Study On The Synthesis Of 1, 3-Benzodioxoles And Dimethoxypropane

1,3-Benzodioxoles, which have been reported in many patents recently, are important intermediates used in pesticide-synthesizing process. 2,2-Dimethyl-4-hydroxy-l,3-benzodioxole, a benzodioxole synthesized by condensation reaction of pyrogallol and acetone, is a intermediate of pesticide carbamate commended by WHO.Two steps lead to the formation of benzodioxoles: firstly, and most importantly the synthesis of 2,2-dimethoxy propane; secondly, the exchanging reaction of 2,2-dimethoxypropane and pyrogallol. Various methods including indirective two-step synthesis , freezing-drying and catalytic rectification were used to synthesize 2,2-dimethoxypropane.1.In indirective two-step synthesis way, the yield in the condensation reaction was high. The influences of reaction temperature, reaction time, the type and amount of water carrying agent, catalysts and the ratio of reactants on the reaction were investigated. The influence of catalysts on the exchanging reaction was investigated too. However, due to the low yield and too many byproducts, this method could not be applied to industrial production.2.In freezing-drying method, the influences of drying efficiency and amount of drying agent, reaction time, reaction temperature and ratio of reactants on the reaction were investigated. Results showed that 3A molecular sieves was ideal drying agent. Larger amount of drying agent ,lower temperature, and higher ratio methanol would resulted in higher conversion.3.In catalytic rectification method, methanol and acetone flowed through the catalytic bed, when the molar ratio of methanol to acetone increased, the yield of 2,2-dimethoxypropane increased. Also the yield increased with the lower bed temperature, when the rectificationcolumn temperature was 56.5 ℃,the yield reached the highest.however, -10 ℃ was the optimum temperature when cost and energy consumption were taken into consideration. The content of main product increased when methanol was added into the system more rapidly.4.1n the exchanging reaction of 2,2-dimethoxypropane and pyrogallol, the optimum reaction mode was mixing all the pyrogallol with certain amount of DMP. In the procession of reaction , DMP was added to the system continuously and methanol was distilled out.Under temperature 125℃, 800ml solvent xylene was add to the system per mole pyrogallol. When the ratio of DMP/pyrogallol was more than 3, pyrogallol converted completely. Certain amount of acetone (40%) in the system had no apparent effect on the reaction, while same amount of methanol was not beneficial for the higher conversion and yield. 2-Methoxypropene was found to be the effective reactant instead of dimethoxypropane the first time.In conclusion, higher yield and convenience of manipulation could be obtained in the preparation of 2,2-dimethoxypropane by the catalytic rectification method, the same effect could be obtained for the final product by the exchanging reaction . Both of them availed the pesticide's synthesis.