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The reduction of 2-chloro-benzoic acid
THE
REDUCTION
OF
2-CHLORO-BENZOIC
ACID
J. A. HARRIZON and K. SCOFFHAM Electrochemistry Research Laboratories. School of Chemistry. University of Newcastle upon Tyne, Newcastle-upon-Tyne. NE1 7RU. England (Rrcrmwl Abstract-The
electrodes.
reduction
of
2-chloro-benzoic
I 1 Auyust acid
INTRODUCTION The
reduction of substituted aromatic carboxylic acids to the corresponding aldehyde and alcohol goes with Iow current yield on mercury[l,t]. The mechanism probably proceeds by way of the aldehyde hydrate as both aldehyde and alcohol appear as products: RCOOH RCHO
+ 2e + 2H + = RCH(OH)Z RCH(OH), Z$ RCHO + HZ0 + 2e + 2H + + RCH*OH.
A detailed investigation of the variation of the products with time at the mercury coated rotating copper disc has been carried out[2]. Other systems have been investigated mainly from a synthetic point of view[3,4]. It is the purpose of the present note to extend the measurements to other metals, lead, tin, zinc and carbon and to investigate 2-chloro-benzoic acid. The hope is that introducing the chloro group will he an additinnal guide to the mechanism of the electrode reaction. EXPERIMENTAL
has
1975) been
studied at the Hg, Pb, Sn, Zn
and
C
treated with air-agitated dilute nitric acid and twicedlstilled. The anode was constructed from a platinum sheet. The rotating disc cell consisted of an approximately 300ml cathodic compartment separated from the anode by a fine glass frit. The anode was directly below the rotating disc. As the cell was horizontally mounted it was necessary to have a side arm in the anode compartment to avoid build-up of oxygen formed in the anode reaction. The mercury electrode was a mercury pool, I3 cm2 in area separated from a carbon anode by a glass frit. The reference electrodes used throughout the experiments were saturated calomel. A junction to the solution under investigation was made in a glass frit. The potential was controlled by a TR 70-2A potentiostat (Chemical Electronics Ltd). Experimental
procedure
The electrolytes were carried out as follows. In both the mercury pool cell and the rotating disc cell the amount of solution contained in the working electrode portion was 250 ml. The pH was measured before and after the run. The solution was deaerated with NZ_ With both cells, once contact was made between the working electrode and solution the working potential was applied immediately to prevent dissolution of the metal by corrosion. The electrolyses were carried out at room temperature. The electrolysis currents were followed by using a single pen Servoscribe RE 51 I .20 potentiometric recorder.
Anhydrous di-sodium hydrogen orthophosphate, 3-aminobcnzoic acid, 2-chloro-benzoic acid, benzyl alcohol, monochloro benzene and potassium chloride were all B.D.H. chemicals. Sodium dihydrogen orthophosphate was a Hopkin and Williams Ltd. AnalaR chemical. 2-chlorobenzaldehyde was obtained from Ralph N. Emanuel Ltd. and 2-chlorobenzyl alcohol Analysis was received from the Aldrich Chemical Co. Inc. The products of the reaction cell were extracted Thrice-distilled water was used as a solvent. The base ether. This of solvent with 8 x 100 portions electrolyte solution consisted of 0.5 M sodium dihydextract was reduced to 50ml by evaporation of the rogen phosphate, 0.1 M disodium hydrogen phosether using a Buchi rotary evaporator. A 3 ml sample phate and 0.1 M potassium chloride. The aromatic of the remaining extract was removed and used for acid was at as high a concentration as possible consisanalysis. The analysis procedure was tested by maktent with its solubility, in order to maximise the ing up a mixture of the reaction products. All analyses amount of product at low potential. The system is were carried out by glc using a 1.5 m x 5 mm column only partially buffered for part of the run. but as there of 10% Silicone Gum Rubber SE 52 stationary phase is R large amount of hydrogen given off in the case on a solid support of BO/lOO grade Diatoport S in of Hg and Pb this was unavoidable. The cathode an F and M 810 instrument, with flame ionisation materials were mercury, tin, zinc, lead and glassy cardetection. Comparison was made with standard solubon. The tin, zinc and lead were 5 N standard, tions of similar concentrations prepared in ether. The obtained from Koch-Light Laboratories. They were oven temperature was 140°C and the injection port cast in carbon mouids of 3.14 cm’ cross-section to and detector temperatures were 140 and 160°C remake rotating disc electrodes. The glassy carbon was spectively. Retention times were approximately as folohlxined from Le C‘arbone Co. The mercury was 585
K.
