THE TRIMERIZATION OF ISOTHIOCYANATES UNDER HIGH-PRESSURE

The trimerization of methyl isothiocyanate in the presence of triethylamine was accelerated under high pressure to give 1,3,5-trimethyl-1,3,5-triazine-2,4,6(1 H,3 H,5 H)-trithione in high yield. Trialkylamines such as triethylamine were good catalysts of the trimerization under high pressure. Pyridine also catalyzed the trimerization, but 2-methylpyridine and 2,6-dimethylpyridine had no catalytic activity. The rate of the trimerization of methyl isothiocyanate was proportional to the amount of triethylamine catalyst so far as a limited amount of triethylamine was used. Ethyl isothiocyanate trimerized in high yield on the same reaction conditions as the trimerization of methyl isothiocyanate, however, isothiocyanates having more bulky groups such as propyl, butyl, allyl, phenyl, and cyclohexyl trimerized in poor yields on such reaction conditions. Propyl and butyl isothiocyanates in the presence of DBU trimerized in good yields under 800 MPa at 1300-degrees-C for 20 h. Although allyl isothiocyanate, which has a C-C double bond, polymerized by DBU catalyst or at increased temperature, the trimer was obtained in good yield in the presence of triethylamine under 1200 MPa.