501*‘ 24;, 1946- c.‘ R. BOE1TGE_R, JR, ErAL I ELECTROLYTIC PINACOL PRODUCTION Filed Jul-y 11,_ 1942 2,408,036 - retested septa, 1946 2,408,036 ' .1 ‘r ' accents ELEGTRGLYTIC PINACWL ERUQUUEIIQN rice lit. oettger, .llrn, Roselle, Thomas S. (?bers, Newark, andiwber G. ?ictterbech, mahway, N. St, assignors to Standard (iii He veiopment @ompany, a corporation oi Deiaware Application July 11, 19%, Serial No. 450,513 ' c easy (oi. soc-tr) 3 The present invention pertains to a method of preparing vicinal glycols by electrolytic reduc tion'of iretones and generaly to all types of carbon to carbon reductive condensation reactions. Speci?cally, this invention is concerned with the reduction of acetone electrolytically to tetrame'thylethylene glycol. i, It is the object of the present invention to pro-, 2%. converting acetone to pinacol have been unsatis factory either because pinaool current e?ciency in‘ the overall current e?cienclv or both were too ow. ' . It has now been found that the formation or‘ toxic lead alkyls which diminish the e?ectiveness of the cathode can be minimized and the reduc tion of iretones to vicinal glycols e'?ected with good current e?clency and high ratio otglycols method of electrolytically forming vicinal glycols 10 to other reduction products hy utilizing cathodes, and especially pinacols from the corresponding . the surfaces of which contain about 30-80% of vide the art with a novel and highly advantageous ' iretones, and also to provide the art with novel electrodes for effecting the reduction of organic copper or other metal of similar low hydrogen over-voltage and about 70-20% of lead. ' The‘ cathodes in accordance ‘with the present The electrolytic reduction of ketones can take 15 invention may he'prepared in various ways. The simplest procedure would involve merely mixing place at the cathode surface according to‘any ?nely divided lead and copper in the desired pr0-‘ .one of the followingireactionsz ‘ compounds. ‘ . . R: C C/ m/ \013 (69s. R1 \CHOH portion and compressing the mixture into sheets of the desired dimensions. Alternatively the cathodes could be prepared by coating lead par~ .20 ticles with copper and subjecting a mass of such coated particles to high pressure and possibly to a heating or sintering treatment. This procedure yields a copper matrix in which lead particles are evenly distributed. By" reversing the procedure 25 and using copper particles coated with lead it is. possible to obtain ‘a lead matrix with copper par ticles uniformly distributed therein. Substantially the same results are obtained if Other side reactions result in the formation of metal alky1s,. especially when the reduction is effected in acid medium with lead cathodes. An electrolytic method for effecting the reduc tive condensation reaction whereby acetone is 30 only the surface of the cathode corresponds to the above composition. Such cathodes can be made simply by forcing metal powder, wire strands, screening or the like of low hydrogen overvoltage metals into the surface of a lead sheet under heavy pressure. Instead of copper converted to pinacol (tetramethylethylene glycol) 35 powder, screening, or the like, one may also use ,using a lead cathode and an acid catholyte is other metals of low hydrogen overvoltage‘ or al described in German Patent 113,719 (1899). loys such as nickel, brass or Monel metal. Several German patents pertaining to the elec The ketones which may be treated in accordtrolytic reduction of acetone to tetramethylethyl 40 ance ‘with the present invention correspond to enie glycol were issued in the period 1912-1920. Among these patents were D. R. P. 306,304 (1917), the general formula R 306,523 (1918) and 324,919 (1920). ‘ The principal developments made in this period appear to have R. been the use of mixed metal and alloy cathodes, such as 4 to 10% copper-96 to 90% lead mixtures 45 and 10% tin-90% lead alloy and the use of hori- ’ wherein the R stands for a member of the group zontally suspended cathodes to prevent the metal 9 ' alkyls formed from accumulating on and decreas ing the activity of the electrode surface. All of (the prior, processes for electrolytically consisting of alkyl and aryl radicals and alkyl and aryl radicals substituted by a group which is not reducible under the conditions employed 1.. e., 50 halogen, carboxyl, etc. Such ketones include, for . 