REFORMATSKY REACTION IN WATER - EVIDENCE FOR A RADICAL-CHAIN PROCESS

The Reformatsky reaction of 2-bromo esters and carbonyl compounds in t he presence of zinc can be carried out in concentrated aqueous salt so lutions without any cosolvent. The reaction of bromoacetates is greatl y enhanced by catalytic amounts of benzoyl peroxide or peracids and gi ves satisfactory yields with aromatic aldehydes. Preparative yields co mparable to those of the traditional procedure are obtained with ethyl 2-bromoisobutyrate. This ester needs no catalyst and reacts even with saturated aldehydes and aromatic ketones, although in law yields. A r adical chain mechanism, initiated by electron abstraction from the org anometallic Reformatsky reagent, is proposed. Two nonchain pathways, i nvolving radicals directly produced od the metal surface, may compete, especially in the case of secondary and tertiary halides.