The invention relates to the technical field of
chemical synthesis of pesticides, in particular to a preparation method of a key intermediate-3-
iodine-5, 5-dimethyl-4, 5-dihydroisoxazole of a high-efficiency herbicide pyroxasulfone, which comprises the following steps: by taking
glyoxylic acid and
hydroxylamine hydrochloride as initial raw materials, carrying out oximation reaction to obtain
glyoxylic acid oxime; then efficiently completing an
iodination reaction through a
potassium iodide /
iodine elementary substance
system under a mild condition, and controlling the reaction process to reduce the generation of byproducts so as to obtain high-purity diiodoformaldoxime; and finally, carrying out
addition reaction with isobutene under the condition of normal pressure to finally obtain the target product with high purity and high yield. The core innovation point of the invention is to develop and verify multiple types of novel iodination catalysts, solve the problems of excessive
iodine source, poor selectivity and long reaction period in the traditional
iodination reaction, and realize collaborative improvement of reaction efficiency, selectivity and economy. The method has the characteristics of more efficient
route, more controllable conditions,
safer operation, further improvement of yield and purity, higher cost
advantage and the like, and the industrial application value is remarkably enhanced.