ELECTROCHEMICAL REDUCTION OF NITROBENZENE A T CONTROLLED POTENTIALS W.
H. HARWOOD
Continental Oil Go., Ponca City, Okia. RAY M. H U R D AND WADE
H. JORDAN, J R .
Tracor, Inc., Austin 7, T e x .
Nitrobenzene was reduced electrochemically a t a mercury cathode a t various controlled potentials in acid electrolytes. Potential control to f1 mv. was achieved b y use of a recently developed instrument which i s capable of supplying the high currents required to obtain sufficient quantities of product to make a complete analysis of the product mix. O f nine possible products, only four were obtained in measurable quantities. The composition of the product mix i s a sensitive function of both the potential and length of electrolysis.
HE electlosynthesis of ethane by Kolbe in 1849 marks the Tbeginning of organic electrochemistry. Since that time, electro-organic chemical reactions have been the subject of historic and continuing interest in the laboratory, but attempts to utilize this knowledge for preparative work on an industrial scale have been rather scattered (3, 4, 6, 7 7 , 77). Only in the pharmaceutical industry have significant applications been made in utilizing the techniques of organic electrochemistry. The idea of using a n electrode with a controlled potential as a reagent having specific oxidizing or reducing powers originated with Fritz Haber in 1898 ( 8 ) . Unfortunately, equipment was not available in Haber's time which could provide the potential control necessary for a n extensive study. The development of polarography led investigators once more to the study of controlled potential electrolysis. Lingane and Swain collaborated in 1943 (70) to show how a controlled cathode could perform relective reductions in organic chemicals which were impossible with chemical reducing agents. I n the past six years, excellent review books on organic electrochemistry have been written by Swann (76), Clark (5), ,411en ( 2 ) , and Meites (72). The latter two have dealt primarily with controlled potential electrolysis. Two other reviews of a more specific nature have been prepared by Allen ( 7 ) and Thiessen (78), the former on cathodic processes and the latter on the Kolbe electrolysis. Elving has recently published a more theoretical review on the mechanisms of organic electrode reactions (7). One of the major obstacles in the study of controlled potential electrolysis has been the lack of a source of electrical energy Lvhich itas capable of maintaining close potential
72
l & E C P R O C E S S D E S I G N A N D DEVELOPMENT
control lvhile providing currents large enough for synthesis of sufficient quantities of material for complete analysis. Investigators in the past have identified the major product and, at times, have had to measure disappearance of starting material as the only method of following the course of reaction. However, a recently developed instrument will control either cathodic or anodic potentials to within 1 mv. of a desired value \vhile providiny a current of up to 30 amperes (available from Anotrol Division, Continental Oil Co., Ponca City, Okla.). \Vith the aid of this instrument, a program was initiated to determine accurately how well one could direct the path of a n electrochemical reaction with controlled electrode potential. The reaction chosen for study was the electrochemical reduction of nitrobenzene [the reaction for which Haber (8) first postulated the use of controlled potential electrolysis in 1898 1. The various reduction and coupling reactions possible are shown in Figure 1 : five reductions, three condensations, two rearrangements, and one coupling with the solvent. It is perhaps naive to anticipate that the use of controlled potential will regulate a system incorporating six reactions which are not electrochemical. It was believed, however, that some regulation would be possible due to the fact that the intermediates are electrochemically generated. Experimental
Electrolysis. T h e electrolyses were carried out in airfree acid solutions utilizing a mercury cathode. .4 schematic of the cell (made from a I-liter flask) is shown in Figure 2. The mercury pool, -4, used as the cathode. had a surface area of approximately 30 sq. cm. -4platinum gauze. B. rvas used
as an anode and the anode and cathode compartments were separated by a medium porosity fritted-glass disk, C. Kitrogen was bubbled through the solution via D to sweep out the dissolved oxygen, and the cathode potentials were measured and controlled with respect to a saturated calomel electrode, E. The reference electrode was joined to the cell through a n agar-salt bridge to prevent diffusion of chloride ions into the catholyte. The paddle stirrer, G. was maintained just above the mercury pool surface and turned at 300 r.p.m. Electrical contact was made with the cathode via side a r m F. The catholyte and anolyte volumes were 750 and 60 ml., respectively. Conditions of electrolysis were selected after a study of the polarization curves taken in acid, neutral, and basic media. These curves were obtained on a small mercury pool cathode (area = 1 sq. cm.) and are shown in Figure 3. I n acid and neutral solutions, there are two well defined limiting currents of almost equal heights, while in alkaline solutions the height of the first wave is approximately twice that of the second. These results are in good agreement with previously reported work on the polarography of nitrobenzene using the dropping mercury electrode ( 9 , 73. 74) in regard to half-wave potentials, but not in regard to the relative heights of the two waves. However, in acid solutions the theoretical 2 to 1 ratio in the height of the two waves, from over-all reactions of
+ 4e + 4 H f @NO?+ 6e + 6 H -
@NO?
