A-G-R1 CULTUR5. PC CV
,I
;L
. ' U. S. Department of Agriculture, Forest Servic e
FOREST PRODUCTS LABORATOR Y
In cooperation with the University of Wisconsi n
MADISON, WISCONSIN ',S
II
1'
..
1
1i
.
_
1,
.
I p.
.
7-
EFFECT OF PRETREATMENTS OF WOOD ON TH E
LIGNIN DETERMINATION; DISTRIBUTION OF
METHOXYLS IN WOO D
By GEORGE J . RITTER
Chemist
and
JAMES H . BARBOU R
Junior Chemist
■.,/'
AS S
4 min
r
li t
*I
'
_1 . 1
Published in
INDUSTRIAL AND ENGINEERING CHEMISTR Y
July 15, 193 5
•,.
Ir,:,
-
Various treatments have been proposed (2, 5, a) for wood previous to the : igniu determination by the 72 percent sulphuric-acid method .
The purpose of such pretreatments has been to reduce the likelihood o f
contaminating the lignin residue with decomposed extraneous materials .
Pretreatments both with benzene-alcohol solution (5) and with alcohol and hc,t water (a) have been recommended for Nort h
American woods . A pretreatment with 0 .5 percent sodium hydroxide ha s
been recommended for Australian woods (2) . Although the three propose d
pretreatments have merit for removing certain kinds of extraneous mate m 3 *NIP are, however, inadequate for removing other interferin g
extraneous substances found in some woods . Other modifications (6, 1 ,
10, 11, 12) of the sulphuric-acid method and a discussion (4) of th e
effect of the alkaline pretreatment have been published .
G. M. Kuettel of the Forest Products Laboratory has demonstrate d
that other troublesome extraneous materials, namely, catechol tannins ,
interfere with the lignin determination . The present paper proposes a
modification of the sulphuric-acid method, which insures the removal o f
catechol tannins by means of a preliminary treatment of the wood . It i s
recognized that the method with its proposed modification may still b e
inadequate _fox a a}aa .t ,ve lignin determination of some woods havin g
unu
'1
if still other extraneous materials .
The proposed modification is based on the fact that catecho l
tannins, which are incompletely soluble in the benzene-alcohol solutio n
and hot-water pretreatments previously described for North American woods ,
are dissolved by pretreating the wood with 95 percent alcohol . when
analyzing wood containing no tannins the proposed pretreatment of th e
wood with alcohol is, of course, unnecessary ; however, when analyzin g
woods in which the twnni. .n runt t is unknown it is a safeguard .
1
-Presented before the Division of CelUse Chemistry at the g9th Meeting
of tbm American Cheal Society,
.ty, April 22-26, 1 935 .
4
-1 1:k ~1I
.
II I
I
7I
};
t
f1 I ~
J
'J
I
three preliminary extractiv e
ecommended conta'
extraction with alcoho l
;cod . The fir s t con
raction withel-cohol dMil6hol tannins ; the second ,
00
aaad
the third, an ex'emove #azi p
:at
L
*
ith hod
o r00
s,ng water-soluble materials .
, the solid extraneous mate ved
t
ted wood were absent afte r
rial ta the cell!
the
wept for an occasi
• bus indicating the remova l
as
f okactiv . The womb
~e remaining after the thre e
rent sulphuric acid to dissolv e
itiONOOMMI
eated with
ids
eavi
as a sc~ •#esidue . A
The met
'U
L
-II
.7,1
I
.11
1 -
rr
r
are 4o .r the Determination of LignininWood
010
I-
y 2
0m-
s of
3 are weighed-
;II
~~s.~ r ti~wr
ir corre ion
ferre# % a t
#ner,
,l.ati
•dis}g I
J
r
4 -
desired, ~nin is'
rh.e ash content (determined i n
,
11.0
i ~
-.
- ._est of the Metho d
-
‘a.lh
I
a obtained b y
_r ding ti
ed (5,
4n which
i
Cougar
:ir
>
moil 1
.11
I
-' .I
bed werelkompare d
icatioh e
.~, ned according t o
those
r hot water fo r
is substituteE
s of (1) ligni n
e made
the
the isolated lignin, an d
j
+o
o,
1- -I
- -
s-
r
r
•II
1F
-r ~
in the form of sawdus t
ately in a tared alundum
then eracted
hours in a Soxhlet
material is next extracted fo r
-ume) . The solven t
hol-benzene solution
_IQ
of by suction to re suction the residue washed
400 cc .of hot wate r
ne
n extracted for 3
metered, washed witer, and finally dried .
