Converting an Alcohol Into a Sulfonate Ester

Another way a primary or secondary alcohol can be activated for a subsequent reaction with a nucleophile—instead of converting it into an alkyl hahde—is to convert it into a sulfonate ester. A sulfonate ester is formed when an alcohol reacts with a sulfonyl 

The reaction is a nucleophilic substitution reaction in which the alcohol displaces the chloride ion. Pyridine is the solvent and it is also the base that removes a proton from the intermediate. 

MECHANISM FOR THE CONVERSION OF AN ALCOHOL INTO A SULFONATE ESTER 

Several sulfonyl chlorides are available to activate OH groups. The most common one is para-toluenesulfonyl chloride (abbreviated as TsCl). The sulfonate ester formed from the reaction of TsCl and an alcohol is called an alkyl tosylate (abbreviated as ROTs). 

Once the alcohol has been activated by being converted into a sulfonate ester, the appropriate nucleophile is added, generally under conditions that favor Sn2 reactions. (Notice that in all cases, the added nucleophile is a much better nucleophile than the chloride ion that also is present in the solution, since it was the leaving group in the synthesis of the sulfonate ester.) The reactions take place readily at room temperature because the sulfonate ester has an excellent leaving group. Sulfonate esters react with a wide variety of nucleophiles, so they can be used to synthesize a wide variety of compounds. 

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Converting an alcohol into a sulfonate ester (Section 11.3). The mechanism is shown on page 489. 

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