Thermodynamic study on aqueous dilute solutions of organic compounds. Part 1.—Cyclic amines
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 CnH2nNH (n= 4,5,6) and CnH2nNCH3(n= 4,5), from either the ideal gas state (ΔXh, X=H,S,G) or the liquid state (ΔXs, X=H,S,G) to dilute aqueous solution. Heats of solution of compounds of the type CnH2nNH with n= 2,3,7 and heats of vaporization (ΔHv) for all the above compounds are also reported.
In the CnH2nNH series the heat of solution, which is exothermic, has a maximum at n= 4, whereas ΔHv 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 ΔHh values are practically equal. On the other hand, a sensible decrease of ΔSh is caused by introducing a methyl group on the nitrogen atom. Possible interpretations of the observed effects are suggested.