E. Fig.
I.
CurrentGpoten~ml
V
curve for 0. I M 2-chloro
acid in the base electrolyte Potential swerp rate 0
solution
at
I V s ‘, rotation
benzoic a Pb rotating disc. speed 120 rad s ‘.
monochlorobenzene (l%), benzaldehyde (~OS), alcohol (64s), 2-chlorobenzaldehyde (54s) and L-chlorobenzyl alcohol (11%). lows:
SCOFFI1AM
the total product at lead and mercury electrodes, measured by glc, as a function of potential. This graph represents the partial current due to the reduction of the organic acid. A similar rate was observed in a l-h and 3-h run. Although the curves are not of high precision, they show, in spite of hydrogen evolution, a wave type curve. This is much more negative than the prewave in the current. The limiting rate of 4 to 5 x 10m5 moles h-’ cm-’ can be compared with the expected value ADC = 4 x 10m3 moles h-’ cm-“. <‘learIy the hmlting rate 1s not diffusion controlled. This is unlikely to bc due to the change in pH, caused by the H2 evolution reaction, as the 1 and 3 h runs gave a similar result. The rate of reaction also seems to depend on the metal, and if it is assumed that the rate of Hz evolution is the same, it is somewhat easier on mercury. Figure 2 also shows similar measurements on tin and zinc. The corrcsponding current-potential curves are shown in Fig. 3. It is significant that the rate of product formation seems to follow the current potential curve. The current-potential curve indicates that the reaction proceeds without pamlIe hydrogen evolution and this is substantiated by an approximate correspondence
benzyl
RESULTS Rare cwy.
of’
reduction
tin.
zinc
of 2-chlorohmzoic und carbon
acid on lead.
mer-
Current-potential curves at the rotating lead disc and the mercury pool show that almost all the current could be accounted for by hydrogen evolution. The curves have a prewave shown in Fig. 1 for lead, with and without the aromatic acid. As will be shown by the product analysis the prewave is probably due to the reduction of a proton which merges into the reduction of water. The height of the prewave is approximately the value expected from neasurements in 0.5 M hydrochloric acid alone and occurs at the same potential. The reduction 01 H&I seems to be enhanced by the organic acid. The rate of the organic acid reduction itself was measured using chemical analysis. Figure 2 shows the rate of appearance of
E. v 2. Total product in IV5 mole h-‘cm-’ produced by clectrolysing 0.1 M 2-chloro benzoic acid in the base electrolyte solution at (1) Pb rotating disc electrode (233 r-ad s-l): (2) Hg pool; (3) Zn rotating disc (60 rad s-l); Fig.
(4)
Sn
rotating
disc
(60
rad
5-l).
r
I --07
-0.9
-1
E.
I
V
Lb)
E,
V
Fig 3. Current-potential trode; (a) 0.1 M 2-chloro (b) in base
electrolyte
curve at a Sn rotating disc elecbenzoic acid and base electrolyte; alone. Sweep rate 0. rotation
speed 60 rad s-l.
