich m ost o f the work w as d o n e , the
r ea ctio n is fir st order in hydroxide io n , fir s t order in m a le ic hydrazide
m on oanion, s e c o n d order in ferricyan id e io n , and in v e r se s e c o n d order
in ferrocyanid e io n . If the m a le ic hydrazide co n cen tra tio n is s e t b elo w
app roxim ately 0.03 M , w ith the other co n d itio n s rem aining th e sa m e , the
m a le ic hyd razide rea ction .ord er b eco m es greater than fir s t order, p o s ­
s ib ly s e c o n d o r d e r .. On the other hand, if the hydroxide co n cen tra tio n is
s e t b e lo w 0.1 M , w ith th e other c o n d itio n s c o n s ta n t, the r ea ctio n order
w ith r e s p e c t to hydroxide a ls o in c r e a s e s . There is a p o s s ib ilit y th a t.a t
hydroxide co n cen tra tio n ab ove 0.35 M , the rea ctio n order drops to b e lo w
o n e . H o w ev er, th is la tter e ffe c t cou ld be due to a p o s s ib le change in
the m a le ic hydrazide m onoanion con cen tra tio n at high hydroxide c o n c e n ­
tration s ( s e e A p p en d ix).
The v a ria b le ferrocyanid e data sh o w that the rea c tio n is in v e r se ,
seco n d .o rd er in ferrocyanid e from 0.005 M to 0.02,M , but the order d e ­
c r e a s e s at higher ferrocyanid e c o n c e n tr a tio n s . This d e c r e a s e could
a c tu a lly be a r e su lt o f som e m e c h a n istic c h a n g e , but it is more lik e ly
due to the ch an ge in .th e io n ic str en g th , w hich w a s a llo w e d to vary from
0.60 M to 1.00 M . The io n ic stren gth v a r ie d , s in c e , at th e tim e the
47
exp erim en tal r e s u lts w ere ta k e n , it w a s not r e a liz e d .th a t th e e ffe c tiv e
io n ic stren gth o f p o ta ssiu m ferrocyanid e is ten tim es it s a c tu a l m olarity .
The d isa p p ea ra n ce o f ferricyan id e w a s a lw a y s found to be seco n d , order
in ferricyan id e a s lon g a s a t le a s t a te n -fo ld e x c e s s o f ferrocyanid e w a s
p r e se n t. T hus, if the rea ctio n order is a ssu m ed to be in v e r se seco n d
order in ferrocyanid e at a ll co n cen tra tio n s and is fir st order im hydroxide
at high c o n c e n tr a tio n s ,. then any p roposed m echanism h as to fit eith er o f
the fo llo w in g rate la w s w ith e x c e s s ferrocyanid e p r e se n t.
d[FE (C N )g~]
kj [M H " ]2 [O H - ] 2 [F e(C N )2 " ] 2
dt
—
[kn + .[M H "] [O H - ]] [F e(C N )g~] 2
d [F e(C N )2 "]
k]; [M H " ]2 [O H " ]2 [F e(C N )2 " ] 2
---------------------- = ------------------------ :---- —--------- :— •-------------——2 (2)
dt
[kn + ■[M H."]] . [kn l + [O H "]] [F e(C N )^ ']
Probable V alu es o f
, k
, and k ^
There is a p o s s ib ilit y that the s e c o n d io n iza tio n co n sta n t o f m a le ic
hydrazide is in the region, o f 4 x 1 0 ^2 M , w h ich is the hydrogen ion c o n ­
cen tration a t w h ich m ost o f the exp erim en ts w ere d o n e. If the seco n d
io n iz a tio n co n sta n t i s in th is r eg io n , then there w ould be tw o s p e c ie s o f
m a le ic hydrazide p r e se n t in a p p recia b le co n cen tra tio n s in th e reaction
m ixture. This w ould mean th a t, w ith a c o n sta n t m a le ic hyd razide c o n ­
c en tr a tio n , the r e la tiv e co n cen tra tio n s o f m onoanion and dian ion w ould
48
ch an ge w ith changing, hydroxide c o n c e n tr a tio n . T herefore, the graph o f
kexp v e r s u s hydrazide co n cen tra tio n (F ig . 9) w o u ld .h a v e more than one
v a r ia b le . N ot o n ly th e hydroxide con cen tra tio n but a ls o th e m a le ic
hyd razide m onoanion concentration, is ch a n g in g . This w ould lea d to a
curvature su c h a s is show n at high hydroxide c o n cen tra tio n s in F ig . 9 .
By u sin g the data in F ig . 9 and the formula d erived in the A ppendix,
a v a lu e for
o f 3.6 i s o b ta in e d . This corresp onds to a Kq2 o f 3 x 1 0 ^
for th e s e c o n d io n iz a tio n c o n sta n t o f m a le ic hydra z i d e .. The amount o f
m a le ic hydrazide d ian ion p r e se n t in a g iv en so lu tio n can be found w ith
th is c o n s ta n t. If Icexp is p lo tted a g a in s t the m a leic hydrazide dianion
con cen tration found by ap p lyin g the ex p erim en ta lly d erived sec o n d io n i­
z a tio n c o n sta n t to both the va ria b le hydroxide and m a le ic hydrazide .
d a t a , a good stra ig h t lin e fit is o b tain ed at dian ion co n cen tra tio n s o f
ab ove 1.5x10
M (F ig. 13). The m a le ic hyd razide d ia n io n data derived
from the va ria b le hydroxide exp erim en ts seem to have a s lig h tly higher
kexp a s s o c ia t e d w ith it the v a ria b le to ta l m a le ic hydrazide d a ta , but
th is is probably due to a s lig h tly in a ccu ra te v a lu e for
• The curvature
a t high hydroxide co n cen tra tio n s in F ig . 9. i s g rea tly r e d u c e d , if not
e lim in a te d , a t high hydroxide co n cen tra tio n s in F ig .1 3 . This sh ow s that
eith er th e
o f m a le ic hydrazide is about 3.6 (K ^ = 3 x 1 0
or that .
on e o f th e fa s t s te p s prior to th e rate determ ining ste p h as th is for its
Kj3 (m echanism 2 ).
