III HII III II I I I * LS um I III I THE ELECTROLYTIC REDUCTION OF O-NITRODIPHENYL IN ACID, ALKALI AND NEUTRAL MEDIA Thesis for the Degrea of M 3. MICHIGAN STATE COLLEGE Peter Pawak - I 942 I _‘ Ill“ ItIH‘. . , ,I.V I‘ll .1!» It THE ELECTROLYTIC REDUCTION OF O-NITRODIEHENYL IN ACID, ALKALI AKD NEUTRALiMEDIA by PETER PAWLYK A THESIS Submitted to the Graduate School of’Eichigan State College of Agriculture and Applied Science in partial.tulfilment or the requirements for the degree of MASTER OF SCIENCE Department of Chemistry 1942 Lg» -77 The author wishes to thank irofeeeora Arthur J. Clark and Dwight E. Ewing; Professor Clark, head of the department of chemistry for the grant of an aeoistantehip in physical chemistry and Dr. Ewing, his major professor, for guidance and assist- ance in thiefl wor THE ELECTROLYTIC EEDUCTIOE CF 0-H TR DIPIVNYL IN ACID, ALKALI AND NEUTRAL RFDIA INTRODUCTION The electrolytic reduction of aromatic nitro compounds gives an extensive series of reactions. Kendall1 in 1882 was granted a patent on the reaction in which nitrotoluene and nitrobenzene were cathodic— ally reduced to the corresponding amino derivatives when electrolyzed in a catholyte containing dilute sulfuric acid. In 1893, much work was done in this field. Investigators like Haussermang. Gattermant, Noyes and Clements4, Qatterman and Keppert5, and Elbe6 reduced nitrobenzene under varying conditions to obtain a series of products. The brilliant work of Elbe was especially significant. Since varying the conditions of reductions caused a variation in the products formed, there was need for a theory to account for these products. This theory of what intermediates formed in the redut- tion of nitrohsnzene was satisfactorily established by Haberv. This was made possible by the fact that 8 Bamberger reduced chemically by a series of diffi- If: cult reactions, nitrosobenzene to phenylhydroxylamine. He also was able to reverse this reaction. Until recently much work has been done on the reduction of mono and dinitro aromatic compounds, 9 little work however, according to Hartley and Lyons has been done on the reduction of o-nitrodiphenyl due to the difficulty of obtaining the product. Now, since diphenyl can be made cheaply and abundantly, it is possible that more work.will be done. In 1934, Hartley and Lyons succeeded in reducing o-nitrodiphenyl to o-azoxybiphenyl and the hydrazo compound. it should therefore be possible to reduce the compound in a manner similiar to nitrobenzene in alkaline solution to o~biphenylamine. The object of this research was to reduce the o-nitrodiphenyl to obtain 2, amino 5, hydroxy- diphenyl. By anaIOgy it seemed that this was possible in acid solution. A series of runs were made in acid medium and conditions varied to obtain the desired compound. A series of runs were also made in neutral and alkaline media. in these latter media, very good results were obtained and the chief product formed was o—azoxybiphenyl; in the correSponding acid runs results were for the most part negative. it was possible in some of the acid runs to obtain a few grams of crude crystals. The main difficulty was the separation of the products in the reaction mass. EXperiments were carried out in acid, alka- line and neutral media. The following factors were varied: (l) acidity or alkalinity (2) Current density (3) temperature (4) choice of electrodes EXPERIMENTaL: The apparatus consisted of; a liter beaker, a porous cup, a mechanical stirrer; lead, and carbon anodes and a monel metal guaze cathode. The solvent for the compound was 95% ethyl alcohol. In the neutral runs, ten grams of sodium acetate were added to the catholyte. The anolyte in both alkaline and neutral media was saturated sodium carbonate solution. Ten per cent sodium hy- droxide was used to vary