The Synthesis Of Anisaldehyde Dimethyl Acetal By Indirect Electrochemical Oxidation

The traditional chemical synthesis method of anisaldehyde dimethyl acetal (p-MBDMA) which would produce environment pollution and economic burden, because of complex process, long reaction time and the using of strong oxidant. Instead, the electrochemical method greatly reduces the emissions of pollutants and the production cost. In addition, the simple process of electrochemical synthesis of p-MBDMA has good industrialization prospects.Firstly, a high performance liquid chromatography (HPLC) method for determination of the process of p-MBDMA electrochemical oxidation was established. The p-MBDMA that produced by direct electrochemical oxidation synthesis in the anhydrous system is easy to be hydrolyzed in water. The results indicated that p-MBDMA can be hydrolyzed to be anisaldehyde rapidly and completely in the acidic mixed solution of methanol, acetonitrile and water. So a HPLC method for determining p-MBDMA indirectly was built, which depends on the hydrolysis reaction of p-MBDMA. The best mobile phase of water- methanol-acetonitrile (5:3:2, V/V), pH= 3 adjusted by phosphoric acid was selected. The HPLC method that has been applied to the electrochemical synthesis of p-MBDMA, can determine the content of a few products simultaneously, accurately and reliably.Then the direct electro-oxidation behavior of anisole is studied by using linear sweep voltammetry (LSV) and galvanostatic electrolysis. The influence of factors such as supporting electrolyte, initial substrate concentration, current density, reaction temperature and so on was studied in the optimized capillary gap cell. In the capillary gap cell whose anodic and cathodic electrode staggered and electrode spacing was 1 mm. The experimental results showed that the optimum process condition is isostatic graphite as electrode materials, benzene sulfonate of 0.5%wt, initial anisole concentration of 0.5 mol·L-1 and current density of 3 A·dm-2, the reaction temperature of 40～50℃. The recovery rate of benzene sulfonate and methanol is 34.74～63.16% and 50.16～75.90%, respectively.Finally, the electrochemical behavior of KF-CH3OH system and anethole in the system was investigated by LSV, constant-potential electrolysis and galvanostatic electrolysis. The results showed that the oxidation peak attributes to CH3OH oxidation in the KF-CH3OH system whose peak current increased as the KF concentration and scan rate increase; The hydrogen bond between KF and CH3OH is benefit to form methoxy radical; The adsorption of F-on the graphite electrode surface is in favor of the direct electrochemical oxidation of anethole. Constant-potential electrolysis experiments were carried out in CH3OH with anode potential of 0.9 V. The experimental results showed that the directly electrochemical oxidation product of anethole was p-MBDMA. So the mechanism of anisole directly electrochemical oxidation to p-MBDMA was investigated in the KF-CH3OH system, which combines of the ECEC reactions and rearrangement reactions. The influence of factors such as supporting electrolyte content, initial substrate concentration, current density, reaction temperature and so on was studied in the optimized capillary gap cell. The experimental results showed that the optimum process condition is KF of 0.5%wt, anisole initial concentration of 0.8 mol-L" and current density of 3 A·dm-2, the reaction temperature of 30～40℃. This work provides a new synthesis method for p-MBDMA, and this method is simple, environmentally friendly, with the prospect of industrialization.