[CH3:1][S:2][C:3]1[CH:4]=[C:5]([CH:7]=[CH:8][C:9]=1[N+:10]([O-])=O)[NH2:6].[ClH:13].[H][H]>[Pd].C(O)C>[ClH:13].[CH3:1][S:2][C:3]1[CH:4]=[C:5]([NH2:6])[CH:7]=[CH:8][C:9]=1[NH2:10]In a Paar hydrogenation bottle, a mixture of 3-methylthio-4-nitroaniline (7.7 g), 5% Pd/C catalyst (8.0 g), concentrated hydrochloric acid (7 ml) and ethanol (200 ml) is treated with hydrogen at 3.43 kg/cm2 for 45 minutes (until 0.8 kg/cm2 hydrogen is absorbed). The mixture is filtered through diatomaceous earth and the filtrate evaporated to dryness afford 3-methylthio-p-phenylenediamine hydrochloride. The salt is dissolved in water, the solution made alkaline (pH 9-10) with 50% sodium hydroxide and the diamine extracted with methylene chloride (3×150 ml). The combined extracts are dried over magnesium sulfate and evaporated to dryness to afford 4.75 g of title product, a brown solid, which is used as is.
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