the alkalinity of the oath- olyte in alkaline runs. In the acid runs the anolyte was ten per cent sulfuric acid or ten per cent acetic acid. The laboratory desk switchboard was used and the source of direct current generated by a dynamo. The emperimental procedure consisted of setting up the cell thus; the anode with the anolyts was placed in the beaker containing the catholyte. The monel metal gauze cathode was wrapped about the 'porous cup and attached to the negative pole by means of a heavy copper wire. The whole cell was placed in a water bath so that the temperature could be regulated. The mechanical stirrer was inserted into the catholytc and used throughout the reduction. In neutral runs the catholyte consisted of: 250 ml. of 95% ethyl alcohol 10 grams of sodium acetate 15 grams of o-nitrodiphenyl In experiment #8 and #9, these variations were made in the catholyte: in experiment #8, thirty grams of o-nitrodiphenyl were dissolved in 350 milli- liters of 95% ethyl a1conol; in the ninth experiment. 58.5 grams of o-nitrodiphenyl were dissolved in 450 milliliters of ethyl alcohol. The anode in these first nine runs was carbon; the anolyte was saturated sodium carbonate. The cath- ode was a monel metal gauze whose area was approximately 1.85 square decimeters. The cathode current density in each of the first nine experiments was 3.28 amperes per square decimeter. After the reduction was completed, compressed air was passed through the reduction mass to oxidize any hydrazo compound formed to~the azoxy compound. The beaker containing the reduction mass was allowed to stand overnight on an ice bath before filtering off the crude product. The results obtained are listed in Table I. TABLE I REDUCTION OF O-NITRODIFHEEYL 1K NEUTRaL LOLUTIOH Expt. Time Temp 00 Yield % Theo Theo Amp Hr 0.2? Hr. Cell (Grams) Yield Amp Hr Used 1 2.00 40-70 9.5 ' 72.5 4.25 12.00 56.59 2 2.00 50-52 12.0 90.9 5.51 12.00 46.00 5 2.00 48-50 15.5 100.4 0.11 12.00 50.85 4 2.00 50-52 10.0 75.0 4.50 12.00 28.20 5 2.00 70-75 11.2 76.0 5.19 12.00 45.25 6 2.67 50-60 12.5 90.0 5.52 16.00 46.00 7 2.67 40-52 12.5 95.0 5.75 16.00 56.90 s 5.50 50-52 20.0 75.9 9.12 21.00 45.50 959 4.50 50-52 22.0 62.2 14.61 27.00 54.25 * C.E. a Current Efficiency A second series of runs were made in which the alkalinity and the current density were varied. Since there is a tendency for the carbon anode to flake, a lead anode was used instead. The concentra- tion of the 0-nitrodiphenyl in the catholyte was also changed. In the runs tabulated in table II the follow- ing factors remained constant throughout this series of runs: Anode- A lead strip 3.5 cm. wide, .25 cm. thick and 15 cm. long. Anolyte- Saturated sodium carbonate solution. Cathodeclhonel metal gauze. Catholyte- 25grams of o-nitrodiphenyl 250 ml. of 95p ethyl alcohol Temperature 25 cell- 50-2°C. To vary the alkalinity of the catholyte, volumes of ten per cent sodium hydroxide were measured out with a pipette and added to the catholyte. When the volume of sodium hydroxide added caused the cath- olyte to separate into two distinct layers, the follow- ing procedure was used; forty per cent in the corre- Sponding amounts required. Hence in the tenth and eleventh runs in this series one hundred milliliters of 40? sodium hydroxide and two hundred milliliters TABLE II REDUCTION OF O-EITRODIPHENYL IN ALKALINE SOLUTION Expt Cathod Time Vol 10% Yield % Theo Theo Amp 111‘ CeEc* C.D. Hr. NaOH ml Grams Yield Amp Ur Used 1 2.28 5.5 --- 12.5 56.9 5.25 21.00 27.40 2 5.28 5.5 10 12.7 57.9 5.25 21.00 27.85 2 4.27 2.80 20 11.0 50.0 5.05 22.40 22.45 4 4.27 2.80 --- 11.2 51.0 5.15 22.40 25.67 5 4.92 2.50 25 16.0 72.9 7.55 22.50 52.67 6 5.47 2.40 50 22.0 100.0 10.10 24.00 42.09 7 5.47 2.40 100 15.5 70.6 7.12 24.00 29.71 8 5.47 2.40 150 12.5 56.9 5.75 24.00 25.96 