Thermochemistry of amines: strain in six-membered rings from experimental standard molar enthalpies of formation of morpholines and piperazines

Author： Verevkin S.P.

Publisher： Academic Press

ISSN： 0021-9614

Source： Journal of Chemical Thermodynamics, Vol.30, Iss.9, 1998-09, pp. : 1069-1079

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Abstract

The standard (p°=0.1 MPa) molar enthalpies of formation Δ_fH_m°(l) at the temperature T=298.15 K were measured by means of combustion calorimetry for morpholine (A), N-methyl-morpholine (B), N-ethyl-morpholine (C), and N,N-dimethyl-piperazine (D). The standard molar enthalpies of vaporization Δ^g_lH_m° of these compounds and, in addition, the enthalpy of sublimation of piperazine (E) Δ^g_crH_m°=(72.1±1.3) kJ·mol^-1, were obtained from the temperature dependence of the vapour pressure measured in a flow system. Strain enthalpies (ring-correction terms) of cyclic amines were derived from the measured enthalpies of formation of the gaseous compounds. These experimental results, together with data available from the literature, provided a quantitative understanding of the inter-relations of structure and energetics of amines and a further improvement of the group-contribution methodology for estimation of the thermodynamic properties of organic compounds.Δ_fH_m°(l)/kJ·mol^-1Delta^g_lH_m°/kJ·mol^{- 1}Δ_fH_m°(g)/kJ·mol^-1A- 187.24±0.7944.97±0.36-142.27±0.87B-195.65±0.9639.62±0.2 6-156.03±0.99C-225.6±1.542.07±0.31-183.5±1.5D-33.7±1.24 3.80±0.3110.1±1.2