Electrosynthesisof BenzoicAcid from Chlorobenzeneby
CarbonDioxideFixationMethod
Suliman, Norhuda
AbdulNlanaf.
MohdAfis , Normala
AishahAbdulJalil'. Hartini
-----tluilf,iETlyati
Hairomr,[4ohdRazifHarunrandsugengTriwahyono'z
rFacultyof Chemic€land
Engineering,
NaturalResources
ScienceStudies,
'lbnu SinaInslituleforFundamenlal
a1310UTIVI
Skudai,Johor,[4alaysia
lJniversiliTeknologilvlalaysia,
my
'Corespondingauthotemailadd€ss: aishah@ftkksa.utm.
Abstract
by usinga simpleelectrolysissystemvia
methodof chlorobenzenes
An alternativedechlorination
Electrolysis
of chlorcbenzene
was carriedout
developed.
carbondioxidefixationtechniquehas been
platinum
Reaction
in an N,Nanode
and
a
cathode.
with
an
aluminium
cell
fitted
in a one-compartment
bromide(TPAB)at ooc,
(DMF)solutioncontainingO.1Mof tet€propylammonium
dimethylformamide
100 Ncc/minof CO, flow rate and 120 m/,/cm'of currentdensitywas found to be the optimum
yieldot benzoicacid.Thisconditions
wasthen
whichgaveT2o/a
of thiselechocafuoxylation,
conditions
in oder to convertit to theircorresponding
appliedto l,2iichlorobenzeneand 1,3-dichlorobenzene
benzoicacids.
chlofobenzene,benzoicacid, c€rbon dioxide,fxalon
Keywol.dsj Electfosynthesis,
lntloduction
is the simplestaromaticchloride,and formsthe framewofk of highlytoxico€anic
Chlorobenzene
polychlorobiphenyls
(PCBs),dioxinsand furans[1].Such componentswhichare
chloridessuch as
and
producedin a broad range of industrialprocessesare hazardousdue to their carcinogenic
compoundssuchas
mutagenicactivity.Thereare variousmethodsfor eliminalionof organochlorine
by biologicaltreatmentl2l, steamreforming[3], catalyticreactions[4], and incinerationHowever,
and couldalso produce
expensive,
ttiesemethodsrequirelongerrcactiontime and hightemperature,
another
is incomplete
moretoxicmaterialssuchas dioxinsandfuransif the combustion
[5].Therefore,
in oder to overcometheseproblems.
techniqueis necessary
alternative
reductionwhich is expectedto offer an
One of the promisingmethodsis by eleckochemical
is
safe, clean,cheapand easy to control
This
technique
of dechlorination.
effectiveconsequence
organics
halidescan be simplyreducedby
In
many
cases,
as
a
reagent
since it use electron
[6].
studieson the fast and efficient
and ambientpressure.Furthermore,
at roomtemperature
electrolysis
of PCB
may contributeto a new technologyfor the safe detoxification
of chlorobenzene
electrolysis
and dioxinswith lowenergyconsumption
[7]. However,eventhis techniqueis efficientand desirable
wastewhichcontainschlorine
of electrochemical
amongthe otherireatmentmethods,finalpurification
ions, precipitantor complexesstill is a problem.Therefore,hereinwe repod anotheraltemative
by usingcarbondioxidefixationmethod Benzojc
of chlorobenzene
dechlodnation
electrcchemically
processof electrochemical
waste but could
produced
the
disposal
is
not
only
simplify
acid that was
for examplein preparingcompoundsbearingsubstituents
alsooffersa greatnumberof advantages,
(F, CN, CO, R, co, and OR) that are not compatiblewith the preparationof organometallic
compounds
[8].
Matedalsand Methods
Materials
and 1,3-dichlo1,2-dichlorobenzene
werechlorobenzene,
usedin this experiment
The substaates
(D[4A),
(THF),
N-methyl-2-pyrdimethylacetamide
tetrahydrofuran
solvents
were
whilethe
robenzene
(DMF) Supportingelectrolytes
rolidinone(Nl\4P),acetonitrile(N/eCN)and N,N-dimethyl-formamide
perchlorate(TEAP),tetraethylammonium
bromide
used in this study were tetraethylammonium
from FlukaChemikaand
(TEAB)andtetrapropylammonium
bromide(TPAB).Theywercall purchased
usedas received.
