Increased intensity of tert-butoxyl radical emission in 4-chloro-2-methylphenoxyacetic acid (MCPA) synthesis

The important herbicide, 2‐methyl‐4‐chlorophenoxyacetic acid (MCPA) was synthesized by the chlorination of 2‐methylphenoxyacetic acid with tert‐butyl hypochlorite in the presence of methyl N,N‐dimethylglycinate as a catalyst, giving a high yield and regioselectivity. The reaction was investigated using the spin‐trapping technique in electron paramagnetic resonance measurement conditions, with nitrosodurene as a spin trap. Increased intensity emission of the tert‐butoxyl radical (2.9 times in relation to the starting level) was observed after the catalyst had been introduced into the reaction mixture, indicating a free radical mechanism for the reaction. © 1999 Society of Chemical Industry