The solution of 4.6 g of m-trifluoromethylbenzylmercaptan in 30 ml of dimethylformamide is added to the slurry of 1.08 g of 50% sodium hydride in mineral oil (washed 2 times with hexane), under nitrogen while stirring at room temperature. After several minutes, a clear yellow solution is obtained, which is combined with that of 5.0 g of 3-nitro-2,5-pyridinedicarboxylic acid dimethyl ester in 50 ml of dimethylformamide. The mixture is warmed on the steam bath for 30 minutes at 90° and stirred at room temperature overnight. It is acidified with 2 ml of acetic acid and diluted to 400 ml with a mixture of ice and water. The precipitate formed is collected and recrystallized from methanol-diethyl ether (1:1), to yield the 3-(m-trifluoromethylbenzylmercapto)-2,5-pyridine-dicarboxylic acid dimethyl ester melting at 102°-106°.