cell equippedwith a magneticstirrerand a
was car ed out in a one-compartment
Electrolysis
(2 x 2 cm'), aluminiumbar anodeand a
platinum
plate
cathode
with
a
serumcap.The cellwas fltted
out
in
a
DlllF
soluton {10m1)containing01lvl of
path
was
carried
The
electrolysis
for CO2.
tube
was used as a model
and tolueneas a standardmaterial.Chlorobenzene
TPAB. chlorobenzene
substrateand five parameterswere studied in order to obtain the optimumconditionsof this
currentdensityand typeof anodematerials,
The paEmetercweretemperature,
electrocarboxylation.
solvents and supportingelectrolytes.Progress of the reaction was analyzed by FID gas
(AgilentTechnologies)
withHP-5column
chromatograph
Resulisand Discussion
stirringrcactionwithoutcurrentpassedgaveonly20%
Blanktest resultshowsthat conventional
and no benzoicacidwas producedat all. Therefore,in ordefto enhance
of chlorobenzene
conversion
and yield of benzoicacid,firstlythe effectof currentdensityon
the conversionof chlorobenzene
was carriedout at 0'C with magnesiumanodeand
was studied.Electrolysis
electrccarboxylation
platinumcathodeunderfour differentvaluesof currentdensity,whichwere 30, 60, 120 an"d180
at 120 mA'/cm'gave
mA,/cm2.
As shownin Figure1, after2 F/molof currentpassed,the electrolysis
(10%) Therefore,
yield
(60%)
acid
and
maximum
of
benzoic
of
c-hlorobenzene
highest
conversion
the
120mA,/cm'asthe optimumcurrentdensityin thiseletrocarboxylation.
we considered
^40
;
6
;60
Co.ve6ronof chlorobenzene
.9
e40
20
1m
60
90
curent densily(mAJcm'z)
onelectroc€rborylalion
ofchlorobenzene
Figure1i Effectof€urenldensity
Next,the efiectof typeof anodematerialswas studiedand the resultis shownin Table1. All data
was achievedwhenzincwas useas an
of chlorobenzene
weretakenat 3 F/mol.Completeconversion
atall. Theconversion
becamelowerwhenmagnesium,
anode:howeverno benzoicacidwas Droduced
yield
up to 3-9dloAnd it was
benzoic
acid
was
increased
of
copperand carbonwere used,but the
whichgave 3570,
in
material
this
electrocarboxylation
was
optimum
anode
the
foundthat aluminium
of aluminaum
higher
electrical
conductivity
maybe
due
to
the
yield
acid.
This
is
of
benzoic
the highest
comparedto othermaterials.On the otherhand,zinc metaldid not pedormwell in this non-aqueous
solventto producebenzoicacid sincemay be it relatedto what was reportedby lto that zinc show
highertendencyin producingcarbonmonoxide,oxylateand glyoxylatein the similarsystem[9]. The
effectof typeof cathodematedalswas alsostudiedby replacingthe platinumcathodewithcarbonand
as a cathodecomparedto
stainlesssteel.However,bothof them did not show betterperformance
platinumin thiselectrocarboxylation.
of chlorcbenzene
Table1: Effectof lvpeof anodematerialon elecirccarboxylalion
Typeof anodematerial
(%)
Convercion
YieldofBenzoicacid(%)
Zr
t\,49
100
45
77
40
49
9
35
3
7
Cu
c
(2 mmoD,
(anode)[,]-Pt(cathode),0.1[4
0'C, 120mAJcm',
Chloobenzene
TEAP-DMF,
Toluene(2 mmol)
werecarried
the electrolyses
of thiselectrocarboxylation,
In orderto findthe optimumtemperature
whichwereOoC,roomtempe€tureand 70dC.As shownin Figure2,
out at threedifferentlemperatures
and the highestof benzoicacid (35%).
at 0'C gave77Voconversionof chlorobenzene
electrolysis
(24"c)
seem
do
not
appropriate
in this system.While,the
at
room
temperature
Howevef,the rcaction
was carriedout at 70"C,but this tempe€ture
conversion
was increasedup to 93%whenelectrolysis
tempe€ture
to benzoicacid.We can seethat increasing
chlorobenzene
was notsuitablein converting
will favorthe decreasingof benzoicacid. Lowertemperaturemay increasethe solubilityof carbon
whichis classifiedas an aproticsolventand this may enhancethe
dioxidein dimethylfomamide,
undersuchcondition[8].Therefore,aimingto a simpleand mild
stabilityof the reductionintermediate
in thiselectrocarboxylation.
