Studying the dimerization reaction during the abstraction of halogen from organohalides by laser photoemission, controlled-potential electrolysis, and voltammetry

To continue earlier investigations into the dimerization reaction during th e cathodic cleavage of a carbon-halogen bond and, in particular, to find an accessible way for synthesizing 1,4-butanediol, a comparative study of the dimerization of ethylene halohydrins and butyl and allyl halides is perfor med. On the basis of the data obtained by the laser photoemission (LPE), co ntrolled-potential electrolysis, and voltammetry techniques, a general mech anism of the electrode reactions involving these compounds and their interm ediates is proposed and recommendations on the optimization of the 1,4-buta nediol synthesis are elaborated. According to LPE data, at pH less than or equal to 8,1, the beta-hydroxyethyl radical reduction occurs with a precedi ng formation of a complex with a proton donor, whereas a direct electron tr ansfer is characteristic of the butyl radical. This difference in mechanism s is offered as the main reason for the lesser capability of ethylene haloh ydrins to electrochemical dimerization as compared with butyl halides, wher e the octane yield reached up to 80-84%. The earlier assumption about a hig h electrocatalytic activity of the copper cathode in dimerization of ethyle ne halohydrins is confirmed, and possibilities of an iron cathode in this p rocess are revealed. The dimer yield is found to increase in alkaline solut ions and at lowered temperatures, specifically, at pH 11 and temperatures o f 0-5 degrees C, the 1,4-butanediol yield reached similar to 17%.