Wurster's blue
Encyclopedia
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 electron
s 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 (August 7, 1854 - 29 November 1913).
It finds use as a redox
indicator in the oxidase test
and is also used in electron transport chain analysis; it is capable of donating electrons to cytochrome C.
the hydrochloride form finds use in analytical chemistry as a reagent
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 , therefore highly oxidizing conditions should be avoided in titrations relying on TMPD, or reached only during the final stage of the titration. The second oxidation step is not well separated from the first on the redox scale, so some instability will be encountered on the oxidizing side of 0.276, and it is impossible to prepare pure aqueous solutions of Wurster's Blue due to its dismutation to the unstable diaminium and TMPD.
Phenylenediamine
Phenylenediamine may refer to:*o-phenylenediamine or OPD, a chemical compound C6H42*m-phenylenediamine or MPD, a chemical compound C6H42*p-phenylenediamine or PPD, a chemical compound C6H42...
, which loses two electron
Electron
The electron is a subatomic particle with a negative elementary electric charge. It has no known components or substructure; in other words, it is generally thought to be an elementary particle. An electron has a mass that is approximately 1/1836 that of the proton...
s 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
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...
Casimir Wurster (August 7, 1854 - 29 November 1913).
It finds use as a redox
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
indicator in the oxidase test
Oxidase test
The oxidase test is a test used in microbiology to determine if a bacterium produces certain cytochrome c oxidases. It uses disks impregnated with a reagent such as N,N,N′,N′-tetramethyl-p-phenylenediamine or N,N-Dimethyl-p-phenylenediamine , which is also a redox indicator...
and is also used in electron transport chain analysis; it is capable of donating electrons to cytochrome C.
the hydrochloride form finds use in analytical chemistry as a reagent
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 , therefore highly oxidizing conditions should be avoided in titrations relying on TMPD, or reached only during the final stage of the titration. The second oxidation step is not well separated from the first on the redox scale, so some instability will be encountered on the oxidizing side of 0.276, and it is impossible to prepare pure aqueous solutions of Wurster's Blue due to its dismutation to the unstable diaminium and TMPD.