NNNN TETRAMETHYL p PHENYLENEDIAMINE DIHYDROCHLORIDE

N,N,N′,N′-tetramethyl-p-phenylenediamine dihydrochloride (TMPD) is an oxidizable compound that serves as a reducing co-substrate for heme peroxidases. It is also used as a test reagent in microbiology for the classification of cytochrome oxidase positive aerobic microorganisms.

Kovacs reagent is a biochemical reagent consisting of isoamyl alcohol, para-dimethylaminobenzaldehyde (DMAB), and concentrated hydrochloric acid. It is used for the diagnostical indole test, to determine the ability of the organism to split indole from the amino acid tryptophan. The indole produced yields a red complex with para-dimethylaminobenzaldehyde under the given conditions.[1] This was invented by the Hungarian-Swiss Chemist, Ervin Kovats (Erwin Kovacs) (1927–2010). This reagent is used in the confirmation of E. coli and many other pathogenic microorganisms.

Wurster's blue is the trivial name given to the chemical N,N,N′,N′-tetramethyl-p-phenylenediamine, also known as TMPD. It is an easily oxidised phenylenediamine, which loses two electrons in one-electron oxidation steps; the radical cation is a characteristic blue-violet colour, which gives the compound part of its name. The remaining part of its name comes from its discoverer, the German chemist Casimir Wurster 

The term "Wurster's blue" is often reserved for the radical cation, the colorless diamine being called tetramethylphenylenediamine (TMPD). The midpoint potential for titration of the first electron is given as 0.276 V vs NHE, and this transition is useful in potentiometric titrations as both a redox mediator and indicator. The two electron-oxidized form (di-iminium) is unstable in aqueous solutions,[1] therefore highly oxidizing conditions should be avoided in titrations relying on TMPD, or reached only during the final stage of the titration.