49
o = v a ria b le hydroxide data
x = v a ria b le m a leic hydrazide data
m a le ic hyd razide d ian ion , M x l O
FIGURE 13
kexp V S. MALEIC HYDRAZIDE DIANION
[F e(C N )g~] = 0.001 M , [F e(C N )^ " ]= 0.01 M , U = 0.65,
T = 2 5.0 ° C , Kb2 = 3.6
. 50
Probable v a lu e s for
and
can a ls o be c a lc u la te d . Equation 2
can be rearranged to eq u ation 3 ( s e e A ppendix).
[M H ~]
kn [F e(C N )g " ]2
kexp
k jC O ^ lC M H " ]
. [Fe(CN )g™ ]2 .
kj [O H - ]
Then i f
^ i s p lo tted v e r su s the recip ro ca l o f m a le ic hydrazide
11exp
m onoanion co n cen tra tio n (F ig .1 4 ), and s in c e the hydroxide and ferro cy a nid e co n cen tra tio n s are. k n ow n , a v a lu e for kj can be found from the Y
in tercep t and a v a lu e for k ^ from the s lo p e . L ik ew ise., a v a lu e for kj and
kjjj can be ob tain ed from eq u ation 4 and F ig . 15.
[O H -],
kr a [ F a ( C N ) ^ ] 2
[F e(C N )^ " ]2
------------ - ------------1------: I . +
I
k^xp
kj[M H ][O H ]•
kI [M H ]
I4)
The v a lu e s for kj and k ^ from the m a le ic hyd razide p lo t (F ig. 14)
are 0.3 4 .Sc m ole
sec
and 2 .8 x 1 0
m ole X. r e s p e c tiv e ly . The v a lu e from
the hydroxide p lo t (F ig . 15) is 0.50 £ m ole * sec * for kj and 0.2 5 m ole I ^
for k jjj. The v a lu e s for k^ and k ^ from the m a leic h y d ra zid e data did not
tak e kjjj in to a c c o u n t, s in c e it w a s a ssu m ed to be sm a ll r ela tiv e to 0.25.
S in ce th is i s not true it m ust be incorporated into eq u a tio n 3 . If th is is
done the v a lu e for kT c h a n g e s to 0.68 £ m ole * sec * w h ile kTT rem ains the
sa m e . If k ^ is tak en into a cco u n t for th e v a ria b le hydroxide d a ta , kj b e com es 0.78 Z m ole
-I
sec
-I
and k ^ rem ains c o n sta n t. As can be s e e n , th e
v a lu e s o f k ^ [[O H ] + k ^ J and k ^ [ [ M H " ] ] + k ^
are q u ite c lo s e at
FIGURE 14
MALEIC HYDRAZIDE TIMES INVERSE
VS .
INVERSE MALEIC HYDRAZIDE
[Fe(C N )*3] = O1OOlM, [Fe(C N )^*]= 0.01 M , [N aO H ]=0.25, U= 0.65, T=ZS1QOC
52
x k
25-
10
[hydroxide]
FIGURE 15
HYDROXIDE TIMES INVERSE k
VS. INVERSE HYDROXIDE
[Fe(CN)^ ]]= 0.001 M z [F e(C N )g ] = 0.01 M , [m aleic hydrazidej = 0.05 M ,
U= 0 .6 5 , T= 25.00 C
53
1.4x10
-2
-2
2 n -1
and 1.9x10 . m ole Jl r e s p e c tiv e ly . T h ese tw o term s and the
tw o 'v a lu e s for kj can e a c h be a v era g ed to g iv e the fo llo w in g , e q u a tio n .
d [F e(C N )g" ] '
.dt
0.73 [M H - ] 2 [O H - ] 2 [F e(C N )g"] 2
[ l . 7 x ! 0 -2 + [M H - ] [O H - ]] [F e(C N )-4 ] 2
For eq u ation I , kj and k ^ can a ls o be ev a lu a te d from F ig . 14 and
F ig . 15, s in c e k ^ is eq u al to eith e r k ^ [OH ] or k ^ [M H ] o f eq u ation
2 and k^ is eq u al to. th e avera g e o f the tw o v a lu e s found for k^ in eq u a ­
tion 2 before k ^ and k^^. w ere taken into a c c o u n t. The co m p lete eq u a ­
tion is :
d [F e(C N )2 - ]
13-1 2
-n 2
,"n2
0.42 [M H - ] 2 [OH ] 2 [F e(C N )2 -]
[0.010 + [M H - ] [OH- ]] [F e(C N )4 -] 2
F in a lly , if the d ian ion o f m a le ic hydrazide is a ssu m ed to be th e
•active s p e c i e s , the r e la tiv e v a lid ity o f eq u a tio n s 5 and 6 can be d eter­
m in ed . T h u s, su b stitu tin g 3.6 [M H- ] for [M H ] [ OH ] in eq u ation s 5
and 6 g iv e s eq u a tio n s 7 and 8 r e s p e c tiv e ly .
d [F e(C N )2 - ]
2.0 [ M I T ] 2 [F e(C N )2 -] 2
dt
|4.8 XlO- 2 + [M H= ]] [F e(C N )4 - ] 2
d [F e (C N )2 - ]
1.2 [M H= ] 2 [F e(C N )2-] 2
(8)
dt
[2.8 x IO- 2 + [ M H^]] [F e(C N )4 " ] 2
54.
N o w , w h en 'k eXp is .p lo tt e d a g a in s t
[-MH-T2
n-3
2 .8 x 1 0 u +- [M H ~]
[MH~ ] 2
(F ig . 16) and
rt-3
4.8 x IO , + [MH= ]
(F ig . 17), there is . found a m u ch .b etter straigh t lin e fit
in F ig . 17 than, in F ig . 16. T h erefore, eq u a tio n s I, 6, and p o s s ib ly 8 seem
to be the g en era l exp erim en tal eq u a tio n s for th e r e a c tio n .
