THE SURFACE NATURE OF GRIGNARD-REAGENT FORMATION - CYCLOPROPYLMAGNESIUM BROMIDE

The reaction of cyclopropyl bromide with magnesium in diethyl ether yielded directly, during formation of the Grignard reagent, approximately 25-30% cyclopropane. Also formed in the reaction was approximately 25% cyclopropylmagnesium bromide. The reaction, when conducted in perdeuterated diethyl ether and in diethyl ether in the presence of the radical trap deuterated dicyclohexylphosphine, showed that the cyclopropane is formed mainly by disproportionation of the cyclopropyl radicals on the magnesium surface (approximately 85%) and only a small amount (approximately 15%) by reaction of a ''freely diffusing radical'' with the solvent. The reaction in methanol-O-d yielded almost exclusively 1-deuteriocyclopropane. These results provide further experimental evidence that the basic assumption of the D-model ''that all radicals leave the surface and diffuse freely in solution'' is not valid.