I V s- ’ :
The reduction
of 2-chloro-henzoic
acid
587
for 1 h and 3 h show no sign of dechlorination products. On the other hand reduction on tin and zinc give a wider variety of products. As before thcsc were identified by comparison with standards in the glc. The identifiable products are shown in Table 1. In addition, in both the runs on tin and zinc there were some possibly higher molecular weight products which could not be identified but which were observed on the glc at a retention time of about 200s. The amount formed is probably small. DISCUSSION
4. Yield irl gms II ’ nf the p, oducts f,nrmed at the rotating disc (233 rad s- ‘) in 0. I M 2.chloro benzoic acid in the base electrolyte solution. (I) 2-chloro benzaldehyde [A); (2) 2-chloro benzyl alcohol (m): benzaldehyde ( Y ): benzyl alcohol (0). Fig. Ph
between the current passed and the total amount of product in the case of tin. For example at E = 725 mV, 4.5 x 1W4 moles of product were formed compared with the charge (4~) passed equivalent to 1.6 x 1O-4 moles. A film was formed on the electrode which was organic in nature but it hardly impeded the reaction. For zinc the current efficiency for the formation of simple products is less than for tin. For example at E = - 1180mV, 1.7 x 10w4 moles of product were formed compared with the charge (4~) passed. equivalent to 1 x 10e3 moles. In this experiment an organic film was formed which reduced the current more than in the case of tin. Measurement of the total product was also made on a glassy carbon rotating disc electrode (223 rad s-l) at one potential, E = - 1850 mV, only. One product was found after a 2.5 h tun, namely 7 x IO-” moles of bcnzyl alcohol with a trace of 2-chlorobenzyl alcohol. The current was very variable and the amount of hydrogen depended on the extent of film formation. If the reaction was interrupted, on applying a negative potential again a very low current was observed. A film had formed which could only be removed mechanically.
The dlstrihution of the various products is shown in Fig. 4 and Fig. 5 for lead and mercury. Dechlorination products on this time scale only appear at more cathodic potential> than E = - 1850mV. This result seems to be a potential effect and not a time effect as runs at E = ~ 1850 mV on both mercury and lead
Figure 6 shows the reduction of 3-amino benzoic acid on a lead rotating disc electrode compared with the base electrolyte. This is one of the few aromatic acids which is reduced on Pb at more positive potentials than the base electrolyte. Because a high concentration of the organic acid is necessary to bring the reduction from the background the pH of the solution 1 and 2 in Fig. 6 is different. However, curve I 1s essentially the reduction of H,O. It is significant that the prcwave of Fig. 1, for 2-chlorobenzoic acid is suppressed. Unfortunately in this case the products are too unstable to follow quantitatively with the glc. However. the reduction is certainly limited by the interfacial rate and has a 120 mV Tafel slope. It would seem likely that the reduction of 2-chlorobenzoic acid on lead and mercury has similar kinetics, although
Fig. 5. Yield in gms hK’ of the products formed at the Hg pool electrode in 0.1 M 2-chloro benzoic acid: (1) benzaldehyde (x ): (2, benzyl alcohol (Ll); (3) 2.chloro benzaldehyde (A): (4) 2.chloro benzyl alcohol.
Table Metal
- 675 -772s -950 - 1080 -1180
A* henzaldehyde: IXIIH
A-
E(mW
Sn Sn 8n Ztl Zn
II
Yield
0 0 0
7.3 x IO_ s 0 Bt benzyl
alcohol:
B-t 4 1 6 I 1
x x x x x
C: 2-chloro
I in moles after a CY
10-s 10-4 IW5 IO_’ IO 4 benzaldehyde:
I
8 x IO-h 2 x 10-5 1 x 10-5 0 I x 10-3
I>rj2-chloro
h run
Dti
El1
10-3 3 x 10-h 1 x 10-A 0 2 x 10-s
2x IO s 3 x 10-3 3 x 10-5 0 4 x 10-5
I x
benzyl
alcohol ;
El\ Chloro
benzene.
