Synthesis of m-phenoxybenzaldehyde starting from chlorobenzene and m-cresol: Some aspects of process development

m-Phenoxybenzaldehyde (MPB) is an important intermediate for synthetic pyre throids, In the present paper, an economic process scheme was developed to synthesize MPB starting from cheaper reactants, The process scheme was star ted with the synthesis of m-phenoxytoluene (MPT), Oxidation of MPT by air g ave MPB, hut the selectivity was found to be high at low conversions of abo ut 10%, and if the conversion level was increased, then large amounts of th e undesired m-phenoxybenzoic acid (MPBA) was formed, To obtain the desired aldehyde, Rosenmund reduction of MPBA was carried out to give high yields o f the MPB, The effects of different parameters such as catalyst, substrate concentration, temperature, etc., were studied for all three of the reactio ns, viz., Ullmann ether synthesis, oxidation, and Rosenmund reduction, MPT mas prepared from chlorobenzene, a relatively cheaper starting material, in the presence of poly(ethylene glycol) as cosolvent and cuprous chloride as the catalyst. A selectivity of 97% was obtained with 86% conversion to the product, Oxidation of MPT was carried out by air in the presence of cobalt acetate as catalyst and sodium bromide as catalyst promoter, The selectivi ty with respect to the aldehyde and the ester was 37.4 and 30.6%, respectiv ely, at a restricted overall conversion of 24%, The process parameters were controlled to achieve high selectivity towards the aldehyde, The acid, for med as the side product, was reduced to the aldehyde by Rosenmund reduction via the acyl chloride, At a conversion level of 85%, a selectivity of 87% to MPB was obtained using Pd/C.