Pigments disazo

Azo pigments, subdivided into the monoazo and disazo pigments, have the azo group (—N=N—) in common. The synthesis of azo pigments is economically attractive, because the standard sequence of diazonium salt formation and subsequent reaction with a wide choice of coupling components allows access to a wide range of products. 

All members of this pigment family share good lightfastness, combined with poor solvent and migration resistance. These properties define and limit their application. Monoazo yellow pigments are used extensively in air-dried alkyd resin and in emulsion paints, and certain inks used in flexo and screen printing. Other applications are in letterpress and offset inks, as well as in office articles. 

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The monoazo and disazo pigments contain one or more chromophoric groups usually referred to as the azo group. However, it... 

One area which requires special comment is a study (13) which showed that certain diaryUde pigments processed ia polymers above 200°C and particularly above 240°C decompose to give off 3,3 -dichlorobenzidine, an animal carciaogen. As a consequence diaryUde pigments (not, however, condensation disazo pigments) are not recommended for use ia any appHcations where they might be exposed to temperatures exceeding 200°C. 

Disazo pigments made from substituted benzidines... 

Benzidine is an aromatic diamine that can be tetrazotised and coupled to two molecules of a coupler such as acetoacetanilide. This gives a yellow disazo pigment that can be regarded as a double molecule of the monoazo pigments described above. The possibilities of making a... 

For orange colours, simple 2-naphthol derivatives are the most commonly used coupling components as, for instance, in 2,4-dinitroaniline—>2-naphthol (4.118 Cl Pigment Orange 5). As in the yellow series, superior disazo pigments can be prepared using 3,3 -dichlorobenzidine as tetrazo component with derivatives of 1 -phenyl-3-methylpyrazol-5-one as couplers. 

The resulting extinction coefficient remained constant within the accuracy of the measurements. In the transition from monoazo to disazo pigment, however, the value of the maximum molar extinction coefficient is more than doubled, because the effect of the two azo linkages is enhanced by additional interaction via the diphenyl moiety. This, however, does not improve the conjugation the shade does not shift remarkably ... 

Monoazo and disazo pigments contain one and two azo functions, respectively. Compounds with more than two azo groups (tris, tetra,. .., polyazos), however, have failed to gain commercial recognition as pigments. 

In the industrial context, the term disazo pigments is used exclusively to refer to pigments which possess two azo groups and contain the diaminodiphenyl skeleton according to the general formula ... 

Structurally, there are two basic types of disazo pigments, depending on whether the bifunctional element is introduced through the diazonium compound or through the coupling component. A bifunctional diazo component results in products of the type... 

The general structure of a typical disazo pigment based on a bifunctional coupling component is... 

Bisacetoacetarylide pigments are considered disazo pigments that are obtained from bifunctional coupling components. The latter are obtained by bisacetoace-tylation of aromatic diamines, especially of 4,4 -diaminodiphenyl or 1,4-di-aminophenyl derivatives with 2 equivalents of diketene or acetoacetic ester ... 

In the early 1950s, Ciba research succeeded in synthesizing red disazo compounds of relatively high molecular weight. These products were known as disazo condensation pigments [1,2], Such compounds may be structurally visualized as disazo pigments, formally composed of two monoazo units, which are attached to each other by an aromatic diamino carbonamide bridge ... 

Yellow as well as red disazo pigments are derivatives of this parent structure. Both types are prepared by essentially the same but slightly modified route. 

Moreover, there are patents claiming monoazo and disazo pigments, starting from compounds such as... 

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