Coupling of diazonium salts

Coupling of diazonium salts with aromatic rings... 

Equally popular are azo couplings of diazonium salts that keep the nitrogen atoms in the product. The solid-solid version is very suitable with appropriate phenols such as 296 and 299. The waste-free and quantitatively obtained azo dye salts can be neutralized. The free dyes have the hydrazono structure (297, 298) or the azo structure (300) [99-100] (Scheme 45). The prescription should be carefully followed for safety reasons ... 

Azo couplings of diazonium salts with primary or secondary amines give triazenes which are normally hard to get in pure form. It is, however, quite easy to get triazenes with aliphatic or aromatic amines if solid-state techniques are applied that give rise to pure products in quantitative yield [98-100]. The di-methyltriazenes 309 have been quantitatively obtained by very cautious addition of gaseous dimethylamine (exothermic ) [98] (Scheme 47). Extreme care has to be taken for safety reasons ... 

Azo coupling of diazonium salts with aromatic (or pseudoaromatic) hydrocarbons is possible if the coupling agent is highly substituted. For example, azo compounds have been produced from pentamethylbenzene [12], benzpyrene [13], and azulene [1-4]. 

B. Coupling of Diazonium Salts with Active Methylene Compounds... 

Intramolecular coupling of diazonium salts with ortho substituents bearing an active methylene grouping or its equivalent gives rise to cinnolines, which may be considered a class of cyclic azo compounds. Three name reactions are cited here for reference only. 

Perhaps the best-known method of preparing aromatic azo compounds involves the coupling of diazonium salts with sufficiently reactive aromatic compounds such as phenols, aromatic amines, phenyl ethers, the related naphthalene compounds, and even sufficiently reactive aromatic hydrocarbons. Generally, the coupling must be carried out in media which are neutral or slightly basic or which are buffered in the appropriate pH range. The reaction may also be carried out in nonaqueous media. While some primary and secondary aromatic amines initially form an A-azoamine, which may rearrange to the more usual amino-C-azo compound, tertiary amines couple in a normal manner. 

Two molecules of a diazonium salt may couple with loss of some nitrogen. In the Bogoslovskii reaction, this reaction has been developed as a means of preparing o,o -dihydroxyazo compounds, which are difficult to obtain by other means. This reaction involves the use of a cuprous complex as the reaction catalyst. Self-coupling of diazonium salts also takes place in the presence of sodium sulfite. 

Generally the coupling of diazonium salt is carried out under neutral to slightly alkaline conditions. In coupling with amines or phenols, it has been demonstrated that the active species are the diazonium cation, the free amine,... 

S. M. Parmerter, The coupling of diazonium salts with aliphatic carbon atoms. Org. React. 10, 1 (1959). 

A method frequently used to determine aromatic amines in water-soluble dyes involves their extraction with chloroform, followed by diazotization of amines and coupling of diazonium salts with a reagent R-salt (disodium-3-hydroxy-naphthalene-2,7-disulfonate) or pyrazolone T (4,5-dihydro-5-oxo-l-(4-sulfophenyl-)l/7-pyrazole-3-carboxylic acid). The separated products are detected by UV-VIS spectrophotometry or fluorescence (210-212). 

Coupling of Diazonium Compounds with Hydrazones. The most common method for the production of formazans is the coupling of diazonium salts with aryl hydrazones in an alkaline medium, possibly in presence of an organic solvent. 

Jamrogiewicz, M. Wagner-Wysiecka, E. Luboch, E. and Biemat, J.F. (2004) Effect of /3-cyclodextrin on coupling of diazonium salts, XXIX International Symposium on Macrocyclic Chemistry, Cairns, Australia, Abstracts, KL - ISMC - 9. 

Electrochemical functionalization - reductive coupling of diazonium salts The electrochemical functionalization of SWCNTs, deposited on an Si/Si02 substrate, with 4-nitrophenyl groups succeeded by the reduction of 4-nitrobenzene-diazonium salt in a mini-electrochemical cell with platinum counter and (pseu-do-)reference electrodes. A probe needle was used to make contact with one of the Au-Pd bonding pads on the substrate and allowed the application of an electric potential to the electrode (-1.3 V vs. Pt for >30 s) and to any SWCNTs underneath the electrode [177b]. 

S. J. Parmerter, The Coupling of Diazonium Salts with Aliphatic Carbon Atoms, Org. React. 1959, 10, 1-142. 

This four-component reaction represents a straightforward method for the preparation of unsaturated esters and amides [156-159]. The system Pd(OAc)2/SIPr HC1 has been reported to efficiently catalyze the coupling of diazonium salts with boronic acids in the presence of CO and ammonia [160] to yield the corresponding amides in good yields (Scheme 17). 

Coupling of Diazonium Salts with Acrylonitrile (cf. method 28) ArN,+Cl- + H,C=CHCN ArCH,CHClCN... 

The coupling of diazonium salts with aromatic phenols and amines yields azo compounds, which are of tremendous importance to the dye industry. 

Problem 23.20 (a) Coupling of diazonium salts with primary or secondary aromatic amines (but not with tertiary aromatic amines) is complicated by a side reaction that yields an isomer of the azo compound. Judging from the reaction of secondary aromatic amines with nitrous acid (S. 23.10), suggest a possible structure for this by-product. 

Diazotisation of 15N-aniline followed by coupling of diazonium salt 216 with pyrazol-3-ones 215a,b gave 4-phenylhydrazono derivatives 217a,b. Through the use of 15N labeling and NMR spectroscopy it was shown that pyrazol-3-ones 217a,b exist entirely in the hydrazone form in deuterated chloroform. In hexadeuterated... 

The Coupling of Diazonium Salts with Aliphatic Carbon Atoms ... 

Reduction of azo compounds to amines, with fission of the N=N double bond, assumes practical importance because so many azo compounds are readily accessible, even on an industrial scale, by coupling of diazonium salts with reactive molecules. In this way a large number of primary amines can be obtained free from isomers, which is not always easy to achieve by other... 

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