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13.22 g (50 mM) of 2-thioxanthine and 13.34 g (60 mM) of phosphorus pentasulfide were heated under reflux in 160 ml of pyridine for 3 days. At 5-10° C., 66 ml (132 mM) of 2N NaOH were added. The solvents were evaporated in vacuo, the residue treated with 200 ml of water and evaporated again. The residue was again suspended in 200 ml of water and collected. The crude product was dissolved in 120 ml of 1N NaOH, treated twice with 0.14 g of charcoal, filtered and acidified with 32 ml of SN HCl to pH 4.5. The solid was collected, washed and dried to give 14.31 g of crude dithioxanthine. This was dissolved in 300 ml of chloroform; some insoluble material was filtered off, and the solution passed through 71.5 g of silica gel in a column. Crystallization from isopropanol gave 12.17 g (86.8%) of 2,6-dithioxanthine with mp 196-200° C.

1. customThe solvents were evaporated in vacuo
2. additionthe residue treated with 200 ml of water
3. customevaporated again
4. customcollected
5. dissolutionThe crude product was dissolved in 120 ml of 1N NaOH
6. additiontreated twice with 0.14 g of charcoal
7. filtrationfiltered
8. customThe solid was collected
9. washwashed
10. customdried