Coupling Components Groups

Azo-stilbene dyes formed by diazotization of a condensation product containing primary amino groups and coupling with azo dye coupling components, eg. Direct Brown 29 (Cl 40505) (6) ... 

Secondary Disazo Dyes. There are about 250 dyes of known constitutions in this group. They are made by diazotizing an aminoazo compound, the amino group of which derives from the original coupling component and coupling it to a suitable intermediate. Intrasil Orange YBLH... 

With azo dyes derived from 4,5-dihydroxy-2,7-naphthalenedisulfonic acid [148-25-4] (chromotropic acid) as the coupling component, metal complex formation occurs with the perihydroxy groups without oxidation. 

Naphthol AS Coupling Components. Naphthol AS components are the aryhdes of either o-hydroxyarylcarboxycHc acids or acylacetic acids. They are free of sulfo and carboxyl groups, but form salts with bases these salts dissolve in water to give colloidal solutions, which couple with diazo components to form colored pigments. The whole class derives from the anilide of 3-hydroxy-2-naphthoic acid [92-70-6] Naphthol AS (85) (Cl Azoic Coupling Component 2). 

Heterocyclic Azo Dyes. One long-term aim of dyestuffs research has been to combine the brightness and high fastness properties of anthraquinone dyes with the strength and economy of azo dyes. This aim is now being realized with heterocychc azo dyes, which fall into two main groups those derived from heterocychc coupling components, and those derived from heterocychc diazo components. 

The transfer of simple alkyl groups (R in the table—mostly -Bu or Me), from tin to palladium complex 6 is a very slow process, and the substituent R (see table) is transferred selectively. The leaving group X on the coupling component... 

Coupling Components Containing Activated Methyl, Methylene, and Methine Groups 332... 

The replacement of an electrofugic atom or group at a nucleophilic carbon atom by a diazonium ion is called an azo coupling reaction. By far the most important type of such reactions is that with aromatic coupling components, which was discovered by Griess in 1861 (see Sec. 1.1). It is a typical electrophilic aromatic substitution, called an arylazo-de-hydrogenation in the systematic IUPAC nomenclature (IUPAC 1989c, see Sec. 1.2). 

First, the azo compounds formed from coupling components containing OH groups or primary or secondary amino groups are subject to tautomeric equilibria... 

The term coupling component referred originally to aromatic hydrocarbons, particularly benzene and naphthalene derivatives, which were required to have a hydroxy or an amino group as a substituent (sometimes, but not necessarily, accompanied by other substituents such as sulfonic acid groups). The presence of the hydroxy or amino group increases the C-nucleophilicity of the coupling component. In most cases this is a necessary requirement because the diazo components are relatively weak electrophiles. If the coupling component is phenol or a derivative of phenol ... 

There are apparent exceptions to the rule that aromatic compounds are azo coupling components only if they contain a hydroxy or an amino group. A long time ago Meyer and Tochtermann (1921) demonstrated that the 2,4,6-trinitrobenzenedi-azonium salt couples with mesitylene, isodurene (1,2,3,5-tetramethylbenzene), and pentamethylbenzene (see also Smith and Paden, 1934). That result was surprising at the time, but today it is, of course, understandable the diazonium salt used is pro-... 

The third group of heteroaromatic coupling components includes ring systems with electron-donor substituents. In principle they correspond to their (carbo)aro-matic analogues, the phenols and anilines. 

Barbituric acid can be considered as a cyclized malonic acid diamide (malonyl-urea). It is therefore a cyclic diketone that may be classified, in the sense of the compounds discussed in Section 12.6, as a coupling component with a methylene group activated by two carbonyl groups in the a- and a -positions. The reaction with arenediazonium salts was studied by Nesynov and Besprozvannaya (1971). These authors obtained coupling products (in good yield) that they considered to be arylhydrazones. Coupling with 4-(phenylazo)benzenediazonium chloride was studied by Chandra and Thosh (1991). The lH NMR spectra of these compounds are consistent with the arylhydrazone structure 12.68. 

Compounds acting as coupling components must have a high electron density on the reacting carbon atom. Therefore diazonium ions react only at aliphatic carbon atoms which are activated by electron-withdrawing groups (usually acyl or nitro). There is... 

Coupling Components Containing Activated Methyl Groups etc. 

Methylene coupling components with carbonyl groups in a,a-positions are very important, particularly acetoacetanilide derivatives (Scheme 12-40, X=NHAr), for the production of yellow monoazo dyes and pigments (Hansa Yellows see Zollinger, 1991, p. 180). 

Another synthetic application of an azo coupling reaction was found by Hecken-dorn (1987, 1990). In aqueous acetone a series of dialkyl (chloroacetamido)malo-nates, which are coupling components with a CH group activated by two carbonyl groups, were found to react with arenediazonium ions as in Scheme 12-44. The primary product cannot be isolated because it cyclizes easily to give a 1,2,4-triazin-5-one derivative (12.90). ... 

The overall mechanism of the substitution proper in azo coupling reactions can be summarized as shown in Scheme 12-83. This scheme is simplified, insofar as charges in the coupling component and additional charges (e.g., of sulfonate groups) in the diazo compound are neglected, and it does not include information on reversibility. 

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