4-Nitrotoluene or para-nitrotoluene is an organic compound with the formula CH3C6H4NO2. It is a pale yellow solid. This compound is mainly used to prepare dyes. 4-Nitrotoluene or para-nitrotoluene is an organic compound with the formula CH3C6H4NO2. It is a pale yellow solid. This compound is mainly used to prepare dyes. Together with other isomers, 4-nitrotoluene is prepared by nitration of toluene. It undergoes the expected reactions, e.g. hydrogenation gives p-toluidine. The principle application involves its sulfonation to give the 4-nitrotoluene-2-sulfonic acid (with the –SO3H group adjacent to methyl). This species is produced on a large scale since it can be oxidatively coupled to produce stilbene derivatives which are used as dyes. Representative derivatives include the molecular and salt forms of 4,4'-dinitroso- and the 4,4'-dinitro-2,2'-stilbenedisulfonic acids. Arthur Green and André Wahl reported the formation of disodium 4,4'-dinitrostilbene-2,2'-disulfonate in the late nineteenth century using sodium hypochlorite as an oxidising agent, and improved processes using air oxidation in liquid ammonia have been developed. There is some evidence for toxicity and carcinogenicity in mice.