Acetals specific acid catalysis

Pos twe-Tone Photoresists. The ester, carbonate, and ketal acidolysis reactions which form the basis of most positive tone CA resists are thought to proceed under specific acid catalysis (62). In this mechanism, illustrated in Figure 22 for the hydrolysis of tert-huty acetate (type A l) (63), the first step involves a rapid equihbrium where the proton is transferred between the photogenerated acid and the acid-labile protecting group ... 

This is known as specific acid catalysis, specific in that H3O is the only acidic species that catalyses the reaction the reaction rate is found to be unaffected by the addition of other potential proton donors (acids) such as NH4 , provided that [H3O ], i.e. pH, is not changed, indirectly, by their addition. The mechanism of the above acetal hydrolysis is believed to be. 

Przystas and Fife427 have studied the hydrolysis of substituted benzaldehyde methyl 8-quinolyl acetals such as (135) in 50% dioxane-water at 30 °C. These acetals are subject to both general and specific acid catalysis. A variety of divalent metal ions (Cu11, Co11, Ni11, Mn11 and Zn11) exert... 

Specific acid catalysis, but not general catalysis, is found for acetal and... 

The difference between the hydrolysis of an orthoester and the hydrolysis of an acetal is that profanation and C-O bond cleavage occur together in the former. In the hydrolysis of an acetal, the protonated form of the acetal is produced as an intermediate in the reaction. While we will not go into details here, the hydrolysis of the orthoester constitutes a case of what is known as general acid catalysis, while that of an acetal is specific acid catalysis. 

Specific acid catalysis is where the rate is affected only by the concentration of the conjugated acid of the solvent, e.g. H30+ ions in aqueous reactions. An example would be the acid catalysed hydrolysis of acetals, R2C(OR)2. It is characteristic of reactions in which there is a rapid, reversible protonation of the... 

In those methods that do not distinguish the labile aldimine adduct from the stable ketoamine component, the former may be removed by incubating red cells in glucose-free isotonic saline or buffered media for 12 hours (D2). However, specific acid catalysis of the aldimine adduct is rapid (30 minutes) and complete at pH 5-6 and is achieved by incubating red cells or hemoly-sate with concentrated (0.2-0.6 M) buffers (e.g., borate, acetate) in the pH... 

Specific acid catalysis of acetals, ketals and glycosides... 

It was pointed out in the mechanistic discussion concerning acetal and ketal hydrolysis that general acid catalysis occurs only for acetals and ketal having special structural features. Usually, specific acid catalysis operates. The question of whether general acid catalysis could be observed in intramolecular reactions has been of interest because intramolecular general acid catalysis is postulated to play a part in the mechanism of action of the enzyme lysozyme, which hydrolyzes the acetal linkage present in certain polysacharides. One group of molecules that has been examined as a model system are acetals derived from o-hydroxybenzoic acid (sali-... 

The hydrolysis of acetals normally involves a specific-acid catalysis mechanism. However, the hydrolysis of tropone diethylketal is found to use a general-acid catalysis mechanism. Why is there this difference ... 

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