Thermodynamic properties of organic compounds in aqueous solutions. Apparent molal heat capacities of amines and ethers

Abstract

Apparent molal heat capacities Φ_Cp of some cyclic monoethers and diethers as well as of open and cyclic secondary and tertiary amines and their chloride salts have been determined by adiabatic calorimetry in the temperature range 20–60°C, at concentrations 0.4–1.0 mol kg^–1.

In monofunctional compounds the contribution to Φ_Cp from the functional group is similar to the contribution of this group to C_p2 of the pure liquid; on the other hand the contribution to Φ_Cp from the methylene group is greatly enhanced with respect to the contribution to C_p2(≃ 6 cal (mol CH₂)^–1°C^–1), ranging from 22 ± 2 for open chain compounds to 18 ± 2 cal (mol CH₂)^–1°C^–1 for cyclic compounds. The introduction of a second polar centre brings about a large decrease in Φ_Cp values. Comparisons are made between Φ_Cp data and other thermodynamic quantities. Data are finally discussed in terms of water-hydrocarbon and water-polar centre interactions.