A Density Functional Theory Study on the Reaction Mechanism for Synthesis of 2,5-Dihydroxyterephthalic Acid by Aromatization
Using density functional theory(DFT)calculations,the reaction mechanism of the preparation of 2,5-dihydroxyterephthalic acid(DHTA)from l,4-cyclohexanedione-2,5-dimethyl ester(DMSS)was investigated.Specifically,the solvent effect on the transformation of DMSS from its ketone form to enol form was emphasized using the IEFPCM solvent model,and the role of iodine in catalyzing the aromatization of DMSS enol form was explored.The computational results show that the energy barrier for the isomerization reaction between DMSS ketone and enol forms is significantly reduced with the assistance of solvent molecules.During the aromatization process,iodine first reacts with hydrogen peroxide to generate the active species iodic acid,which catalyzes the iodination reaction of DMSS enol form.Then the intermediates undergo subsequent elimination and interconversion to generate 2,5-dimethyl-1,4-benzenedicarboxylic acid dimethyl ester(DMDHT),further hydrolyzed to DHTA.Meanwhile,the solvent effects on the interconversion between DMSS ketone and enol forms were verified through nuclear magnetic resonance hydrogen spectrum testing,and the performance evaluation tests show that the purity and yield of DMDHT products from the iodine-catalyzed reaction are higher than those from the uncatalyzed reaction.
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