Azo violet

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Azo violet
Azo violet.svg
Names
IUPAC name
4-[(E)-(4-Nitrophenyl)diazenyl]benzene-1,3-diol
Other names
(E)-4-[(4-Nitrophenyl)diazenyl]benzene-1,3-diol
4-(4-Nitrophenyl)azobenzene-1,3-diol
Magneson I
p-Nitrophenylazoresorcinol
4-Nitrophenylazoresorcinol
Identifiers
3D model (JSmol)
ChEBI
ChEMBL
ChemSpider
ECHA InfoCard 100.000.735
EC Number
  • 200-808-5
UNII
Properties
C12H9N3O4
Molar mass 259.318 g mol−1
Appearance dark red to brown crystalline powder
Density 1.45 g/cm3
1 g/L H2O; 4 g/L Ethanol
Hazards
Flash point 261.7 °C (503.1 °F; 534.8 K)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references
Azo violet (pH indicator)
below pH 11.0 above pH 13.0
11.0 13.0

Azo violet (4-(4-nitrophenylazo)resorcinol) is an azo compound with the chemical formula C12H9N3O4. It is used commercially as a violet dye and experimentally as a pH indicator, appearing yellow below pH 11, and violet above pH 13.[1] It also turns deep blue in the presence of magnesium salt in a slightly alkaline, or basic, environment.[2][3] Azo violet may also be used to test for the presence of ammonium ions[citation needed]. The color of ammonium chloride or ammonium hydroxide solution will vary depending upon the concentration of azo violet used.

Properties[edit]

Azo violet at pH ~7.

The intense color from which the compound gets its name results from irradiation and subsequent excitation and relaxation of the extended π electron system across the R-N=N-R’ linked phenols. Absorption of these electrons falls in the visible region of the electromagnetic spectrum. Azo violet's intense indigo color (λmax 432 nm) approximates Pantone R: 102 G: 15 B: 240.

Synthesis[edit]

Azo violet can be synthesised by reacting 4-nitroaniline with nitrous acid (generated in situ with an acid and a nitrite salt) to produce a diazonium intermediate. This is then reacted with resorcinol, dissolved in a sodium hydroxide solution, via an azo coupling reaction.

Azo Violet Synthesis.svg

This is consistent with the generalized strategy for preparing azo dyes.

Generalized Azo Dye Synthesis.jpeg

Reactivity[edit]

Tautomerization of Azo Violet

The chemical character of azo violet may be attributed to its azo group (-N=N-), six-membered rings, and hydroxyl side groups. Due to steric repulsions, azo violet is most stable in the trans-configuration, but isomerization of azo dyes by irradiation is not uncommon. The para-position tautomerization of azo violet provides mechanical insight into the behavior of the compound in an acidic environment, and thus its use as a basic pH indicator.

The predicted 1H-NMR of pure azo violet shows the hydroxyl protons as the most deshielded and acidic protons. The participation of these hydroxyl groups' electron-donation to the conjugated π system likewise influences azo violet's λmax and pKa value.

Pure Azo Violet NMR

References[edit]

  1. ^ "Azo Violet 25GM from Cole-Parmer". Cole-Parmer. Archived from the original on 28 October 2016. Retrieved 28 October 2016.
  2. ^ Feigl, F.; Anger, V. (2012-12-02). Spot Tests in Inorganic Analysis. Elsevier. ISBN 9780444597984.
  3. ^ Gopalan, R. (2009-01-01). Inorganic Chemistry for Undergraduates. Universities Press. ISBN 9788173716607.