Viscosity B coefficients for some substituted anilinium cations in aqueous solution at 25° and 35°

Abstract

The variation with concentration of the viscosity and density of aqueous solutions of anilinium chloride, and of some C- and N-methyl substituted anilinium chlorides, has been measured in the presence of sufficient hydrochloric acid to suppress hydrolysis. A suitable method of evaluating viscosity B coefficients for these organic cations from these data has been developed. It has been shown that the ratio of the B coefficient for the organic cation (B₊) to its limiting apparent molar volume (Φ₊°) increased slightly with increasing methyl substitution in the ring. For the N-methylated cations, on the other hand, B₊/Φ₊° fell rapidly as the number of substituent groups increased. This behaviour can be understood by assuming that increasing N-methyl substitution makes it progressively more difficult for a primary hydration shell to form around the charged nitrogen atom, and that insertion of methyl groups in the aromatic ring has little effect on this hydration process.