Disazocondensation Pigments

This chapter deals exclusively with disazocondensation pigments in the traditional sense, i.e. disazo pigments synthesized by condensing a (di) amine with an azocarbonic acid. Other disazo pigments containing carbonamide units, such as Pigment Blue 25 or Pigment Red 164, are not further considered. 

Further improvements in pigmentary character were sought along the following lines 

The general goal of increasing molecular size and incorporating carbonamide groups is achieved in two ways  

Extension of bisacetoacetarylide disazo pigments by condensation of an anilide onto the diazobase unit carrying a carboxylic group to yield type I yellow pigments (1). 

Condensation of two monoazo acetoacetarylide or naphthol units, each carrying a carboxylic acid function with a diamine, to yield type II yellow (2) or red to brown pigments (3). 

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General structural formula of disazocondensation pigments are thus Yellow type I... 

In all cases the commonly accepted hydrazo form is depicted, even though no explicit proof for this tautomeric form has been disclosed for disazocondensation pigments. This form was however shown to be the energetically favored configuration for many monoazo pigments ). 

The following is a complete compilation of chemical structures of disazocondensation pigments with an assigned Colour Index (Cl) Pigment Name. Also given are Chemical Abstracts Registration Numbers, as well as Cl constitution numbers (if known). 

The availability of pure and economical 2-hydroxynaphthalene-3,6-dicarboxylic acid has recently led to a very interesting development not only in the field of disazocondensation pigments but for naphthol azo pigments in generaf 1 Cis and trans symmetrical disazocondensation pigments can thus be obtained, as depicted in 4, 5 and 6. 

Disazocondensation pigments are available in many commercial forms. Most of the pigments are sold as pure dry powders. Particle sizes are fairly large, providing more or less opaque forms with excellent fastness properties. Some electron micro-... 

Many disazocondensation pigments are used in application-specific predispersed forms such as pigment preparations, chips, concentrates or masterbatches from dispersion houses. Such sales forms are mainly useful where extreme fineness of particle size and complete wetting out of the pigment surface must be obtained, so as to secure top strength, gloss and transparency combined with constancy of color and... 

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