ACIDITY AND BASICITY SCALES FOR POLAR-SOLVENTS

Acidity and basicity scales for polar solvents are examined and compared with the mean spherical approximation parameters derived from the Gibbs energy of solvation of the alkali metal and halide ions in 18 polar solvents, both protic and aprotic. On the basis of an analysis of data for the Gibbs energy of transfer of 1-1 electrolytes and standard redox potentials for simple reactions in a variety of these solvents, it is concluded that the most appropriate scales are the acceptor number AN and donor number DN introduced by Gutmann. The extrathermodynamic assumption for separating cationic and anionic contributions to thermodynamic quantities for electrolytes based on equal solvation of the tetraphenylarsonium and tetraphenylborate ions is reexamined. This assumption appears to be valid in aprotic solvents but questionable for protic ones.