Quinacridone substitutions

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,... 

The chemical synthesis of linear turns-quinacridones and their substituted derivatives that have been marketed subsequently is a complicated multi-stage sequence, making such pigments very expensive and sustainable only where high-fastness red pigments are essential, as in the car industry. There are four routes of synthesis, details of which have been given by Pollack [27]. 

The Sandoz company used the dibromoterephthalic acid method. This acid was made from p-xylcnc by brominating it to form 2,5-dibromo-p-xylene and then oxidising this to 2,5-dibromoterephthalic acid. Reaction of one mole of this acid with two moles of an arylamine in the presence of copper(II) acetate gives 2,5-bis(arylamino)terephthalic acid, which can be ring-closed to a linear quinacridone. Unsymmetrical substitution using two different arylamines is possible. 

Lightfastness and weatherfastness of quinacridone pigments (Sec. 3.2) deteriorate in the order 2,9 - 3,10 - 4,11 substitution. It is assumed that decreasing the distance between substituents and NH function disturbs the formation of hydrogen bonds [14] a tendency which culminates in the very poor light and weather resistance of 5,12-N,N -dimethyl quinacridone. 

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. 

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). 

Methods of changing the shade of a quinacridone pigment, other than changing the chemical modification and the substitution pattern, include the formation... 

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-... 

Quinacridone pigments are manufactured by either the condensation of 2,5-diarylamino-terephthalic acid or the oxidation of dihydroquinacridones followed by subsequent conditioning to produce the product in a pigmentary form of colloidal dimensions. For example, in the first process, the use of 2,5-dianilinoterephthalic acid results in the formation of trans linear quinacridone, PV 19, by a simple ring closure condensation where water is evolved as a by-product. Substitution of the aniline used to produce the diarylaminoterephthalic acid will result in pigments such as PR 122 where ditoluidinoterephthalic acid is used at the condensation stage. 

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. 

Today a maroon containing about 60% quinacridone and 40% quinacridonequinone and a gold containing about 75% quinacridone-quinone are sold commercially. Solid solutions can also be prepared between variously substituted linear trans-quinacridones. and a scarlet containing a mixture of approximately 60% quinacridone and 40% 4,11-dichloroquinacridone (an orange) is also on the market. 

The transparent colorants which were used were a yellow (Fc203), red (Carmine), blue (iron blue) and green (Cr203). Other colorants such as phthalocyanine blue, phthalocyanine green, quinacridone red can be substituted for these pigments and actually such pigments are available. 

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... 

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. 

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