The Influence of Intramolecular Hydrogen Bonding on Proton-Transfer Reactions. A Temperature-Jump Study of Acid-Base Reactions Involving Substituted Salicylic Acids

Article abstract of DOI:10.1021/j150663a008

The temperature-jump relaxation technique has been used to study the kinetics of proton transfer between salicylic acid derivatives (3,5-dinitrosalicylic acid, DNSA, and thiosalicylic acid, TSA) and a second donor/acceptor system (ammonia or cacodylic acid).Depending on the system, the investigations have been carried out between pH 6.0 and 9.0.The concentration dependencies of the observed relaxation time demonstrate that not only the direct proton-transfer process but also the hydrolytic or protolytic pathway, respectively, contribute to the overall reaction under the given conditions.The rate constants for proton transfer from the monoprotonated salicylate anions to the acceptors NH3, cacodylate^-, and OH^- are far below the diffusion-controlled values, even if these reactions are thermodinamically favored.This decrease in reactivity indicates that the proton to be transferred is engaged in an internal H bond in the mononegative salicylate anions.The strength of the internal H bond is much lower in TSA than in DNSA.