C6H4SO3H2

C6H4SO3H2, more commonly known as benzenesulfonic acid or phenylsulfonic acid, is an organic compound with the chemical formula C6H4SO3H2. It is a strong organic acid and a derivative of benzene where one hydrogen atom is replaced by a sulfonic acid group (-SO3H). The parent compound, benzenesulfonic acid, has the structure C6H5SO3H. However, the formula C6H4SO3H2 suggests a disulfonic acid, meaning there are two sulfonic acid groups attached to the benzene ring.

There are three possible positional isomers for benzenedisulfonic acid: 1,2-benzenedisulfonic acid (ortho), 1,3-benzenedisulfonic acid (meta), and 1,4-benzenedisulfonic acid (para). These isomers differ in the relative positions of the two sulfonic acid groups on the benzene ring. Benzenedisulfonic acids are typically formed by the sulfonation of benzene with fuming sulfuric acid.

These compounds are soluble in water and are strong acids. They are important intermediates in organic synthesis, particularly in the production of dyes, pharmaceuticals, and detergents. For instance, they can be converted to phenols or undergo other electrophilic aromatic substitution reactions. The specific properties and applications can vary depending on the positional isomer. Benzenedisulfonic acids are corrosive and should be handled with appropriate safety precautions.