THERMOCHEMICAL COMPARISONS OF SOLID AND HOMOGENEOUS ACIDS AND BASES - PYRIDINE AND POLYVINYLPYRIDINE AS PROTOTYPE BASES

By means of a previously established thermochemical technique, the basic properties of polyvinylpyridine slurries in acetonitrile are compared with those of solutions of pyridine through their heats of interaction with a series of carboxylic and sulfonic acids. An excellent correlation between the heats of interaction obtained by titration calorimetry, DELTA-H(titr), for the homogeneous versus heterogeneous systems is obtained which is similar to that for a previous correlation of DELTA-H(titr) for a series of bases into solutions of p-toluenesulfonic acid versus slurries of a microporous sulfonic acid resin. In both cases it appears that only the most available surface sites are being titrated since DELTA-H(titr) values correlate poorly with corresponding heats of immersion. Important differences between homogeneous and solid acid-base systems are stressed and an inherent lack of symmetry between the nature of acid-base interactions at the surfaces of acidic and basic solids.