A process for the preparation of phenylthiopyrimidines which comprises: (a) reacting a thiopyrimidine; with sulfuryl chloride in the presence of a suitable solvent to form the sulfenyl chloride of said thiopyrimidine; (b) reacting said sulfenyl chloride of said thiopyrimidine with a phenol or substituted phenol, optionally in the presence of a Friedal-Crafts catalyst, to form a thiopyrimidinyl phenol; and (c) reacting said thiopyrimidinylphenol formed in step (b) with a base and an alkylating agent to form the end product.