Novelties of solid−liquid phase transfer catalysed synthesis of α-isopropyl-p-chlorophenyl acetonitrile from p-chlorophenyl acetonitrile

Abstract

C-Alkylation is an important class of synthetic reaction employed in the fine chemical industry. Although a number of C-alkylation reactions are reported under liquid−liquid (L−L) phase transfer catalysis (PTC) leading to intensification of reaction rates, there is a dearth of information on similar reactions under the solid−liquid (S−L) PTC including kinetics and mechanism. S−L PTC offers higher rates of reaction and better selectivities to the desired product vis-à-vis L−L PTC. This contribution reports the novelties of S−L PTC for C-alkylation of p-chlorophenyl acetonitrile to α-isopropyl-p-chlorophenyl acetonitrile which is an important intermediate in the synthesis of a pyrethroid insecticide named fenvalerate. p-Chlorophenyl acetonitrile can be mono- or dialkylated, depending on the reaction conditions, and it is a versatile synthetic intermediate in the sense that the nitrile function can be hydrolysed, reduced, or added to by organometallics after an alkylation has been carried out. It is found that the S−L PTC process is more intensified and selective. The mechanistic details of C-alkylation under basic conditions and the unexpected side reaction of oxidative decyanation are studied. The production of water as a byproduct in the reaction to form the omega (ω) phase and the mechanism in reference to the S−L−ω-phase system is described. A numerical model is composed to calculate the values of various pseudo rate constants and validate the simulated profiles against experimental data. The finer aspects of selectivity in C-alkylation reaction are analysed.