9 5.47 2.40 200 14.5 66.0 6.65 24.00 27.70 10 5.47 2.40 100** 16.0 72.9 7.55 24.00 20.65 11 5.47 2.40 200** 14.0 65.7 6.42 24.00 26.29 * 6.0. = Current density in amperes per seuare dosimeter C.E. = Current efficiency **40§ sodium hydroxide solution was used in the last two experiments. of 40% sodium hydroxide were used respectively, in place of four hundred and eight hundred milliliters of 10% sodium hydroxide. results in this series are recorded in Table II. In this second series of runs both the alkalinity and the current density were varied to determine the effect upon the yield. A third series of runs was then made. The object of these runs was to determine whether or not another current density could be found with which we could parallel or obtain better results than those of the sixth run in the second series. 1n this third series of runs the following conditions were held constant: 'éggggy A lead strip as in series number 2. Anolyte- Saturated sodium carbonate. Cathode- monel metal gauze. Catholyte- 250 ml. of 95% ethyl alcohol 25 grams of o-nitrodiphenyl 50 31. of 10% sodium hydroxide Temperature 91 _c_e_l_1_- 48-50%. In this series only the cathode current density was varied. The results of these experiments are recorded in Table III. REDUCTION OF O-NITRODIPHERYL 1h ALKALINE SOLUTION 10 TABLE III EXpt. Cathodg Time Grams 5 Theo Theo Amp Hr c.r.* C.D. Hr. Yield Yield Amp Hr Used 1 2.19 6.00 11.0 50.0 5.05 24.00 20.91 2 5.28 5.60 22.0 100.0 10.10 21.60 46.75 5 4.5 ~.80 20.0 90.9 9.18 22.40 59.19 4 5.48 2.40 22.0 100.1 10.10 24.00 42.09 5 6.58 2.00 16.5 75.1 7.58 24.00 5 .57 6 7.75 1.72 17.5 79.5 8.05 24.08 55.40 7 8.75” 1.50 17.5 79.5 8.05 24.00 55.40 * 0.0. : Current Density C.E. 8 Current Efficiency ll This third series of runs concluded the research on reduction in neutral and alkaline medium. The crude product obtained from these reductions was treated in the following manner. Air was bubbled through the mass to oxidize any of the hydrazo compound formed. The crystals were then filtered by auction and washed two or three times with hot water. When dry they were light orange in color and a series of melting points on different runs showed a melting point of 140-206. One recrystallization of the crude product from a mixture of carbon tetrachloride and ethyl alcohol yielded slightly golden tinted crystals melt- ing at 154.500. One recrystallization from acetone yielded golden plates melting at 155-15400. The product was identified, after being pur- ified by the conventional qualitative organic methods. The pure compound was found to be soluble in cold concentrated sulfuric acid and since it contained nitrogen it was listed as an t’indii’i‘erent compound." Next a series of tests for functional groups like the hydroxyl and amino were carried out. These tests gave negative results. Then some of the pure compound was subjected to hydrolysis and reduction. It was found that no hydrolysis took place. Reduction did take place with zinc dust and alkali. The compound was also reduced by stannous chloride in an alcoholic solution. Since the compound reduced easily and went through a deep color change in the course of reduction. it was considered an azoxy compound. A derivative, 3, Z'diphenylbenzidine was prepared by treating a hot alcoholic solution of the product with stannous chloride. After several recrystallizations this derivative melted at 150-151°c. The literature gave 151°C as a melting point. A series of nitrogen determinations using a KJeldahl method were made. The average of these deter- minations was 7.98%. The calculated percentage for o-azoxybiphenyl is 6%. Molecular weight determinations were run by the Beckmann freezing point method. Thiophene free Benzene was used as a solvent. The following results were obtained: (1) see (2) 352 (a) sec (4) see (5) 352 (e) 356 The molecular weight of O-anoxybighenyl is :50. lu PART II a"; 0 ‘4‘ 'T?"