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The electroreduction of CO2 to malate on a mercury cathode
Tetrahedron
THE A.
~10.53. pp. 4623-4626 1969.
Letters
ELECTROREDUCTION
Bewick
(Received
and G. P.
OF CO2 TO MALATE
Greener,
dioxide
and water
wish to report
the discovery
the production
of more
Carbon mercury
dioxide
cathode
irreversible followed
was
in aqueous
of formate.
red
chemical
tests
eatholyte dried
using
were
defined
acid
Paper
spectrum
of material
pure malic
acid
The malate amount
of malate
the presence after
acid.
removal
1969)
synthesis.
of carbon
at controlled
column
ammonium volts
(vs.
obtained
We
dioxide
salts.
from
with
gave
exactly
catholyte
electroIyses
with a smaller tests
a positive
120).
in position
gave the same
chromatogram
Further-
indication
The elluent
solvent.
but
species.
acid was liberated
acid/water
corresponding
a preparative
I.R.
state
by chemical
of formate any free
and can be
together
carboxylate
on a
An
steady
of another
(Amberlite
a butanol/acetic
potential
N.H.E.)
(1) and identified
Accordingly,
on the untreated from
organic
and found to be malate
w&s expected
spot was obtained
chromatography
The products analysed
indicated
with
electrochemically
at about -1.4
an ion exchange
for
of So1:)I:eInpton.
14th October
for the fixing
begins
on the catholyte
and run on paper
process
of quaternary
volts.
both an ti and a p hydroxy
feedstocks
Mw
CATHODE
University
publication
in areat
molecules.
Formate
spectroscopy
for
Printed
ON A MERCURY
of Chemistry,
solutions
process
of potentials
ideal
of a novel
reduced
out to about -2.6
amount
are
complex
cathodic
at a number
infra
Department
in UK 2nd September 1969; accepted
Carbon
Pergamcn Press.
from
result.
was compared
the
was freeze
A single, to a malic
for
well
acid
standard.
The infra
red
with that from
and found to be identical. was
analysed
in a sample
quantitatively was complexed
4623
by a colourimetric with MO(W).
method.
The excess
The total Mo(IV)
present
4624
NO.53
was reduced
with chlorostannous
spectrophotometrically The acid
at
stoichiometric
acid and the resulting
725 m
equation
blue Mo(III)
The procedure
r* for
was checked
a full electrochemical
is
was estimated with malate
reduction
standards.
of CO2 to malic
roeCH(OH) 4C02
+
lOH+
+
12e-
I CH
*
+
3H20
(1)
I 2 cooIn most cases we have found that the amount of malateproduced basis
of equation
potential
curve
(l),
is shown in figure
electrochemical
in nature.
possibility
of hydrogen
by looking
for amines
the quaternary
only remaining
equation
chemical
route:
arises
reineckate
illustrate
The yieldcannot be purely
as to what the reaction ammonium
on the
can be.
constant
potential
No amines ammonium
via the water
the reduction
electrolysis
were
detected
ions were
molecules
process
The
salt was investigated
of G. L. C. and by quantitatively
(2).
that quaternary
of 109%.
that the reaction
the quaternary
and after
is reduction
in excess
implies
by means
ion before
showed
would
greatly
This
from
in the product
possibility
following
1.
abstraction
with ammonium
analysis
yield
The question
ammonium
of its complex quantitative
to a coulombic
corresponds,
snalysing by means
and the
not consumed.
and,
The
as an example,
if it took place
the
by a completely
COOH CHOH
4c02
+
9H20
-
+ 6H202
)
(2)
CH2 COOH Clearly coulombic
reactions yield
greater
(1) and (2) can be combined than 100%.
as a possibility.
Although
available
this reaction
to drive
the potentials
at which
We felt
we satisfied
we were
operating.
reluctant
ourselves
we expected
in suitable
ratios
at first
,that there
that hydrogen
to give
to postulate was enough
peroxide
The high coulombic
any desired reaction
free
energy
would be reduced
yields
(2)
observed
at
would
4625
NO.53 Accordingly,
only be obtained if the hydrogen peroxide was not reduced. investigated the electrochemical experimental
we
reduction of hydrogen peroxide under our
The reduction was found to be ve,ry slow and verified
conditions.
that hydrogen peroxide or an equivalent species could be involved in the reduction of carbon dioxide. The novel combined chemical and electrochemical suggested has a number of interesting
features.
mechanism that we have
Prom our results it follows that
it is possible to synthesise malic acid with the consumption of only ‘18 of an electron per molecule of carbon dioxide.
