Hofmann decomposition of quaternary ammonium salts under phase-transfer catalytic conditions

Abstract

The known Hofmann degradation of quaternary ammonium salts under basic phase-transfer catalytic conditions has been studied. The base-catalysed isomerization of p-allylanisole to p-methoxy-β-methylstyrene was used as a kinetic probe to find experimentally the rate constant and activation energy of the Hofmann decomposition without isolating the quaternary ammonium basic salt R4N+B–(B–= base anion). Reactions performed at various temperatures showed that the higher the temperature the greater was the initial rate but the lower the final conversion in the isomerization reaction. The quaternary ammonium hydroxide was found to catalyse the isomerization and the Hofmann degradation more effectively than the corresponding alkoxide. This indicates that the former is a stronger base in the non-polar aprotic solvents common in phase-transfer catalysis.