ransferred to a large class-stoppered weighin g
-ed with 25 cc .of 72 percent sulphuric acid a t
ature it is maintained for 2 hours . The result rg:r to an Erlenmeyer flask, diluted with wate r
and then boiled for 4 hours under a
e is filtered on a tared alundum crucible ,
means of hot water, dried, and weighed . The
'elated on the basis of the oven-dry unextracted
pro
:
*►' ~oor
g ib tie
it
-
IL
I
I JJ
JJ
-
'
'
(3) the percentage of the total meior1 that is recoV,
l i 3s . th e
n-contadim
t¢oodda,
isolated lignin . Tha test was made on t
a
namely, r Od
LoWOVrond and white e--l
Table 1 t ht tifflE4A econtents as determ>
;
is of th e
proposed met i.ord are Ii.gted in column 2 ; those obtai*nog 1
ro previousl y
described methods (•, 3) are listed in . eolumns 3 oad. 5, respectively ;
and those obtained by substituting hot alcohol for kmt - Ater A 4 pre
pre treatment of the wood are listed in co1W
treatment
.
Discussion of Result s
Apparent. L.
;-nnYields
There is a pt5sitive increase in the apparent 7:ignin ytie'l i n
going stepwise in Table 1 from eolum . 2 to volkW*n 5~. Iz then. elves the y
offer no explanation as to whether the differences in yiel,s ; fir 4** to'
an inclusion of increasing amounts of contaminants as the yields tLOr''O.pAke
. or to a removal of 4ec-reasing . amounts of 1i;g i .
Aids incr.,
They are useful, however, when correlated with. the data ial'Table 2,• k
showing that the changes in the apparent lignin e e t4 after
erent
extractive treatments of the wood are due to an inc] o .
amounts of contaminants.. Defor'e it can be demo istit ted tha. 1
percentages offoreig . r ateTjais are included in the hii . heir
area
it is necessary to compare scme characteristie chem=ical pxaper&y ' 5th ,
apparent lignin residues, such as the met,ol c!onrt•ent .
Mme
Netho
1 Content of the Lignin Residue s
The methoxyl content of the lignin was :
lac d fur cY e ;0t
ing the lignin residues, which were isolated by Ole Cdi
modifies, oo
the method as indicated in the column headings of - ' .gble 1 . The rio0kIlt s
for comparison are recorded in Table 2 .
The melkoxyl content determined by the Zeisel method '('1) i s
highest in colurat 2 and successively decreases in columns 3, 4, and 5 .
These results considered in conjunction with those in the correspondin g
columns of Table 1 show that the higher methoxyl contents of the ligni n
residues are associated with the lower apparent lignin yields . Suc h
data suggest the presence of larger amounts of materials having a lo w
methoxyl content as the percentages of the apparent lignin yields in creases . That such is the condition can be shown by' calculating . the
methoxyl content of the various apparent lignin residues on a commo n
basis as is shown in Table 3 . These calculated data, made on th e
basis of the unextracted wood, result from multiplying the methoxy l
content of Table 2 by the content of its parent substance, the ligni=n- ,
in Table 1 .
Inasmuch as Ite 4 gag In Table 3 are a composite of the methoxyl
and the lignin yields, they 4wrefore include any errors that might hav e
beau made during the methoxyl and the lignin determinations . A slight
R1069
3-
eroctit in 0100 of the procedures would acciMpO for the lowest methoxyl
val-ae fib
+e.cit
i column 5 of Table j . It would seem that thi s
value s ro :d tfgtxal t;
aibtrs or even be slightly higher since, beside s
met y1i
li in, Aight .include methoxyls associated wit h
lemon; T
tities + .'extraw4i us mzAerials than are present in the othe r
i,dues ; Allow ±, r sliiht m
In the determinations, th e
flat.
f;07ar Tales IN* the methb* cont
vkp , nin residues from eac h
iew IXO$A%,, t;hmy° alre within experi 174 04 4120 in cl ue t eemen
mental accuracy„ It is,. gh0eestre, concluded from these results tha t
the diffeltenee in l._ a
y cello . etueen columns 2, 3, L . , Sd 5 in Tabl e
a ials having fiery 1it'tT4l t! r
1 is dumi to the present .off+
t .*m mel
tract of t
any, methoxyl . The preseuv6 'big' i5nixc tk
X03 was skew clua
ti~wlj':
by means of . n ab o dria saltss abdameting
the pro p
O
that at least' some e'f tyre ; rims are rerm
a
alcoholic t moeiext of the woodN
ry
A
s
thoxyl
It. Its apprgp n. ie to tientiwta here that tea some w
$
a.
