Electrolytic Reduction of Acetone to Pinacol

A continuous process has been developed for the electrolytic reduction of acetone to pinacol which upon dehydration is converted to 2, 3‐di‐ methyl butadiene. The following observations were made during this investigation: (1) The process consists of electrolyzing a 4/1 acetone‐20% sulfuric acid mixture maintained at 15° to 20° C in the cathode compartment of a metal‐free electrolytic cell with a newly developed lead‐deposited copper cathode at a c. d. of one amp./dm.2 of effective cathode surface. Using these operating conditions in a 267‐1/3 hour continuous run, the acetone to the extent of 10% to 20% conversion was reduced to pinacol hydrate (50% to 55% current efficiency), isopropyl alcohol, and propane in approximate mol ratio of 16.8/2/1; 60% of the acetone converted going to pinacol. (2) In order to maintain the high 50% to 55% pinacol current efficiency, it was found necessary to renew the cathodes with fresh ones once every 24 hour period of operation. However, the cathodes are easily prepared by electrodepositing a relatively thin film of lead on a copper surface. (3) Studies made with numerous alternate type of cathodes indicated that zirconium‐deposited copper is the only other one that shows any promise.