OoCas the optimumtemperature
we considered
conditionof electrolysis,
100
9
.q
:6 0
640
I
az o
40
80
Temperature
CC)
of chlorobenzene.
Figure2: Effectoftempefalureon eleclroc€rboxylation
(anode)Al-Pl(calhode),
0.1M TEAP-DIMF
Currenlpassed: 3 F/mol,
( 2 mmoD,
Toluene(2 mmol)
chlorobenzene
120m,rJcmz,
The effectof solventwas alsostudiedin orderto enhancethe yieldof benzoicacid.As tabulated
in Table2, the sequenceof the optimumsolventsis DN4F> NMP> [4eCN> DMA> THF. DMFgave
comparedto othersolventsaftet2 Flmol of currentwas
the highestyield of carboxylicacid (18o/o)
This is may
passed.Thus,DVIFis considered
to be the optimumsolventfor thiselectrccarboxylation.
be due to its highestamountof dielectricconstantamongthe othersolvents.DMSOalso is a good
solventfor manyinorganicsaltsand organiccompoundss nce it has the highestamountof dielectric
constant,howe;er, ii not appropriatein this reactiondue to it freezingpoint is at 20'C. While'
in acetonhile or lesspolarsolvents,wouldincreasedthe voltagedue to the precipitation
electrolysis
on the surfaceof the electrodeduringthe reaction
of chlorobenzene
Table2: Effectof tvpeof solventon eleclfocarboxylation
Yieldof Benzoicacid(%)
eJ
TetEhydrofu|an
CIHF)
(DI\,lA)
Dimethylacetamide
(NMP)
pyrrolidone
N-methyl-2
Acetonitrile(l\,4eCN)
(D[4F)
N,N-dimethylfomamide
0
0
23
7
76
18
n. iz mmoD
t"n
is also an imporlantparameterin this electroNext,the effectof typesof supportingelectrolytes
used in the expeimentsweretetraethylAs shownin Table3, supportingelectrolytes
carboxylation.
bromideAccording
bromideand tetrapropylammonium
tekaethylammonium
ammoiiumperchlorate,
of suppofting
the
effectiveness
the
sequence
of
at
2
F/mol,
to the resuitwhich were all taken
rateconstant
>
will
decrease
the
>
in
size
of
cation
The
increasing
TPAB
TEAB.
are
TEAP
electrolytes
of elecfontransferfromelectrodeto subskate[10].This is the reasonbehindthe smallestyield(8%)
bromideat 2 F/molcomparedto the tetraalkylammonium
of benzoicacid by tetrapropylammonium
ion benefits
rateconstantof the tetraprcpylammonium
smaller
ionsof TEAPand TEAB.However,the
termination
later
through
time
and
causing-a
yield
increases
benzoic
acid
the
of
when
the electrolysis
TPABis the onlysalts
electrolyte
of currentpassed.Table3 showsthat comparedto othersupporting
the highest
the currentpassedto 14 F/moland eventuallygave61olo,
that couldcontinueconducting
yieldof benzoac
acid.
on electfocarboxylalio.
of chlorcbenzene
eleclrclyte
Table3: Effectot lypeof supporting
(SE)
Electrolyte
Typeof Supporting
perchlorate
(TEAP)
Tetraethylammonium
bromide(TEAB)
Tetraethylammonium
bromide{TBAP)
Tetrapropylammonium
bromide(TBAP)"
Tetrapropylammonium
Conversion Yieldof Benzoic
76
83
90
18
10
I
61
(2 mmol)Toluene(2 rnnro)
(anode)Al'Pt(calhode),
o.1M SE Ol\4F,
O"c,120 rnA/cm',chlorcbenzene
pa$ed.
