Dichloroacetyl chloride is an important intermediate in the production of insecticides and herbicides, and is also widely used in the field of auxiliaries and pharmaceutical synthesis. The main synthesis methods are dichloroacetate acyl chloride method and trichloroethylene oxidation method. The latter is to put trichloroethylene in an acid-resistant autoclase, add a certain amount of azo compounds or peroxide catalysts, at 110℃,0.6~1.0MPa through oxygen reaction for 10hr, and then fractionation to obtain a purity of 95~97% of the product. So far, domestic manufacturers have been using this synthetic route, and there are generally disadvantages such as complicated processes, high equipment requirements and poor product quality. At present, the synthesis of dichloroacetyl chloride by photocatalytic air oxidation process has been used in large-scale industrial production abroad, and products with purity greater than 99% are directly obtained (3~5). Therefore, it is of practical significance to conduct in-depth research and discussion on this technology.
When trichloroethylene is oxidized with oxygen or air, the product varies due to the different sides of the catalyst used, such as the use of Lewis acid as the catalyst, the main product is chloral; If the peroxide is used as the catalyst, the product is a small amount of low molecular polymer, and the use of ultraviolet catalysis, without any separation process can get a high quality product.
Dichloroacetyl chloride is easily hydrolyzed, and its hydrolyzed products are dichloroacetic acid and hydrogen chloride. If the air is not dry or not dry completely, the reaction speed and the quality of the final product will be seriously affected. After the reaction at 70℃ for 20 hours, the content of dichloroacetic acid in the mixture was 16.2%, and 25% of trichloroethylene remained unreacted. Therefore, in the reaction process, the air should be ensured to be adequately dehumidified.
Conclusion The synthesis of dichloroacetyl chloride by photocatalytic air oxidation is relatively simple and the product quality is good. The domestic has been able to solve the problem of high power ultraviolet light source for industrial production, such as the process to industrial scale, will reduce the cost, increase the international competitiveness of the product.
