Abstract Studies of electroreduction of methylphenyltin dichloride a dihydride enabled us to follow the formation of bis (chloromethylphenyltin). This dimer decays rapidly in the solid state. Migration of a phenyl group and disproportionation of the resulting chrloromethyltin derivative intitiate the formation of amalgamated tin and trisubstituted organotin compounds during electrolysis of the dichloride.