Quinacridone manufacture

An important use of dialkyl succinates is in the preparation of dialkyl succinyl succinates (35,53—56), which are intermediates in the manufacture of quinacridone pigments. The reaction is carried out in the presence of alkaU metal alkoxides (eq. 2). 

In the manufacture of quinacridone pigments only the first and last of the four routes outlined have been operated commercially. Synthesis is followed by the milling processes necessary to give products with the crystal structure and particle size required for their use as pigments. 

Most pigments derived from vat dyes are structurally based on anthraquinone derivatives such as indanthrone, flavanthrone, pyranthrone, or dibromoan-thanthrone. There are other polycyclic pigments which may be used directly in the form in which they are manufactured. This includes derivatives of naphthalene and perylene tetracarboxylic acid, dioxazine (Carbazole Violet), and tetrachloro-thioindigo. Quinacridone pigments, which were first introduced in 1958, and recently DPP pigments have been added to the series. 

Several synthetic pathways for the commercial manufacture of quinacridone pigments have been published. In this context, only those routes are mentioned which were developed for industrial scale production. There are four options, the first two of which are preferred by the pigment industry. It is surprising to note that these are the methods which involve total synthesis of the central aromatic ring. On the other hand, routes which start from ready-made aromatic systems and thus might be expected to he more important actually enjoy only limited recognition. 

The typical quinacridone synthesis may be exemplified by the manufacture of unsubstituted 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. 

The polycyclic colorants which are discussed in this context (and this is also true for copper phthalocyanine and quinacridone pigments) as a rule evolve from the manufacturing process as products with relatively coarse particles, which is in contrast to azo pigments (Sec. 2.2.3). 

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. 

Common red quinacridone dye nucleating agent is preferably used for nucleation of polypropylene for light weight polypropylene nets." Dye is added in quantity of 10 to 100 ppm." The same solution was patented for manufacture of polypropylene grids.""... 

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... 

Quinacridone pigments are manufactured commercially by two distinct processes The original thermal or solvent process developed at DuPont and the more widely utiUzed polyphosphoric acid (PPA) process. Each process, with its own inherent advantages and disadvantages, differs significantly from the other but shares a common feature, the key starting material dimethyl succinoylsuccinate (DMSS) 7. Because of its crucial status in the manufacture of quinacridone pigments the synthesis of 7 also merits some discussion. 

The alternative commercial process for manufacturing quinacridones, the PPA process, also commences with DMSS 7 which is converted to 12 by acid-catalyzed reaction with the appropriate aromatic amines in water miscible alcohol solvents. Generally without isolation, the dihydrodiester 12 is oxidized by some of the agents described for the oxidation of the dihydroquinacridone 16 and hydrolyzed by base in the aqueous alcohol solvents to the water soluble disodium 2,5-diaryl-aminotere-phthalates that when acidified afford excellent yields of the corresponding 2,5-diaryl-aminoterephthalic acids 17. Typically this 3-stage synthesis is conducted as a 1-pot process [18] (Scheme 18.9). 

The Chapman rearrangement also has been applied to the synthesis of the parent quinacridone as well as other derivatives not readily accessible by other methods. However, this synthesis is mostly of theoretical interest and at present has no manufacturing utility. 

Solid solution products also may be formed during the quinacridone synthesis stage by incorporation of the appropriate intermediates in the desired ratios. Generally this cosynthesis method is better suited to the PPA manufacturing process, e.g., PR 282 (see Section 18.4). 

While some manufacturing processes for quinacridones directly deliver products that are fully pigmentary, most others, with the exception of products from the PPA process, require particle size reduction before commercial use. Generally, relatively large particle size pigments, which are more effective at light scattering, are opaque and relatively weak in tinted shades. Particle size reduction renders... 

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