2,408,036 4 example, acetone, methyl ethyl ketone, diethyl ketone, methyl propyl ketone, ethyl propyl ketone, acetophenone, and benzophenone. ' . By using mixtures of di?’erent ketones. it is possible to prepare certain mixed glycols. For example, acetone may be condensed with methyl about 40 per cent. ethyl ketone to form the glycol corresponding to“ the formula cm on. “ The anolyte may be a sulfuric acid solution of about 10' to'40 per centstrength. The electrolyte is preferably maintained at temperatures between about 0° C. and about 25° C. The current density .10 applied may vary between about 0.1 and about \C__,c/ . (ls/tn it... ' - :. catholyte is one containing about 4 volumes of acetone for each volume of sulfuric acid of about 20 per cent strength. The acid, however, may vary in strength between about 10 per cent and‘ 4 amperes/sq. dm., the preferred current density being within the range of about 1.5 to about 2 ampere‘s/sq. dm. n or methyl ethyl ketone may be ‘condensed for ° ' ‘ The following examples serve to illustrate our example with~acetophenone to form the glycol 15 invention but it is to be understood that our invention is not limited thereto. _ _ 7 ' Example 1 576 cc. of a 4/1 acetone-10 per cent sulfuric The glycols formed in accordance with the" present . invention correspond to the general‘ - formula: ‘ 20 acid solution were placed in the cathode come ' partment of a cell as shown in the drawing. The anolyte used was 10 per cent sulfuric acid and - the‘ anode was lead. The cathodes used, con tained 60% copper and 40% lead. ‘ Electrolysis was eifected at about 16° C. at a '- current density of 1.67 amps/sq. dm. and at , 5.4 volts. The run‘ was continued for 4 hours and a total ofv 11.2 ampere hours were supplied I wherein each R. stands for an alkyl or aryl radical or an alkyl or aryl radical substituted by a sub stituent such as halogen, carboxyl; ‘etc. ' ’A cell-suitable for carrying out the vreduction to the cell. Upon conclusion‘ of the electrolysis 30 the catholyte was stripped of isopropyl alcohol and unreacted acetone and pinacol' (tetramethvl- _ ethylene glycol) was separated as the hexahydrate I by cooling and ?ltering the stripped catholyte. of ketones in accordance with the present inven 8.0 grams of pinacolv hydrate and 2 grams of tion is shown diagrammatically in the accoml 35 isopropyl alcohol were obtained corresponding panying drawing. The single unit cell shown to a current e?lciency based upon‘ pinacolof consists of a rectangular jar or the like 22 ar 17%. The mole ratio of pinacol to isopropyl ranged in a cooling bath a. An anode e of lead - or the like is arranged inside an acid‘ resistant diaphragm d, which divides the cell into ‘an anode and cathode compartment. As shown, two cathodes c of the composition indicated above are arranged in the cell. The details of the cell are not critical to our alcohol was 1/1. " l 1 Example 2 3430 cc.- of" 4/1 acetone-10 per cent sulfuric acid solution were placed in the cathode com partment of a single unit cell as shown in the drawing. .The anolyte'used was 10 per cent sul furic acid and the anode was lead. The cathodes invention and the cell may be altered in numerous 45 used were prepared by rolling copper gauze under ways. For example, anumber of cells could be pressure onto lead sheets. Rough measurement combined in a single tank and if desired the indicated that the surface consisted of about 70% process could be carried out continuously by of copper and 30% of lead. providing a circulating pump, an over?ow means The electrolysis was effected at about 16° C. for drawing off the electrolyte from the cell, means so at a current density of about 0.84 amp/sq. dm. for‘ separating electrolysis products from the with and at 6.2 to 7 volts.‘ The run was continued for drawn catholyte and means for making the elec 8 hours and a total of 40.2 ampere hours were trolyte up to initial strength for re-introduction supplied to the cell. Upon conclusion of the elec into the cell. . . . . trolysis the catholyte was treatedas described in The use of a diaphragm is recommended since the products formed at the cathode are liable 55 Example 1 to'separate the pinacol hydrate. 42.9 gramsof pinacol hydrate and 11.2v grams of iso to be oxidized at the anode. The use of a dia propyl alcohol were obtained corresponding .to a phragm may be avoided if ‘desired by the use current e?iciency based upon pinacol of 25.3% and" a current e?lciency based upon isopropyl of a high anodic current density or by the use of 60 alcohol of 25%. The mole ratio ,of pinacol to isopropyl alcohol was 1/1. anodes having a low oxygen overvoltage, i. e., nickel‘ or by a combination of two or more of Ewample 3 ' of anolyte and catholyte of unequal densities in cells provided with .horizontal electrodes, the use these expedients. ' 2340 cc. of a 4/1 acetone-25 per cent sulfuric Aside from the nature of the cathode surface. the factor which has the greatest effect upon 65 acid solution were treated in a cell similar to that used in the foregoing examples. The anolyte was the course of the reaction in the cell is the con 25 per cent sulfuric acid and the anode was lead. 5 ‘ centratlon and type of electrolyte used. Acid The cathodes‘ were prepared bycompressing 20 media have given the best results. The ratio of mesh copper wirescreen into a lead