Synthesis of Quinizarin from P-dichlorobenzene
|Keywords||1,4-Dichlorobenzene Quinizarin Dechlorination Friedel-Craftsacylation reaction Reaction Mechanism|
1,4-dihydroxyanthraquinone, named quinizarin, is a key intermediates of finechemicals, which has widely used in the synthesis of vat dyes (e.g. C.I. Pigmentviolet12), disperse dyes(e.g. C.I. Solvent Orange86) and reactive dye intermediates.Recent studies found that it can also be used in the synthesis of medical intermediates,such as antitumor drug, anticancer medicines and so on. In this paper, we’llsummarize a new synthesis method of production of quinizarin and make efforts toexplain possible mechanism of the reaction. Main contents have been given asfollows.The existing industrial production methods and potential synthetic route havebeen obtained by access to the information about the synthesis of quinizarin throughextensive literature. Taking into account the defects of the existing industrializationsynthesis method of quinizarin such as the raw materials hydroquinone toxic,susceptible to oxidation and low utilization;1,4-dichlorobenzene smells strongunpleasant pungent odor with low melting point (42~43°C). Meanwhile, it is volatileso that the industrial operating environment is also too harsh. These disadvantages aredifficult to overcome. P-dichlorobenzene, a white crystalline with camphor smell andlow toxicity, which is not easily oxidized and non-volatile, can be considered as anoptimal raw material to synthesis of quinizarin. We chose p-dichlorobenzene route asthe research target and design a new route for the synthesis of quinizarin scientifically:Phthalic anhydride, phosphorus pentachloride and p-dichlorobenzene were chosen asthe main raw material. There were four-step to synthesis of the target product, that isanhydride acylation reaction, friedel-crafts acylation reaction, cyclization reaction andchlorine hydroxy reaction. We obtained the optical conditions of anhydride acylatingreaction through experiments as follows: When the acid anhydride: phosphoruspentachloride is1.05:1(mole ratio), phosphorus pentachloride could be run outcompletely. A slight excess of acid anhydride was used in order to ensure that thephosphorus pentachloride was complete. The reaction yield could be up to94.78%.To discuss the Friedel-Crafts acylation optimum conditions via single factorexperiments was as follows: The feasible reaction temperature is110to115°C andthe reaction time is preferably5to6h. Chloride: p-dichlorobenzene: anhydrousaluminum chloride is1.05:1:1(molar ratio). Under such reaction conditions, themaximum yield of the product was80.12%. The optimum conditions for the cyclization reaction was as follows: The reaction time was between50~60min andthe reaction temperature is between140~160°C,2-(2,5–dichloro-benzoyl)benzoicacid: sulfuric acid=1:8(mass ratio), the yield could be up to89%; By single factorexperiments and orthogonal experiments, five aspects that is boric acid feedingquantity, feeding quantity of sulfuric acid and sulfuric acid concentration, the reactiontime and temperature have been studied in the process of1,4-dichloro-anthraquinoneto quinizarin. We obtained the optimal conditions for this reaction was as follows:sulfuric acid concentration was96%; the mass ratio of sulfuric acid to1,4-dichoro-anthraquinone is13.8:1.0; The mass ratio of boric acid:1,4-Dichloroanthraquinone was3:10, reaction time was60min. The reactiontemperature was between220~230℃appropriately. We obtained nearly yield of71.0%for quinizarin by repeatedly experiments. The total yield of quinizarin was47.98%.In addition, we proposed a two-step synthesis of quinizarin by adopted a carefulstudy of the experimental process and streamlined the reaction steps. We also read alarge number of documents to make a thorough research for chlorine hydroxy reaction,trying to explore and explain the possible mechanism of chlorinated anthraquinone tothe quinizarin.