‘.\‘f"‘ -A-L.'a 1“: .L; ad“! L.-.¢L The following reductions were carried out in acid medium. The first few runs yielded negative results. some of the last ones are fairly encouraging. ‘in carrying out reduction in acid medium the conditions were varied as in the neutral and alkali experiments (see page 5 ) in an attempt to obtain an appreciable yield of 2 amino, 5 hydroxy- diphenyl. The catholyte in some of the acid runs was completely miscible; in other cases it was an emulsion. A porous cup was used as a diaphragm throughout these experiments. Twelve separate experiments were carried out in acid medium. The conditions of the eXperiments and results obtained on each are tabulated in the following pages. in addition to these esperiments, repeat trials were made on caperiments 1,3,5 and 9. 1n repeating the nineth esperiment, the hydrochloric acid was eliminated. Results- Results- 14 EXperiment‘; anode— nickel metal snolyte- Dilute sulfuric acid (ldfi) Cathode- nickel metal-~Temp of cell—50°C. Current density~8 amps/sq. deem. Catholyte- 5 gm. of o—nitrcdiphenyl 200 ml. of 95% ethyl alcohol 200 ml. of concentrated sulfuric acid. Unreacted o-nitrodiphenyl and approximately 0.5 grams of organic compound. this latter compound seemed to be a mixture. h1periment A; ggggg- Lead Anolyte- 10% sulfuric acid Cathode- sickel Current Density- 8 amps/sq. deem. Temperature of 23;}? 50°C. Catholyte- 15 gm. o-nitrodiphenyl 100 ml. 95% ethyl alcohol 260 ml. 80% sulfuric acid. Very little reduction compound. Practically all of the o-nitrodiphenyl was recovered. Experiment lII 5319.312“ Lead Anolyte- 20% sulfuric acid Cathode- Bickel Current Density- 9 amps/sq. deem. Temperature 22 cell- 50°C. Catholyte- 15 gm. o-nitrodiphonyl 50 ml. 98% ethyl alcohol 250 ml. 40% sulfuric acid 30 ml. 1% gelatine Results- hone fine white needle like crystals, ether and water soluble; and an unseparable mass of organic and inorganic crystals. EXperiment‘I! £22327 Lead Anolyteo 20% sulfuric acid Cathode- hickel Current Densitv- lO amps/sq. deem. Temperature 2; 0011- 50-5206. Catholyte— 15 gms of o-nitrodiphenyl 300 m1. of 20% sulfuric acid 20 m1. of 5% gelatin Results- No reduction after ten hours. A skin formed on the cathode. Results- 1e Experiment 1. Anode- Carbon Anolyte- 10% sulfuric acid Cathode- monel metal gauze Current Density- 6 amps/sq. deem. Temperature 23 cell- 50-5500. Catholyte- 200 m1. of 95% ethyl alcohol 15 gm. of o~nitrodiphenyl 5 m1. of concentrated sulfuric acid hired crystals plus a black viscose oil. Experiment‘zl Anode~ Carbon Anolyte- 10% sulfuric acid Cathode- Monel metal gauze Current Density- 6 amps/sq. dccm. Temperature gflcell- 50°C. Catholyte~ 15 gm. of o-nitrodiphenyl 100 ml. of distilled water 50 m1. of concentrated sulfuric acid 200 ml. of 95% ethyl alcohol Results- No reduction. 1? Experiment VII Anode- Carbon Anolvte- 10% acetic acid Cathodg- Monel metal Current Density- 8 amps/ea. deem. Catholyteu 25 gm. o-nitrodiphenyl 10 ml. concentrated acetic acid 250 ml. 95% ethy alcohol Results- Some organic crystals and a large amount of oil. Experiment VIII £5932: Lead Anolyte- 50% sulfuric acid Cathode- Monel metal gauze Current Deneity- 10 amps/sq. deem. Catholyte- 25 gm. o-nitrodiphenyl (sulfonated) 250 ml. of distilled water Results- A large mass of crystals difficult to separate. lb Experiment IX Anode- Lead Anolzte- 10% sulfuric acid Cathode- Supper Current Deneitg- 6 amps/oi. deem. Uatholyte- 15 gm. o-nitrodipnenyl 120 ml. concentrated Hydrochloric acid 80 m1. concentrated sulfuric acid 10 gm. zinc sulfate Results- Four grams of violet colored crystals contain~ ing the chloride ion and behaving like an amine salt. EXperiment E Anode- Lead