N,N-dimethyl-4-nitrosoanilinium chloride

In the process, it is typically formed by nitrosation of N,N-dimethyl-p-phenylenediamine and then reacts with sulfur-containing intermediates (such as aminothiophenol derivatives). This step leads to coupling and subsequent oxidative cyclization, ultimately forming the phenothiazine ring system that defines methylene blue. The nitroso group plays a key role in facilitating the condensation and ring formation reactions. N,N-dimethyl-4-nitrosoanilinium chloride is an important intermediate in the synthesis of Methylene blue.