'c ted 1441 the t rvimao s. .Na i k4is
holm eL iamise
:as well ,s v i:t t i 14gViOw The di {, `r -,;ion o f
re- ho is 14=1 these three
;d.r'ood and . white oak i 4
f
i*OKt c #
s1
in
;bete i+.
&Bo
ks
ion Of tffaft rl
Methoxyl do4opmi
.o
e wage on tk fnextracted r is
wood ex ct.ed with a.l g'®ho1,, alcohol- nzene soluflan ,
o4,
and tie "a;
. d- 1iga n% Mae met1ao l conteA of
r-ials ana %t 00le ila t
wiao . calciuat.e-d by difference *
_-
.
-•
•;
Me-,,
Data t~n lines 40.1 am& 4 mf 'mobile )$ are 'E result of expel
4entattUQA1 ..
:ose in 1 ts . &
fined by suction ; thos a
. 5 wVre o p
in 14fa6 to. 9, i*el!
of by cal ation la ze w9o dt • lze methoxyl
eon,t
-of the. eztx
• tlaterials i .s hi$4 6oAp%WOd with that of th e
carrespondz g result i i. .te od'k (line 3') . A p
>,bility of removing
some hereto-Q- l.osixmatreri from tie we•od d '
,pvetreatment
• ,s proved an
hat watt is melegmized: NoTpelver'o Astil the pasa.
'
content
of th e
iiegrericmetiail F ac't, the late pe
.init4g to time owtilsq0t
Te' ous matarial ma
3-ta~lAxe &i a a Minden as recorded i n
ho--7~
Tablz `#, _ ild
i
.,nstitutw thepart
1*6 met
:, %racte d
R
T
•
-•
_
i.der w'
th e
Wit I
g
X~
thoxyl bine a
e r-owoo . o oce
6se is
''
■comb
ti s ; .,+_
white oak holocellul.ose (line
of th9 ilia
~aa, the
that
soak t
n
r
,
II
u
1
{
Summary and Conclusion s
The accuracy of the determination of lignin in wood by means o f
the 72 percent sulphuric-acid method is affected by the amount and kin d
of extraneous materials incompletely removed from the wood by means o f
preliminary treatments .
Successive extractions of mood with 95 percent alcohol, alcohol benzol solution, and hot water make the 72 percent sulphuric-acid metho d
for the lignin determination more adaptable to North American woods .
If the kind and amounts of extraneous materials present in a
given species of wood are known, the preliminary treatments can b e
modified accordingly. For example, if catechol tannins are absent th e
extraction with 95 percent alcohol may be eliminated .
The methoxyl groups of redwood and white oak woods are dis tributed among the extraneous materials, the holocellulose, and th e
lignin .
Literature Cite d
(1) Bray, M . W ., Paper Trade Jour ., g7, 59-68 (1928) .
(2) Cohen, W . E ., and Dadswell, H . E . , "Chemistry of wood, Part 1 1 "
Melbourne, Commonwealth of Australia, Council of Scientific an d
Industrial Research, 1931 .
(3) Friedrich and Salzberger, Monats ., 53 and 5L ,98 9 (1 929) .
(4) Harris, E . E ., Ind . Eng . Chem ., Anal . Ed ., 5, 105 (1933) .
(5) Mahood, S . E ., and Cable, D . E ., Ind . Eng . Chem ., 14, 933 (1922) .
(6) Norman, A . G ., and Jenkins, S. H ., Biochem . Jour ., 28, 21+7 (193+) .
(7) Peterson, C . J ., and Walde, A . W ., Ind . Eng . Chem ., Anal . Ed., ,
216 (1932) .
(8) Ritter, G . J ., and Kurth, E . F ., Ind . Eng . Chem ., 25, 1250 ( 1 933) .
(9) Ritter, G . J ., Seborg,' R . M ., an_d Mitchell, R . L ., Ibid . , 4, 202
r
(1932) .
(10) Ross, J . H ., and Hill, A . C ., Pulp & Paper Mag . Can ., 27, 15, 541
(1 929) .
(11) Schwalbe, H ., Papier-f abr . , 23, 171- (1925) .
(12) Sherrard, E . C ., and Harris, E . E ., Ind . Eng . Chem ., 24, 103 (1932) .
(13) Sherrard, E . C ., and Kurth, E . F ., Jour . Amer . Chem . Soc ., 51, 312 9
(1929) .