Anolzt - 10% sulfuric acid Cathode- monel metal Current Density- 3.17 amps/sq. deem. Catholytee 15 gm. C-nitrodignenyl 300 ml. 95% ethyl alcohol '5 ml. concentrated sulfuric acid I") n ‘0 ml. of distilled water C Results- steam distillation yielded unreacted o-nitrc- diphecyl plus a mixture or gravish blue crys- tals. (Approximately 0.5 gm.) Results- Results— Experiment g £22327 Lead Anolzte- 10% sulfuric acid Cathode- Zinc Current Densitz- 3.02 ampe/sq. deca. Catholzte- 300 ml. 95% ethyl alcohol 15 gm. o-nitrodiphenyl 25 ml. concentrated sulfuric acid 50 ml. distilled water Unreduced O-nitrodiphenyl recovered. Experiment XII léngggg Lead Anolzte- 10% sulfuric acid Cathode- Monel metal gauze Catholzte- 300 ml. concentrated sulfuric acid 25 gm. o-nitrodiphenyl Fifty ml. of liquid mixture boiling from ee-ve°c. DISCUSSION: PART‘Q The reduction of o-nitrodiphenyl in neutral and alkaline medium was divided into three parts. From the series of runs listed in Table I it was found that the results were easily reproduced. The concen- tration of o-nitrodiphenyl in the reduction mass could be Itepped up to twenty-five grams per two hundred fifty milliliters of solution providing the solution was warmed to 40-5000. before reducing. The carbon anode while satisfactory had a tendency to flake. Hence a new anode material was sought. In these neutral runs, the cell had a rather high resistance and it took time for the current to reach a desired value. To overcome this, the cell was warmed up to 50-6000. for an interval of approxi- mately five minutes. The temperature did not have any noticeable effect on the reduction. It was found that a temper- ature below the boiling point of alcohol was desired so as to minimize the loss of solvent due to evapora- tion. Temperature control was easily maintained. The cell warmed up with the passage of current through The solution. The prOper temperature was obtained by means of a water bath. In the second series of runs shown by TableII the alkalinity and current density were varied and a new anode used. A lead anode was found satisfactory. It was found that increase in current density with increasing alkalinity~ up to fifty milliliters of ten per cent sodium hydroxide- gave better yields. after the amount of alkali exceeded fifty milliliters of sodium hydroxide, the crystals of o-azoxybiphenyl were oily and unreacted o-nitrodiphenyl was recovered from the reduction mass. When more than fifty milliliters of ten per cent sodium hydroxide solution was added the yields were correSpondingly decreased. a decrease in yield was accompanied by a correSponding increase in the oiliness and a darkening of the crude product. It was found that the poorest yield of o-qaoxybiphenyl was obtained when two hundred milli- liters of forty per cent sodium hydroxide were added to the catholyte. If more than this amount were added the catholyte solution separated into two layers. In the third series of runs the alkalinity was held constant and the current density was varied. It was found that the best results were obtained at (\3 h: current densities of 3.28 amperes per siuare decimeters and 5.48 amperes per eduare decimeter. The crude product could be recrystallized from the following solvents and mixture of solvents; acetone, a mixture of equal parts by volume of chloro— form and ethyl alcohol, and a mixture of ninty per cent carbon tetrachloride and ten per cent ethylalcohcl. Acetone and the mixture of carbon tetrachloride and ethyl alcohol were the best solvents for recrystalli- zation. Recrystallization of egual weights of the crude product from each of the solvents gave better yields in the case of acetone. 