THE REACTION OF ORGANOPHOSPHORUS RADICALS WITH VINYL-ACETATE AND ACRYLONITRILE IN THE PRESENCE OF AN AMINOXYL RADICAL SCAVENGER

The radical-trapping technique employing 1,1,3,3-tetramethyl-1,3-dihydro-2H-isoin (1) as a radical scavenger has been used to study the reaction of diphenylphosphinoyl (2) and dimethoxyphosphinoyl (3) radicals with vinyl acetate and acrylonitrile. The phosphorus-centred radicals were generated by hydrogen abstraction from diphenylphosphine oxide and dimethyl phosphite respectively. Diphenylphosphine oxide was approximately three times as reactive as dimethyl phosphite towards hydrogen abstraction by t-butoxyl radicals and four times as reactive as tetrahydrofuran (towards abstraction of an alpha-hydrogen). Diphenylphosphinoyl radicals were found to be relatively nucleophilic and, in competition experiments, reacted about an order of magnitude faster with acrylonitrile then with vinyl acetate. Dimethoxyphosphinoyl radicals were rather less nucleophilic and reacted only twice as fast with acrylonitrile as they did with vinyl acetate. In the presence of excess aminoxyl (1), both diphenylphosphinoyl and dimethoxyphosphinoyl radicals were efficiently scavenged to produce stable phosphinic and phosphate esters respectively. The rate of scavenging was close to diffusion-controlled (c. 1.8x10(9) l. mol(-1) s(-1)).