Anion-cation Cooperative Catalysis By Ionic Liquids On The Carbonates Participated Green Reactions

Ionic liquids have many advantages compared with conventional solvent, such as negligible vapour pressure, high thermal and chemical stability, wide liquid temperature range, non-toxic, strong solubility and catalytic activity. They have been widely used in organic synthesis, electrochemistry, chemical separation and the polymer materials. Ionic liquid is a kind of supramolecular aggregates in itself, the anion and cation of ionic liquid interact each other to form three-dimensional supramolecular network structures through several non-covalent force, such as hydrogen bonds,π-πstacking,π-anion. The supramolecular properties of ionic liquids provide an opportunity for ionic liquids to effectively and greenly catalyze the organic reactions. In recent years, many ionic liquid-catalyzed organic reactions involving carbonates which are considered as low toxically, environmentally benign and green chemical raw material, have been attracted great interest.The ionic liquid-catalyzed organic reactions between electrophile and nucleophile were investigated in this thesis, in which carbonates and aniline, indole were used as reactants. Main content included:experimental and theoretical investigation of reaction of aniline with dimethyl carbonate catalyzed by acid-base bifunctional ionic liquids; Anion-cation cooperative catalysis by ionic liquids on the reaction of aniline and ethylene carbonate; Anion-cation cooperative catalysis by ionic liquids on the reaction of aromatic amines with propylene carbonate; Hydroxyalkylation of indole with cyclic carbonates catalyzed by ionic liquid.In the first section, a novel acid-base bifunctional ionic liquids 1-(2-(1’-piperidinyl) ethyl)-3-methyl imidazolium trichlorolead ([PEmim]PbCl3) was synthesized and applied in the reaction of aniline with dimethyl carbonate for producing methyl-N-methyl-N-phenylcarbamate. The reactivity of [PEmim]PbCl3 which has acid-base dual-active is significantly higher than basic [PEmim]Cl and acidic PbCl2. The studies of reaction mechanism show that the higher reactivity of [PEmim]PbCl3 is accounted for its ability to activate both aniline and dimethyl carbonate by the acidic and basic sites cooperatively. Density functional theory (DFT) calculations simulate the structures and charge properties of [PEmim]PbCl3, complex of [PEmim]PbCl3 and aniline, and complex of [PEmim]PbCl3 and dimethyl carbonate. DFT calculations show that bond length of N-H in aniline and C=O of dimethyl carbonate increases 0.0142 A and 0.0073 A, respectively. NBO charge of N in aniline and carbonyl C of dimethyl carbonate increases 0.007 negative charge and 0.044 positive charge, respectively, when the interaction between reactants and ionic liquid was formed. [PEmim]PbCl3 can increase the electrophilicity of dimethyl carbonate and the nucleophilicity of aniline by its acid and base sites.In the second section, in order to optimize the reaction parameters, the effects of reaction time, temperature and catalyst amount on the reaction of aniline and ethylene carbonate were investigated. Under the optimized conditions(130℃,9 h, amount of catalyst:5 mol%), the yield of 3-phenyloxazolidin-2-one reached 90%. Then we studied the effect of ionic liquids which have different cation and anion on the reaction of aniline and ethylene carbonate. The catalytic activity follows the order of 1-butyl-3-methyl-imidazolium ([Bmim])> 1,2-dimethyl-3-butyl imidazolium ([Bmmim])> 1-butyl-pyridinium ([Bpy]), which is consistent with the order of hydrogen bond donor ability. Simultaneously, the catalytic activity of imidazolium based ionic liquids follows the order Cl> Br> BF4> PF6> C(CN)2COEt≈NTf2> BPh4, which is consistent with the order of the hydrogen bond acceptor ability. The dual activation of nucleophiles and electrophiles by the cations and anions of ionic liquids is crucial to promote the reaction in high yields. Reaction mechanism was also investigated by 1H NMR and ESI-MS. In 1H NMR, the proton in 2-position of imidazolium ring of [Bmim]BF4 shifted fromδ9.48 to 9.33 in the presence of ethylene carbonate, which indicates that the proton in 2-position of imidazolium ring interacts with ethylene carbonate. The interception of supramolecular cationic species involving [Bmim]BF4, aniline and ethylene carbonate further confirm that ionic liquid [Bmim]BF4 simultaneously activate aniline and ethylene carbonate.We studied the reaction of aromatic amines with propylene carbonate for synthesizing 5-methyl-3-aryloxazolidin-2-one catalyzed by ionic liquid. The effects of reaction temperature, time and amount of catalyst were investigated in detail. Under the optimized conditions (140℃,7 h, amount of catalyst:5 mol%), the yield of 5-methyl-3-phenyl-oxazolidin-2-one was 99%. Ionic liquid can be reused five times without any obvious decrease of activity. The effects of cations and anions of ionic liquids were also studied. It was found that the catalytic activity of cation follows the order of 1-butyl-3-methyl-imidazolium ([Bmim])> 1,2-dimethyl-3-butyl imidazolium ([Bmmim])> 1-butyl-pyridinium ([Bpy]), which is consistent with the order of hydrogen bond donor ability. Simultaneously, the catalytic activity of imidazolium based ionic liquids follows the order OAc> Cl> Br> BPh4, which is consistent with the order of the hydrogen bond acceptor ability of anions. The anion-cation cooperative effect of the ionic liquids was also simulated by the density functional theory (DFT). The calculations show that distances of cations of ionic liquids and C=O of propylene carbonate follows the order [Bmim]< [Bmmim]< [Bpy]. The distance of the proton in 2-position of imidazolium ring of [Bmim] and C=O of propylene carbonate is the shortest (2.022 A). [Bmim] activate propylene carbonate throught the hydrogen bond interaction between the proton in 2-position of imidazolium ring and C=O of propylene carbonate. The distances of anions of ionic liquids and N-H in aniline follows the order OAc< Cl< Br< BPh4. Anions of ionic liquids activate aniline throught the hydrogen bond interaction between anions and N-H in aniline. Ionic liquid can simultaneously increase the electrophilicity of propylene carbonate and the nucleophilicity of aniline through the hydrogen bond interactions.We studied the hydroxyalkylation of indole with ethylene carbonate and propylene carbonate catalyzed by ionic liquid. Hydroxyethyl indoles, hydroxypropyl indoles and their derivatives were simply and eco-friendly synthesized. Without any other organic solvent, we systemically studied the effects of reaction temperature, time, amount of catalyst and molar ratio of reactants on the reaction of indole and ethylene carbonate catalyzed by [Bmim]BF4. Under the optimized conditions (150℃,9 h), the conversion of indole reached 96%, the total yield of the hydroxyalkylation products 1-(2-hydroxyethyl)indole (la) and its derivatives 1-(2-(2-hydroxyl)-ethoxyethyl)indole (2a) and 1-(2-(2-(2-hydroxyl)ethoxyethyl)oxyethyl)indole (3a), reached 90%. The catalytic activity of ionic liquid is affected by the anions and follows the order of BPh4< BF4< Br< Cl< OAc, which is consistent with the hydrogen bond acceptor ability of the anions of ionic liquids. In the reaction of indole with propylene carbonate, when the reaction condition was 150℃,9 h, the conversion of indole reached 87%, the yield of main product 1-(2-hydroxypropyl) indole (1b) reached 70%. The selectivity of the main product was improved may be due to steric effects of propylene carbonate.