Catalysis in the reactions of acetals.
2015-11-19T08:58:46Z (GMT) by
The evidence for the generally accepted mechanism of the hydrolysis of acetals, ketals and glycosides is reviewed. A brief account of the proposed mechanisms for the action of the enzyme lyso-zyme is given. Some of the underlying assumptions are discussed and some criticisms are offered. Some of the more important attempts to observe "non-general" hydrolytic behavoir are discussed and the reasons for some of the failures are evaluated, Acetals with potential neighbouring nucleophiles' where in principle assistance to bond rupture in the acid catalysed hydrolysis of the acetal group is possible, have been synthesised and the kinetics of their hydrolysis investigated. It is demonstrated that catalysis is not general and in the examples studied it is necessary to lower the polarity of the hydrolytic medium in order to observe any participation Reasons for this are discussed. Steric effects in the hydrolysis of 2-methoxy methoxy benzoic acid have been investigated and it is demonstrated that substituents ortho to the formal group increase the intramolecularly catalysed rate of hydrolysis irrespective of their electronic substituent effects. A satisfactory theory is developed to explain the facts. Mixed aryl methyl acetals of benzaldehyde have been synth-esised and their hydrolysis is shown to be general acid catalysed. The facts are rationalised by a development of a previous theory. A brief section is devoted to the use of statistical methods in the calculation of rate constants and some computor programs to implement these are listed in the appendix.