Relative solvolysis rates of ethyl sulfonates and halides

Sulfonate esters are exceedingly useful substrates in nucleophilic substitution reactions because of their high level of reactivity and because, unlike alkyl halides, they may be prepared from alcohols by reactions that do not directly involve the carbon atom at which subsequent substitution is to be effected. These properties are particularly important in cases where the stereochemical and structural integrity of the substrate must be maintained in converting an alcohol to a derivative capable of undergoing nucleophilic substitution. Sulfonate esters are commonly prepared by reaction of an alcohol with a sulfonyl halide in the presence of pyridine  

Tertiary alcohols are converted to sulfonate esters with difficulty, and, because of their high reactivity, it is often impossible to isolate the sulfonate ester. Special procedures are sometimes effective, but more commonly, tertiary alcohols are converted to p-nitrobenzoates for solvolytic studies. 

Trifluoromethanesulfonate (triflate) is an exceptionally good leaving group, enabling nucleophilic substitution reactions to be carried out on normally unreactive substrates. Acetolysis of cyclopropyl triflate, for example, occurs 10 times faster than acetolysis of cyclopropyl tosylate. Similar rate enhancements are seen in systems in which the direct displacement mechanism is operative, as summarized in Table 5.7. 

A poor leaving group can be made more reactive by coordination to an electrophilic species. Hydroxide ion is such a poor leaving group that under normal circumstances, it is not displaced from sp -carbon by another Lewis base. It has been estimated that the reaction 

One of the best leaving groups is molecular nitrogen from diazonium ions. Diazonium salts are usually prepared by nitrosation of primary aliphatic or aromatic amines  

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Table 5.11. Relative Solvolysis Rates of Ethyl Sulfonates and Halides" ...

Relative solvolysis rates of ethyl sulfonates and halides... 

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