| The indirect electrooxidation synthesis is mainly employed on the preparation of benzaldehyde in this paper. In electrochemical process, Pb is used as electrode material, and the area of cathode and anode has a relation of 1:5. Super saturation solution of MnSO4 is used as reactant liquid. By comparing the curve of cyclic voltammograms and the linear scan obtained at the three-electrode system, the reaction processes are illustrated. Based on this, ultrasonic wave has been introduced firstly as energy source instead of stirring in the reaction. By comparing the curve of linear scan and the cyclic voltammograms obtained from stirring with those obtained in the presence of ultrasound, it can be seen that, at the same current, electrolysis potential of the former is lower than that of the latter, which demonstrates that the former consumes less energy. According to the cyclic voltammograms of the former, approximate potential and current needed to electrolyze electrolyte of certain concentration has been obtained. Applying two-electrode system, at the acidic condition,oxidative solution of Mn3+containing a little of MnO2 can be obtained by galvanostatic electrolysis of Mn2+, then mix it with toluene into a airtight glass conical flask and in the presence of ultrasonic wave. Toluene will be oxidized to benzaldehyde.The paper consists of two parts, as follows:1. Preparation of benzaldehyde by ultrasonic indirectelectrooxidation(1). The preparation of oxidative liquid by electrolyzingin the presence of ultrasonic wave.In this part, oxidative liquid is prepared though indirect electrolysis coupled with ultrasonic wave. And the effect on conversation of oxidative liquid and current efficiency is studied due to concentration of H2SO4 and MnSO4, electrolytic current, ultrasonic power, and reaction time at the room temperature. Furthermore, best conditions of the reaction are founded: concentration of H2SO4 is 5. 4mol/L; concentration of MnSO4 is 0. 315mol/L; electrolytic current is 0. 7A, ultrasonic power is 250Wx80%, reaction time is 4000s. On these conditions, conversation of oxidative liquid reaches to 98.41% and current efficiency to 80.21%.Meanwhile, the processes and results by stirring is contrasted with that by ultrasound, concluding that results obtained by applying power ultrasonic are not necessarily better than that by stirring at any value, but a best power value of 250WX80% existed. The ultimateeffect of electrolysis at this power is much better than that by stirring. More experiments have been undertaken in various conditions such as applying ultrasonic wave only, coupling ultrasonic wave to stirring, puffing gas at high pressure with ultrasonic wave, none of which has a better effect than stirring only. (2). Preparation of benzaldehyde by oxidizing toluene.In the presence of ultrasonic wave, using the oxidative liquid derived from last step to oxidize toluene, therefore benzaldehyde is achieved. By investigating the factors such as ultrasonic power, mole ratio of oxidative liquid and toluene, reacting temperature and acidity, the best condition is achieved: ultrasonic power, 250WX80%; mole ratio, 4. 5:1; reacting temperature, 60oC; acidity, 6. 2mol/L; which results in the least reacting time of 1.0 hour and benzaldehyde conversation of 85-95%. Compared to stirring, ultrasonic wave has a better effect and a shorter time but similar receiving rate.HPLC is employed to analyze benzaldehyde and quantify its content. Chromatography conditions are column temperature 35C; methanol as mobile phase; UV detection wavelength 245nm; flow rate 1.0ml/min. 2. Electrolyte' s recyclingMn(II) ion achieved at first step can be reused by adjusting acidity. After being completed repeatedly about 20 times, current efficiency decreases by 3% nearly, which is much smaller than that when using mechanicalstirring.
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