Azo coupling

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In organic chemistry, an azo coupling is an reaction between a diazonium compound (R−N≡N+) and another aromatic compound that produces an azo compound (R−N=N−R’). In this electrophilic aromatic substitution reaction, the aryldiazonium cation is the electrophile, and the activated carbon (usually from an arene, which is called coupling agent), serves as a nucleophile. Classical coupling agents are phenols and naphthols. [1] Usually the diazonium reagent attacks at the para position of the coupling agent. When the para position is occupied, coupling occurs at a ortho position, albeit at a slower rate.

Contents

Uses of the reaction

Aromatic azo compounds tend to be brightly colored due to their extended conjugated systems. Many are useful dyes (see azo dye). [2] Important azo dyes include methyl red and pigment red 170.

Azo printing exploits this reaction as well. In this case, the diazonium ion is degraded by light, leaving a latent image in undegraded diazonium salt which is made to react with a phenol, producing a colored image: the blueprint. [3]

Prontosil, the first sulfa drug, was once produced by azo coupling. The azo compound is a prodrug that is activated in-vivo to produce the sufanilamide.

The reaction is also used in the Pauly reaction test to detect tyrosine or histidine residues in proteins.

Additionally, through the azo coupling reaction between the aromatic diazonium ion and aromatic amino acid residues, this reaction also be used to form or to modify proteins such as tRNA synthetase. [4]

Examples of azo C-coupling reactions

Illustrative is the reaction of phenol with benzenediazonium chloride to give a Solvent Yellow 7, a yellow-orange azo compound. The reaction is faster at high pH. [2] Many other azo dyes have been prepared by similarly. Several procedures have been described in detail. [5] [6] [7]

Azo-coupling-A-mechanism-2D-skeletal.png

Naphthols are popular coupling agents. One example is the synthesis of the dye "organol brown" from aniline and 1-naphthol:

Synthesis of organol brown from aniline and 1-naphthol Synthesis of Organol Brown N.svg
Synthesis of organol brown from aniline and 1-naphthol

Similarly, β-naphthol couples with phenyldiazonium electrophile to produce an intense orange-red dye.

Besides activated aromatic coupling agents, other nucleophilic carbons also couple with diazonium salts as illustrated by the synthesis of azo pigments.

Synthesis of C.I. Pigment Yellow 13, a diarylide pigment. FormationPigYellow13.svg
Synthesis of C.I. Pigment Yellow 13, a diarylide pigment.

Examples of azo N-coupling reactions

Azo N-coupling under basic condition Azo N coupling.jpg
Azo N-coupling under basic condition

In alkaline media, diazonium salt can react with most primary and secondary amines, which exist as a free base to produce triazene. [9] This chemical reaction is called azo N-coupling, [10] or the synthesis of azoamines. [11]

The dye called aniline yellow is produced by the reaction of aniline and a diazonium salt. In this case the C- and N-coupling compete. [2]


Related Research Articles

<span class="mw-page-title-main">Amine</span> Chemical compounds and groups containing nitrogen with a lone pair (:N)

In chemistry, amines are compounds and functional groups that contain a basic nitrogen atom with a lone pair. Formally, amines are derivatives of ammonia, wherein one or more hydrogen atoms have been replaced by a substituent such as an alkyl or aryl group. Important amines include amino acids, biogenic amines, trimethylamine, and aniline. Inorganic derivatives of ammonia are also called amines, such as monochloramine.

<span class="mw-page-title-main">Dimethylaniline</span> Chemical compound

N,N-Dimethylaniline (DMA) is an organic chemical compound, a substituted derivative of aniline. It is a tertiary amine, featuring a dimethylamino group attached to a phenyl group. This oily liquid is colourless when pure, but commercial samples are often yellow. It is an important precursor to dyes such as crystal violet.

In organic chemistry, an aryl halide is an aromatic compound in which one or more hydrogen atoms, directly bonded to an aromatic ring are replaced by a halide. Haloarenes are different from haloalkanes because they exhibit many differences in methods of preparation and properties. The most important members are the aryl chlorides, but the class of compounds is so broad that there are many derivatives and applications.

<span class="mw-page-title-main">Acyl halide</span> Oxoacid compound with an –OH group replaced by a halogen

An acyl halide is a chemical compound derived from an oxoacid by replacing a hydroxyl group with a halide group.

