화학공학소재연구정보센터
Journal of Chemical Thermodynamics, Vol.102, 378-385, 2016
Fluorination effect on the thermodynamic properties of long-chain hydrocarbons and alcohols
Structural and thermodynamic insights are reported for the series of fluorinated alcohols {oFTOH; CF3(CF2)(n)CH2OH, with n = 5-12}, with the objective of comparing the phase behaviour of perfluorinated compounds with the analogous linear alkanes and alcohols. As expected the higher vibrational contribution of the -CF2- groups contributes for the higher heat capacities of the perfluorinated compounds. Concerning the fusion/sublimation equilibria, fluorination of the alcohols decreases Delta H and Delta S of phase transitions. Compared to the regular -CH2- alkyl chain structure, the less symmetric -CF2- spiral conformation is characterized by a less efficient molecular alignment in crystal packing, thus explaining the lower Delta H. The lower internal rotational barrier associated with the -CH2- alkyl chains of n-alkanes/alcohols, when compared to -CF2- chains, contributes to the larger values of Delta S observed. Regarding the vaporization equilibria, fluorination leads to greater values of Delta S, which are explained by the larger translational entropy of the heavier perfluoroalcohols, an effect that is more important in the gas than in the liquid phase. (C) 2016 Elsevier Ltd.