Synthesis Of Ionic Liquids And Their Application In The Modification Of Dehydroabietic Acid

Dehydroabietic acid, one of the important natural diterpene resin acids, is the dominant component of disproportionated rosin. A series of derivatives of dehydroabietic acid can be synthesized by the utilization of the active carboxyl group and aromatic ring in the molecule. Ionic liquids, which consist of organic cation and inorganic or organic anion, are liquids with melting point at ambient temperature or near ambient temperature and also known as room temperature ionic liquids. Recently, ionic liquids have been increasingly employed as catalysts and solvents in organic synthesis. But there are few reports about the modification of dehydroabietic acid in ionic liquids. In this paper, 1-butyl-3-methylimidazolium bromide ([bmim]Br), 1-butyl-3-methylimidazo-lium tetrafluoroborate ([bmim]BF₄) and 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆) were prepared by two steps, and then the application of these ionic liquids in the modification of dehydroabietic acid was investigated.1. [bmim]Br, the intermediate of the ionic liquids, was prepared by using n-BuBr and N-methylimidazole as raw materials under the free-solvent and microwave radiation conditions. The optimum synthetic conditions were obtained by the single factor experiment method, and the best yield amounted to 94.3%. Then, [bmim]BF₄ and [bmim]PF₆ were synthesized by anion exchange under microwave radiation, with high yield of 83.1%, 82.8%, respectively.2. Dehydroabietic acid was extracted from disproportionated rosin under the microwave irradiation. The optimal extraction condition were found by single factor experiments to be as follows: the mole ratio of ethanolamine to disproportionated rosin is 1.1 : 1, feeding time of ethanolamine 5 min, reaction temperature is 75℃, reaction time is 15 min, with isooctane as extractant. The yield of dehydroabietic acid amounted to 80.9%, and its purity was 94.25%. In comparison with conventional extraction method, the microwave-assisted method has higher yield and shorter reaction time.3. Dehydroabietic acid-[(2-acryloyloxy)ethyl] ester (DAEE) was synthesizedby the O-acylation reaction of dehydroabietic chloride with 2-hydroxyethyl acrylate in the presence of [bmim]BF₄ as green solvent and pyridine as catalyst. The yield amounted to 73.3%. The effect of some factors such as reaction temperature, reactant ratio, reaction time and ionic liquid dosage on the yield was investigated. The target product was analyzed and characterized by means of TLC, IR, GC-MS, ¹H-NMR, ¹³C-NMR and elemental analysis.4. Methyl dehydroabietate was obtained via acyl chlorination and subsequent methanolysis of dehydroabietic acid at first. Then, methyl 12-benzyldehydroabietate (MBD) was synthesized by the Friedel-Crafts alkylation reaction of methyl dehydroabietate with benzyl chloride in acidic ionic liquid ([bmim]Br/AlCl₃). Under the reaction conditions, methyl dehydroabietate had convertion rate of 47.44%, and the selectivity to MBD was 72.11% . The target product was characterized by TLC, IR, and GC-MS.