ONHOH
(1)
@NH2
(2)
-
+
is obtained only a t concentrations of nitrobenzene below 10-4M (75), which is much lower than the 0.1M solutions used in this work. The acid system was selected for the electrolyses on the basis of the two approximately equal potential spans available in the limiting current portions of the two waves, and because condensation products are more likelv to be formed in neutral and alkaline solutions. The catholyte used in all runs was 2 N H2S04 in a 40y0 ethyl alcohol-60% He0 mixture; the alcohol was added to increase the solubility of the nitrobenzene and its reduction products. The anolyte was 20% HzS04 in water. The potential controller is a high current capacity potentiostat which features a saturable core reactor controlled by an electronic amplifier. ‘The potential between the reference cell and the cathode is compared to a preset reference voltage, the difference or error signal is amplified and fed back into the control loop, and the voltage applied between the anode and cathode is adjusted to make the error signal zero. The response characteristics of this instrument are such that it will provide potential control to within i l mv. a t currents of up to 30 amperes. The nitrobenzene was a high purity grade received from Matheson, Coleman, and Bell and was used without further purification. Solutions were made from distilled water, absolute ethanol, and reagent grade sulfuric acid.
Table 1. Total Coulombs Passed” 6,200 10,400 14,900 18,200
Analysis. The key to the study of any reaction is the knowledge of the exact composition of the solution. The method used in this research was a combination of infrared and ultraviolet spectrophotometry (Figure 4). T h e procedure was checked by subjecting known syntheric reaction mixtures to the analysis scheme. All values reported are good to within =t5%. Azobenzene and hydrazobenzene have not been reported, as quantitative data are not available. They have been qualitatively detected, particularly in the long-time runs, but there are too many interferences in the ultraviolet and they are such weak infrared absorbers that quantitative data could not be obtained. I t is believed that the amounts of these two products formed are approximately equal to the differences between total nitrobenzene reduced and that accounted for by the analysis of all the other components. However, the accuracy limitation on the analytical procedures does not justify reporting these amounts as true data. Results
Controlled potential electrolyses were made a t - 0.4, -0.6, -0.8, and -0.9 volt Tvith respect to the saturated calomel electrode. These values are, respectively. a t the knee of the first Xvave (-0.4 volt), on the first plateau (-0.6 volt), a t the knee of the second wave (-0.8 volt), and on the second plateau (-0.9 volt). Original intentions were to scan the entire potential range at 100-mv. intervals, but the analysis procedures consumed a n unexpectedly large proportion of the total time available for this Ivork. The initial current densities used ampere per sq. cm. for -0.4 ranged between 2.0 X volt and 3.3 X lo-* ampere per sq. cm. for -0.9 volt as the reduction potential. These decreased with time to a final value of 3.3 X lop4 ampere per sq. cm. \\hen reduction was complete. The main feature of the runs is that p-aminophenol is the major product formed at -0.4 volt with aniline completely absent, while at higher potentials significant amounts of aniline are found. Table I shows the products formed a t -0.4 volt at various periods during the reduction. The amount in the ‘‘% QN02” column is the percentage of the initial amount of nitrobenzene required to account for the component present in the product, and the number in the .‘% c o d ” column is the percentage of the total coulombs passed which are required to form that component bv electrolysis. The results
Volt vs. S.C.E.
Products Formed in Controlled Potential Reduction of Nitrobenzene at -0.4
Unreacted Nitrobenzene -~ Grams 3.70 2.40 0.72 0.24
The experimental procedure was to add 750 ml. of catholyte to the cell, then add anolyte, set the reference voltage a t - 1.O volt, and pre-electrolyze for a t least 2 hours while bubbling with nitrogen to remove any reducible substances. Five milliliters of nitrobenzene were then added, the desired potential was set, and the electrolysis was begun. Recordings were made of the current passed, and from these the total coulombs passed were determined.
