Hydration of the complex of 4-methylquinoline N-oxide with chloroacetic acid in benzene

Abstract

Vapour pressure osmometry (v.p.o.) and ¹H n.m.r. measurements of the 4-methylquinoline N-oxide complex (B) with chloroacetic acid (HA) in benzene containing different amounts of water provide evidence for an interaction interpreted in terms of the overall equilibrium (BHA)₂+ H₂O [graphic omitted] BHA + BHA,H₂O, equivalent to a system of two competing equilibria 2(BHA) [graphic omitted] (BHA)₂ and BHA + H₂O [graphic omitted] BHA,H₂O. Quantitative treatment of the v.p.o. and n.m.r. data gave K₁ 1.78 ± 0.47 molal^–1, K₂ 24.35 ± 7.57 molal^–1, and K₃ 13.68 ± 4.89. The previously reported anomalously high value for the difference between the chemical shift of dimer (δ_d) and monomer (δ_m) was an effect of residual moisture. Instead, δ_d–δ_m= 0.95 p.p.m.