Abstract: The byproduct 1-(dimethylamino)-2,3-dithiocyanatopropane(2) can be recycled and partly converted into its isomer 2-(dimethylamino)-1,3-dithiocyanatopropane(1), the key intermediate of Cartap, and finally achieved dynamic equilibrium, which can be used to increase the yield.  Effects of temperature, catalyst and solvent on the tautomerization of compound 1 and its isomer 2 were investigated. The rearrangement mechanism was studied by density functional theory(DFT) method at B3LYP/6-31G(d) level. The calculation results indicated that the ring closure leading to aziridinium ion and further ring opening by thiocyanate at less substituted aziridine carbon atom via an SN2 mechanism. The solvent effect(toluene, chloroform, acetone, methanol, ethanol, acetonitrile and DMSO) on tautomerization was also taken into account via polarizable continuum model(PCM).  Ionization of a neutral substrate results in charge separation, and solvent polarity has a greater effect at the transition state than that for the reactants. Polar solvents lower the energy of the transition more than the solvents of lower polarity. The results show that the solvent effect plays an important role which was supported by experiment data.

Key words: Cartap; , Reaction mechanism; , Density functional theory; , Aziridinium ion; , Solvent effect