Sodium iodide sulfonyl esters

The sulfonyl halides (ArSOjCl) convert the alcohol into a sulfonate (ArSOjOR), which is a better leaving group than the hydroxyl group. This allows a range of nucleophilic substitutions to be carried out, many of which parallel those found with alkyl halides. Alkyl halides such as iodides are formed by the nucleophilic substitution of the sulfonate by an iodide ion. The reaction in this case proceeds with inversion of configuration. Treatment of the sulfonate esters with bases such as sodium methoxide or collidine (2,4,6-trimethylpyridine), or even just heating them, can lead to the elimination of toluene-4-sulfonic acid and the formation of an alkene. 

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