Thermodynamic study of deuterium exchange in water + methanol systems

Abstract

Molar excess enthalpies are reported for the systems H₂O + CH₃OH, H₂O + CH₃OD, H₂O + CD₃OD, D₂O + CH₃OH, D₂O + CH₃OD and D₂O + CD₃OD at 298.15 K. The results are analysed to give the enthalpies of the deuterium exchange reactions CH₃OH(l)+ HDO(l)= CH₃OD(l)+ H₂O(l) and CH₃OH(l)+ D₂O(l)= CH₃OD(l)+ HDO(l). A new analysis of previously published partial molar enthalpies of solution gives enthalpies of reaction in good agreement with those obtained from our excess enthalpy results. These calorimetric values are in striking disagreement with statistical mechanical enthalpies of reaction.