Journal of Industrial and Engineering Chemistry, Vol.6, No.6, 431-436, November, 2000
Investigation of Process Optimization in Synthesis of Thioxanthone from 2,2'-Dithiobisbenzoic Acid and Cumene
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The synthesis of isopropylthioxanthone, a photoinitiator, from 2,2'-dithiobisbenzoic acid (DTSA) or thiosalicylic acid (TSA) and cumene in sulfuric acid was investigated in the perspective of the reaction mechanism and stoichiometry. The yield of product was sensitive to the strength of sulfuric acid used as the reaction medium. With a higher strength of sulfuric acid, a higher yield of product was obtained. The substitution of DTSA with cumene to the isomeric products, 2-isopropylthioxanthone 3, and 4-isopropylthioxanthone 4, via thioarylether intermediates 5 and 6 respectively is an oxidative reaction and requires oxidants in the reaction system. Fuming sulfuric acid containing oxidative sulfur trioxide resulted in a high yield of product by accelerating the formation of intermediates 5 and 6 in contrast to the competitive sulfonation in sulfuric acid that increased the content of water in reaction medium and resulted in low yield of product due to the retardation of the formation of intermediates 5 and 6. The ratio of isomeric products 3 over 4 varied with the strength of the sulfuric acid: A stronger strength of sulfuric acid produced relatively higher content of 3 over 4. The optimized reaction conditions were five parts by weight of DTSA and ten parts by weight of cumene per one part by weight of DTSA for two hours at room temperature, which yielded 78% of products 3 and 4 (91:9) after vacuum distillation.
Keywords:Photoinitiator;Isopropylthioxanthone;2,2'-Dithiobisbenzoic Acid (DTSA);Thiosalicylic Acid (TSA)
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