Hydrogen Sulfide → 2-Diethoxyphosphorylethanethioamide

A 250-mL round-bottom flask equipped with a dry-ice condenser and drying tube filled with potassium hydroxide pellets, was charged with 50.0 g (0.2822 mol) of diethyl cyanomethyl phosphonate (Aldrich Lot HY0151136Y), 79.0 mL (0.5668 mol) of triethylamine and 53.0 mL (0.6553 mol) of pyridine. To the resulting solution was added 3.3 g (0.390 mol) of hydrogen sulfide via submerged tube. The reaction flask was stoppered and stirred overnight (small samples were withdrawn, evaporated at 55° C. and 10 torr, redissolved in CDCl3 and checked by NMR spectroscopy for completion of reaction). After about 16 hours, the reaction mixture was evaporated at 55° C. and 10 torr, the crystalline residue was taken up in 200 mL of dichloromethane and the resulting solution was washed with 200 mL of a 1:1 water-saturated sodium chloride solution. The aqueous phase was reextracted with 100 mL of dichloromethane. 50 mL of 1:1 water-saturated sodium chloride solution was used to wash the first extract and then the second. The extracts were combined, dried over sodium sulfate, and evaporated to yield 50.46 g of (2-amino-2-thioxoethyl)phosphonic acid diethyl ester as an off-white, crystalline material after drying at 45° C. and 10 tort, 85% yield.