Solvation and Catalysis in Displacement at Phosphorus. Reaction of Imidazole and Benzoate Ion with p-Nitrophenyl and 2,4-Dinitrophenyl Diphenylphosphinates

Article abstract of DOI:10.1021/jo00314a009

The reactions of two phosphorus esters, p-nitrophenyl diphenylphosphinate (I) and 2,4-dinitrophenyl diphenylphosphinate (II), have been investigated in acetonitrile containing variable amounts of water.The effectiveness of imidazole and benzoate ion as catalysts has been investigated.Whereas the reaction of imidazole with II is quite rapid, the reaction with I is very slow.However, I reacts predominantly by the rate term k and shows no k term.Nucleophilic catalysis and the existence of an anhydride intermediate have been confirmed with I by observation of the carbonyl region in the infrared: a C=O peak appropriate for an anhydride appears with C6H5CO2(1-) and then disappears if imidazole is added.This correlates with kinetic evidence for an equilibrium with benzoate ion alone but complete reaction if benzoate and imidazole are both present.The reaction of II has been shown to proceed by reversible formation of 1-(diphenylphosphinyl)imidazole as an intermediate.