Process Development for a Herbicide Intermediate via Catalytic Carboxylation of an Aromatic Diazonium Compound

A laboratory process is described for the preparation of 2-sulfo-4-methoxybenzoic acid (SMBA) via diazotization of 2-amino-4-methoxy-sulfonic acid followed by Pd-catalyzed carbonylation in the presence of water. The most important process parameters were the catalyst precursor and water content. Both a two-step procedure using isolated diazonium compound as well as a one-pot reaction proved to be feasible. A yield of >95% SMBA was obtained after 3−4 h, using 1 mol % PdCl 2 at 8 bar and 60 °C. This is the first technically feasible catalytic carbonylation of an arene diazonium compound.