Azo violet

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

CAS Number

* 74-39-5 N

3D model (JSmol)

* Interactive image
* Interactive image

ChEBI |

* CHEBI:66930

ChEMBL |

* ChEMBL1604790

ChemSpider |

* 11341372 Y

EC Number |

* 200-808-5

PubChem CID

* 5717413

UNII |

* YND5ZT5BS3

InChI

* InChI=1S/C12H9N3O4/c16-10-5-6-11(12(17)7-10)14-13-8-1-3-9(4-2-8)15(18)19/h1-7,16-17H/b14-13+ Y

Key: NGPGYVQZGRJHFJ-BUHFOSPRSA-N Y

* InChI=1/C12H9N3O4/c16-10-5-6-11(12(17)7-10)14-13-8-1-3-9(4-2-8)15(18)19/h1-7,16-17H/b14-13+

Key: NGPGYVQZGRJHFJ-BUHFOSPRBO

SMILES

* Oc2cc(O)ccc2/N=N/c1ccc(cc1)[N+]([O-])=O

* Oc2cc(O)ccc2/N=N/c1ccc(cc1)N(=O)=O

Properties

Chemical formula

| C12H9N3O4
Molar mass | 259.318 g mol−1
Appearance  | dark red to brown crystalline powder
Density | 1.45 g/cm3

Solubility in water

| 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).

N verify (what is YN ?)
Infobox references

Azo violet (pH indicator)

below pH 11.0 |  | above pH 13.0
11.0 | ⇌  | 13.0

Azo violet (Magneson I;[1] p-nitrobenzeneazoresorcinol) 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.[2] It also turns deep blue in the presence of magnesium salt in a slightly alkaline, or basic, environment.[3][4] 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. Magneson I is used to test Be also; it produces an orange-red lake with Be(II) in alkaline medium.[5]

## Contents

* 1 Properties
* 2 Synthesis
* 3 Reactivity
* 4 References

## Properties

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

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.

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

## Reactivity

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

1. ↑ "Magneson | C12H9N3O4 | ChemSpider". https://www.chemspider.com/Chemical-Structure.16736227.html.
2. ↑ "Azo Violet 25GM from Cole-Parmer". Cole-Parmer. http://www.coleparmer.com/Product/Azo_Violet_25_GM/EW-00018-GA. Retrieved 28 October 2016.
3. ↑ Feigl, F.; Anger, V. (2012-12-02) (in en). Spot Tests in Inorganic Analysis. Elsevier. ISBN 9780444597984. https://books.google.com/books?id=II06Q8GGqNUC&pg=PA292.
4. ↑ Gopalan, R. (2009-01-01) (in en). Inorganic Chemistry for Undergraduates. Universities Press. ISBN 9788173716607. https://books.google.com/books?id=Fs4zQ-hNTz8C&pg=PA70.
5. ↑ Gopalan, R. (2009) (in en). Inorganic Chemistry for Undergraduates. Universities Press. ISBN 978-81-7371-660-7. https://books.google.com/books?id=Fs4zQ-hNTz8C.

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*[CID]: Compound ID