%
@iTO?
%
caul
62 40 12
...
4
...
, , ,
,..
Azoxybenzene Grams 0.64 1.10 0.90 0.70
9 6 %
@AVO? coul
13 22 19 15
30 30 18 12
$-Phenetidine ciC
Gram
@‘YO2
Absent
, ,
0.10 0.46 0.71
2 7
11
p-Aminophenol L /0
cniil
.. 3 9 11
Grams 1.2 1.8 3.2 3.2
%
Total Recouery a/o
%-
@.VO?
coul
@.TO$
cod
25 37 62 60
76 66 77 62
100 101 100 90
106 99 104 85
Complete ,eduction of 5 ml. of nihobenzene taken would require 14,700 coulombs at 3 faradayslmole ( t o atoxybenrene); mole ( t o p-aminophenol or p-phenetidine); and 28,200 coulombs at 6 faradays/mole (to aniline).
VOL. 2
-
%
NO.
18,800 coulombs at 4 faradays/
1
JANUARY
1963
73
Table II.
Products Formed in Controlled Potential Reduction of Nitrobenzene at -0.6 Volt Cnreacted Nitro benzene Grams 70 @No2 4 10 68
Total Coulombs Passed 5.360 8,140 10,930 1',280 21,190 34,580
%caul
Grams
2
0 14
1.12
p-Phenetidine
5,360 8,140 10.930 17;280 21,190 34.580
Grams 0.52 0.57 0.64 0.90 1.22 2.19
Absent
Trace 0 0 0 0
14 19 34 52
2
4 3 5 4
3 5 8
are shown graphically in Figure 5 . Among the points of interest is the slight decrease in p-aminophenol a t the last point. This is believed to be in part due to the slow conversion to p-phenetidine, as noted by the low and delayed yield of this compound. The azoxybenzene exhibits a maximum a t about 10,000 coulombs. This was observed at all potentials. with the position of the maximum being somewhat potentialdependent. Tables 11, 111, and I Y give the results for electrolyses at controlled potentials of -0.6, -0.8, and 0.9 volt, respec tively, and again the results are shown graphically in Figures 6, 7, and 8. The aniline yield has risen from 0.0% at -0.4 volt to 50% at -0.8 volt. The lower current efficiency a t longer electrolysis times-Le., a higher number of coulombsis believed to be mainly due to reduction of azoxybenzene to form azo- and hydrazobenzene. This was indicated in several electrolyses by the rearrangement of the hydrazobenzene into benzidine, which precipitated out as benzidine sulfate. For a comparison of controlled potential reduction with uncontrolled potential reduction. electrolyses were carried out utilizing a constant current qource and adjusting the current density such that the initial cathode potential3 were -0.4, -0.6, and -0.9 volt. resuectively (Table V). In all cases, the potentials became more negative as the electrolyses progressed. The current densities required were the same as the initial current densities put out by the automatic controllere.g.? 2.0 X lop2 ampere prr sq. cm. for -0.4 volt. In an effort to pursue the comparison of controlled and uncontrolled potential electrolyses further, a series of experi-
70 c o d
23
20 -
% @1.V02 % c o d 10 11 12 17 20 41
34 25 21 19 20 22
p-Phenetidine
6,700 9,600 28,500 28,700
74
70 @avo2
Grams 1.10 1 29 1.01 0.85 0.47 0.43
caul
... ...
...
...
, . .
, . .
0.21 0.20
3 3
2 2
l & E C PROCESS D E S I G N A N D DEVELOPMENT
Gram 0.28 0.42 0.68 0.97
70 @NO2
%caul
22 27 21 17 10 9
59 46 27 14 7 4
Total Rrcouery,
@.vo
Yo COUl
10c 100 81 79 72 82
93 96 84 76 72 50
Discussion
Chemical processes occurring in homogeneous systems, even when complicated by the existence of consecutive and side reactions, can be characterized in regard to product buildup if the rate constants of all the individual steps are known. This is also true in heterogeneous systems, although the calculations are usually additionally complicated by mass transport kinetics, say to and from a catalyst surface. For electrochemical systems like nitrobenzene reduction, complete characterization would require determination of all electrochemical and chemical rate constants, plus the consideration of mass transport aspects. Such a procedure is far beyond the scope of the present work; in fact, the results reported here are but the first step in such a program. They do, however, establish the existence of most of the processes, both chemical and electrochemical, which are postulated in Figure 1. Comparison of product yields given in Tables I to I V also clearly shows that the mixture of reaction products is a sensitive function
-0.8 Volt vs. S.C.E. Azoxybenzene Gram 7 0 @'iVoZ 0.89 18 0.92 19 0.23 5 0.20 4
p-Ammophenol 70
S.C.E.
