AalI mechanism

This reaction, while rare, has been observed for various N-tert-huiyl amides in 98% sulfuric acid, where the mechanism was the AalI mechanism, and for certain amides containing an azo group, where a BalI mechanism was postulated. Of the two first-order acyl cleavage mechanisms, only the AacI has been observed, in concentrated sulfuric acid solutions. Of course, the diazotization of unsubstituted amides might be expected to follow this mechanism, and there is evidence that this is true. ... 

This reaction, while rare, has been observed for various N-f-butyl amides in 98% sulfuric acid, where the mechanism was the AalI mechanism,564 and for certain amides containing... 

Many of the esters which are hydrolyzed by the AalI mechanism in acid are also hydrolyzed with alkyl-oxygen fission under neutral condi-tions60,67 74 75 84 85 88 89. These reactions have the high enthalpies and entropies of activation characteristic of unimolecular reactions, and involve the ionization of (usually) tertiary alkyl esters, to the carbonium ion and a carboxylate anion in the rate-determining step, viz. 

Solomon et al. [35] concluded that the observed high-order kinetics for esterification and polyesterification reactions ruled out unimolecular AacI AalI mechanisms, and that the Aac2 mechanism was the most likely. 

Alternatively, the protonated ester may undergo a unimolecular reaction via the cleavage of either the acyl-oxygen bond (Aac 1 mechanism) or the alkyl-oxygen bond (AalI mechanism) (Scheme 9). In both cases, an intermediate carbo-cation is formed, which, in the AacI pathway, is an acylium ion. Alkyl-oxygen... 

Hydrolyses with maximum curve (type I and II behavior) are easily explained by the Aac2 mechanism. The initial rate increase is attributed to the increasing concentration of the protonated ester. The rate then decreases since concentration of water required for the hydrolysis step decreases rapidly with increasing acid concentration (Scheme 8). The final rate increase suggests a transition to the A1 process (Aac 1 for type I esters and Aal 1 for type II esters). There is also a change in the mechanism for type III esters. Since the participation of vinyl and phenyl cations are unlikely, a change to the Aac 1 mechanism was suggested. Finally, the hydrolysis pathway for type IV esters is the AalI mechanism. 

Hydrolysis kinetics for thiolesters deal with triphenylmethyl thiolben-zoates (AalI mechanism), hydrolysis and Ag -assisted n-butylaminoly-sis of ethyl thiolbenzoate, and thiolesters with an activating group attached to the carbonyl group. "... 

To sum up the acid-catalysis mechanisms, Aac2 and AalI are the common mechanisms, the latter for R that give stable carbocations, the former for practically... 

Positive-Tone Imaging Chemistry. The ester, carbonate, and ketal acidol-ysis reactions that form the basis of most positive tone CA resists are thought to proceed by specific acid catalysis (28). In this mechanism (type AalI), illustrated here for the hydrolysis of tert-butyl acetate (29), the first step is a rapid equilibrium where the proton is transferred between the photogenerated acid and the ester ... 

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