Oxidation Of Benzyl Alcohol And Toluene To Benzaldehyde By Manganese Compounds Series With On-Line Ultrasound

As an important species of organic compound, benzaldehyde was widely used in synthesis of many kinds of chemicals, such as pharmaceuticals, spiceries, cosmetics, dyes, pesticide, etc. Studying theoretically and practically on the methods for its preparation has been all along a significant project for the chemist, since it has both good economic benefits and high academic values.At present, green reaction, small equipment, integrated process is the development trend of chemical and chemical industry. The development of safe, clean and efficient production process has become an urgent task of chemistry and chemical industry. Ultrasound imposed on chemical reactions could speed up chemical reactions and strengthen the process, so this was one of the most promising method.In this paper, benzaldehyde was prepared with benzyl alcohol and toluene as substrate, manganese compounds series as oxidant, using the traditional chemical methods under ultrasound. The yield of the target product benzaldehyde was studied at the same time. The oxidation process of toluene was a series of reactions, so it was essential of selecting highly selective oxidant for the preparation of benzaldehyde. The purpose of this study was to find a suitable oxidant and to prepare the target product benzaldehyde.At first, benzaldehyde was prepared with benzyl alcohol as substrate by potassium permanganate with manganese dioxide as supporting reagent under heterogeneous and ultrasonic conditions. And the influence of oxidants' constitution, ultrasonic frequency and reaction time on benzyl alcohol's transformation efficiency and benzaldehyde's selectivity and yield was discussed. Meanwhile the different stirring means, ultrasound and magnetic stirring was compared. The results indicated that benzyl alcohol's transformation efficiency and benzaldehyde's selectivity and yield was 96.09%,98.50% and 94.64% respectivly with potassium permanganate as oxidant, manganese dioxide as supporting reagent and the quality ratio of them 1:3, ultrasonic frequency 40KHz and reaction time 1.5h. The result was satisfactory. Meanwhile, the test results showed that the yield of target product benzaldehyde can be improved notably by exerting ultrasound. The solid-product MnO₂ was the same as the supporting reagent, so there's no need for purification , the recycling of the product was very easy. This method featured with simple operation, rapid reaction, high selectivity, little by-product, together with high yield of the target product.Secondly, the oxidation of toluene to benzaldehyde was studied by different manganese oxidants under ultrasonic radiation and free solvent conditions. And the best reaction conditions were determined by single-factor test and orthogonal experiments. The following conclusions arrived: 1. Manganese dioxide, potassium permanganate, potassium permanganate supported on manganese dioxide (AR) and self-manganese complex salt were employed for oxidizing toluene to benzaldehyde. The results show that the last one had best results. 2. The best reaction conditions were determined as follows by the orthogonal experiments: ultrasonic frequency was 25 kHz, reaction temperature was 70℃and the reaction time was about 5 hours. 3. Free solvent condition could improve the rate and selectivity of the oxidation. Meanwhile, it featured with warm reaction condition, short reaction time and easy separation of the product.Thirdly, the Mn³⁺ solution with good stability was acquired, under the condition of KMnO₄ and MnSO₄ as material, certain concentration of H₂SO₄ and homogeneous oxidation. Under ultrasound benzaldehyde was prepared by selective oxidation of toluene with the above solution as oxidant. And correlative factor on the stability of Mn³⁺ solution and the yield of benzaldehyde was discussed. Results showed that the Mn³⁺ solution with high concentration and good stability was obtained when the concentration of H₂SO₄ was 4.0 mol/L and molar ratio of KMnO₄ and MnSO₄ was 1:12. Meanwhile, selective oxidation of toluene was promoted and high yield of benzaldehyde was obtained with ultrasound 175W+59KHz, reaction temperature 60℃, molar ratio of toluene and Mn³⁺ 4:1 and H₂SO₄ 7.0 mol/L.