ments was made at -0.4 volt to determine the effect of other variables on the yield of p-aminophenol. An increase of acid concentration had little effect, but the effect of temperature was more striking. Figure 9 shows a comparison of controlled and uncontrolled potential electrolyses as a function of temperature. At a sufficiently high temperature (90' C.), the irreversible arrangement of phenylhydroxylamine to form p-aminophenol is so rapid that this compound is formed in 100yo yield even with uncontrolled potential.
Table 111. Products Formed in Controlled Potential Reduction of Nitrobenzene at Total Coulombs L'nreacted Nitrobenzene Aniline Passed Grams yo @'NO? % COUl Grams % @NO? 70 cou1 0.45 10 42 6,700 3 55 59 0.72 16 46 9,600 2.15 36 2.33 52 51 28,500 0 09 2 2.15 48 47 28,700 0.17 3 Gram
VI.
Azoxy benzene
p-Arninophenol
%caul
%
Gi am
Aniline 70 @NO2
Total Recouery,
70 Caul
39 28 2 2
%
70 @'VOS
70 coui
@A-O>
Cod
5 8 13 18
15 15 9 12
92 79 75 76
96 89 64 63
0*is FieD-;
0
o N O N2O2* NlTqOBENZENE
l NNITROSOBENZEYE lTROSOBENZEYE
* O h H O H -ON142
/
PHENYLHYDROXYLAMINE
/
\
I
ANILINE
\
I
REARRANGEMEkT V
N
A
O
t
i
V
I
N
E
P-AMINorHENoL
CONDENSATICY
CONDEhSATiON
Oy:NO 4 0
\
REACTION WITH E T H Y L ALCOHOL H
AZOXYBEYZENE
~
N
~
O
C
~
H
~
p-PHENETIDINE
I
I CONDENSATICP'
Figure 1. Reduction products of nitrobenzene in acid electrolytes Figure 2. pool
of the operating potential of the electrode, a situation \vhich can be realized only if the electrochemical rates and chemical rates are of approximately equal magnitude. From the way in which the concentrations of the various products change with time at different potentials, it is possible to draw some general conclusions about the relative rates and potential dependency of the individual steps. Thus, the appearance of asoxybenzene establishes that the first step is a two-electron reduction of nitrobenzene to nitrosobenzene. The rate of formation of nitrosobenzene is limited by mass transport a t potentials above -0.4 volt us. S.C.E. (beginning of the limiting current region) and is therefore potentialindependent. The second step, reduction of nitrosobenzene to phenylhydroxylamine. and the subsequent reduction of phenylhydroxylamine to aniline are both potential-dependent,
Cnreacted Grams 3.22 1 ,32 0.32 0 14
,Yitrobenzene @IVO~
54 22 5 2
yocoul ... ... ... ...
Grams 0.56 1.01 1.54 1.40
Aniline 70 @NO2 12 22 34 31
Grams 0.65 0.94 0.79 1.84
p-Aminophenol % @NO2 12 18 15 35
~p-Phenetidine
8,390 15,860 23,920 29,100
Grani
% @'TO2
...
...
0.29 0.21 0.53
4 3 8
Table V. Component
since the reactants in these two steps are produced directly at the electrode surface and are thus in position for further reaction. Both nitrosobenzene and phenylhydroxylamine are more easily reduced than is nitrobenzene, so that a t any potential more negative than the initial -0.4 volt required to initiate the byhole process by nitrobenzene reduction, any of the products shown in Figure 1 ma)- be formed. The effectiveness of potential control in this system thus derives from the potential dependence of the subsequent electrochemical steps rather than from the initial reduction of nitrobenzene. The effect of a competition bet\veen the chemical and the electrochemical step is illustrated especially in Figure 9: Lvhich shorvs the yields ofp-aminophenol as a function of temperature. The rearrangement of phenylhydroxylamine to p-aminophenol is so accelerated \vith increasing temperature that eventually
Products Formed in Controlled Potential Reduction of Nitrobenzene at -0.9 Volt
Table IV. Total Coulombs Passed 8,390 15,860 23,920 29,100
Electrolysis cell with mercury
70 coul
'5' 2 5
70 C O U ~
41 39 40 30
VI.
