High-purity isothiocyanate compound preparation method for industrial production

A method for preparing an isothiocyanate compound of formula (I),

• A-N═C═S (I)
• in formula I:
• —N═C═S is isothiocyanate group;
• A is —XR1 or —CR2R3R4, wherein
• X is —(CH2)n—, and n is an integer of 0-6;
• R1 is selected from the group consisting of methyl, tert-butyl, isopropyl, methylthio, methoxy, allyl, methallyl, cyclohexyl, methylsulfinyl, naphthyl, methyl cyclohexyl, morpholinyl, diethylamino, benzoyl, ethoxycarbonyl, tert-octyl, chlorine, trimethylsilyl, substituted or unsubstituted phenyl;
• wherein, one or more hydrogen in the substituted phenyl are substituted by substituents selected from the following group:
• halogen, methyl, bromomethyl, ethyl, methoxy, nitro, azido, trifluoromethyl, difluoromethoxy, methylthio, cyano, trifluoromethoxy, trifluoromethylthio, tert-butoxycarbonyl, and ethoxycarbonyl;
• R2, R3, and R4 are each independently H, phenyl or C1-3 alkyl;
• wherein the method comprises:
• (1) reacting, in the presence of an organic base, A-NH2 with CS2 in organic solvent so as to obtain a first reaction mixture containing dithiocarbamate,
• wherein the organic solvent is an ethyl acetate, and ratio of the A-NH2 to the CS2 is 1:1.05-2;
• (2) adding, in the presence of an optional base catalyst, a desulfurizing agent to the first reaction mixture to carry out a desulfurization reaction so as to obtain a second reaction mixture containing the isothiocyanate compound of formula (I),
• wherein the desulfurizing agent is selected from the group consisting of methyl chloroformate, p-toluenesulfonyl chloride, solid phosgene, elemental iodine, chlorosilane, chlorophosphate, dicyclohexylcarbodiimide, dicyandiamide, triphenylphosphine, di-tert-butyl dicarbonate, cyanuric chloride, or combinations thereof;
• (3) purifying the second reaction mixture by post-processing to obtain the isothiocyanate compound of formula (I);
• wherein in (3), the post-processing comprises:
• washing the second reaction mixture and concentrating so as to obtain an acid-washed crude product;
• distilling the acid-washed crude product so as to obtain a distilled crude product containing the isothiocyanate compound of formula (I);
• and
• subjecting the distilled crude product to rectification under vacuum so as to obtain a pure isothiocyanate compound of formula (I).