MNDO Studies on Malononitrile Dimerization

As a starting reagent in organic synthesis, malononitr i le-dicyanomethylene has an established posit ion because of its reactivity in the addi t ion, self addi t ion, and condensation reactions leading to various carbocyclic and heterocyclic systems [1]. The a im of our work is to investigate the reaction path of malononitrile dimerizat ion and the structure of the reaction product using q u an tum mechanical methods. It was shown that malononitr i le undergoes a Thorpetype dimerizat ion in aqueous solution [2]: i) in the presence of bases [1], ii) in the autocatalyt ic format ion at high pressure, 8000 k g / c m 2 at 323 — 343 K [3], iii) and under hydrogen pressure in the presence of the Pt catalyst with the apparen t activation energy 85.8 kJ /mol [4] l , l ,3tr icyano-2amino-1 -propane is the main product in all cases. Bloch and Toupance [5] showed that the initial formation rate of the d imer in dilute aqueous solution is proport ional to the square of the total malononitri le concentrat ion and displays a maximum when the pH of the med ium equals the pK;, of the following acid-base pair at a given tempera ture :