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On the Relation of Entropy and Enthalpy of Fusion in Triglycerides
This contribution presents an extensive literature survey of the calorimetric properties, namely enthalpy and entropy of fusion, of alkylâbased molecules. Building on the wellâknown linear correlation of the named properties to the carbon number in nâalkanes, saturated fatty acids (FA), and saturated monoacid triglycerides (TAGs), the calorimetric properties of TAGs are reviewed. No straightforward correlation using a single ordering parameter, i.e., carbon number, can be derived for TAGs. This is not surprising due to the complexity of this particular class of molecules differing in alkylâchain distribution over the glycerol backbone and chain saturation. A linear correlation of enthalpy and entropy of fusion is evident for molecule classes for which both properties correlate linearly with the carbon number, e.g., nâalkanes. Despite the complexity of TAGs, it is possible to establish a linear correlation between enthalpy and entropy of fusion even though no underlying single ordering parameter can be identified. A linear fit reveals discrepancies between saturated and unsaturated molecules but independence of polymorphic forms and chain length differences in mixedâacid TAGs. Moreover, the slopes of the linear fits for data on nâalkanes, saturated FA, and saturated monoâacid TAGs are found to be in the vicinity of the melting temperature of polyethylene