A kinetic study of the reaction between 2-p-methoxyphenyl-4-phenyl-2-oxazolin-5-one and 2,2,6,6-tetramethyl-1-piperidinyl-N-oxide

Abstract

The reaction between 2-p-methoxyphenyl-4-phenyl-2-oxazolin-5-one and 2,2,6,6-tetramethyl-1-piperidinyl-N-oxide (TEMPO) in benzene as the solvent generates quantitatively 4,4'-bis-[2-p-methoxyphenyl-4-phenyl-2-oxazolin-5-one]. Studies performed by means of EPR spectroscopy and kinetic experiments carried out using UV-VIS spectrophotometry have shown that the reaction occurs via a captodative radical intermediate. Kinetic experiments lead to a rate constant equal to 1.38 x 10(-2) s(-1) and a reaction rate law which is first order in oxazolinone and independent of TEMPO concentration. These results are explained in terms of a reaction mechanism with a rate-limiting step involving the formation of a mesoionic tautomer of oxazolinone. Hydrogen abstraction from the mesoion by TEMPO gives captodative radicals that generate the observed product through a fast recombination reaction.