R1069
-5-
S
Table 1 .--Effect of the removal of extractives on the lignin yield s
obtained from woo d
(Percentages based on oven-dry (105° C .) weight of the unextracted wood . )
Lignin in wood extracted with - Species
1
i
Redwood (heartwood)
Average
White oak
4
Average
•
R1069
t Alcohol,
Alcohol: alcohol- : benzene and
:benzene, and : hot water
hot water :
2
: Alcohol . Alcohol :
and
. . benzene
: alcohol- :
only
: benzene .
3
. ( 29 .76
( 30 . g U( 30 .54
. ( 30 .77
( 30 .36
( 30 . 147
( 30 .58
. ( 30 .32
( 30 . 49
. ( 30)42
30 .31
.
31 .13
31 .20
30.90
30.96
31 .00
31 .00
31 .02
31 .02
31 .02
4
5
31 .75
31 .85
31 .83
31 .56
31 .71
. 32 .50
: 32 .60
32 .28
. 32 .06
: 32 .16
32 .28
32 .08
32 .03
31 .99
:
.
:
30 .44
31 .03
31 .74
: 32 .24
. ( 22 .99
: ( 22 .56
( 22 .81
( 22 .76
( 22,92
(
23 .35
23 .50
23 .11
23)48
23 .15
24 .74
24 .87
24 .80
24 .81
24 .70
26 .0)4: 26 .14
: 26 .1 6
: 26 .1 7
26 .07
25 .99
22 .81
23 .32
24 .78
: 26 .10
-6-
Table 2 .--Methoxyl content of lignin isolated from wood subjected t o
different extractive treatment s
(Percentages based on the oven-dry (105° C .) weight of the isolated lignin . )
Methoxyl in lignin isolated from woo d
extracted with -Species
:
.
1
2
.
White oak
:
: Alcohol, : Alcohol : alcohol- : benzene
onl y
: benzene :
;
4
5
13 .41+
13 .43
13 .52
13 . 1+3
13 . 3 1+
13 .29
:
:
:
12 .6 8
12 .79
12 .7 5
13 .6 1+
13 . 1+6
13 .35
:
12 .7 1 +
( 20 .10
19 .14
( 20 .10
(
19 .13
18 .39
.
:
17 .8 9
17 .8 8
17 .8 9
20 .10
19 .13
18)+3
.
17 .89
( 13 .75
( 13 .57
Average
R1069
: Alcohol. benzene
and
water
3
( 13 .61
Redwood (heartwood)
Average
Alcohol,
alcoholbenzene
and water
:
-7 -
18 . 1+7
jected t o
Table 3 .--19fethoxiTI contentoflignin ;...1);pAsAL
different extrabtive tr t2arr
(Percentages based on oven-dry (105° C .) t oigK of the -u xtrac1 ' ror.0
Methoxyl in lignin isolated from woo d
extracted with - Species
I
: Alcohol,
. alcoholbenzene,
:
water
: Alcoholbenzene,
water
: Alcohol, : Alcohol : alcohol- : benzen e
: benzene :
onl y
Redwood (heartwood) 1+.15
4 .17
4 .23
4.l 0
White oak
4+.58
4.46
4+ .56
4.67
Table 4 .--Distribution ofmethoxyl in woo d
(Unless otherwise specified, percentages are based on the oven-dry (105° C, )
weight of the unextracted wood . )
: Redwood : White oak
Wood fractions
1. Methoxyl in
2. Methoxyl in
Methoxyl in
. Methoxyl in
5. Methoxyl in
6.
r
7.
g.
9.
10.
unextracted wood
5 .71
extractedi wood
4 .70
y . ..
extraneous materials (1 - 2) 1 .01
:
lignin from extracted wood 4 .17
:
holocellulose from extracted woo d
(2-- 4)
:
.53
Percent of total wood methoxyl in extraneous
materials (3
1)
17 .70
Percent of total wood methoxyl in lignin-(4 . 1) . : 73 .00
Percent of total wood methoxyl in holocellulose (5 - 1)
9.30
Percent of extracted wood methoxyl in holocellulose (5 . 2)
: 311 .25
Percent of extracted wood mOthOxyl in lig Ti n
( ''a - 2)
: 3SS .72
.
:
:
:
6 .3 S
5 .91
.47
4.55
:
1 .3 6
:
:
7 .4 0
71 .3 0
:
21 .30
.
323 .02
:
376 .9 5
-Wood was extract@d consecutively with a&€
, a'l~bl ] --~2~ eno eV'
then washed with alcohol to remove berg e, &ad fi .
extras
hot water . .
-Lignin was isolated from wood extracted
o
3-Calculated on the basis of the extracted weed .
a
to d
e. ti
,•
. , „
I;
:, ,
1
.J