588
removed from the 2-chloro benzaldehyde or alcohol as the 1,2-dichlorobenzene is reduced at more negative potentials[5]. On carbon the chloro group is removed more easily and the aldehyde is probably strongly adsorbed, as the reaction goes straight to the alcohol. The results on tin and zinc show that the rate of the electron transfer reaction is significantly enhanced. It is clear that the reaction is more complex than that at lead and mercury. However. the most Interesting fact is that a new reaction occurs. the decarboxylation of the organic acid. A similar reaction is known in classical organic chemistry and can be carried out using copper powder[6, 71. It will be useful to confirm this result and optimise the electrochemistry to effect this reaction alone.
E,
REFER EI\ICES
V
Fig. 6. Current-potential curve for the reduction of 3-NH1 benroic; acid at a Pb rotating disc: (1) in base electrolyte alone: (2) 0.1 M 3-NH2 benzoic acid in base electrolyte. speed 60 rad SC’. sweep rate 0.1 v s-1, rotation
1. 2. 3. 4.
the rate is higher on mercury. The distribution of aldehyde and alcohol is presumably then determined by the slow aldehyde dehydration step. The appearance of dechlorinated products is probably caused by I direct reduction at the metal surface of the chloro group. It seems likely that the chloro group is
5. 6. 7.
J. H. Wagenknecht. /. orq/. Chent. 37 (1972) 151.3. _I. A. Harrison and D. W. Shnesmith. J. r~lrcvr~on~~ul. Chem. 32 (1971) 125. See I_. Eberson, Oryarlic t;Iecrrocl~~n,isri-~: (Edited by M. Baizer) p. 413, Marcel Dekker (1973). 0. R. Brown, J. A. Harrison and K. S. Sastry. J. PI(,~rroanal. Chen,. 58 (1975) 387. S. 0. Farwelt, F. A. Rctand and R. D. Gecr. J. elrcrronnul. Chrrn. 61 (197% 303. Fieser and Fieser, Rrugenrs fbr Oryanl~~ 5’ynthr.si.s. Vol. I, p. 157. John Wiley, New York (1967). Fieser and Fieser. Rccry~nts fur Or+mz~’ S~~nrhrsiu. Vol. 2, p. 82. John Wiley. New York (1969).
REDUCTION
OF
2-CHLORO-BENZOIC
ACID
J. A. HARRIZON and K. SCOFFHAM Electrochemistry Research Laboratories. School of Chemistry. University of Newcastle upon Tyne, Newcastle-upon-Tyne. NE1 7RU. England (Rrcrmwl Abstract-The
electrodes.
reduction
of
2-chloro-benzoic
I 1 Auyust acid
INTRODUCTION The
reduction of substituted aromatic carboxylic acids to the corresponding aldehyde and alcohol goes with Iow current yield on mercury[l,t]. The mechanism probably proceeds by way of the aldehyde hydrate as both aldehyde and alcohol appear as products: RCOOH RCHO
+ 2e + 2H + = RCH(OH)Z RCH(OH), Z$ RCHO + HZ0 + 2e + 2H + + RCH*OH.
A detailed investigation of the variation of the products with time at the mercury coated rotating copper disc has been carried out[2]. Other systems have been investigated mainly from a synthetic point of view[3,4]. It is the purpose of the present note to extend the measurements to other metals, lead, tin, zinc and carbon and to investigate 2-chloro-benzoic acid. The hope is that introducing the chloro group will he an additinnal guide to the mechanism of the electrode reaction. EXPERIMENTAL
has
1975) been
studied at the Hg, Pb, Sn, Zn
and
C
treated with air-agitated dilute nitric acid and twicedlstilled. The anode was constructed from a platinum sheet. The rotating disc cell consisted of an approximately 300ml cathodic compartment separated from the anode by a fine glass frit. The anode was directly below the rotating disc. As the cell was horizontally mounted it was necessary to have a side arm in the anode compartment to avoid build-up of oxygen formed in the anode reaction. The mercury electrode was a mercury pool, I3 cm2 in area separated from a carbon anode by a glass frit. The reference electrodes used throughout the experiments were saturated calomel. A junction to the solution under investigation was made in a glass frit. The potential was controlled by a TR 70-2A potentiostat (Chemical Electronics Ltd). Experimental
procedure
The electrolytes were carried out as follows. In both the mercury pool cell and the rotating disc cell the amount of solution contained in the working electrode portion was 250 ml. The pH was measured before and after the run. The solution was deaerated with NZ_ With both cells, once contact was made between the working electrode and solution the working potential was applied immediately to prevent dissolution of the metal by corrosion. The electrolyses were carried out at room temperature. The electrolysis currents were followed by using a single pen Servoscribe RE 51 I .20 potentiometric recorder.
