Preparation of esters

A process for the preparation of an ester of formula I ##STR4## wherein Ar represents a phenoxy substituted phenyl group and R is an alkyl group optionally substituted by halophenyl or alkylphenyl or a cyclopropyl group optionally substituted by alkyl, halogen, isobutenyl, dichlorovinyl or dibromovinyl, which process comprises contacting an aromatic aldehyde of the formula ArC(O)H and a (cyclo)aliphatic acyl halide of the general formula RC(O)Hal, in which formulas Ar and R have the same meaning as in formula I and Hal represents a halogen atom having an atomic number of from 9 to 53, inclusive, with water, a water-soluble cyanide, a substantially water-immiscible aprotic solvent and a quaternary onium phase transfer catalyst of the formula II ##STR5## wherein X represents a nitrogen, phosphorus or arsenic atom, R.sup.1, R.sup.2, R.sup.3 and R.sup.4 each an alkyl, aralkyl, alkaryl or aryl group and Y a monovalent ion, or a sulfonium compound of the formula III ##STR6## wherein R.sup.5 R.sup.6 and R.sup.7 each represents an alkyl group and Y a monovalent ion and recovering the desired ester product from the reaction mixture.