P o s s ib ilit y o f a P seudo In verse F irst Order in Ferrocyanide
To d e te c t if the reaction , is p o s s ib ly in v e r se fir s t order in ferrocy a n id e at high ferrocyah id e c o n c e n tr a tio n s.a graph o f
kexp 1 [F e(C N )g ] * v e r su s
[Fe(CN)^ ]
(F ig. 18) w a s prepared. This
graph should, have a p o s itiv e slope, i f the rea ctio n is-, in verse seco n d ofdbr,
a zero s lo p e if it is in v e r se fir st ord er, and a n e g a tiv e s lo p e it it is zero
order. As can be s e e n from the graph, there is no c le a r cut answ er to the
p o s s ib ilit y that the rea ctio n is not a lw a y s in v e r se seco n d , order in ferroc y a n id e . W hen Jcexp 1 v e r su s ^ F e (C N )|- J
is p lo tte d , th is sam e
curvature is show n (F ig . 19). Figure 19 a ls o sh o w s k____,["^^-1 v ersu s
'
^Fe(C N )g~J2.
e x PL
|J. J
This p lo t tr ie s to ta k e in to a cco u n t th e e f f e c t o f the
ch an ge in. io n ic str e n g th . It a ssu m es, that the. rea ctio n is fir st order in
r e s p e c t to its io n ic str e n g th . This graph sh o w s l e s s curvature than the
oth ers but s t ill show s, the r ela tio n sh ip to be c o m p le x , a s a n tic ip a te d .
55
o
40
[m a leic hydrazide d ia n io n ]2
[o.048 + m a le ic hydrazide dianion]
FIGURE 16
EVALUATION OF kTT = 0.0048 M
II
—
[Fe(C N )2 ' ] = 0.001 M , [Fe(CN) g"] = 0.01 M ,
d = 0.65, T = 2 5 .0 °C , Kb9 = 3.6
Mx l O
56
[m a leic hydrazide dianion]
, M x 10
["0.0028 + m a le ic hydrazide dianiori]
L
FIGURE 17
J
EVALUATION OF I y = 0.0028 M
[Fe(C N )g‘] = 0.001 M , [Fe(CN)^"] = 0.01 M ,
U 0 .6 5 , T= 2 5.0 ° C , Kb2 = 3.6
57
Fe(CN)
, M xlO
FIGURE 18
TEST FOR POSSIBLE FIRST ORDER FERROCYANIDE DEPENDENCE
[Fe(C N )^-] = 0.001 M , [NaOH] = 0.25 M , H= 0 .6 0 -1 .0 0 ,
[m aleic hydrazidej = 0.05 M , [N aC lj = 0.25 M , T= 25.0°C
58
o = s a lt corrected data
x = un w eigh ted data
o
o
O
X
X
O
X
*
k"‘
exp
p
, -I X 0.60
Kexp
e
0 k -------------1---------------i-------------- 1--------------- 1---------------1
0
5
10
15
20
25
v4_ 2
a
F e(C N )g
, M x lO 4
FIGURE 19
EXPLORATION OF POSSIBLE SALT CORRECTION IN
VARIABLE FERROCYANIDE DATA
[Fe(CN)^"] = 0.001 M , [m a leic hydrazidej = 0.05 M ,
[NaOH] = 0 .2 5 M , U= 0 .6 0 -1 .0 0 , [N aC l] = 0.25 M , T = 2 5 .0 °C
59
P o s s ib le Sim ple R eaction Schem es
There are se v e r a l ob v io u s m ech an ism s that have to be c o n sid e r e d .
The fir st o f th e s e is:
If the s te a d y sta te approxim ate is u s e d , th is w ould g iv e the fo l­
low in g rate e x p r e s s io n :
.60
d.[Fe(CN)g ]
dt
2 Jc1Ic2 Ic3 CMH-] [OH"] [F e(C N )3 J 2
(9)
k_p_2 [F e(C N )-4] [ h 2o] + J ^ k 3 [H2 O] [F e (C N )^ ] + ^ k 3 [F e ( C N ) |-]2
W ith an e x c e s s o f ferrocyanid e being, p r e se n t, th is eq u ation cou ld be
approxim ated a s
(
10 )
The factor o f 2 is found in the numerator o f equation. 9 s in c e it should
tak e tw o ferricy a n id es to o x id iz e one m a le ic hydrazide. through, .the rate
. determ ining s t e p .
This m echanism in v o lv e s the in itia l formation, o f the double a n io n .
In a sim ila r com pound, lum inol (5 -a m in o -2 ,3 -d ih y d r o -1 ,4 -p h th e lo z in e d i-6
one), the fir st io n iz a tio n c o n sta n t is about 10 and the s e c o n d is greater
than" 10 1
. ■W hite e t a l.
think th at th e formation o f the dian ion o f
lum inol is th e fir st step, in it s o x id a tio n by o x y g en in an ap rotic s o lv e n t.
If the d ian ion o f m a le ic hydrazide d o e s e x i s t , an upper lim it for the s e c ­
ond io n iz a tio n c o n sta n t w as e stim a te d from the p lo t o f kexp versus, the
hydroxide con cen tration ( s e e F ig . 9 and A p p en dix). This s e c o n d .io n iz a tion c o n sta n t w ould be about 3 x 1 0
-15
. The fa c t that the. k in e tic s seem to
sh o w a s iz e a b le con cen tration , o f th is d ian ion being formed in the r e a c ­
tion s o lu tio n a ls o fu rth ers-th is sch em e; h o w ev er, eq u ation 10 d o es not
61
m atch eq u ation 6 , s in c e the first m echanism w ould require the rate to be
o n ly in v e r se fir s t order in fe r ro c y a n id e .
A se c o n d lik e ly m echanism is:
rf
N -H
„
+ Fe(CN) p
k.
^
Fe(C N )g~
I
o_
O.
IV
XI
A
-h
n
+ OH
k2
x
A
n
HgO +
k-2
o.
O1
XI
X
o'
O
A ^X N
I
A
a
o.