Anhydrous di-sodium hydrogen orthophosphate, 3-aminobcnzoic acid, 2-chloro-benzoic acid, benzyl alcohol, monochloro benzene and potassium chloride were all B.D.H. chemicals. Sodium dihydrogen orthophosphate was a Hopkin and Williams Ltd. AnalaR chemical. 2-chlorobenzaldehyde was obtained from Ralph N. Emanuel Ltd. and 2-chlorobenzyl alcohol Analysis was received from the Aldrich Chemical Co. Inc. The products of the reaction cell were extracted Thrice-distilled water was used as a solvent. The base ether. This of solvent with 8 x 100 portions electrolyte solution consisted of 0.5 M sodium dihydextract was reduced to 50ml by evaporation of the rogen phosphate, 0.1 M disodium hydrogen phosether using a Buchi rotary evaporator. A 3 ml sample phate and 0.1 M potassium chloride. The aromatic of the remaining extract was removed and used for acid was at as high a concentration as possible consisanalysis. The analysis procedure was tested by maktent with its solubility, in order to maximise the ing up a mixture of the reaction products. All analyses amount of product at low potential. The system is were carried out by glc using a 1.5 m x 5 mm column only partially buffered for part of the run. but as there of 10% Silicone Gum Rubber SE 52 stationary phase is R large amount of hydrogen given off in the case on a solid support of BO/lOO grade Diatoport S in of Hg and Pb this was unavoidable. The cathode an F and M 810 instrument, with flame ionisation materials were mercury, tin, zinc, lead and glassy cardetection. Comparison was made with standard solubon. The tin, zinc and lead were 5 N standard, tions of similar concentrations prepared in ether. The obtained from Koch-Light Laboratories. They were oven temperature was 140°C and the injection port cast in carbon mouids of 3.14 cm’ cross-section to and detector temperatures were 140 and 160°C remake rotating disc electrodes. The glassy carbon was spectively. Retention times were approximately as folohlxined from Le C‘arbone Co. The mercury was 585
K.
E. Fig.
I.
CurrentGpoten~ml
V
curve for 0. I M 2-chloro
acid in the base electrolyte Potential swerp rate 0
solution
at
I V s ‘, rotation
benzoic a Pb rotating disc. speed 120 rad s ‘.
monochlorobenzene (l%), benzaldehyde (~OS), alcohol (64s), 2-chlorobenzaldehyde (54s) and L-chlorobenzyl alcohol (11%). lows:
SCOFFI1AM
the total product at lead and mercury electrodes, measured by glc, as a function of potential. This graph represents the partial current due to the reduction of the organic acid. A similar rate was observed in a l-h and 3-h run. Although the curves are not of high precision, they show, in spite of hydrogen evolution, a wave type curve. This is much more negative than the prewave in the current. The limiting rate of 4 to 5 x 10m5 moles h-’ cm-’ can be compared with the expected value ADC = 4 x 10m3 moles h-’ cm-“. <‘learIy the hmlting rate 1s not diffusion controlled. This is unlikely to bc due to the change in pH, caused by the H2 evolution reaction, as the 1 and 3 h runs gave a similar result. The rate of reaction also seems to depend on the metal, and if it is assumed that the rate of Hz evolution is the same, it is somewhat easier on mercury. Figure 2 also shows similar measurements on tin and zinc. The corrcsponding current-potential curves are shown in Fig. 3. It is significant that the rate of product formation seems to follow the current potential curve. The current-potential curve indicates that the reaction proceeds without pamlIe hydrogen evolution and this is substantiated by an approximate correspondence
benzyl
RESULTS Rare cwy.
