Abstract: The sulfaguanidine intermediate,di-(p-nitrophenyl)disulfide,prepared by the interaction of p-nitrochlorobenzene and sodium disulfide,is always contaminated with large amount of a by-product—the monosulfide which is difficult to remove by ordinary methods.Our experiments showed that the separation of the mono- sulfide from the disulfide can be achieved by converting the disulfide into soluble sodium p-nitrothiophenolate leaving the monosulfide unchanged. The method is as follows:5 parts of the crude product is heated for 30 minutes with 2 parts of sodium hydroxide(final concentration 13%)in a medium of 50% alcohol.After cooling and standing,the crystals of the sodium p-nitro- thiophenolate are collected by filtration and dissolved in hot water.Filtered while hot,the filtrate is acidifed with 15% hydrochloric acid.The greenish yellow pre- cipitate formed is collected,washed with small amount of water and dried in warm air.The product was identified as p-nitrothiophenol,m.p.75—77℃,and could be partially or completely oxidized by air to di-(p-nitrophenol)disulfide,m.p.181℃. Yield,99%.The effect of the concentration of alcohol and the amount of sodium hydroxide was also studied.