sheet. Rough ketone to water in the catholyte should be high. However, a ratio of 4/1 appears to be approxi 70 measurements gave about 40% lead and 60% I copper on the exposed surface of the cathode. mately the upper limit economically because of The electrolysis was effected at about 16° C. the high resistivity of the solution which would . and a current density of about 1.67 am./sq. dm. greatly increase the power cost. In the producand at 5.8 to 6.8 volts. The run was continued tion of tetramethylethylene glycol the preferred 75 for 5 hours. ' v ' . ‘ 2,408,086 5. duction of an aqueous'sulfuric acid‘ solution of A comparison run was made in. a similar cell a ketone of the formula with the same volume and strength of catholyte and with a lead anode. The“ cathode used was a . B " mixture containing 4% copper and 96% lead. / _ The electrolysis was effected at about 16° C. at R a current density of 2.0 amps/sq. dm. and at 6.3 to ‘7.8 volts. > . wherein It stands for-a member of the group ' consisting oi’ alkyl' and aryl radicals and alkyl and aryl radicals substituted by a group which The results of both of the foregoing runs are summarized in the following table: ' ‘ Pmmlhydrm Time, Amp‘ hrs. totéi 18° “Wuh- (grams) IPinacolO a ) Iso ro ' 11110 c E p w 5 , pinacol/ _ ' Total Intervall Total Intervall Total Interval‘ Total Intervall 50% Cu 40% Pb .......... .. 2 20 21.3 4 40 40.0 56.5 18.5 2 24 0.3 as 4 c 48 i vv12 11.5 28.3 11.2 10.8 5 - 4% Cu96%1’b ___________ ' 50 21.3 18.7‘ 5.2 :12 25.2 8.9 11.1 23.1 11.5 as 25.2 222 ace 80.4 ................. -. 0.2 as 15.8 ......... -. 8.7 as 11.1 10.0 23.5 19.0 20.8 10.5 1101mm isglpropyl °°h° n5 1.08/1 1115 1.2/1 23.2 1 1.3/1 0.41/1 1 Readings and analysis were made at thelstated time intervals given. is not reducible under the conditions employed No lead alkyls were ‘stormed with the cathode having the copper screening rolled thereon but 25 the improvement which comprises effecting‘ said reduction in a diaphragm cell in contact with a . large amounts of lead alkyls were formed and cathode consisting of from 60 to 80% of copper coated the surface of the 4% copper, 96% lead and from 40 to 20% of lead at ‘at temperature.‘ cathode. below about 25° C. and at a current density of " vWe claim: ’ 1. In the process of producing glycols corre 80 between about 0.1‘ and about 4 amperes per sq. dm.‘ 3. The process as de?ned in claim 2 wherein - sponding to the general formula the ketone and sulfuric acid are used in the ratio of about 4 volumes of ketone to 1 volume of acid. . 4. In the process of preparing tetramethyl ethylene glycol by the ‘electrolytic reduction of an aqueous acid solution of acetone the improve wherein R stands for a member of the Broup. consisting of alkyl and aryl radicals and substi tuted alkyl and aryl radicals by the electrolytic ment which comprises effecting the reduction in a diaphragm cell in contact with‘a cathode con sisting of from about 60 to 80% of copper and 40 to 20% of lead at a temperature below about reduction of an aqueous acid solution of a ketone of the formula R 25° C. and at a current density of between about . 0.1 and about 4 amperes per sq. dm. - - 5. .In the process of preparing tetramethy ' \c=o ethylene glycol by the electrolytic reduction of an ' aqueous sulfuric acid solution of acetone‘ the 3 improvement which comprises e?ecting the re duction in a diaphragm cell in contact with a wherein R stands for a member of the group con sisting of, alkyl and aryl radicals and alkyl and. aryl radicals substituted by a group which is not ' cathode consisting of from about 60 to 80% 0! copper and 40 to 20% 0! lead at a temperature reducible under the reaction conditions employed the improvement which comprises effecting said 50 below about 25° C. and at a current density of be tween about 0.1 and about 4 amperes per sq. dm. reduction in a diaphragm cell in contact with a 6. In the process of preparing tetramethyl ‘cathode consisting of from 60 to 80% of copper ethylene glycol by the electrolytic reduction of a and 40 to 20% of lead at a temperature below about 25? C. and at a current density of between . solution of about 4 volumes ‘of acetone in about 55 ,one volume of aqueous sulfuric acid of about 20% ‘ about 0.1 and about 4 amperes per sq. dm. strength the improvement which comprises ef 2. In the process of producing glycols corre fecting the reduction in a diaphragm cell in con sponding to the general formula ' tact with a cathode consisting'of from about 60 to 80% of copper and 40 to 26% oi lead at a temperature below about 25° C. and at a current density of between about 0.1and about 4 ampere: _ wherein R stands for a member of the group con sisting of alkyl and aryl radicals and substituted alkyl and aryl radicals. by the electrolytic re per sq. dm. CHARLES R. BOET'I‘GER,_J,R_. mouse a. CHAMBERS. . ‘03m 0. sto'rrmsox. '