Amidines. Part 31. pKa values of N1,N1-dialkyl-N2-phenylformamidines in water–ethanol solutions

Abstract

The pK_a values of three series (30 compounds in all) of N¹,N¹-dialkyl-N²-phenylformamidines (XC₆H₄NCH–NRR) have been measured in water–ethanol mixtures. The obtained pK_a values of the amidines have been correlated with Hammett-type substituent constants and the pK_a values of the corresponding primary amines determined in the same solvent. The applicability of various σ values is discussed and it is shown that, in each case, for substituents on the phenyl ring at the amino nitrogen atom σ° values should be used. It is found that the slopes of regression lines for correlations with Hammett-type constants depend on the substituents at the amino nitrogen atom, as well as on the solvent.