Electro Catalytic Carboxylation Of Aryl Imines In The Presence Of Carbon Dioxide

As entering into the21century, the greenhouse is recognized to be one of serious environmental problems. Carbon dioxide is the largest contribution to the greenhouse effect, which mainly result from the increasing consumption of fossil fuels such as coal, gas and oil. Carbon dioxide is also recognized to be a naturally abundant, cheap, recyclable and nontoxic building block in organic synthesis. To reduce the greenhouse effect, many efforts have been devoted to carbon dioxide fixation. Moreover, the conversion and utilization of carbon dioxide have been becoming more and more important from the ecological and economic points of view.In recent years, organic electrosynthesis has been recognized as a convenient, clean and ecofriendly synthetic technology. Organic electrosynthesis has received considerable attention in green chemcal applications as attactive alternatives to general organic sythesis because they exhibit many disirable prpperties, such as mild reaction condition, high selectivity, low pollution, low cost. In the bulk electrosynthesis, the substrate could be reduced or oxidized by getting or losing electrons, avoiding the use of other reducing agent and oxidant. Due to high chemical stability of carbon dioxide, electrochemical fixation of carbon dioxide is one of the effective way of carbon dioxide chemical fixation. Thereore, synthesis of some valuable chemicals has been devoted to the studies of the electrocarboxylation of several substrates, including unsaturated ketones, aldehydes, olefins, halides and amines under mild conditions.Amino acids are an important class of organic compounds which contain-NH2and-COOH group. Amino acids are wildly used as an elementary substrate to compose the necessary protein to biological movement. Traditionally, amino acids are synthesized via general organic reactions such as Gabriel reaction, Hell-Volhard-Zelinsky reaction or using propanedioic acid eater as the reactant. However, the synthetic procedures are comparatively complex, fussy and some reaction conditons are unfriendly. Drawing inspiration from generic electrocarboxylation, to make the production of amino acids by electrocarboxylation practical and commercial useful, it is desirable to develop a new and environmental method. The details are given as follows:(1) Electrocarboxylation of unsaturated methyl2-(benzyIideneamino)acetateThe electrochemical behavior of methyl2-(benzylideneamino)acetate has been studied in0.1mol.L-1TEABF4-DMF on GC electrode by cyclic voltammograms, showing a diffusion controlled irreversible reduction process. The electrocarboxylation reaction of methyl2-(benzylideneamino)acetate has been developed in the presence of carbon dioxide using magnesium as an anode in an undivided cell.2-phenylbut-2-enedioic acid dimethyl ester and amino acid derivatives were obtained under galvanostatic control. Furthermore, the influence of some operational factors was studied such as the nature of electrode materials, different supporting electrolytes, charge and current density. Under the optimized conditions, the carboxylic products were obtained to total yields (10.9%-31.6%). Based on cyclic voltammograms of methyl2-benzylideneamino acetate in the absence and precence of CO2and the electrolytic products, a possible electrocarboxylation mechanism was postulated in DMF under CO2atmosphere.(2) Electrocarboxylation of unsaturated methyl2-(4-methylbenzylideneamino) acetate to synthesized amino acid derivativesUnder mild conditions, electrocarboxylation of methyl2-(4-methylbenzylidene amino)acetate was carried out under galvanostatic control using0.1mol·L-1TEABF4-DMF saturated with CO2as solvent, Mg as a sacrificial anode in an undivided cell. Two classes of carboxylated products were abtained. And their yields were influenced by various operational conditions including the nature of electrode materials, different supporting electrolytes, charge and current density. Under the optimized conditions, the total carboxylation yields were up to18.4%.(3) Electrocarboxylation of unsaturated methyl2-(4-fluorobenzylideneamino) acetate to synthesized amino acid derivativesThe electrochemical behavior of methyl2-(4-fluorobenzylideneamino)acetate has been studied in0.1mol.L-1TEABF4-DMF on GC electrode by cyclic voltammetry. Two irreversible and well-resolved reduction processes were obtained. Compared with the cyclic voltammograms of methyl2-(4-methylbenzylideneamino) acetate, the second reduction peak potential is more negative. In an undivided cell, methyl2-(4-fluorobenzylideneamino)acetate was electrolysed to get the amino acid derivatives containing fluorine. Furthermore, the influence of some operational conditions were studied such as the nature of electrode materials, different supporting electrolytes, charge and current density. After a preliminary optimization, the total carboxylic yield of29.9%was obtained.