There must be, therefore,
mechanism in which a single electron
can successively
activate several
We envisage that an adsorbed layer of tetraalkylammonium essentially
a CO2 molecule
involved in the process
cations prwides
receives
are a matter of conjecture.
an electron to form an anion radical.
the adsorbed layer may well cause such intermediates
an
Presumably
The mediation of
to react with more CO2
The size of the transition state which may be achieved could be
determined by the properties relative
molecules.
non-aqueous environment where this sort of reaction might take place.
The intermediates
molecules.
a chain electron transfer
of the adsorbed layer which would also determine the
orientation and availability
abstraction process. with the properties
This specific
of water molecules
allowing the resulting hydrogen
action of the adsorbed layer could be compared
of ion exchange membranes or enzymes.
The synthesis is not only of interest as a means of making a useful material from readily available and inexpensive a relatively
small amount of electric
starting materials
power but has far reaching implications
analogy with the photosynthetic fixation of CO2 is sought. seeking to modify the highly specific to achieve different results.
with the consumption of if an
We are, at present,
conditions on the electrode
surface in order
4626
No.55
Yield (mg./coulomb) (0.11 mg/coulomb
corresponds
to a lOG% coulomb yieldbased solely on eqn.(l))
0.6
o-2
1.8 Figure 1.
I
I
1*9
2.0
E(vs.Ag/AgCl,O*lNCl-)
I 2'1
2.2
2.3
Yield of Malic Acid as a Function of Potential
log(i inpA)
,Ag/AgCl,O.lNCl-)
Figure 2.
Current - Potential Curves for the Reduction on a Mercury Cathode
of CO2
(Electrode Area 0.06sq.cm.)
REFERENCES 1. J. E. Teeter and P. Van Rysselberghe, Proc.6th Meeting C.I.T.C.E. pp.538-542(Butterworth) 2. G. D. Baccom, Boll. Chim. Farm., 97 (1958), 454.
(1955)
THE A.
~10.53. pp. 4623-4626 1969.
Letters
ELECTROREDUCTION
Bewick
(Received
and G. P.
OF CO2 TO MALATE
Greener,
dioxide
and water
wish to report
the discovery
the production
of more
Carbon mercury
dioxide
cathode
irreversible followed
was
in aqueous
of formate.
red
chemical
tests
eatholyte dried
using
were
defined
acid
Paper
spectrum
of material
pure malic
acid
The malate amount
of malate
the presence after
acid.
removal
1969)
synthesis.
of carbon
at controlled
column
ammonium volts
(vs.
obtained
We
dioxide
salts.
from
with
gave
exactly
catholyte
electroIyses
with a smaller tests
a positive
120).
in position
gave the same
chromatogram
Further-
indication
The elluent
solvent.
but
species.
acid was liberated
acid/water
corresponding
a preparative
I.R.
state
by chemical
of formate any free
and can be
together
carboxylate
on a
An
steady
of another
(Amberlite
a butanol/acetic
potential
N.H.E.)
(1) and identified
Accordingly,
on the untreated from
organic
and found to be malate
w&s expected
spot was obtained
chromatography
The products analysed
indicated
with
electrochemically
at about -1.4
an ion exchange
for
of So1:)I:eInpton.
14th October
for the fixing
begins
on the catholyte
and run on paper
process
of quaternary
volts.
both an ti and a p hydroxy
feedstocks
Mw
CATHODE
University
publication
in areat
molecules.
Formate
spectroscopy
for
Printed
ON A MERCURY
of Chemistry,
solutions
process
of potentials
ideal
of a novel
reduced
out to about -2.6
amount
are
complex
cathodic
at a number
infra
Department
in UK 2nd September 1969; accepted
Carbon
Pergamcn Press.
from
result.
was compared
the
was freeze
A single, to a malic
for
well
acid
standard.
The infra
red
with that from
and found to be identical. was
analysed
in a sample
quantitatively was complexed
4623
by a colourimetric with MO(W).
method.
