Esters protonated, unimolecular cleavage

For example, in the case of protonated carboxylic acids in HS03F-SbF5-S02 solution, a reaction analogous to the rate-determining step in the unimolecular cleavage of esters is observed leading to the acyl cation and oxonium (hydronium) ion [Eq. (3.67)]. 

Unimolecular cleavage in this case corresponds to the dehydration of the acid, but in the case of protonated esters the cleavage pathway depends on the nature of the alkoxy group [Eqs. (3.68)-(3.70)]. 

By raising the temperature of solutions of protonated carboxylic acids and esters, unimolecular cleavage reactions are observed. These reactions can be considered within the framework of the two unimolecular reaction pathways for acid-... 

The AacI (acid-catalyzed, unimolecular, acyl-oxygen cleavage) mechanism is shown in Figure 7.17. The reaction is unimolecular because the rate-limiting step involves dissociation of ROH from the protonated ester. This... 

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... 

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