Azo violet
{{Chembox
| Verifiedfields = changed
| Watchedfields = changed
| verifiedrevid = 462568192
| ImageFile = Azo violet.svg
| IUPACName = 4-[(E)-(4-Nitrophenyl)diazenyl]benzene-1,3-diol
| OtherNames = (E)-4-[(4-Nitrophenyl)diazenyl]benzene-1,3-diol
4-(4-Nitrophenyl)azobenzene-1,3-diol
Magneson I
p-Nitrophenylazoresorcinol
4-Nitrophenylazoresorcinol
|Section1={{Chembox Identifiers
| CASNo_Ref = {{cascite|changed|??}}
| CASNo = 74-39-5
| SMILES = Oc2cc(O)ccc2/N=N/c1ccc(cc1)[N+]([O-])=O
| PubChem = 5717413
| ChemSpiderID_Ref = {{chemspidercite|correct|chemspider}}
| ChemSpiderID = 11341372
| EC_number = 200-808-5
| UNII = YND5ZT5BS3
| ChEMBL = 1604790
| ChEBI = 66930
| SMILES1 = Oc2cc(O)ccc2/N=N/c1ccc(cc1)N(=O)=O
| 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+
| InChIKey = NGPGYVQZGRJHFJ-BUHFOSPRBO
| StdInChI_Ref = {{stdinchicite|correct|chemspider}}
| StdInChI = 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+
| StdInChIKey_Ref = {{stdinchicite|correct|chemspider}}
| StdInChIKey = NGPGYVQZGRJHFJ-BUHFOSPRSA-N
| MeSHName =
}}
|Section2={{Chembox Properties
| Formula = C12H9N3O4
| MolarMass = 259.318 g mol−1
| Appearance = dark red to brown crystalline powder
| Density = 1.45 g/cm3
| Solubility = 1 g/L H2O; 4 g/L Ethanol
}}
|Section3={{Chembox Hazards
| FlashPtC = 261.7
}}
}}
{{pH indicator template
| indicator_name = Azo violet
| low_pH = 11.0
| low_pH_color = Yellow
| low_pH_text =
| high_pH = 13.0
| high_pH_color = DarkViolet
| high_ph_text =
}}
Azo violet (Magneson I;{{Cite web |title=Magneson {{!}} C12H9N3O4 {{!}} ChemSpider |url=https://www.chemspider.com/Chemical-Structure.16736227.html |access-date=2022-07-30 |website=www.chemspider.com}} 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.{{cite web | url=http://www.coleparmer.com/Product/Azo_Violet_25_GM/EW-00018-GA | title=Azo Violet 25GM from Cole-Parmer | publisher=Cole-Parmer | accessdate=28 October 2016 | archive-url=https://web.archive.org/web/20161028152543/http://www.coleparmer.com/Product/Azo_Violet_25_GM/EW-00018-GA | archive-date=28 October 2016 | url-status=dead }} It also turns deep blue in the presence of magnesium salt in a slightly alkaline, or basic, environment.{{Cite book|url=https://books.google.com/books?id=II06Q8GGqNUC&pg=PA292|title=Spot Tests in Inorganic Analysis|last1=Feigl|first1=F.|last2=Anger|first2=V.|date=2012-12-02|publisher=Elsevier|isbn=9780444597984|language=en}}{{Cite book|url=https://books.google.com/books?id=Fs4zQ-hNTz8C&pg=PA70|title=Inorganic Chemistry for Undergraduates|last=Gopalan|first=R.|date=2009-01-01|publisher=Universities Press|isbn=9788173716607|language=en}} Azo violet may also be used to test for the presence of ammonium ions{{Citation needed|date=October 2016}}. 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.{{Cite book |last=Gopalan |first=R. |url=https://books.google.com/books?id=Fs4zQ-hNTz8C |title=Inorganic Chemistry for Undergraduates |date=2009 |publisher=Universities Press |isbn=978-81-7371-660-7 |language=en}}
Properties
File:Aqueous azo violet (Magneson I).jpg
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.
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This is consistent with the generalized strategy for preparing azo dyes.
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Reactivity
File:Tautomerization of Azo Violet.jpg
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.
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