X
o
+ F e(C N )^ '
Fe(CN) g~ +
3
O
II
62
This m echanism h as a rate, la w of:
d [Fe(CN) g ]
( H)
k .jk .2 [F e (C N )^ ][H 2^ + k^kg [F e(C N )=-] Jye(CN)
+ k g k ^ O H ^ F e tC N )^ :
If the fir st term in .the denom inator o f equation, l i is a ssu m ed to be
large: relative, to the other term s when, large e x c e s s e s , o f ferrocyan id e are
p r e se n t, then eq u ation 11 s im p lifie s to:
2
(
12 )
A gain, the k in e tic s o f th is m echanism are o n ly in v e r se fir st order
in fe r ro c y a n id e . H o w ev er, th is m echanism d o e s not require the formation
o f the d ia n io n .o f m a le ic h yd razid e. I n s te a d , the m a le ic hydrazide radi­
c a l i s deprotonated. to the s e m i-d ia z o q u in o n e . This w ould mean that
there w ould be o n ly one n egative, charge on th e m a le ic hyd razide m o le­
c u le at any one tim e. In th is c a s e -the Kj39 equilibrium e a rlier a ssu m ed .to .
Z
...
.
be b etw een m o le c u le s IV and IX w ould in s te a d be formed by the eq u ilib ria
b etw een m o le c u le s XI and.X- This w ould require, both XI and X to be
fa irly lon g liv e d . ra d ica l s p e c ie s . . The sem i-q u in o n e is known, to be a .
30
s ta b le in term ed iate in th e qu in on e/h yd roq u in on e sy ste m . M a leic .
hyd razide sh ou ld b eh ave sim ila rly to th is s y ste m .
63
The third perm utation on the g en era l m echanism is:
The rate la w for th is m echanism w ould be:
d [Fe(CN) g~]
dt
__________________ 2 L1Ic2 Ic3 [M H -] [Q H -] [F e (C N )^ ]2________________
[Fe(C N )^"]2 + ^ k 3 [Fe(CN) 4"] 2 [ o h "]+ k2 k3[F e(C N )g~][oH "]
^
64
If equation. 13 is sim p lifie d it b eco m es:
d[Fe(C N )g ]
dt
(14)
4-12
. ^ [F e (C N )I-]
This fin a lly m atches: part o f the e x p erim en ta lly derived, rate, la w
(eq u ation 6 ). If th e product o f the hydroxide and. m a le ic hyd razide m ono. anion con cen tration s, is-large, relative, .to 0,01, then eq u ation 6. red u ces to:
2
(15)
w h ich is id e n tic a l to eq uation 1 4 .. U n fortu n ately, th is m echanism has
two main d r a w b a c k s„ N orm ally, ferricyan id e a b str a c ts an electro n from a
n e g a tiv e s p e c ie . This m echanism w ould req u ire.it to a b str a c t a n .e le ctro n
from a neutral s p e c ie to form, a p o s itiv e o n e . The s e c o n d d iffic u lty is
. that in .th is m echanism
m ust be larger than
for the proton rem oval.
M any proton tr a n sfe rs are among the f a s t e s t reaction s, known; h o w ev er,
the elec tr o n transfer required in r ea ctio n k_g could be fa ste r than k^ due
to a c a g e e f f e c t . This s o lv e n t c a g e co u ld help lo c a liz e th e ferrocyanide
m o le c u le relative, to it s r e a c tiv e p o s itio n on the m a le ic hyd razide m o le­
c u le .(XII) „ If k_2 w ere much larger than, kg , th is w ould a llo w very lit t le
o f the free m a le ic hyd razide cation, to be. r e le a s e d in th e s y s te m . A
further deterrent from th is-m ech a n ism is that no e a s il y r a tio n a lized e x ­
p lan ation can be given, for the apparent r e a lity o f K^g.
65
P o s s ib le C om plex R eaction S chem es
All three o f the ab ove m ech an ism s have a ssu m ed that a s soon a s
the d iazoq u in on e is formed it w ill im m ed iately break down into the pro­
d u cts o f th e r e a c tio n . H ow ever, there co u ld be a s lo w ste p o f som e typ e
fo llo w in g the formation o f the d ia z o q u in o n e. This cou ld be the addition
o f w a te r .
O
rate determ ining
O
II
XIII
O
O
--------------- — :--------- >
rate determ ining
O
XIV
II
It could a ls o in v o lv e an internal rearrangem ent o f th e m o le c u le .
O
O
------------ d------------- >
rate determ ining
+
O
II
XV
66
T hen, i f the form ation o f the diazoquihone- (II) is. a ssu m ed to be
r e v e r sib le in a ll three o f the p reced in g m e c h a n ism s, th e-th ree cou ld be
e x p r essed , by the fo llo w in g rate la w .
d[Fe.(CN)g“]
dt
2 ABCDE
II(16)
FGH..+ EFG + DEF + CDE
w here
M echan ism la
M echan ism 2a
M echanism 3a
A =
[M H ~]
[ m h ~]
M
B =
k1 [OH™]
kj [Fe(CN) g™]
k1 [F e(C N )^ ]
C =
k2 [Fe(CN) g™]
k2 [O H ']
k2 [Fe(CN )2 ']
D =
k3 [Fe(CN)g"]
E =
k4 [H2 O]
F =
^ [ H 2 O]
G =
k jF e(C N )g™ ]
k_2[H2o ]
H =
k^3[Fe(CN)g™].
k-3 [Fe(C N > 6 l
. kg [F e(C N )2 -]
k4 [H2 o ]
k3 [OH~]
.
k4 [H2 ° ]
' '
k .r [Ee(CN)^"]
' k- i N c N ) ^ ]
■k. 2[Fe(c N ) r ]
'
k-3 [H2D]
The k in e tic s o f e a c h .o f th e s e m echanism s, w ill sim p lify at high
ferrocyanid e co n cen tra tio n s to:
d [Fe(CN) g"]
2
2 k 1k2 k3k4 [M H ''][o H ''][F e(C N )g _] .
4-~|2 Prk- l k- 2 k-3 [F e(C N )^ -]2 [H2O]
(17)
67
This is again in d istin g u ish a b le k in e tic a lly in w ater from equation
1 5 , the ex p erim en ta lly derived rate eq u ation at high m a le ic h yd razid e,
h y d ro x id e, and ferrocyan id e co n cen tra tio n s .
