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-dihyd ro-2H-isoin (1) as a radical scavenger has been used to study the reac tion of diphenylphosphinoyl (2) and dimethoxyphosphinoyl (3) radicals with vinyl acetate and acrylonitrile. The phosphorus-centred radicals were generated by hydrogen abstraction from diphenylphosphine oxide an d dimethyl phosphite respectively. Diphenylphosphine oxide was approxi mately three times as reactive as dimethyl phosphite towards hydrogen abstraction by t-butoxyl radicals and four times as reactive as tetrah ydrofuran (towards abstraction of an alpha-hydrogen). Diphenylphosphin oyl radicals were found to be relatively nucleophilic and, in competit ion experiments, reacted about an order of magnitude faster with acryl onitrile then with vinyl acetate. Dimethoxyphosphinoyl radicals were r ather less nucleophilic and reacted only twice as fast with acrylonitr ile 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 ester s respectively. The rate of scavenging was close to diffusion-controll ed (c. 1.8x10(9) l. mol(-1) s(-1)).