Quinacridone thermal process

Analytical studies of the PPA reaction processes by real-time infrared spectroscopy [19A] demonstrate that cycUzation to the corresponding quinacridones is very rapid at the typical reaction temperatures and although not confirmed directly, probably proceeds by a two-stage sequential mechanism. Analogous to the thermal process high dilution conditions favor monomolecular reactions and subsequently the quaUty of the ultimate products. The by-products of bimolecular reactions occasionally have been detected in some quinacridone pigments... 

In contradistinction to the thermal process, the cycUzed product remains in solution in the hot PPA, presumably in the form of a solvated zwitterionic phosphoric acid salt such as 24 (Scheme 18.11, n= 1—4). The quinacridone product in its cmde state then is obtained by precipitation when the reaction solution is drowned into an appropriate protic solvent (the equivalent of an acid pasting process). As the properties of the solvents have profound effects on the subsequent polymorphic phase and quahty of the resulting pigments, a specified selection is required for each product code. 

Compared to the thermal process, quinacridone production in PPA occurs at significantly lower temperatures (120-140 °C) utilizing the already oxidized intermediates (diarylaminoterephthalic acids, 17) to synthesize the crude products directly. Therefore, excluding the synthesis of DMSS, production of most quin-... 

The thermal requirements for pigments which are targeted for PETP melt extrusion are particularly severe. However, it is important to consider the individual conditions at the various stages of polymer coloration. Pigments, for instance, which are added during the so-called condensation process in a glycol dispersion prior to transesterification or condensation in the autoclave, are exposed to temperatures between 240 and 290°C for 5 to 6 hours [43]. These harsh conditions are only tolerated by very few polycyclic pigments, primarily by representatives of the quinacridone, copper phthalocyanine, naphthalenetetracarboxylic acid, and pery-lene tetracarboxylic acid series. 

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. 

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