3 'aRT I The reduction in the acid solution gave less satisfactory results. Difficulty was first encountered when the o-nitrodiphenyl tended to form a skin on the cathode and thus end the process of reduction. This was overcome by increasing the con- centration of the acid in the catholyte and increasing the rate of stirring of the catholyte. The next difficulty is the fact that the nature of the compound is such that only a small fraction of the o-nitrodiphenyl reduced under the conditions of research work. It was always possible to recover more than fifty percent of the unreacted o-nitrodiphenyl by steam distillation. There is also evidence that the compound is decomposed some what during the reduction. This is shown by the oils that form and the charring of the solution after reduction. It is also evidenced by the fact that in some instances aromatic compounds or mixtures were recovered which gave no positive test for nitrogen. The third difficulty is the separation of the reaction mass after reduction. This had been accomplished thus; the reduction mass is made alkaline :4 and the unreacted o-nitrodiphenyl steam distilled off; next, the solution is acidified and the phenolic com- pounds, if any, are distilled off. The mixtures of organic compounds obtained have been too small to permit extensive identification work. - Exocriment nine in the acid runs has produced fair results, and is furnishing the basis for further work. SUMMARY It has been shown that o-nitrodiphenyl can ‘ be easily reduced in alkaline medium to produce quantitatively o-aaoxybiphenyl of a high grade of purity. This reduction is possible with good results at two current densities; ;.28 amperes per eguare deo- imoter and 5.46 amperes per sduare decimeter. It is also possible to reduce o-nitrodiphenyl in acid solution. Here there are many difficulties to be overcome, the chief one being the separation of the reduction mass. Simplification of this problem will make it possible to reduce the compound to 2 amino 5 hydroxydiphenyl, and whatever other intermediates are possible. It is also probable that o-nitrodiphenyl may be reduced in a manner similar to nitrobenzene in acid solution. However, since the compound, o-nitro- diphenyl is nitrobenaene with a phenyl group in the ortho position, this phenyl group may alter the nature of the compound so as to account for some of the difficulties encountered to date in this work. If it is possible to obtain a reduced compound in acid solution, conditions can then be regulated to possibly obtain a series of compounds or "intermediates". 1. 2. 5. 4. 5. 5. 6. 7. 8. 9. 1. 2. 3. 4. Lib REFERENCES D. R. P. (German patent) 21,181 (1882) Hausserman, 6., Chem. Ztg. 17, 129 and 209 (1893) Elbe - ibid 17, 209 (1893) Gatterman, L., Chem. Ztg. 17, 210 (1893) Ber. 26, 1844 (1893) and 27, 1927 (1894) Noyes, A. A. and Clements, A. A., Ber. 26, 990 (1893) Noyes, A. A. and Dorrance, Ber. 28, 2:49 (1895) Gatterman, L. and Keppert, ber. 26, 2810 (1893) Gatterman, L., Ber. 29, 3040 (1896) Elbe, K. , Z. Electrochem. 2, 472 (1896)_ Haber, Z. Electrochem., 4,'197 and 506 (1898) Haber and Schmidt, 5. Physik. Chem. 52, 271 (1900) Bamberger, Ber 27, 1555 (1894) Hartley and Lyons, Proc. of Indiana Academy of Science 44, 124-128 (1934) TEXTS Electro-drganic Chemistry - Brockman, C. J. (1928 edition) Electra-Chemistry - Brockman,c. J. (Industrial Chemical Monographs) Qualitative Organic Analysis - Kamm, Oliver- second edition Applied and Theoretical Electrochemistry - Thomson, J. J. - U ., o_ . ‘ Q ~ ‘32 ' \ s ‘r , "c“ ‘ fi-l: I 45. ‘ .- ‘ .w') o n . a i i t :V g '$ ‘3 -. W"“‘éi' "4‘ "’ Hols-‘9'"P’H- s1 a... ...... acnprzo 1:3}... ..1‘ 5.5.17.2” fikffl. ”...... .1»... ... Woo:d.1-\ A ...“...Prf \1._.{% .’ ......x aw . ...1.5.. .... 054.41“...fo . 3.19““ Q 4 ‘HMJ. ‘ \IM . . h. “+9. Ix ‘. . . myhhflm ....fit. . - . . .....v ., MICHIGAN STATE UNIVERSITY LIBRARIES IIIHIII lullll um I 31293 3103 1262