Process Optimization For DMSS Synthesis And Purity Analysis Of Quinacridone Intermediates

Quiacridones, as high performance pigments of excellent fastness properties such as lightfastness and heat stability, have been widely used in many areas. Dimethyl succinylsuccinate (DMSS) is the key intermediate for pigment quinacridone production. Currently, synthesis of DMSS is through self-condensation of dimethyl succinate (DMS), though different solvent systems have been used as reaction medium. It is still quite a challenge to select the right solvent systems in order to balance DMSS yield, cost, ease of solvent recovery, safety, environmental friendliness, etc. In this study, mineral oil, an easily available, safe, non-toxic, low cost solvent, has been attempted to replace aromatic hydrocarbons. Addition of different polar non-proton co-solvents has also been studied to improve yield. Furthermore, systematic analysis of the solvency properties of the co-solvents with the solubility parameter theory indicates that solubility parameter of the co-solvent is critically important to the DMSS yield. As a result of the study of three-dimension solubility parameters in a Teas Graph, the effective co-solvent area has been found. The process was then optimized to achieve the best yield by using the orthogonal experimentation technique. Purity of DMSS can seriously affect the quality of quiancridone intermediates—2,5-diarylaminoterephthalic acids and eventually the quality of quinacridone products. Thus, DMSS purity analysis methods based on HPLC and UV/Vis were also designed respectively. Systematic purity analysis on DMSS samples made by following different process parameters indicates they are all of relatively high purity, though yield can fluctuate a lot. This further suggests that the purification part of the DMSS synthesis is sound.Quality of quinacridone pigments supplied by Chinese manufactures is noticeably inferior to those from western suppliers. Manufacturing of quinacridone pigments for different applications involves processes and reactions of many steps. Lack of purity control for key intermediates in each step during the production is one of the most important reasons for this huge quality disparity. In this paper, except purity study on DMSS, methodologies of purity analysis based on HPLC and UV/Vis respectively have also been developed for the analysis of a series of quinacridone intermediates , 2,5-diarylaminoterephthalic acids of different structures, different arylamines. After selecting the right solvents and optimizing each operation parameters, purity analysis methods based on HPLC and UV/Vis have proved to be consistent, reliable, and complementary. They thus can all be used in quinacridone pigment manufacturing process for quality control of intermediates.