A fourth rea ctio n sch em e is the s e lf-o x id a tio n -r e d u c tio n o f the
se m i-d ia z o q u in o n e . The s e m i-d ia z o q u in o n e , w hich co u ld be formed by
the fir st two s te p s o f eith er m echanism one or tw o , cou ld form eith er
the d iazo q u in on e and the dian ion or a dim er.
rate determ ining
rate determ ining
68
A ssum ing th at kg « ' k _ 2 , th is w ould g iv e a th e o r e tic a l rate Idw of:
This is. e f f e c t iv e ly the sam e a s the other h a lf o f eq u ation 6 when
(19)
dt
[F e(C N )^ -]2
If a s lo w s t e p , su ch as. th e a d d itio n .o f w a ter, e t c . , fo llo w ed the .
form ation o f th e d ia z o q u in o h e , then a t low. hydroxide or m a le ic hydrazide
co n cen tra tio n s , the o v e r a ll rate la w w ou ld be sim ila r to equation. 6. If
the d ian ion o f m a le ic hydrazide is a s ta b le s p e c ie in aq u eo u s b a s ic s o ­
lu tio n ,
then m ech an ism s 4 and 4a are r e a so n a b le . S in ce at high hydrox­
id e and m a le ic hyd razide c o n cen tra tio n s the m a leic hyd razide dianion
co n cen tra tio n w ould be high and the rev e r se rea ctio n c o u ld be fa st r e la ­
tiv e to the rea ctio n w ith w ater.
9 10
11
31 ■
C lem ent 1 , K ealy , and R. G eer
have claim ed, to have is o la te d
on e o f the dim ers (VII) a s an ox id a tio n product o f m a le ic h y d ra z id e . Both
C lem ent and Kealy worked in nem -aqueous s o lv e n ts w ith o x id a n ts other
than fe r r ic y a n id e . H ow ever, G eer's co n d itio n s w ere sim ila r to the e x ­
perim ental c o n d itio n s in th at ferricyan id e w as the o x id a n t and. w ater w as.
the s o lv e n t. G eer h as found th at the dim er i t s e l f is rapidly o x id iz e d by
e x c e s s ferricyan id e to r e le a s e n itro g en . This dimer m igh t a ls o be.form ed
.
69
by the rea ctio n o f the d iazoq u in o n e w ith a m a leic h y d ra zid e. Interm edi­
a te XVI, w hich may a ls o be formed by the rea ctio n o f the diazoq u in on e
w ith m a le ic h y d ra zid e, sh ou ld e x p e l nitrogen to g iv e a b ic y c lic dik eto
compound XVII.
The fu lly saturated compound sim ila r to XVII is s ta b le
s o lu tio n s .
32
in aqu eou s
H ow ever, w h ile Kealy w a s a b le to is o la t e th e d im a leic com ­
pound (V ), it w as u n sta b le in the p r e se n c e o f w ater. T herefore, it is
p o s s ib le that compound XVII cou ld form, but it should not be sta b le to
the reaction c o n d it io n s . If th is compound w ere a tta ck ed by b a se or
w a ter, it would probably g iv e eith er m a le ic hydrazide and su c c in a te ion
or s u c c in ic hyd razide and m aleate io n . G eer has a ls o found both
s u c c in ic and m a leic a c id s a s products o f th is r ea c tio n .
R eaction S chem es W hich Fit the K inetic R esu lts
If the d iazoq u in on e formed through m echanism 3 r e a c ts w ith the
d ian ion o f m a le ic h yd ra zid e, it w ould g iv e an e x p r e ssio n eq u iv a len t to
eq u ation 6 . This dim erization m echanism i s h igh ly im probable s in c e , if
the d ian ion d o e s e x i s t , the d ia zo q u in o n e w ould probably be formed by
70
m echanism , o n e . A ls o , a d iazoq u in on e formed through m echanism 3 cou ld
rea ct w ith the monoanioh-.form o f.m a le ic hydrazide
and ;the d ep roton ate.
This m echanism w ould a ls o g iv e an o v e r a ll e x p r e ssio n e q u iv a len t to
eq u ation 6
H o w ev er, s in c e .th e deprotonation w ould be the rate d eter­
m ining s t e p , th is la s t m echanism , i s u n lik e ly a s norm ally deproton ations
are extrem ely f a s t r e a c tio n s . Both o f th ese' m ech an ism s w ould have the
fo llo w in g rate e x p r essio n :
d [Fe(CN) g ]
GHIJ + FGHI + ERFH +■ DEFG + CDEF
dt
w here
2 ABCDEF
A =
[m h "]
B ■=
K1 [F e(C N )|‘]
C =
k2 [Fe(C N )S"]
D =
k 3 [OH"]
E =
k4 [M B ]]
F =
k5 [OH"]
G -
K1 [Fa(CN) | ‘]
H =
k_2 [Fe(CN) g-]
X — k_3 [H 2 O] ■
.I
(20)
71
Upon sim p lify in g equation 20 by the assu m p tio n that ferrocyanide
is p r e se n t in large e x c e s s , the eq u ation b eco m es:
d[F e(C N )g-]
dt
2
[ m h "]2 [O H ']2 [F e(C N )g~]2
(21)
[k_1k_2 k_3k_4 [H20 ] + ^ k jk .jk ^ C M H lC o H l] [F e (C N )|" ]2
If the d ihydroxy d iazoq u in o n e XIV r e a c ts w ith a d ia n io n o f m a leic
h yd ra zid e, th is too w ould g iv e the correct rate e x p r e s s io n . The b ic y c lic
compound XVIII formed cou ld ag a in break down to the rea c tio n p ro d u cts.
If the ad d ition o f w ater g a v e compound X/II in ste a d o f XIV, then
th is cou ld d eco m p o se to s u c c in ic a c id and p o s s ib ly m a lea ld eh y d ic a cid
(XIX) but not the m a le ic a c id o b se r v e d .
