Molecular structure and acid/base properties of 1,2-dihydro-1,3,5-triazine derivatives

Abstract

It is shown that guanidine and its N,N-dimethyl-derivative react with substituted carbodiimides, affording hitherto unknown 1,2-dihydro-1,2,3-triazine derivatives. The structures of three novel compounds of this type and their perchlorate salts were elucidated by spectroscopic (IR, ¹H and ¹³C NMR and ¹⁵N solid-state NMR) and X-ray diffraction methods. The acid/base properties were also determined experimentally and by using DFT calculations with the B3LYP functional. The most basic compound was found to be dihydrotriazine 3, the basicity of which with the pK_a value of 23.3 is of the same order of magnitude as that of tetramethylguanidine. Acidity measurements revealed that all the compounds studied are very weak acids with pK_a values in the range of 25.8–30.8 pK_a units in acetonitrile.