Reassessment of the methyl derivatization reaction of carbamates with sodium hydride/dimethyl sulfoxide/methyl iodide for their determination by gas chromatography

A deep revision of the carbamate methyl derivatization reaction with sodium hydride/dimethyl sulfoxide/methyl iodide was carried out. Representative carbamates, R(1)-NH-COO-R(2), mainly N-methyl and N-aryl ones, have been studied in order to clarify which carbamates undergo this reaction. Two possible reaction routes are proposed; the route depends on the carbamate substituent (-OR(2) group) more than on the methyl or aryl groups joined to the NH moiety as literature indicates. The classification of carbamates in N-methyl and N-aryl is not suitable to predict the methylation pathway. A laboratory-made closed reactor allows handling the reagents involved, minimizing hazards and simplifying the procedure for rapid analysis.