pTsOH

p-Toluenesulfonic acid (pTsOH) is an organosulfur compound with the formula C7H8O3S. It is a strong, non-volatile Brønsted acid widely used as an acid catalyst in organic synthesis. The molecule consists of a benzene ring bearing a para methyl group and a sulfonic acid group (SO3H). It is a colorless solid that dissolves readily in water and polar organic solvents and is stable under typical reaction conditions. The conjugate acid is highly dissociated in aqueous solution, with a pKa around −2 to −3, making it one of the stronger common organic acids.

Preparation of pTsOH typically involves sulfonation of toluene with concentrated sulfuric acid, which yields a mixture of ortho- and para-toluenesulfonic acids; the para isomer is the desired product and is purified.

Applications of pTsOH are broad in organic synthesis. It serves as a strong, homogeneous acid catalyst in esterifications, acetalizations, rearrangements, and various condensation reactions conducted in polar solvents. Its high acidity combined with non-volatile, thermally stable properties makes it convenient for reactions where volatile mineral acids are undesirable. The conjugate base, p-toluenesulfonate (TsO−), forms salts that are good leaving groups in nucleophilic substitutions and related transformations, contributing to the utility of tosylate chemistry in protecting-group strategies and substrate activation.

Safety: pTsOH is corrosive and irritant to skin, eyes, and mucous membranes. It should be handled with appropriate protective equipment, in a well-ventilated area, and stored in a cool, dry place.