The Research On The Electrochemical Synthesis Of Ethylvanillin From Oxalic Acid

Ethylvanillin is a rare high-grade flavour needed to be synthesized.At present,ethylvanillin has mostly been prepared in the world by pyrochemical oxidation of condensation compound of o-ethoxyphenol and glyoxylic acid,which is of the problem that the catalysts such as cupric oxide were removed difficultly in the end. Preparing ethylvanillin by electrochemical oxidation is worthy of being studied for such advantages as no catalysts, easy control of reaction conditions, high selectivity, high productivity , little electric energy, without pollution, etc.3-Ethoxy-4-hydroxy mandelic acid was synthesized from o-ethoxyphenol and oxalic acid electrolyte which had been concentrated and filtrated before using.The single factor and orthogonal experiments were performed to determine the optimum condition:part sodium hydroxide solution drop with oxalic acid electrolyte, temperature 50 ℃, time 5h,sodium hydroxide concentration 2mol/L,the mol ratio of glyoxylic acid to o-ethoxypheol to sodium hydroxide 1.0:1.2:2.5 .On the optimum condition ,the maximum yield of 84.45% was obtained.Electro-oxidation of 3-ethoxy-4-hydroxy mandelic acid on platinum electrode was studied.Through the measurement of steady state polarization curves and cyclic voltammetry curves,the apparent activation energy was found to be 29³9kJ/mol,the exchange current density 0.00 l⁰.002mA/cm².The electro-oxidation reaction was confirmed to be an irreversible first order one.Poly o-toluidine(POT)-Cu²⁺ film electrode prepared on nickel matrix by cyclic voltammetry and soaking was of excellent catalytic activity to the reaction of electrochemical oxidation of 3-ethoxy-4-hydroxy mandelic acid and was of the merit of easy preparation,low cost and stable electrochemical performance.The electro-oxidation experiments of 3-ethoxy-4-hydroxy mandelic acid in one-room electrolytic bath were carried out according to the following conditions:POT-Cu²⁺ anode,nickel cathode,50℃,solution was the mixture of 0.5mol/L 3-ethoxy-4-hydroxy mandelic acid and 1.5mol/L sodium hydroxide,anodic electropotential 0.55V(vs.SCE),constant potential electrolysis lasted one hour.Ethylvanillin was obtained afer decarboxylation of the above electrolyte with 5.4mol/L H₂SO₄.During the process of electrolysis, conversion was 61.85%, yield 89.47% and current efficiency 95.70% compared with that conversion 39.35%, yield 77.47% and current...