Chapter 15 - Acid-base catalysis

Abstract

Reactions involving acids and bases represent a very large and important section of modem chemistry. They are widely used in chemical synthesis and technology, and many biochemical reactions occur with the participation of acids. Charge transfer reactions occupy the central place in this area. According to Bronsted, an acid is a compound capable of donating a proton, and a base is a compound capable of withdrawing a proton. Aprotic acids (Lewis acids) exist (and are used as catalysts) along with protic acids. Lewis acid is a substance capable of being an acceptor for an electron pair of a base while lewis bases are substances that act as donors of an electron pair. The definitions of a base according to Bronsted (proton acceptor) and Lewis (electron pair donor in the reaction with an acid) virtually coincide. However, the definitions of an acid diverge, as we can see. The Bronsted acid is a proton donor, and the Lewis acid is an acceptor of a base (a substance beating an unshared electron pair). Pearson introduced a concept of hard and soft acids and bases. Hard acids form more stable compounds with hard bases, and soft acids form more stable compounds with soft bases.