One-step Synthesis Of Quaternary Ammonium Salts From Ammonium Or Aminium Salts And Carbonates Over Ionic Liquid Catalyst

In order to investigate the process for synthesizing quaternary ammonium salts with different anions via a one-step reaction of ammoium/aminium salts and a proper alkyl source, for example, carbonates, our work focuses on those aspects as follow:1. Synthesis and characterization of 1,3-dialkylimidazolium ionic liquids1-Ethyl-3-methylimidazolium bromide (EMImBr) and 1-buthyl-3-methylimidazolium bromide (BMImBr) were synthesized by the reactions between 1-methylimidazole and ethyl bromide or buthyl bromide. The following ionic liquids were produced from EMImBr or BMImBr by anion-exchange procedures: EMImAc, BMImAc, EMImBF₄, BMImBF₄. [BMIm]₂SO₄ was synthesized from the corresponding 1,3-dialkylimidazolium chrolide and sulfuric acid. The purity of those prepared ionic liquids was characterized with FT-IR and ¹H-NMR.2. Synthesis and characterization of aminium saltsThe aminium salts were prepared by neutralizing amines with stoichiometric amount of corresponding acids and then dried in vacuum. 37 aminium salts were used in our study. Charecterizations were conducted with FT-IR and ¹H-NMR.3. Study on the quaternization of ammonium saltsBy using ammonium carbonate and dimethyl carbonate as reactants,and EMImBr as catalyst, the effects of reaction temperature, reaction time, mole ratio of reactants and content of catalyst on the yield of tetramethylammonium salt were intensively investigated. The following optimum operating conditions were determined: reaction temperature of 443 K, reaction time of 8 h, mole ratio of reactants and catalyst of 1:8:0.8. The reactions between ammonium bromide and dimethyl carbonate over different ionic liquid catalysts were carried out under this conditions. The results indicate that the tetramethylammonium salt yield is dependent on both the anion type of the catalyst and the substituting groups on the imidazole ring. The product yield decreased according to the order of EMImBr > BMImBr > EMImAc, BMImAc > BMImBF₄ > EMImBF₄ > [BMIm]₂SO₄. When EMImBr acted as catalyst, the yield of tetramethylammonium bromide was 96.5%. In the subsequent study, we explored the reactions between various ammonium salts and dialkyl carbonates by using EMImBr as catalyst. The results show that the tetralkylammonium salt yield is dependent on both the anion type of the ammonium salt source and the alkyl group on dialkyl carbonates. When dimethyl carbonate reacts with different ammonium salts, the tetramethylammonium salt yield decrease order corresponding to the ammonium salt is NH₄Br, NH₄NO₃, NH₄Cl > NH₄F > (NH₄)₂SO₄ > (NH₄)₂C₂O₄, (NH₄)₂CO₃, NH₄Ac, (NH₄)₃PO₄ · 3H₂O. For the same ammonium salt, dimethyl carbonate is a much better...