Commercially Available Quinacridone Pigments

A considerable number of mono- to tetra-substituted quinacridones has been described so far. A publication which includes the literature up to the year 1965 already lists more than 120 compounds, and many exhibit more than one crystal modification [23], However, this diversity of compounds does not reflect commercial variety. Only very few species have been offered, and even less command a major share of the pigments market. 

Heading the list are two crystal modifications of Pigment Violet 19 (the parent compound of the quinacridone series). Both the red-violet (3- and the red -y-mod-ification are encountered in the market, while the pure a-form is not lightfast and durable enough to have any commercial value. However, traces of the a-modifi-cation are found in a variety of types. 

Of the substituted quinacridone systems, it is primarily the 2,9-dimethyl derivative (Pigment Red 122) which enjoys appreciation for its excellent fastness properties and its pure bluish red shade. Besides, the list also includes 2,9-dichloro, 3,10-dichloro, 4,11-dichloro, and 4,11-dimethyl quinacridones. Some of these are available as mixed phases with other quinacridone derivatives [24], 

73920 mixed crystal phase with quinacridone quinone H H Cl H H CI scarlet 1 (4,ll-dichloro 3) 

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Representative commercial quinacridone pigments are listed in Table 28. Each specimen is offered in only one crystal modification. Unsubstituted quinacridone is somewhat of an exception in that two crystal phases are commercially available. 

P.R.206 is a mixed crystal type and consists of unsubstituted quinacridone and quinacridone quinone. The ratio between the two components as well as the crystal modification is not yet known. P.R.206 affords a very dull, yellowish shade of red, referred to as maroon. The pigment is considerably weaker than perylene pigments. All commercially available types of P.R.206 are more or less transparent and are used mostly in metallic finishes for automobiles, to which they lend reddish shades of copper. The pigment is often found to be difficult to disperse. The finishes frequently exhibit rheological problems, especially at high pigment concentration. 

P.R.179 types demonstrate excellent weatherfastness. They are as weatherfast or even more weatherfast than substituted quinacridone pigments. The various types differ considerably in their flop behavior. Some of the commercially avail-... 

Today two commercial synthetic routes are available for the manufacture of quinacridone pigments and some substituted derivatives. The key starting material in either synthesis is dialkyl sucdnoylsucdnate (7), which is synthesized from dialkyl succinate in the presence of a sodium alkoxide catalyst, usually sodium methoxide. The first step is a Claisen condensation, and this is followed by a Dieckman cydization, yielding the disodium salt 8, which upon addification yields 7 (Scheme 18-2)1 1... 

Artists colors utilize quinacridones because of demand for specific colors with long-lasting properties. More detailed information regarding applications of specific quinacridones is available in many commercial publications and in books devoted to pigment technology [69]. 

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