Xanthine → 2-Thioxanthine

Reaction equation

[NH:1]1[C:10](=[O:11])[C:9]2[NH:8][CH:7]=[N:6][C:5]=2[NH:4][C:2]1=O.P12(SP3(SP(SP(S3)(S1)=S)(=S)S2)=S)=[S:13].[OH-].[Na+]>N1C=CC=CC=1>[NH:1]1[C:10](=[O:11])[C:9]2[NH:8][CH:7]=[N:6][C:5]=2[NH:4][C:2]1=[S:13]

Participants

Procedure

2.77 g (8.0 mM) of xanthine and 2.13 g (9.6 mM) of phosphorus pentasulfide were heated under reflux in 50 ml of pyridine for 7 days. At 0° C., 10.6 ml of 2N NaOH were added within 15 minutes. The solvents were evaporated in vacuo and the residue suspended (slow crystallization) in water. The solid was collected and washed, redissolved in 50 ml of 1N NaOH and 50 ml of isopropanol, treated twice with 0.3 g of charcoal, filtered neutralized with 5N HCl to pH 7. The isopropanol was distilled off with addition of water and the solid collected, washed and dried to give 2.60 g (89.7%) of crude thioxanthine, which was dissolved in 40 ml of dichloromethane and filtered through 30 g of silica gel: 1.91 g (65.9%) of 6-thioxanthine were recovered, mp 153-4° C.