Diazomethane derivatization of sulfamethazine: formation of isomeric products

Reaction of 4-amino-N-(4,6-dimethyl-2-pyrimidinyl)benzenesulfonamide (sulfamethazine) with diazomethane yields not only 4-amino-N-(4,6-dimethyl-2-pyrimidinyl)-N-methylbenzenesulfonamide but also 2-(4-aminobenzenesulfonimido)-1,4,6-trimethyl-1,2-dihydro-pyrimidi ne. Yields of the latter compound are highly variable and the compound does not show a response to gas chromatography. Thus, results of gas chromatographic determinations of residues of some sulfa drugs in edible meat tissues may be erroneous when diazomethane derivatization is used.