Electrochemical reduction of benzonitrile in the presence of bromobenzene and tetra-N-butylammonium benzenethiolate in dimethyl sulfoxide (Me2SO) forms diphenyl sulfide (67%) and benzene (38%). The reaction consumes 0.37 faraday per mol of bromobenzene, indicating that an SRNl chain reaction is occurring. Reaction in Me2SO-d6 gives a decreased yield of benzene (17%), 57% of which was monodeuterated, which along with coulometric data indicates that a major termination pathway is abstraction of hydrogen atoms from Me2S0 by phenyl radicals. Photoinitiated reactions in the presence and absence of tetra-N-butylammonium ions indicate that they are also a significant source of hydrogen atoms in termination. Evidence from reactions of 4-bromotoluene with benzenethiolate ion indicates that fragmentation of the diary1 sulfide radical anion intermediate is an important reaction in these systems. The presence of benzonitrile suppresses that cleavage. Flora Hewlett Foundation G r a n t of Research Corporation for partial support of this work and the National Science Foundation for equipment grants allowing t h e purchase of t h e HP 5992 GCMS a n d electrochemical instrumentation. T h e authors also t h a n k t h e Hewlett-Packard Corporation for t h e gift of t h e HP 5880 gas chromatograph. Registry No.Bromobenzene, 108-86-1; tetrabutylammonium benzenethiolate, 4670-62-6; benzonitrile, 100-47-0; p-bromotoluene, 106-38-7; potassium benzenethiolate, 31 11-52-2.

Während die elektrochemische Reduktion von Brombenzol (II) in DMSO/Tetrabutylammonium‐benzolthiolat in einer 1.74 F/mol‐Reaktion zu 93% Benzol (IV) ergibt, bewirkt der Zusatz von Benzonitril (I) als Redoxkatalysator (voltammetrischer Eignungstest), daß die aus (II) hervorgehenden Phenylradikale in so großer Entfernung von der Elektrode entstehen, daß sie für eine nucleophile Substitution zur Verfügung stehen und nicht weiter zum Anion reduziert werden.