Chlorthal-monomethyl is made by first producing technical-grade chlorthal through the established phthalate-based synthesis in which the tetrachlorinated aromatic core is constructed and then converted to the corresponding acid chloride. The monomethyl ester is formed by reacting this acid chloride with methanol under controlled conditions that limit further esterification, yielding the mono-ester rather than the di-ester. After the reaction, the mixture is neutralised, washed to remove residual reagents, and the crude ester is purified, typically by distillation or crystallisation, to meet technical specifications before being incorporated into herbicide formulations.
