Process For Aryl Halide Intermediates Based On Diazonium Salts

This thesis deals with development of process for highly selective synthesis of key intermediates of pesticides, such as 3,5-dichloroaniline and 2,3-dichloropyridine and its derivatives, based on the Sandmeyer chlorinated reaction or reduction reaction of aryl diazonium salts.Firstly, a process for the key intermediate of Chlorantraniliprole,2,3-dichloropyridine, has been developed through the Hoffman degradation, chlorination, diazotization and Sandmeyer reaction from niacinamide. The reaction conditions was optimized and the target product 2,3-dichloropyridine could be obtained in 63% overall yield with> 95% purity. The chlorination, diazotization and Sandmeyer reaction steps in this process could be conducted in one-pot manner from the 3-amino pyridine. In addition, a similar process starting from 2-amino pyridine to synthesize 2,3-dichloropyridine was also explored to afford 2,3-dichloropyridine in 45% yield. This preliminary result showed that a more economic process could be possible from the cheap starting material of 2-amino pyridine. Synthesis of the advanced intermediates of 2-Hydrazino-3-chloro-pyridine and 1-(3-chloro-2-pyridyl)-3-pyrazolidone-5-carboxylate of Chlorantraniliprole from 2,3-dichloropyridine was also explored.Secondly, a process for 3,5-dichloroaniline from 4-nitroaniline through chlorination, deamination by diazotization and hydrogen replacement of the diazo group, followed by reduction of nitro group. The reaction conditions was optimized and the target product 3,5-dichloroaniline could be obtained in 84% overall yield via one-pot reaction of chlorination, diazotization and deamination by hydrogen replacement of the diazo group.