Solid−liquid phase-transfer-catalysed methoxylation of chloronitrobenzenes to nitroanisoles

Abstract

Nitroanisoles are important precursors in the organic process industry and are made from chloronitrobenzenes by using sodium hydroxide and methanol under liquid−liquid phase-transfer catalysis, which requires higher temperatures, leading to loss in selectivity. Synthesis of p-nitroanisole was carried out from p-chloronitrobenzene (PCNB) and solid sodium methoxide by using tetrabutylammonium bromide as a catalyst under solid−liquid phase-transfer catalysis (S−L PTC) as opposed to the standard liquid−liquid (L−L) PTC system. The advantages of the S−L PTC are that the reaction is conducted at room temperature with 100% conversion and 100% selectivity. The kinetics and mechanism are also established for this reaction. The methoxylation of o-chloronitrobenzene (OCNB) was also studied. The rate of methoxylation of PCNB was much greater than that of OCNB at 30 °C. m-Chloronitrobenzene does not react with sodium methoxide under otherwise similar conditions. For the reaction of PCNB with sodium methoxide, the diffusional resistance was found to be unimportant. The rate of the reaction was found to be of first order with respect to both the concentration of catalyst and the substrate.