X III
X IX
72
H ow ever, m a le a ld eh y d ic a cid (XIX) co u ld eith e r go through a m odified
C annizzaro reaction to g iv e m a le ic a c id and 4 -h y d ro x y cro to n ic a cid or be
o x id iz e d under the rea ctio n c o n d itio n s to m a leic a c id .
T herefore, any o f the p reviou s three m echanism s w ill g iv e a rate
la w sim ila r to eq u ation 6. They are: (A) the s e lf-o x id a tio n /r e d u c tio n
se m i-d ia z o q u in o n e r ea ctio n w ith a s lo w ste p fo llo w in g the formation o f
the diazoq u in on e; (B) th e d iazo q u in o n e formed by m echanism 3 reactin g
w ith a m o le c u le o f m a le ic hydrazide m onoanion and deprotonating;
(C) the dihydroxy d iazoq u in on e XIII or XIV, formed by m echanism l a , 3 a ,
or 3 a , reactin g w ith the dian ion o f m a le ic h y d ra zid e.
C om parison o f the K in etica lly C orrect M ech an ism s
The dihydroxy r e a c t io n s , C , introduce an extra ste p w hich m akes
for more co m p lica ted reaction s y s te m s . It w ould probably tak e at le a s t
tw o w ater m o le c u le s p o sitio n e d c o rrectly to g iv e the 1,4 add ition to form
XIV. This w ould g iv e a three body k in e tic problem , but then w aters o f
s o lv a tio n are a lw a y s orien tated about th e compound and so the three
m o le c u le s cou ld be norm ally orien tated correctly for the rea ctio n to tak e
73
p l a c e . The ex ch a n g e o f protons from on e w ater m o le c u le to another is
known to be very rapid, s o the bridging m echanism co u ld be very rapid.
This m echanism w ould ag a in in v o lv e the u se o f the d ian ion o f m a leic
h yd razid e.
O
/
N —O—H
E
N
O
I
I
H
C
CX1
Vv
O H
XIV
II
The B s e r ie s o f r e a c tio n s , c o n s is tin g o f m echanism three (page
63), co u p led to the ad d ition of m a le ic hyd razide is im probable for the
r ea so n s m entioned in the la s t s e c t io n . It cannot be e n tir e ly d isreg a rd ed ,
h o w ev er, s in c e it is the s im p le s t m echanism w hich p red icts the correct
p r o d u c ts.
The A s e r ie s o f r e a c tio n s , w ith the s e lf-o x id a tio n /r e d u c tio n o f the
se m i-d ia z o q u in o n e (p age 67), is in many r e s p e c ts the m ost s a tis fy in g .
I th a s o n ly one main drawback in that G eer
31
has found m oderate am ounts
o f dimer formation under co n d itio n s s lig h tly d ifferen t from the reaction
c o n d it io n s . The proposed m echanism s w h ich form the dim er VII or the
b ic y c lic compound XVII w ould not be fir st order in hydroxide and m a leic
h y d ra zid e. There is a lw a y s , o f c o u r s e , the p o s s ib ilit y that there are
se v e r a l com peting m ech an ism s under the sam e exp erim en tal c o n d itio n s .
V
74
Further Work
The a c tu a l m echanism could have b een c la r ifie d c o n sid e ra b ly by
the stop p ed flo w e x p e r im e n ts. All o f th e s e m ech an ism s h ave assu m ed
th at the oxidation, o f m a le ic hydrazide by ferricy a n id e is s t e p w is e . In­
s te a d , tw o m o le c u le s o f ferricyan id e and on e o f m a le ic hydrazide. cou ld
form a c o m p le x , in w h ich c a s e the in itia l rate o f.th e sto p p ed flo w e x ­
perim ents w ould sh o w a s e c o n d order d ep en d en ce on th e ferricyanid e ,
co n c en tr a tio n . The fir st order d ep en d en ce in the in itia l ra tes has b een .
a ssu m e d , but co u ld not k in e tic a lly be d istin g u ish e d from a se c o n d order
d ep en d en ce a s lon g a s an e x c e s s o f ferrocy a n id e is p r e se n t.
If the in itia l rate d o e s have, a fir s t order d ep en d en ce in ferricyar
n id e , then it can be determ ined if the fir st step o f the o x id a tio n is the
form ation o f th e m a le ic hyd razide d ian ioh IX o f if the form ation o f the ,
m a le ic hyd razide ra d ica l XI i s the f in a l.s t e p . In the former c a s e , there
w ould be a hydroxide d e p e n d e n c e , w h ile in the la tter there w ould n o t.
The tem perature d ep en d en ce o f the in itia l rea ctio n co u ld a ls o have b een
stu d ied w ith the sto p p ed flow rea ctio n and th is w ould h ave further e lu c i­
dated th e m ech an ism .
If any o f the in d icator s tu d ie s had w o rk ed , th is a ls o w ould have
show n w hether th e d ian ion d o e s e x is t in a p p recia b le q u a n titie s in
aq u eou s b a s e . Another p o s s ib le m ethod for exam ining th e formation o f
m a le ic hydrazide d ian ion i s to u se it a s it s own in d ic a to r . There w ould
75
probably be a d iffe re n c e b etw een the u ltra v io let sp ectra o f it in the
m onoanion form and in the dianion form.
The v a ria b le ferro cy a n id e. work sh ou ld probably be rep eated over a
greater range o f con cen tration and w ith a c o n sta n t io n ic stren g th . If the
r ea ctio n d o e s in d eed turn out to a lw a y s be in v e r se s e c o n d order in ferro­
c y a n id e , then it w ould be very in te r e stin g to exam ine the rea ctio n at.
varying io n ic s tr e n g th s .
O x id izin g m a le ic hyd razide w ith other a g e n ts su c h a s hydrogen
p eroxide w ould a ls o be in te r e s tin g . Some therm odynam ic data could be
ob tain ed from o x id iz in g the compound e le c t r o ly t ic a lly . This has the a d van tan ge th at in product s tu d ie s the iron com pounds do not h a v e to be
rem o v ed . H o w ev er, the sam e products or product ra tio s m ight not be
ob tain ed if d ifferen t o x id iz in g m ethods are u s e d .
