Comment on “prediction of vapor pressures of solid organic compounds with a group contribution method”

In a recent paper appearing in this journal, Coutsikos et al. [1] presented a group contribution method for estimating vapor pressures of organic solids. The estimation required the compound’s molar entropy of fusion, fusSm, which was also calculated by a group contribution method developed by the authors. The proposed method gave satisfactory vapor pressure predictions for many organic compounds having vapor pressures well below the Pa level. The entropy of fusion estimations was not nearly as good. As noted by the authors, “the obtained predictions are – as expected from a simple method – not very accurate, but sufficient for purposes of this study.” In fairness, the authors’ intention was not to develop a group contribution method for estimating entropy of fusion per se. Rather the authors needed a numerical value of the entropy of fusion only for substituting into their predictive vapor pressure expression. The intent of this short communication is not to criticize the authors’ excellent work, but rather to inform journal readers of the existence of a second group contribution method for total solid-to-liquid phase change entropy that gives much better entropy predictions for the database examined. In the second method [2–6], the molar total phase change entropy of a molecule, tpceSm, is estimated as the sum of three components: the contribution of the hydrocarbon portion of the molecule, the contribution of the carbon(s) bearing the functional group(s), and the contribution of the functional group(s) as summarized by the three terms of Eq. (1):