Preparation of Mesylates and Tosylates

Alcohols form esters called sulfonates. The formation of the sulfonates shown below is a nucleophilic substitution, where alcohol acts as the nucleohile. The reaction proceeds with retention of configuration, so if the carbon atom bearing the hydroxyl group is stereogenic, it is NOT inverted as it would be in an 5, 2 reaction. 

Tosylates and mesylates are commonly used sulfonates that you need to know for the MCAT. The sulfonate ions are very weak bases and excellent leaving groups. When tosylates and mesylates are leaving groups, the reaction may proceed via an SN1 or SN2 mechanism. 

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