The thermodynamic interaction of N-methyllactams with cyclohexane and methanol

Abstract

The study deals with the dependence of thermodynamic interaction of the N-methylamine group in N-methyllactams with the acid hydrogen atom of methanol on the size of the lactam ring. The heats of mixing of N-methyl-4-butanelactam, N-methyl-6-hexanelactam, N-methyl-7-heptanelactam and N-methyl-8-octanelactam with methanol and cyclohexane were measured, and the data thus obtained were treated in terms of Barker’s quasichemical theory. In a series of N-methyllactam-cyclohexane systems the mixing is endothermic, and the heats of mixing decrease with increasing size of the lactam ring. On the contrary, the mixing of N-methyllactams with methanol proceeds exothermically; first, the heats of mixing decrease depending on the lactam ring size, but for N-methyl-8-octanelactam they are very close to values obtained for N-methyl-4-butanelactam. However, with increasing ring size the energy of interaction between the N-methylamide group and the acid hydrogen atom of methanol increases. Such apparent discrepancy may be explained, in particular, by an opposite effect of the interaction between this group and the alkyl hydrogen atom.