Phenols nuclear substituted by 1 to 3 straight chain or branched chain alkyl substituents of 1 to 10 carbons are prepared by oxidising the aldehyde group of the corresponding alkyl substituted benzaldehyde with an organic peracid, which is derived from a carboxylic acid of pKa in water of at least 4, in the presence of a carboxylic acid of pKa in water less than 4. The formate ester of the phenol, which may be in the reaction product, is hydrolysed or transesterified to form the phenol.