mtoluenesulfonic

4-Methylbenzenesulfonic acid, commonly known as p-toluenesulfonic acid or tosic acid, is an organic compound with the formula CH3C6H4SO3H. It is a strong organic acid, with a pKa of -2.8, making it significantly stronger than sulfuric acid. It exists as a white, hygroscopic solid, and is soluble in water, ethanol, and diethyl ether.

The acid is typically produced by the sulfonation of toluene using concentrated sulfuric acid. The reaction is an electrophilic aromatic substitution where the sulfur trioxide acts as the electrophile. Careful control of reaction conditions is necessary to favor the para isomer.

p-Toluenesulfonic acid is widely used as an acidic catalyst in organic synthesis. Its strength and solid form make it a convenient alternative to mineral acids like sulfuric acid or hydrochloric acid, especially when water needs to be avoided. It is particularly useful for reactions such as esterifications, acetal formations, and the removal of protecting groups. The tosylate anion (CH3C6H4SO3-) is a good leaving group, which is exploited in various substitution and elimination reactions.

Beyond its catalytic applications, p-toluenesulfonic acid is also used in the production of dyes and pharmaceuticals. Its ability to readily form salts is utilized in the purification and isolation of basic compounds. It is also employed in electroplating baths.