Substituted Quinacridones

There are also certain disubstituted quinacridones which are used commercially. The two peripheral rings in such quinacridone systems (53) are partially chlorinated or methylated. In the sequence 57 - 58 - 53 (p. 455), possible substitution sites on the peripheral rings are indicated by dashes (see also tables of chemical structures in the appendix). 

Succinylosuccinic diester is cyclized according to the common route by using chlorinated or methylated aniline. Starting from anilines which are substituted in 2- or 4-position, the reaction affords the symmetrical 4,11- or 2,9-disubstitution products. Reaction with 3-substituted anilines, on the other hand, produces a mixture of both of the symmetrical 1,8- and 3,10-disubstitution products, as well as un-symmetrical 1,10-disubstituted compound. The following chart illustrates this point. 

Fairly recently a large particle size, opaque P-polytype has been commercialized [34]. Several other polymorphic forms of quinacridone have been claimed in the patent literature [35]. 

Quinacridones substituted in the peripheral rings are synthesized by the methods described earlier by including appropriately substituted aniUnes. Anilines that are p- and o-substituted afford 2,9- and 4,11-disubstituted quinacridones, respectively. By contrast, the inclusion of m-substituted aniUnes afford intermediate terephtha-lic acids that possess two distinct sites that compete for cyclization, subsequently resulting in the formation of the three possible isomers 3,10-, 1,8- and 1,10-disub-stituted quinacridones. The 3,10-isomer predominates in the mixture because it is formed by cyclization at the least stericaUy hindered sites of the intermediate product. In some instances, the three isomers can be separated. The individual compounds also can be distinguished by inspection of the NMR spectra of the mixtures [36]. Like the parent compound, many of the substituted derivatives, including 6,13-dihydroquinacridone [37], exhibit polymorphism For example, 

11- di-methyl, and 4,11-difluoroquinacridone range in color from reddish scarlet to orange. Even in DMF or concentrated sulfuric acid solutions, the longest wavelength absorptions of 2,9-disubstituted quinacridones show only an approximate correlation with either a- or cr-i- substituent functions. The longest wavelength 

The colors of 4,11-disubstituted quinacridones, unlike the 2,9-disubstituted counterparts, are dominated by steric rather than electronic effects. As displayed in Table 18.2, the solubility of these compounds (boiling a-chloronaphthalene, b.p. 264 C) increases with increasing bulk of the substituents and correspondingly the photochemical stability in the solid state decreases. 

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Among syntheses which start from preformed aromatic systems, the Sandoz process in particular has stimulated interest. It is the only route which allows the manufacture of asymmetrically substituted quinacridones. A typical synthesis follows. 

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. 

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],... 

A number of other members of this class are also available, although not all are listed in the Colour Index. Their exact chemical and physical properties remain to be published. The list includes mixed phase pigments made of unsubstituted quinacridone with dimethylquinacridone or other substituted quinacridones. Recently mixed crystal phase pigments of two substituted quinacridones have been published [28]. These pigments are considered specialty products for automotive finishes, especially for metallic finishes. 

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-... 

A third route developed by Sandoz (22) shown in Scheme IV allov/s one to make unsymmetrically substituted quinacridones by stepwise condensation (Steps 1 and 2) of the two amines carried out under carefully controlled conditions (23). 

Two substituted quinacridones have been introduced commercially and find use 2,9-dimethylquinacridone. Pigment Red 122 (Xl), and 2,9-dichloroquinacridone, Pigment Red 202 (XII). Both are magenta in shade. 

Using one or more of the three methods, and others which are more complicated (see below), about 150 differently substituted quinacridones have been reported in an extensive list of patents and other publications in the last 40 years. 

A specified mixture of aniline and one or more substituted anilines such as p-toluidine, p-chloro aniUne, and p-anisidine as examples is condensed with DMSS 7 to produce, after subsequent hydrolysis and oxidation of the resulting dihydrodiesters, a corresponding mixture of the diarylaminoterephthalic acids. An example using a para-substituted aniline is shown in Scheme 18.14. Cyclization of this mixture of terephthaUc acids in PPA followed by appropriate conditioning of the recovered crude product affords a ternary solid solution composed of quinacridone 2, 2-substituted quinacridone 27, and 2,9-disubstituted quinacridone 28. Several combinations are reported, providing a wide range of solid solutions and thus colors. 

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