THE REACTION OF CHLORAL WITH HALOBENZENES AND WITH 2,4-DICHLOROPHENOL: SYNTHESIS OF HALOGENATED ETHYLBENZENES AND OF α-METHOXYPHENYLACETIC ACIDS

The Friedel–Crafts reaction of chloral with aromatic compounds to form aryltrichloromethylcarbinols is reviewed. The molar ratio of aluminium chloride to chloral is critical and varies from 0.15 to 2.0 depending on the solvent, steric considerations, and the reactivity of the aromatic ring. The reaction has been used to prepare several new compounds with carbon disulfide or excess aromatic compound as the solvent. From 2,4-dichlorophenol, an o-hydroxy-α-trichloromethylbenzyl alcohol is obtained. Both the phenolic and side-chain hydroxy groups of this alcohol are methylated with equal ease by dimethyl sulfate.It has now been found that changing the solvent from carbon disulfide to methylene chloride results in the hydroxy group of the initial carbinol also being replaced by chlorine. This role of the solvent in controlling the course of the reaction has not been observed previously.The trichloromethylcarbinols are converted into α-methoxy acids by treatment with methanolic potassium hydroxide. Sodium in liquid ammonia removes the α-methoxy group, as well as the halogens, from 3,5-dichloro-α,2-dimethoxyphenylacetic acid.