<span class="mw-page-title-main">Azo compound</span> Organic compounds with a diazenyl group (–N=N–)

Azo compounds are organic compounds bearing the functional group diazenyl.

<span class="mw-page-title-main">Benzoyl chloride</span> Organochlorine compound (C7H5ClO)

Benzoyl chloride, also known as benzenecarbonyl chloride, is an organochlorine compound with the formula C7H5ClO. It is a colourless, fuming liquid with an irritating odour, and consists of a benzene ring with an acyl chloride substituent. It is mainly useful for the production of peroxides but is generally useful in other areas such as in the preparation of dyes, perfumes, pharmaceuticals, and resins.

<span class="mw-page-title-main">Azo dye</span> Class of organic compounds used as dye

Azo dyes are organic compounds bearing the functional group R−N=N−R′, in which R and R′ are usually aryl and substituted aryl groups. They are a commercially important family of azo compounds, i.e. compounds containing the C−N=N−C linkage. Azo dyes are synthetic dyes and do not occur naturally. Most azo dyes contain only one azo group but there are some that contain two or three azo groups, called "diazo dyes" and "triazo dyes" respectively. Azo dyes comprise 60–70% of all dyes used in food and textile industries. Azo dyes are widely used to treat textiles, leather articles, and some foods. Chemically related derivatives of azo dyes include azo pigments, which are insoluble in water and other solvents.

<span class="mw-page-title-main">Diazonium compound</span> Group of organonitrogen compounds

Diazonium compounds or diazonium salts are a group of organic compounds sharing a common functional group [R−N+≡N]X where R can be any organic group, such as an alkyl or an aryl, and X is an inorganic or organic anion, such as a halide. The parent compound where R is hydrogen, is diazenylium.

<span class="mw-page-title-main">Triazenes</span> Organic compounds with a diazoamino group

Triazenes are organic compounds that contain the functional group R1−N=N−NR2R3, where the R are each any of various types of substituent groups. Some anti-cancer medications and dyes are triazenes. Formally, the triazenes are related to the unstable chemical triazene, H2N−N=NH.

Nitrophenols are compounds of the formula HOC6H5−x(NO2)x. The conjugate bases are called nitrophenolates. Nitrophenols are more acidic than phenol itself.

<span class="mw-page-title-main">4-Aminophenol</span> Chemical compound

4-Aminophenol (or para-aminophenol or p-aminophenol) is an organic compound with the formula H2NC6H4OH. Typically available as a white powder, it is commonly used as a developer for black-and-white film, marketed under the name Rodinal.

<span class="mw-page-title-main">Carbazole</span> Chemical compound

Carbazole is an aromatic heterocyclic organic compound. It has a tricyclic structure, consisting of two six-membered benzene rings fused on either side of a five-membered nitrogen-containing ring. The compound's structure is based on the indole structure, but in which a second benzene ring is fused onto the five-membered ring at the 2–3 position of indole.

<span class="mw-page-title-main">2-Nitroaniline</span> Chemical compound

2-Nitroaniline is an organic compound with the formula H2NC6H4NO2. It is a derivative of aniline, carrying a nitro functional group in position 2. It is mainly used as a precursor to o-phenylenediamine.

<span class="mw-page-title-main">4-Nitroaniline</span> Chemical compound

4-Nitroaniline, p-nitroaniline or 1-amino-4-nitrobenzene is an organic compound with the formula C6H6N2O2. A yellow solid, it is one of three isomers of nitroaniline. It is an intermediate in the production of dyes, antioxidants, pharmaceuticals, gasoline, gum inhibitors, poultry medicines, and as a corrosion inhibitor.

<span class="mw-page-title-main">2-Naphthol</span> Chemical compound

2-Naphthol, or β-naphthol, is a fluorescent colorless (or occasionally yellow) crystalline solid with the formula C10H7OH. It is an isomer of 1-naphthol, differing by the location of the hydroxyl group on the naphthalene ring. The naphthols are naphthalene homologues of phenol, but more reactive. Both isomers are soluble in simple alcohols, ethers, and chloroform. 2-Naphthol is a widely used intermediate for the production of dyes and other compounds.

1-Naphthol, or α-naphthol, is an organic compound with the formula C10H7OH. It is a fluorescent white solid. 1-Naphthol differs from its isomer 2-naphthol by the location of the hydroxyl group on the naphthalene ring. The naphthols are naphthalene homologues of phenol. Both isomers are soluble in simple organic solvents. They are precursors to a variety of useful compounds.