F in a lly , an E .S .R . stu d y co u ld be done on the rea ctio n to d eter­
m ine the s ta b ility and r e la tiv e abundance o f free r a d ic a ls in th e rea ctio n
s o lu tio n .
APPENDIX
77
C a lc u la tio n o f a P o s s ib le V alue for Kv
Let
x = [m h ] to ta l
and
y = [m H=]
. \
x - y = [MH-]
If kexp
exp is d ir e c tly proportional to [MEn] the r ela tio n cou ld be e x p r e ss e d as:
C [MH=]
exp
= CY
w here C i s a c o n s ta n t..
Kj-,2 is d efin ed su ch that
kW
[o h - ] [ m h - ] \
Kb2
If
[oH ]
»
[o h -][ x - y]
[ m h =]
x
then
[oH ] is
Y
e ff e c t iv e ly c o n sta n t.
Equation b can be rearranged to:
x [o H - ]
Y
Kb2 + [o h -]
This can be com bined w ith eq uation a to .give:
CX [o H ~ ]
keXP
If Kj32 »
[oH ] »
[oH ] then
%
+ [OH"]
the r ea ctio n w ould be fir s t order in
Kj32 th e reaction w ould be zero order in
JoH ] .
[oH ] .
If
T h erefore, i f a
p lo t o f kexp v s [o H -] g iv e s a stra ig h t lin e fit w ith a s lo p e o f C fo llo w ed
by a portion curved tow ards a zero s lo p e , Kj32 can be c a lc u la te d . If the
lin ea r s e c tio n i s ex ten d ed to a poin t beyond w here the experim en tal
.
78.
p oin ts fa ll b e lo w the l i n e , and if the .poin t w here the lin e in tercep ts any
arbitrary [ o h ] lin e is a ssu m ed to be the keXp w hich w ould e x is t at that
[OH™] i f Kb2 »
[OH™] then:
CX [o h ]
k exp th eo r e tic a l
Kb2
or
Kb2 kexp th e o r e tic a l
CX [onj
H o w ev er,
CX [ o h ]
k exp a ctu a l
Kb2 + [OH™]
[Kfo2 + [OH~]] k e x p a c tu a l
C x [o H ]
' • [^b2 + Ip-^ I ^exp a c tu a l ~
C x[oH ]
S in ce the
[oH "],
-
Kb2 keXp th eo r e tic a l
keXp a c tu a l' anc^ ^exp th e o r e tic a l are know n,
Kb2 can be c a lc u la te d . The v a lu e o f Kb2 obtained from th e data in th is
t h e s is is 3.6.
79
T ypical M ethod for the E valuation o f C o n sta n ts in.R ate E x p ressio n s
.3-1
kj [MH"]2 [OH-] 2 [F e(C N )g~]
d[Fe(C N )g ]
. [k n +[[M H ]] [ki n + [OH- ] ] [ F e ( C N ) |- ] 2
This can be rearranged and in tegrated
,3
d[Fe(C N )g ]
[F e(C N )3~]2
] [kn + CMH- 3][km + [OH™]][Fe(C N )4 - ] 2
kj [m h -] 2 [ o h -] 2
"exp '
[kn +
CMH ]][k m + [OH ]] [F e(C N )4 - ] 2
This eq u ation can be rearranged to:
[o h - ]
k jjjfk jj+ [M H -J] [F e(C N )g-]
2
ft
[k ^ + [MH-]] [F e (C N )g ^
-exp
^ [ m h ] 2 [o h ]
kj [MH ]'
( 22 )
If k „ «
[ m H ] th is further s im p lifie s to:
[OH"]
"exp
4 -12
.[ F e ( C N ) f ]
4* ■
kr [MH ]
]
km [ F e ( C N ) ^ ] 2
kj [ m H ] [ 0 H
(4)
If eq u ation on e i s a ls o in tegrated
d[F e(C N )g“]
k; [MH-] 2 [ o H -] 2 [F e(C N )2-] 2
J]
(I)
• [k + [MH- ][ 0 H
[Fe(C N )4"] 2
HI
L
JLV -jJ
and rearranged, an eq u ation sim ila r to th e sim p lifie d eq u ation 2 i s o b ­
ta in e d .
80
[o n -]
’ krxp-
. Jt11I r e (
C
N
kT [m h "]2 [ o h "]
The term , ^ / [ M H
)
[ F e ( CM) f ] 2
^ [ m h "]
] , from eq u ation 22 is equal to
in eq uation
4 . Therefore , a graph o f [ o h ] / kexp v s l/jjD H ] w ill g iv e both kj and
kjjj for equation. 4 and. k^ and. k ^ for eq u ation 2 3 . Equation 22 m ust be •
s o lv e d to g iv e kj i f k ^ is not much sm a ller than [jVIH ] .
81
T ypical D erivation o f th e K in etics o f a P o s s ib le M e c h a n istic Schem e
k.
. MH
+ OH
HE
-I
MH
+. H0O
Ic
MH= + Fe(C N )?"
-2
MH" + Fe(C N )g~
DQ + H2O
9
MH- + Fe(CN)?"
6
DQ + Fe(CN)
4-
-$• products
Using, the s te a d y s ta te a ssu m p tio n for .the formation, o f [ d q ] ,
dM
= O = k3[M H“] [F e(C N )g"] = k_3 [D Q ][F e(C N )?'] - k4 [DQ][H2oJ
■k4 [M H ~][Fe(C N )~3]
tD o ]
k_3[F e ( C N ) ^ ] +
k4 [H2 o]
Let k_3[Fe(C N )? ] + !^[H2o ] be rep resen ted by a sy m b o l, C .
U sin g the ste a d y s ta te assu m p tio n a ls o for [ m H ] ,
d^ ---
= 0 = k2[MH=] [Fe(CN) g~] + , k_3 [D Q ][Fe(C N )?"j
-
k_2 [MH“J [Fe(CN)?"] - k3 [M H"][Fe(CN)?"]