S.C.E.
AzoxybPntene '7, @hr02 15 20 11
Gram 0.73 0.95 0.51 Trace *p,Y02
28 21 12 22
93 86 68 76
26 18 6
...
Total Recovery,
% coul
5% C O U ~
..
7~ caul 95 83 60 57
Products Formed in Uncontrolled Potential Reduction of Nitrobenzene
Init. Pot. = -0.4 Volt Giams 70 @IVOJ % coul
Init. Pot. = -0.6 Volt Grams @NO? '70 c o d
Init. Pot. = -0.9 Volt Grams % @A'O2
Unreacted nitrobenrene 0.04 1 .. 0.38 6 .. 0.12 2 .. Aniline 2.07 46 46 1.83 40 30 1.92 42 27 Azoxybenzene 0.15 3 2 0.17 3 1 Trace .. .. $-Phenetidine Absenta .. .. 0.13 2 1 0.05 1 0 24 10 p-Aminophenol 1.29 24 16 0.69 13 6 1.29 __ Total recovery 74 64 64 38 69 37 For initial potential = -0.4 volt us. S.C.E., 28,230 coulombs passed; -0.6 volt, 37,680 coulombs passed; -0.9 volt, 44,734 coulombs passed. a This run carried out in H2.904, with no alcohol present, so p-phenetidine could not be formed.
-
~
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1
JANUARY
1963
75
both the further reduction to aniline and the condensation to azoxybenzene are eliminated, and the yield of p-aminophenol reaches 100%. If the potential is uncontrolled a t room temperature, it drifts to more negative values during the electrolysis (eventually limited by hydrogen evolution), and reduction of phenylhydroxylamine to aniline lowers the yield of p-aminophenol. The maximum in concentration of azoxybenzene with electrolysis time is similar to textbook presentations of intermediate product concentration in chemical steps where
6
I
I X
AZOXYBENZEUE p-PHEYETIDIVE
d
p-AVIINOP.IElC.
A--.B-cC
The disappearance of azoxybenzene in the latter stages of electrolysis is due to both electrochemical reduction to azobenzene, and hydrolysis to nitrosobenzene and phenylhydroxylaminc which undergo further reduction. Thus the fall-off in azoxybenzene concentration is accompanied by a n increase in p-aminophenol, p phenetidine, and aniline. The primary conclusion is that potential control in an organic electrochemical system containing several possible consecutive and side reactions is an effective means of directing the course of the reactions. The specific success in maximizing the yield of p-aminophenol indicates that the controlled reducing poLver available through a controlled potential cathode will probably effect higher yields of certain reduction products in other organic systems than are obtainable with chemical reducing agents. An analogous case could be made
0
Figure
2
4
8 IO COlrLOMBS X IO”
6
I2
14
‘8
,6
5. Controlled potential reducfion of nitrobenzene -0.4
volt
VI.
S.C.E.,
I
2.ON H?SOd, 40% ethanol, 25’ C.
I
I
I I
,
I
0
1
I
NITROBElZENE
ze
‘u4
k 3
f 0 LL
2
COULOMBS X ’ O -
Figure 6.
Controlled potential reduction of nitrobenzene
-0.6 volt w. S.C.E., 2 . O N H2SOd, 40% ethanol, 25’ C. C
02
-04
-06
-38 E.VCLTS
- 2
-IC YS
-
-16
C
SCE
Figure 3. Current-voltage characteristics of nitrobenzene as a function of pH
MIL
OFF
ETHER
ADD CHC13
I WATER SOLUTIOY
1
UV AYALYSIS P.AMINOPHEYOL
WATER
1
EVAPORATE CHCl, TO I O m I
V ITROBENZENE D-PHENETIDINE AZOXYBEUZEYE A M INF
Figure 4. 76
Procedure for analysis of electrolysis solution
l&EC PROCESS DESIGN A N D DEVELOPMENT
for anodic oxidation, although this phase of organic electrochemistry has not been studied as extensively as has cathodic reduction. The potentialities in electro-organic syntheris will depend in part on the cost of electricity as a reducing agent relative to that of the commonly used chemical agents. Hydrogen at a cost of some 0.02 mil per gram-equivalent of reducing power is the cheapest reducing agent available, and thus provides a standard by which other agents should be measured. Even for chemicals which market in the cents-per-pound region, the cost of the reducing agent itself at 0.02 mil per gram-equivalent is a very small part of the total and is overshadowed by catalyst costs. Electrochemical reduction may be figured at approximately 1 mil per gram-equivalent and would even at this figure be a small part of total costs of chemicals in the centsper-pound range. Capital equipment costs for electrochemical processes would be the predominant factor. In reactions that require selective reducing power, the situation is somewhat different. While a series of chemical reducing agents for selective reduction has been developed over the past decade, these range in price from 340 mils per gramequivalent (for lithium aluminum hydride) to 85 (for sodium borohydride). Use of such reducing agents is clearly limited
20
I
2c
I
1
32
LO
50
6C
7C
TEMPERATU?E
83
93
0;
‘C
Figure 9. Compaiison of yields of p-aminophenol, controlled vs. uncontrolled potential, as a function of temperature
I
0
e
0
Figure 7.
