Cleavage of the carbon–phosphorus bond in chloromethyl–phosphorus compounds by phosphorus pentachloride

Abstract

A novel carbon–phosphorus bond cleavage is described. Chloromethylphosphonic dichloride (2) and bis(chloromethyl)phosphinic chloride (1) both react smoothly and quantitatively with phosphorus pentachloride at 95–100°, giving carbon tetrachloride and a P(III) fragment containing one less carbon–phosphorus bond: phosphorus trichloride from 2 and trichloromethylphosphonous dichloride from 1. Under the same conditions, tris(chloromethyl)phosphine oxide (3) forms a complex (4) which subsequently breaks down to trichlorobis(trichloromethyl)phosphorane (5), diphenyl chloromethylphosphonate (7) suffers chlorination without cleavage, and tetrakis(chloromethyl)phosphonium chloride (6) is neither chlorinated nor cleaved. A concerted mechanism is proposed which accounts for ail of these results.