Arbuzov reaction of alkyl and silyl phosphites with halogens involving four- and five-co-ordinate intermediates

Low temperature 31P n.m.r. spectroscopy and chemical data have been applied to elucidate the mechanism of the Arbuzov-type reaction between phosphites and halogens. Simple and substituted trialkyl, alkyl 1,2-phenylene, and trisilyl phosphites have been allowed to react with chlorine, bromine, and iodine. In some cases intermediate halogenophosphonium salts (2) and in others halogenophosphoranes (3) are observed which then decompose into the corresponding pure highly reactive phosphorohalidates (4). It was possible to prepare stable phosphonium salts from halogenophosphonium salts (2) and halogenophosphoranes (3).