ACS Organic Chemistry Practice Test

Tosylation converts an alcohol into a good leaving group for subsequent substitution. The reagent is p-toluenesulfonyl chloride, and a base is used to deprotonate the alcohol and to scavenge the HCl produced. The alcohol’s oxygen attacks the sulfonyl chloride, forming the tosylate ester, while the base keeps the reaction conditions favorable by keeping the nucleophile deprotonated and neutralizing the acid byproduct. Using a different sulfonyl chloride would give a different sulfonate (for example, methanesulfonyl chloride gives a mesylate), and running the reaction without a base makes the process inefficient. Thus, p-toluenesulfonyl chloride with a base is the standard way to form tosylates.