Facile interconversion of the isomeric acid chlorides derived from half methyl esters of 3-methoxyphthalic acid

Abstract

The isomeric acid chlorides obtained by treating the half methyl esters of 3-methoxyphthalic acid with thionyl chloride interconvert so readily that it is not practical to isolate one acid chloride free of the other. At equilibrium the main isomer is the acid chloride derived from the 1-methyl ester. When either half ester is treated with thionyl chloride at 20 °C for 2 h and the crude acid chloride so formed treated with 1,4-dimethoxybenzene in the presence of stannic chloride the only benzophenone derivative obtained is that derived from the more stable acid chloride.