Thermodynamic study on aqueous dilute solutions of organic compounds. Part 1.—Cyclic amines

Abstract

The enthalpy, entropy and free energy changes have been determined for the transfer, at 25°C and 1 atm, of cyclic amines of the type C_nH_2nNH (n= 4,5,6) and C_nH_2nNCH₃(n= 4,5), from either the ideal gas state (ΔX_h, X=H,S,G) or the liquid state (ΔX_s, X=H,S,G) to dilute aqueous solution. Heats of solution of compounds of the type C_nH_2nNH with n= 2,3,7 and heats of vaporization (ΔH_v) for all the above compounds are also reported. In the C_nH_2nNH series the heat of solution, which is exothermic, has a maximum at n= 4, whereas ΔH_v values increase in the homologous series from 8.09 kcal mol^–1(n= 2) to 11.04 kcal mol^–1(n= 7). The heats of solution of the N-methyl amines are larger than those evolved on solution of the corresponding secondary, unsubstituted amines, while the ΔH_h values are practically equal. On the other hand, a sensible decrease of ΔS_h is caused by introducing a methyl group on the nitrogen atom. Possible interpretations of the observed effects are suggested.