2
16 COULDMBSXIZ‘
2C
24
28
32
Controlled poteniial reduction of nitrobenzene
-0.8
volt
Acknowledgment
S.C.E., 2.ON HaSO1, 40% ethanol, 25’ C.
VI.
R. M. Hurd and W. H. Jordan acknowledge the financial support provided by the Continental Oil Co. for this research program.
5t
* literature Cited
(1) ,411en, M. J.. Can. J . Chrm. 37, 257 (1959). ( 2 ) Allen, M. J.. “Oraanic Electrode Processes,” Reinhold, New \
I c
C
E
c
2
2:
I6
z0u-olt1‘55
x
:’ ,_
2s
32
2-?
,
3) Chem. Eng. News 38, 64 (March 7, 1960). 4) Chem. Week 87, 65 (Nov. 19, 1960). (5) Clark, W. M., “Oxidation-Reduction Potentials of Organic Systems,” Williams & Wilkins, Baltimore, Md., 1960. (6) Drew, J. W., Moll, G. J., “Small Electro-organic Chemical Plant,” 117th Meeting, Electrochemical Society, May 2, 1960. (7) Elving, P. J., Advan. Chem. Phys. 3, 1-33 (1961). (8) Haber. Fritz. Z. Elektrochem. 4. 506 (1898). (9) Kolthoff, I. ’M., Lingane, J.’ J., “Polarography,” Vol. 11, pp. 748 et seq., Interscience. New York, 1952. (10) Lingane, J. J., Swain, C. G., Fields, h?., J . A m . Chem. SGC. 65, 1348 (1943). (11) McDaniel. A. S., Schneider, L., Ballard, A , , Trans. Elrctrochem. Sac. 3 9 , 441 (1921). (12) Meites, L., “Controlled Potential Electrolysis,” in “Techniaues of Orpanic Chemistrv.” Arnold iVeissberzer. ed.. Vol. I. Part IV, pp. 5281-335, Inte;science, New York, r960. (13) Page, J. E., Smith, J. i V , , il’aller, J. G., J . Phys. Colloid Chem.53, 545 (1949). (14) Pearson, J., Trans. Faraday SGC.44, 683 (1948). fl2) Stocesova. D.. Collection Czech. Chem. Communs. 14. 615 11949). il6\ S\vann. Shedock. Jr.. “Electrolvtic Reaction.‘; in *‘Techniques of ’Organic Chemistry,” Arnold iVeissbrrger: ed.: Vol. 11, pp. 385-523: Interscience, Ne\v York, 1956. (17) Taylor, R. L.: Chem. €5 .Met. Eng. 44, 588 (1937). (18) Thiessrn, G. \V., Record Cliem. Prop. 21, 143 (1960). ~
Figure 8.
Controlled potential reduction of nitrobenzene
-0.9 volt
V.I
S.C.E.
2.ON H,SOI,
40% ethanol, 25’ C.
to production of chemicals marketable in the dollars-perpound region and higher. If electrochemical methods can provide the selective reducing power not available through catalytic hydrogenation and a t costs well below those involved \vith use of the metal hydrides, there appears to be a definite economic area for electro-organic synthesis. T h e immediate requirement is for additional research in the effects of controlled potential on a variety of electro-organic systems.
\
!
RECEIVED for review March 28, 1962 ACCEPTED .4ugust 18, 1962 Division of Industrial and Engineering Chemistry, 141st Meeting, ACS, b‘ashington. D. C., March 1962.
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