S u b stitu tin g for [ d q ] and so lv in g forjlvtH ] ,
Tm h =-I
___________________
L
k_2k_3 [F e(C N )? -]2 + k_2k4 [F e(C N )?-][H 2o ] + k3 k4 [F e(C N )?'][H 2o ]
"
C k2 [MH=] [ Fe(OM>6~]
___________________ __
<3
. 82
Let k_2k_3[F e(C N )g~ ]2 + k_2 k4 [F e(C N )g "][ h 2 o] + k4 k4 [ F e ( C N ) ^ ] [H 2 o ]
be rep resen ted by a sy m b o l, D .
A gain u sin g the s te a d y sta te assu m p tio n .for [ m H ]«
k^M H
-
][oH ]
+ k_2 [MH ][F e(C N )g~]
^ [ m H ^ ^ o] - k2 [MH=] [Fe(CN) g™]
S u b stitu tin g for [m H ] and s o lv in g for[MH ] g iv e s:
[m h =1 = - __________________ D ki [ M H " ] [ ° H~]____________ ___
k_ik_2k_2[F e (C N )|^ [H 2o] + ky k_2k4[Fe(CN)<-][H2o] 2
+ k- l k3 k4 [F e(C N )6"][H2 ° l 2 + k2 k3 k4[Te<CN)6 l 2 |!H20]
Let k_4k_2k_2[F e (C N )^ ] [ h 2 o ] + k_r k_2 k4[F e (C N )^ ][H 2o J 2
+ k ^ k g k ^ F e l C N i g ' J ^ o ] 2 + k2 k3 k4[F e (C N )g -]2 [H2 o ] = E
T herefore, i f [ m H- ] is su b stitu te d into previou s co n cen tra tio n e x p r e s­
s io n s ,
=
k 1k2 k_3[M H ] [ o H ] [ F e ( C N ) g J jF e (C N )g ] / E
+ k 1 k2 k4 [M H"] [o H"] [h 2 o] [Fe( CN) g ™] / E
and
k 1k2 k3[M H ~][0H ™ ][Fe(Fe(C N )g~]2
E
is o b ta in e d .
83
F in a lly , s o lv in g for the d isa p p ea ra n ce o f ferricyanide:
----- ^
.. lb I ., = ;k2 [MH=][F e(C N )g" ] +. k3[M H ~][Fe(C N )g“]
-
k_2[M Hi ][F e(C N )g" ] - k_3[D Q ][Fe(C N )g~]
W hen [ m H- ] , JjvIH ] , and [ d q ] are su b stitu te d in:
-
d ^ tl0 N > -
= ki fc2 k- 2 k- 3 [ MH ' ] [ ° H l [ F e ( C N ) ^ 2[ F e ( C N ) |- ] /E
+
kIk2 k_ 2 k4 [M H"][oH"] [f e (C N) g"][Fe(CN)g"][H2o ] /,
+
Ic1 Ic2 k3 kJM H"] [OH™] [Fe(CN) g”] 2 [H2 o]
+
k1 k2 ]<3 k_3[MH"] [o H~] [Fe( CN) g~] 2 [Fe ( CN) g~ ] / E
Ie1 Ie2 Ie3 k4[MH~] [oH~] [Fe( CN). g ~]2 [H2 ° ]
/E
4-12
- k 1k2 k_ 2 k_ 3[M H ] [ o H ][F e(C N )g ][F e(C N )g ]
- k l k2 k-2 k4 [MH' ] [ 0 H "][F e(C N ,6 " ]l7 e (C N ,6"]l-H20 ] / l
- k 1k2 k3k _3[M H-][oH'"][Fe(CN)g™ ]Z[F e(C N )g" ']/E
This s im p lifie s to:
d[Fe(CN)g~]
dt
2 k 1k2 k3k4 [M H -][0 H -][F e (C N )|-]2/ F
w here F = k_ 1k_ 2k_ 3 [Fe(CN)^"']2 + k_ 1k_2k4[F e(C N )^ “][H 2o]
+ k_1k 3k4[Fe(C N )g']][H 2o ] + k2 k3 k4[F e (C N )g " ]2
84
D erivation o f T ypical K inetic E x p ressio n In volvin g a Square Term
If the [M H =] = Kb2_1[oH ~][M H "]
Ic
and ,
MH= +• F e(C N )g"
k
2 MH-
MH- + F e(C N )g“
-1
_
DQ + MH-
" 2 k3
DQ + H2Q ----- > Products
Then,, if the se m i-d ia z o q u in o n e o b e y s the ste a d y s ta te a ssu m p tion
d k S -1 =
o = k^MH^FelCN)®"] - k_|[MH~][Fe(CN)g-]
+ k2[M H - ] 2 + k_2 [DQ][MH=]
If k_j »
kg,, then p seu d o -eq u ilib riu m is m aintained for[MH J in the fir st
step a n d ,
r. .„-n
Im h J. —
ki [ MH=l l > e (C N )6 l
r
/i _-i
k ^ [F e (C N )|-]
If the ste a d y s ta te a ssu m p tion i s a ls o used, for-[ d q ] , th en
= o = ^ [ M H i] 2 - k„2 [D o ][M H=] - k3 [DQ ][H 2 o]
k2 [ m H-]
[d q ]
k_2 [MH ] + k3 [H2o ]
kj2 k2 [m h “ ] 2 [F e(C N )3 ' ] 2
[d q ]
^ [ F e ( C N ) I " ] 2 k_2 [MH ] + k^H gO ]
d [F e(C N )2 j
2 d(Prod)
k3[DQ][H2o]
85
T he "tw o" i s in th e l a s t e q u a t io n b e c a u s e i t t a k e s tw o m o le s o f f e r r ic y a n id e to form o n e m o le o f p r o d u c t s .
T h e r e fo r e , th e r a te o f r e a c t io n i s
d e te r m in e d b y k ^ j o p j j f lg O ] .
d[Fq(C N )g“]
dt
2 k12 k2 k3 [MH5=] 2 i[ F'e(CN)g"]Z[H 2D]
k _ ^ [k _ 2 [M H = ] + k 3 [H 2 o ] ] [ F e ( C N ) | - ] 2
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Miller, R o b e r t B.
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