of’
reduction
tin.
zinc
of 2-chlorohmzoic und carbon
acid on lead.
mer-
Current-potential curves at the rotating lead disc and the mercury pool show that almost all the current could be accounted for by hydrogen evolution. The curves have a prewave shown in Fig. 1 for lead, with and without the aromatic acid. As will be shown by the product analysis the prewave is probably due to the reduction of a proton which merges into the reduction of water. The height of the prewave is approximately the value expected from neasurements in 0.5 M hydrochloric acid alone and occurs at the same potential. The reduction 01 H&I seems to be enhanced by the organic acid. The rate of the organic acid reduction itself was measured using chemical analysis. Figure 2 shows the rate of appearance of
E. v 2. Total product in IV5 mole h-‘cm-’ produced by clectrolysing 0.1 M 2-chloro benzoic acid in the base electrolyte solution at (1) Pb rotating disc electrode (233 r-ad s-l): (2) Hg pool; (3) Zn rotating disc (60 rad s-l); Fig.
(4)
Sn
rotating
disc
(60
rad
5-l).
r
I --07
-0.9
-1
E.
I
V
Lb)
E,
V
Fig 3. Current-potential trode; (a) 0.1 M 2-chloro (b) in base
electrolyte
curve at a Sn rotating disc elecbenzoic acid and base electrolyte; alone. Sweep rate 0. rotation
speed 60 rad s-l.
I V s- ’ :
The reduction
of 2-chloro-henzoic
acid
587
for 1 h and 3 h show no sign of dechlorination products. On the other hand reduction on tin and zinc give a wider variety of products. As before thcsc were identified by comparison with standards in the glc. The identifiable products are shown in Table 1. In addition, in both the runs on tin and zinc there were some possibly higher molecular weight products which could not be identified but which were observed on the glc at a retention time of about 200s. The amount formed is probably small. DISCUSSION
4. Yield irl gms II ’ nf the p, oducts f,nrmed at the rotating disc (233 rad s- ‘) in 0. I M 2.chloro benzoic acid in the base electrolyte solution. (I) 2-chloro benzaldehyde [A); (2) 2-chloro benzyl alcohol (m): benzaldehyde ( Y ): benzyl alcohol (0). Fig. Ph
between the current passed and the total amount of product in the case of tin. For example at E = 725 mV, 4.5 x 1W4 moles of product were formed compared with the charge (4~) passed equivalent to 1.6 x 1O-4 moles. A film was formed on the electrode which was organic in nature but it hardly impeded the reaction. For zinc the current efficiency for the formation of simple products is less than for tin. For example at E = - 1180mV, 1.7 x 10w4 moles of product were formed compared with the charge (4~) passed. equivalent to 1 x 10e3 moles. In this experiment an organic film was formed which reduced the current more than in the case of tin. Measurement of the total product was also made on a glassy carbon rotating disc electrode (223 rad s-l) at one potential, E = - 1850 mV, only. One product was found after a 2.5 h tun, namely 7 x IO-” moles of bcnzyl alcohol with a trace of 2-chlorobenzyl alcohol. The current was very variable and the amount of hydrogen depended on the extent of film formation. If the reaction was interrupted, on applying a negative potential again a very low current was observed. A film had formed which could only be removed mechanically.
