The Catalytic Synthesis Of Glycerol Acetals(Ketals)

The condensation of cyclohexanone and glycerol catalyzed by varies catalysts was investigated aiming to study the catalytic mechanism and the effects of catalyst's structure and property on the conversion of cyclohexanone and the reaction selectivity. The catalytic activities of Lewis acid, proton acid, solid superacid, heteropoly acid, zeolite, montmorillonite and inorganic anhydride were compared. The reaction parameters on the synthesis of menthone glyceryl ketal and cyclohexanone glyceryl ketal were studied and optimized.The result indicates that AlCl3, concentrated sulfuric acid, SO42-/MxOy solid superacid, Hβzeolite, and P2O5 shown higher catalytic activity;and the assayed Lewis acids performed as both Lewis and Bronsted acid. The main factors influencing the catalytic activity of the metallic inorganic salt were: (1) The structure of the Lewis acids: For hydrochloride or sulfate with same anionic moiety, those containing cationic moieties with stronger Lewis acid intensity or larger hydrolysis equilibrium constant performed higher activity and selectivity for 2-methylol-1,4-Dioxaspiro[4,5]decane (a). In addition, the catalytic activity and selectivity of hydrochlorides were higher than that of sulfates if they contain same cationic moieties. (2) The catalytic activity of the hydrated sulfates was significantly influenced by the calcination temperature. The void structure and acidity of solid superacid, zeolite and montmorillonite effect on their catalytic activities, which performed higher selectivity for a, and therefore could be expected to the carriers of other acid catalysts. Product a was favored kinetically, which will transfor to 3-hydroxyl-1,5-Dioxaspiro[5,5]undecane (b) slowly, the later is more stable thermodynamically. With AlCl3 as the catalyst, the reaction mixture obtained after 2 h at the equiblium reaction, and the content of a changed from 97.7% to 94.8% after placing the mixture at room temperature for 60 days.The effect of reactant ratio, reaction time, amount of the AlCl3 and the solvent on the conversion of cyclohexanone and the reaction selectivity was studied, respectively. The prime influence factor was materials ratio. When the molar ratio of the catalyst to reactants was n(AlCl3):n(cyclohexanone):n(glycerol)=1:1000:1500, 10 mL cyclohexane, reaction 92 oC, 1 h, a cyclohexanone conversion of 97.7% and a selectivity for a of 98.0% was achieved, respectively, the product yield was obtained 90.2% (97.4% of purity, GC). AlCl3 can be reused for another 2 runs without obvious deactivity. The reaction conversion was in inverse proportion to the steric hindrance in acetalization.The condensation of menthone and glycerol possible only generate 1,3-dioxolane according to the GC-MS proof. When the molar ratio of catalyst to reactants was n(AlCl3): n(menthone):n(glycerol)=1:100:150, 10 mL cyclohexane, 2 h, a menthone conversion of 43.6% was obtained; and the product yield was obtained as 35.1% (99.1% of purity, GC).