Aggregation of 4-substituted pyridine N-oxide–trifluoroacetates in benzene

Abstract

The practical molal osmotic coefficients and molal activity coefficients of 4-chloro-, 4-methyl-, 4-phenoxy-, and 4-methoxy-pyridine N-oxide complexes with trifluoroacetic acid in benzene solutions over the concentration range 0.03–0.6 mol kg–1 were determined by vapour pressure osmometry. The non-ideal behaviour of the investigated systems is interpreted on the basis of two association models and the association constants are derived. The logarithms of these constants are linearly correlated with the square of the dipole moments of free N-oxides as expected from theory. For 4-methoxypyridine N-oxide trifluoroacetate the value of ΔH° obtained is –12.4 kJ mol–1. These results are discussed in terms of the structure of aggregates.