14
F/molofcurrenl
" Dalawastakenat
in DMF solutioncontaining
Therefore,we consideredthat electrolysisat OoCand 120 mAJcm'z
bromidewithaluminiumanodeand platinumcathodeas the optimumconditions
tetfapropylammonium
Finally,we stud;edthe flowrateof carbondioxideand the resultis shown
in thiselectrocarboxylation.
did not get
of chlorobenzene
in Table4. Aftef 3 F/molof currentpassed,we foundthatthe conversion
that the
Howevef,
it
was
observed
to
190
Ncc/min
was
raised
up
eventhe flow rate
higherthat 62010
yield of benzoicacidwas increasedwith the increasingof flow rate.By allowingthe currcntto pass
wereincreasedupto 78%and 890/0,
until6 F/molfor 1OOand 190 Ncc/min,we foundthatconversions
for 100 Ncc/minof flow rate at the same condition'the yieldof benzoic
Nevertheless,
respectively.
we considered
that 100
to maximum(72%)but notfor the 190Ncc/minTherefore,
aci; abo increased
Ncc/minas the optimumflow rate in this system and next this conditionwas appliedto 1'2benzoicacid.Howevef,may be due to the
in oder to convertit to its corresponding
dichlorobenzene
benzoicacid
was
70% but no corresponding
sterichindrancethe conversionof l,2iichlorobenzene
was prcducedat all.
ofchlorobenzene
Table4: Effectof CO,nowtateon eleclrccarborylation
Flowrateof CO,
{Ncc/min)
30
80
100
100150
200
190-
Conversion
('/"J
Yieldof Benzoic
acid(%)
26
60
54
78
20
62
89
3
16
72
18
11
(2 mmol),
(anode)M'P(cathode),
0'C, 120mtucm',Chlorobenzene
0.1w|TEAP-DMF,
i
passed
(2
run
uriil
6
F/mol
of
cunenl
was
mmol).
Electrolvsis
To uene
e and the resultis showsin Figure3. In this
ichlorobenzen
Theabovefeactionalsoappliedto 1,3_d
acidor 3was achievedbutthe peakof isophthalic
case.completeconveEionof 1,3-dichlorcbenzene
yield
acid and
Figure
the
of
benzoic
3,
acid could not be traced. As shown in
chlorobenzoic
However,
the
1
lorobenzene.
of
conversion
of
,3-dich
was increasedwiththe increasing
chlorobenzene
yield
passed,
the
was
F/mol
of
current
then
20%
at
6
yield
was
only
of benzoicacid
maximum
and finallythe currentwasterminatedafter9 F/molof currentpasseddueto the increasing
decreased
ofvoltaoe.
_e.*
Q-" ry"""iO
m
8zo
.e 60
€bo
E!,o
i30
"zo
't0
of 1,3-dichlotobenzene.
Figute3: Electtocarboxylation
:3 F/mol,
(anode)Al-P(cathode),
Curenlpassed
01MTEAPDIVF,
(2
(
2
mmol),
Toluene
mmo
120mA,/cm?.
Chlorcbenzene
)
The prcposed reaction mechanism of this dlectrocarboxylationof chlorobenzeneis shows ,n
Figure4. The reactionstarted at anode where aluminiumwas oxidizedto give Al"'cation and donated
th;ee electrons. While at cathode, cO2 received an electron to form anion radical' cor' lhen,
chlorobenzenereceived one electron to form benzene radical, Af and releasingchloine atom' ClThe remainingelectrcnwas receivedby this benzeneradicalto form benzeneanion,Ai Anion radical
of CO, reactedwith benzene anion, Aa to give carboxylatedanion IArcOO ] which, finally pfotonated
by solventto give benzoicacid.
-
A t + A t3*
+ 3e
Cathode: C Or+ e-+ C Or-'
O'.'- Qo - c '.
: cot' .
overar
O" rf- ry"oo"
of chlorobenzene
of electrocarboxylation
Figure4: Theproposedreactionmechanism
Conclusion
by usinga simpleelectrolysis
methodof chlorobenzenes
dechlorination
an alternative
ln conclusion.
Benzoicacidthatwas producednot
systemvia carbondioxidefixationtechniquehasbeendeveloped.
onlysimplifiedthe wastekeatmentof harmfulcompoundsbut alsocouldbe consideredin conveding
thosecompoundsto usefulproductssuchas carboxylicacidsthal havemanyusesespeciallyin the
fieldof phafmaceuticalAcknowledgemenis
for financialsupportsundera Fundamental
TeknologiIVlalaysia
Ourgratitudegoesto Universiti
Foundation
for their
ResearchGrant(No.75048).We wouldalsoliketo thankthe HitachiScholarship
Grant
Instruments
forthe GasChrcmatography
supportespecially
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