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1.0 g 2,3-diamino-5-nitropyridine and 1.125 g 4-methylsulfanylbenzoic acid in 20 ml polyphosphoric acid were heated to 160° C. with stirring for 15 hrs. The mixture was cooled and poured into water. The pH was adjusted to 4-5 by addition of sodium hydroxide and the precipitate collected by filtration. The filtration residue was stirred in 50 ml pyridine at 60° C., cooled and insoluble components removed by filtration. The filtrate was evaporated and the residue used without further purification in the next steps. Yield 0.656 g of 30% purity

1. temperatureThe mixture was cooled
2. filtrationthe precipitate collected by filtration
3. stirringThe filtration residue was stirred in 50 ml pyridine at 60° C.
4. temperaturecooled
5. custominsoluble components removed by filtration
6. customThe filtrate was evaporated
7. customthe residue used without further purification in the next steps