Neighboring-Group Effects in Phosphonate Ester Hydrolysis. Iii. Studies on Syn and Anti-p-Nitrophenyl Phenacyl Methylphosphonate Oxime

摘要

Syn- and anti-p-nitrophenyl phenacyl methylphosphonate oxime along with their precursors, phenacyl bromide oxime and phenacyl chloride oxime, were prepared and their stereochemistry studied by chemical reaction and NMR spectrometry. O-methyl p-nitrophenyl phenacyl methylphosphonate oxime was also prepared. The hydrolyses of these compounds were studied under a wide variety of pH's, temperatures, and solvent compositions. Both compounds were found to be base-catalyzed and hydrolyzed much more rapidly than their carbonyl analog. Both compounds also showed unusually low energies of activation, which accounts thermodynamically for their rapid hydrolysis. Possible mechanisms for the hydrolytic reactions are discussed in light of the kinetic data and sterochemical considerations. The hydrolysis rate of O-methyl p-nitrophenyl phenacyl methylphosphonate oxime was also determined and exhibited little or no neighboring-group effect. (Author)