Azo violet
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| Names | |
|---|---|
| IUPAC name
4-(4-nitrophenyl)azobenzene-1,3-diol | |
| Other names
azoviolet; Magneson; p-Nitrophenylazoresorcinol; 4-Nitrophenylazoresorcinol | |
| Identifiers | |
| 74-39-5 | |
| ChemSpider | 11341372  |
| Jmol interactive 3D | Image Image |
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| Properties | |
| C12H9N3O4 | |
| 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 (4-(4-Nitrophenylazo)resorcinol) is an organic compound with the chemical formula C12H9N3O4. It is used commercially as a violet dye and experimentally as a pH indicator, turning blue-purple in the presence of magnesium salt in a slightly alkaline, or basic, environment. Azo violet may also be used to test for the presence of ammonium ions. The color of ammonium chloride or ammonium hydroxide solution will vary depending upon the concentration of azo violet used.
Azo violet is synthesized from a diazonium salt coupling reaction, from nitrophenol and resorcinol derivatives. The intense color from which the compound gets its name results from irradiation and subsequent excitation and relaxation of the extended pi 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.
Reactivity
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 pi system likewise influences azo violet’s λmax and pka value.
Synthesis of Azo Violet
Azo compounds (Ar-N=N-Ar’) are typically synthesized through a simple electrophilic aromatic substitution in the presence of base. The positively charged diazonium compound or diazonium salt precursor reacts with an electron rich phenol or arylamine. Reactivity is most successful if the electron withdrawing group of the electron-rich aromatic is in the para position.