The dlstrihution of the various products is shown in Fig. 4 and Fig. 5 for lead and mercury. Dechlorination products on this time scale only appear at more cathodic potential> than E = - 1850mV. This result seems to be a potential effect and not a time effect as runs at E = ~ 1850 mV on both mercury and lead
Figure 6 shows the reduction of 3-amino benzoic acid on a lead rotating disc electrode compared with the base electrolyte. This is one of the few aromatic acids which is reduced on Pb at more positive potentials than the base electrolyte. Because a high concentration of the organic acid is necessary to bring the reduction from the background the pH of the solution 1 and 2 in Fig. 6 is different. However, curve I 1s essentially the reduction of H,O. It is significant that the prcwave of Fig. 1, for 2-chlorobenzoic acid is suppressed. Unfortunately in this case the products are too unstable to follow quantitatively with the glc. However. the reduction is certainly limited by the interfacial rate and has a 120 mV Tafel slope. It would seem likely that the reduction of 2-chlorobenzoic acid on lead and mercury has similar kinetics, although
Fig. 5. Yield in gms hK’ of the products formed at the Hg pool electrode in 0.1 M 2-chloro benzoic acid: (1) benzaldehyde (x ): (2, benzyl alcohol (Ll); (3) 2.chloro benzaldehyde (A): (4) 2.chloro benzyl alcohol.
Table Metal
- 675 -772s -950 - 1080 -1180
A* henzaldehyde: IXIIH
A-
E(mW
Sn Sn 8n Ztl Zn
II
Yield
0 0 0
7.3 x IO_ s 0 Bt benzyl
alcohol:
B-t 4 1 6 I 1
x x x x x
C: 2-chloro
I in moles after a CY
10-s 10-4 IW5 IO_’ IO 4 benzaldehyde:
I
8 x IO-h 2 x 10-5 1 x 10-5 0 I x 10-3
I>rj2-chloro
h run
Dti
El1
10-3 3 x 10-h 1 x 10-A 0 2 x 10-s
2x IO s 3 x 10-3 3 x 10-5 0 4 x 10-5
I x
benzyl
alcohol ;
El\ Chloro
benzene.
588
removed from the 2-chloro benzaldehyde or alcohol as the 1,2-dichlorobenzene is reduced at more negative potentials[5]. On carbon the chloro group is removed more easily and the aldehyde is probably strongly adsorbed, as the reaction goes straight to the alcohol. The results on tin and zinc show that the rate of the electron transfer reaction is significantly enhanced. It is clear that the reaction is more complex than that at lead and mercury. However. the most Interesting fact is that a new reaction occurs. the decarboxylation of the organic acid. A similar reaction is known in classical organic chemistry and can be carried out using copper powder[6, 71. It will be useful to confirm this result and optimise the electrochemistry to effect this reaction alone.
E,
REFER EI\ICES
V
Fig. 6. Current-potential curve for the reduction of 3-NH1 benroic; acid at a Pb rotating disc: (1) in base electrolyte alone: (2) 0.1 M 3-NH2 benzoic acid in base electrolyte. speed 60 rad SC’. sweep rate 0.1 v s-1, rotation
1. 2. 3. 4.
the rate is higher on mercury. The distribution of aldehyde and alcohol is presumably then determined by the slow aldehyde dehydration step. The appearance of dechlorinated products is probably caused by I direct reduction at the metal surface of the chloro group. It seems likely that the chloro group is
5. 6. 7.
J. H. Wagenknecht. /. orq/. Chent. 37 (1972) 151.3. _I. A. Harrison and D. W. Shnesmith. J. r~lrcvr~on~~ul. Chem. 32 (1971) 125. See I_. Eberson, Oryarlic t;Iecrrocl~~n,isri-~: (Edited by M. Baizer) p. 413, Marcel Dekker (1973). 0. R. Brown, J. A. Harrison and K. S. Sastry. J. PI(,~rroanal. Chen,. 58 (1975) 387. S. 0. Farwelt, F. A. Rctand and R. D. Gecr. J. elrcrronnul. Chrrn. 61 (197% 303. Fieser and Fieser, Rrugenrs fbr Oryanl~~ 5’ynthr.si.s. Vol. I, p. 157. John Wiley, New York (1967). Fieser and Fieser. Rccry~nts fur Or+mz~’ S~~nrhrsiu. Vol. 2, p. 82. John Wiley. New York (1969).