The excess
The total Mo(IV)
present
4624
NO.53
was reduced
with chlorostannous
spectrophotometrically The acid
at
stoichiometric
acid and the resulting
725 m
equation
blue Mo(III)
The procedure
r* for
was checked
a full electrochemical
is
was estimated with malate
reduction
standards.
of CO2 to malic
roeCH(OH) 4C02
+
lOH+
+
12e-
I CH
*
+
3H20
(1)
I 2 cooIn most cases we have found that the amount of malateproduced basis
of equation
potential
curve
(l),
is shown in figure
electrochemical
in nature.
possibility
of hydrogen
by looking
for amines
the quaternary
only remaining
equation
chemical
route:
arises
reineckate
illustrate
The yieldcannot be purely
as to what the reaction ammonium
on the
can be.
constant
potential
No amines ammonium
via the water
the reduction
electrolysis
were
detected
ions were
molecules
process
The
salt was investigated
of G. L. C. and by quantitatively
(2).
that quaternary
of 109%.
that the reaction
the quaternary
and after
is reduction
in excess
implies
by means
ion before
showed
would
greatly
This
from
in the product
possibility
following
1.
abstraction
with ammonium
analysis
yield
The question
ammonium
of its complex quantitative
to a coulombic
corresponds,
snalysing by means
and the
not consumed.
and,
The
as an example,
if it took place
the
by a completely
COOH CHOH
4c02
+
9H20
-
+ 6H202
)
(2)
CH2 COOH Clearly coulombic
reactions yield
greater
(1) and (2) can be combined than 100%.
as a possibility.
Although
available
this reaction
to drive
the potentials
at which
We felt
we satisfied
we were
operating.
reluctant
ourselves
we expected
in suitable
ratios
at first
,that there
that hydrogen
to give
to postulate was enough
peroxide
The high coulombic
any desired reaction
free
energy
would be reduced
yields
(2)
observed
at
would
4625
NO.53 Accordingly,
only be obtained if the hydrogen peroxide was not reduced. investigated the electrochemical experimental
we
reduction of hydrogen peroxide under our
The reduction was found to be ve,ry slow and verified
conditions.
that hydrogen peroxide or an equivalent species could be involved in the reduction of carbon dioxide. The novel combined chemical and electrochemical suggested has a number of interesting
features.
mechanism that we have
Prom our results it follows that
it is possible to synthesise malic acid with the consumption of only ‘18 of an electron per molecule of carbon dioxide.
There must be, therefore,
mechanism in which a single electron
can successively
activate several
We envisage that an adsorbed layer of tetraalkylammonium essentially
a CO2 molecule
involved in the process
cations prwides
receives
are a matter of conjecture.
an electron to form an anion radical.
the adsorbed layer may well cause such intermediates
an
Presumably
The mediation of
to react with more CO2
The size of the transition state which may be achieved could be
determined by the properties relative
molecules.
non-aqueous environment where this sort of reaction might take place.
The intermediates
molecules.
a chain electron transfer
of the adsorbed layer which would also determine the
orientation and availability
abstraction process. with the properties
This specific
of water molecules
allowing the resulting hydrogen
action of the adsorbed layer could be compared
of ion exchange membranes or enzymes.
The synthesis is not only of interest as a means of making a useful material from readily available and inexpensive a relatively
small amount of electric
starting materials
power but has far reaching implications
analogy with the photosynthetic fixation of CO2 is sought. seeking to modify the highly specific to achieve different results.
with the consumption of if an
We are, at present,
conditions on the electrode
surface in order
4626
No.55
Yield (mg./coulomb) (0.11 mg/coulomb
corresponds
to a lOG% coulomb yieldbased solely on eqn.(l))
0.6
o-2
1.8 Figure 1.
I
I
1*9
2.0
E(vs.Ag/AgCl,O*lNCl-)
I 2'1
2.2
2.3
Yield of Malic Acid as a Function of Potential
log(i inpA)
,Ag/AgCl,O.lNCl-)
Figure 2.
Current - Potential Curves for the Reduction on a Mercury Cathode
of CO2
(Electrode Area 0.06sq.cm.)
REFERENCES 1. J. E. Teeter and P. Van Rysselberghe, Proc.6th Meeting C.I.T.C.E. pp.538-542(Butterworth) 2. G. D. Baccom, Boll. Chim. Farm., 97 (1958), 454.
(1955)