4-Nitrotoluene or para-nitrotoluene is an organic compound with the formula CH3C6H4NO2. It is a pale yellow solid. It is one of three isomers of nitrotoluene.

β-Nitrostyrene Chemical compound

β-Nitrostyrene is an aromatic compound and a nitroalkene used in the synthesis of indigo dye and the slimicide bromo-nitrostyrene.

<span class="mw-page-title-main">Acetoacetanilide</span> Chemical compound

Acetoacetanilide is an organic compound with the formula CH3C(O)CH2C(O)NHC6H5. It is the acetoacetamide derivative of aniline. It is a white solid that is poorly soluble in water. This chemical and many related compounds (prepared from various aniline derivatives) are used in the production of organic pigments called arylide yellows, one example being Pigment Yellow 74.

<span class="mw-page-title-main">3-Hydroxy-2-naphthoic acid</span> Chemical compound

3-Hydroxy-2-naphthoic acid is an organic compound with the formula C10H6(OH)(CO2H). It is one of the several hydroxynaphthoic acids. It is a precursor to some azo dyes and pigments. It is prepared by carboxylation of 2-naphthol by the Kolbe–Schmitt reaction.

References

  1. Smith, Michael B.; March, Jerry (2007), Advanced Organic Chemistry: Reactions, Mechanisms, and Structure (6th ed.), New York: Wiley-Interscience, ISBN   978-0-471-72091-1
  2. 1 2 3 Klaus Hunger; Peter Mischke; Wolfgang Rieper; Roderich Raue; Klaus Kunde; Aloys Engel (2005). "Azo Dyes". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. doi:10.1002/14356007.a03_245. ISBN   978-3527306732.
  3. Pai, Damodar M.; Melnyk, Andrew R.; Weiss, David S.; Hann, Richard; Crooks, Walter; Pennington, Keith S.; Lee, Francis C.; Jaeger, C. Wayne; Titterington, Don R.; Lutz, Walter; Bräuninger, Arno; De Brabandere, Luc; Claes, Frans; De Keyzer, Rene; Janssens, Wilhelmus; Potts, Rod. "Imaging Technology, 2. Copying and Nonimpact Printing Processes". Ullmann's Encyclopedia of Industrial Chemistry . Weinheim: Wiley-VCH. pp. 1–53. doi:10.1002/14356007.o13_o08.pub2. ISBN   9783527306732.
  4. Addy, Partha Sarathi; Erickson, Sarah B.; Italia, James S.; Chatterjee, Abhishek (2017-08-30). "A Chemoselective Rapid Azo-Coupling Reaction (CRACR) for Unclickable Bioconjugation". Journal of the American Chemical Society. 139 (34): 11670–11673. doi:10.1021/jacs.7b05125. ISSN   0002-7863. PMC   5861709 . PMID   28787141.
  5. J. L. Hartwell and Louis F. Fieser (1936). "Coupling of o-tolidine and Chicago acid". Organic Syntheses . 16: 12. doi:10.15227/orgsyn.016.0012 .
  6. H. T. Clarke and W. R. Kirner (1922). "Methyl red". Organic Syntheses . 2: 47. doi:10.15227/orgsyn.002.0047 .
  7. Conant, J. B.; Lutz, R. E.; Corson, B. B. (1923). "1,4-Aminonaphthol Hydrochloride". Organic Syntheses. 3: 7. doi:10.15227/orgsyn.003.0007.
  8. K. Hunger. W. Herbst "Pigments, Organic" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2012. doi : 10.1002/14356007.a20_371
  9. Khazaei; et al. (2012). "azo amine coupling giving triazenes, and triazene's decomposition giving diazonium salt". Synlett. 23 (13): 1893–1896. doi:10.1055/s-0032-1316557. S2CID   196805424.
  10. Wiley Subscription Services (2013). "Synthesis, characterization, and application of a triazene-base polymer". Journal of Applied Polymer Science. 129 (6): 3439–3446. doi:10.1002/app.39069.
  11. Serge Ratton, Bernard Botannet (1981). "Preparation of aromatic azoamines by diazotization/coupling/rearrangement of aromatic amines". US Patent 4275003A.