Tetramethylphenylenediamine (TMPD) is an
organic compound
Some chemical authorities define an organic compound as a chemical compound that contains a carbon–hydrogen or carbon–carbon bond; others consider an organic compound to be any chemical compound that contains carbon. For example, carbon-co ...
with the formula . It is most studied of three isomers of this formula. It is a colorless solid. With two dimethylamino substituents, the ring is particularly
electron rich.
Redox behavior
One-electron oxidation of TMPD gives the deep blue radical cation called Wurster's blue, . It was one of the first radical cations to be reported. Many properties have been described including its rapid rate of
self-exchange:
:
X-ray crystallography
X-ray crystallography is the experimental science of determining the atomic and molecular structure of a crystal, in which the crystalline structure causes a beam of incident X-rays to Diffraction, diffract in specific directions. By measuring th ...
of the TMPD and its iodide salt reveals that oxidation most strongly contracts the C-N(CH
3)
2 and the HC---CH bonds, indicating that oxidation gives a quinoid-like species.
The monocation illustrates an early step in the oxidation of p-phenylenediamine derivatives, which are widely used for
hair dying.
() also easily oxidizes to a radical cation, called Wurster's Red.
The hydrochloride salt of TMPD has been used as a
redox
Redox ( , , reduction–oxidation or oxidation–reduction) is a type of chemical reaction in which the oxidation states of the reactants change. Oxidation is the loss of electrons or an increase in the oxidation state, while reduction is t ...
indicator in the
oxidase test and is also used in electron transport chain analysis as it is capable of donating electrons to
cytochrome c. The midpoint potential for titration of the first electron is given as 0.276 V vs
Standard hydrogen electrode
In electrochemistry, the standard hydrogen electrode (abbreviated SHE), is a redox electrode which forms the basis of the thermodynamic scale of oxidation-reduction potentials. Its absolute electrode potential is estimated to be at 25 ° ...
, and this transition is useful in
potentiometric titrations as both a redox mediator and indicator.
History
TMPD was reported in 1879 by Casmir Wurster (7 August 1854 – 29 November 1913), hence it is known as Wurster's reagent.
Further reading
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References
{{Reflist
Anilines
Diamines
Redox indicators
Dimethylamino compounds