CO₂ Involved In The Electrosynthesis Of Organic Carbonate

Recently, as the more paying to protect the environment of the world, the conception of Green Chemistry is appeared. Green chemistry is also called environment-friednly chemistry, environment-benign chemistry, clean chemistry and sustainable technology. Green Chemistry establish the fundamental purpose is to conserve resources and prevent pollution point of view, to re-examine and reform the traditional chemical, so that we can control the environment from temporary to permanent cure. Electrochemistry is one of green synthesis route since it carries out through gain or loss of electron. In principle, it can avoid other reagent which can decrease the consumption of the substance and reduce the environmental pollution, environment-friendly, "atom economy requirements", is a synthesis of the green.Carbon dioxide (CO₂) is the primary component of greenhouse gases. Converting it to chemical products can both reduce the environmental pollution by controlling the emission of greenhouse gases and utilize the cheap and abundant C1 resource. The electrochemical reduction of carbon dioxide has attracted considerable attention as a possible source of carbon for thesynthesis of organic molecules and as a possible means of energy storage.Nowadays, RTILs have been used as media for electrochemical study because they are highly conductive, non-volatile, non-flammable. Ionic liquids have no measurable vaporpressure; hence, there has been considerable interest in using them in place of volatile organic solvents that can emit problematic vapors.Organic carbonates constitute an important and versatile class of compounds. Recently, the synthetic methodologies as well as the possible utilisation have been amply reviewed and discussed. They have widespread application as solvents for a variety of processes and as efficient protecting groups for alcohols and diols. The most relevant known syntheses of organic carbonates involve the direct or indirect use of phosgene, with all the remarkable drawbacks that the use of such a toxic and corrosive reagent entails. The replacement of phosgene with carbon dioxide in the synthesis of carbonates, starting from hydroxy compounds. The study on electrochemical fixation of CO₂ to organic carbonates, Electrochemical electrochemical fixation of CO₂ has the advantange including high efficiency, simply operation and mild conditions. Specially, application of ionic liquid in fixation of CO2 is a practical significance contents.The details are given as follows:First: Synthesis of Dimethyl Carbonate in Mixed BMImBF₄-CH₃CN Solvent. Cyclic voltammetry obtained at Cu cathode in CO₂-saturated BMImBF₄-MeCN solution and in CO₂-saturated MeCN solvent were studied under mild conditions respectively. It showed that CO₂ was reduced irreversibly to free radical anion CO₂^-. The ionic liquid of the mixed solvent had the catalytic activity for CO₂ electrolysis. The cathodic peak of CO₂ reduction shifted positively in the mixed solvent. DMC was synthesized from CO₂ and MeOH in the mixed solvent in an undivided cell with Mg as anode and Cu as cathode, followed by addition of MeI as an alkylating agent. The synthesis reaction was carried out under mild conditions. The synthesis product was very easy to separated from the mixed solvent. The influence of the volume ratios of BMImBF₄ to MeCN, the electrode materials, the working potential and the MeOH concentrations etc on the DMC yield was examined. Under the optimal contions ,the highest DMC yield reached 79.6%. And a possible reaction machamism of electrosynthesis of dimethyl carbonate (DMC) was proposed.Second: Electrochemical Reduction Carbon Dioxide : Synthesis Aryl Ethyl Carbonates in Ionic Liquid BMIMBF₄ Under mild conditions, the electrosynthesis of aryl ethyl carbonates from carbon dioxide and aryl alcohols, which put in 1-Butyl-3-methylimidazolium tetrafluorobrate (BMIMBF₄) that acts as electrolytes and supporting electrolytes in undivided cell, followed by addition of C₂H₅I as alkylating agent. The electrochemical reduction of carbon dioxide resulted in carbon dioxide radical anion (CO₂^-1). Conparing with organic solvent, the solubility of CO₂ in the ionic liquid BMIMBF₄ is more soluble than. A plausible mechanism of electrosythesis aryl ethyl carbonates in BMIMBF₄ was proposed. The influences of faradays permole of aryl alcohols supplied to the electrode(Q), cathode materia, electric current and temperature etc on the reaction using benzyl alcohol as the model compound was examined to optimize the synthetic conditions. The ionic liquid used for the reaction was recyclable. The selectivity of aryl ethyl carbonates was 100% and the largest yield was 78%.Third: Electrosynthesis of Propylene Carbonate from CO₂ and 1,2-Propylene glycol in mild conditions. Under mild conditions, Electrosynthesis of propylene carbonate from 1,2-Propylene glycol was studied in undivided cell, followed by addition of C₂H₅I as alkylating agent. MeCN was electrochemically and reacted with 1,2-Propylene glycol. The electrochemical reduction of MeCN resulted in MeCN radical anion(^- MeCN). In the course of reaction, acetonitrile acted as not only the solvent but also the dehydrating reagent to eliminate the effect of the water produced from the reaction. A plausible mechanism of electrosythesis propylene carbonate in MeCN-TEABF₄ was proposed. The effects of the electrolyte, supporting electrolytes, current densities and the passed charges on electrolysis were investigated to optimize the electrolytic conditions. The maximal yield is 28.2% on Cu / C electrodes under a constan t current of 17.3 mA·cm^-2 until 2 F·mol^-1 of charge has passed through the cell.Fourth : CH₃COOAg Catalyzed propargylic alcohols and CO₂ to Electrosynthesis ofα-Alkylidene cyclic carbonates. Under mild conditions, Electrosynthesis of a-Alkylidene cyclic carbonates from propargylic alcohols and carbon dioxide was studied in undivided cell. MeCN was electrochemically and reacted with propargylic alcohols and CO₂. The electrochemical reduction of MeCN resulted in MeCN radical anion(" MeCN). In the course of reaction, acetonitrile acted as not only the solvent but also the dehydrating reagent to eliminate the effect of the water produced from the reaction. The combined use of a catalytic amount of silver acetate efficiently catalyzed the incorporation of CO₂ under mild reaction conditions into propargylic alcohols to afford the corresponding cyclic carbonates in high-to-excellent yields. A plausible mechanism of electrosythesis a-Alkylidene cyclic carbonates in MeCN-TEABF₄ was proposed. The influences of the amount of silver acetate, electrolyte, supporting electrolytes, faradays permole of propargylic alcohols supplied to the electrode(Q), electric current and etc on the reaction using benzyl alcohol as the model compound was examined to optimize the synthetic conditions. The maximal yield is 99 % on Cu / C electrodes under a constant current of 17.3 mA cm^-2 until 2 F·mol^-1 of charge has passed through the cell. The selectivity of aryl ethyl carbonates was 100%.