CH3C6H4SO3H

CH3C6H4SO3H is the chemical formula for toluenesulfonic acid, also known as tosic acid. It is a strong organic acid with the chemical structure consisting of a toluene molecule (a benzene ring with a methyl group attached) substituted with a sulfonic acid group. There are three possible isomers of toluenesulfonic acid, depending on the position of the sulfonic acid group relative to the methyl group on the benzene ring: ortho-toluenesulfonic acid (o-TSA), meta-toluenesulfonic acid (m-TSA), and para-toluenesulfonic acid (p-TSA). The para isomer is the most commercially important and widely used.

Toluenesulfonic acid is a white crystalline solid that is soluble in water and many organic solvents. Its acidity is comparable to sulfuric acid, making it a potent catalyst in various chemical reactions. It is commonly employed as an acid catalyst in esterification, etherification, and polymerization processes. Additionally, toluenesulfonic acid is used in the production of dyes, pharmaceuticals, and as a component in some cleaning agents. Its sulfonic acid group also makes it useful in forming salts with bases, which can have applications in various industries. The different isomers have slightly varying properties and catalytic activities, though the para isomer is the most prevalent due to its accessibility and effectiveness.