Catalytic Hydrogenation Of 3,5-dihydroxy Benzoic Acid To 3,5-Dioxocyclohexane Carboxylic Acid

3,5-dioxocyclohexane carboxylic acid is the intermediate of Moddus, a plantgrowth regulator. The reaction condition of the preparation of 3,5-dioxocyclohexanecarboxylic acid via catalytic hydrogenation of 3,5-dihydroxybenzoic acid has beenstudied by orthogonal experiment, using Raney nickel as catalyst.The HPLC analysis method for 1,3-cyclohexanedione as a model compound of3,5-dioxocyclohexane carboxylic acid has been studied. The mixture of reaction canbe separated when the pH of sample is 9, methanol and super-pure water as mobilephase, by gradient elution with total flux 1ml/min and the volume percentage ofmethanol linear increase from 20% to 50% in 15 minutes, using reversed-phase C18column.The evaluation result of hydrogenation of resorcinol have exhibited that theleaching temperature of nickel-aluminum alloy, the catalyst precursors, is the mostsignificant factor to the activity of Raney nickel, the proper leaching temperature is60oC,the proper leaching time 90min.The influence of preparation method ofcatalyst on the selectivity of 1,3-cyclohexanedione is not significant.The influence of different factors, such as preparation method of the catalyst,reaction temperature, the amount of NaOH, and hydrogen pressure, on thehydrogenation of resorcinol has been investigated. The amount of NaOH is the mostsignificant factor to the yield of 1,3-cyclohexandione, the reaction temperature thesecondly significant factor, the preparation method of catalyst and the hydrogenpressure are not remarkable factors.Based on the detailed study of the catalytic hydrogenation of the modelcompound resorcinol, the influence of different factors on the catalytichydrogenation of 3,5-dihydroxybenzoic acid has been investigated. It has been foundthat the reaction temperature is the most significant factor to the conversion of3,5-dihydroxybenzoic acid and the selectivity of 3,5-dioxocyclohexane carboxylicacid, the amount of NaOH is the most significant factor to the yield of3,5-dioxocyclohexane carboxylic acid. The yield of 3,5-dioxocyclohexanecarboxylic acid can reach to 93.4%, when the temperature of reaction is 90oC, thehydrogen pressure 2MPa, the amount of NaOH 6g.