Amidines. Part 13. Influence of substitution at imino nitrogen atom on pKa values of N1N1-Dimethylacetamidines

Abstract

20 N¹N¹-Dimethylacetamidines containing alkyl, aralkyl, or substituted phenyl groups have been synthesized, and their pK_a values in 95.6% ethanol (azeotrope) measured. The pK_a values obtained were correlated with Hammett σ constants. The appliciability of various σ values is discussed, and it is shown that for substituents at nitrogen σ° values should be used. It has also been shown that the pK_a values of amidines correlate well with the pK_a values of corresponding primary amines, and that this correlation can serve for the prediction of the pK_a of amidine. Comparison of the correlations for N¹N¹-dimethylacetamidines with those for N¹N¹-dimethylformamidines indicate that sensitivity of the amidine group to substitution at the imino nitrogen atom depends to a considerable degree on substitution at a functional carbon atom.