Use of TPD-MS and Linear Free Energy Relationships for Assessing the Reactivity of Aliphatic Carboxylic Acids on a Silica Surface

The interaction of acetic, propionic, butyric, isobutyric, valeric, nonanoic, decanoic, and pivalic acids with the surface of fumed silica was investigated by temperature-programmed desorption mass spectrometry (TPD-MS). Mechanisms of the formation of ketenes from chemisorbed fragments of carboxylic acids on the surface of fumed silica were proposed and the kinetic parameters of the reaction were calculated. The Taft correlation equation and the reaction parameter p could be obtained by application of the linear free energy relationship (LFER) principle for this reaction series. The applicability of the LFER method to the study of reactions of adsorbed organic molecules on mineral surfaces occurring during TPD-MS experiments was demonstrated using a series of acids.