The preparation method of pyrazoxazole intermediate

Abstract

The invention discloses a preparation method of metazafenazole intermediate, which uses glyoxylic acid as a starting material, first carries out condensation reaction with hydroxylamine to generate 2‑(hydroxyimino)acetic acid; and then reacts sodium bromate and In the presence of sodium bisulfite, the bromination reaction is carried out to generate dibromoformaldoxime; finally, the cyclization reaction with isobutylene is carried out to generate the intermediate 3-bromo-5,5-dimethyl-4,5-di Hydroisoxazole; wherein, the bromination reaction temperature is 10-60°C, and the molar ratios of glyoxylic acid, sodium bromate and sodium bisulfite are 1:2-1:4. The method of the present invention releases bromine slowly through the reaction of sodium bromate and sodium bisulfite, the reaction is relatively mild, the reaction is easy to control, and by-products are not easily produced, and the product generated by feeding isobutene does not need rectification to remove impurities, and the yield is relatively high .

Description

technical field [0001] The invention belongs to the technical field of preparation of herbicide intermediates, and in particular relates to a preparation method of the intermediate 3-bromo-5,5-dimethyl-4,5-dihydroisoxazole of pyrazafen. Background technique [0002] Pyroxasulfone is an isoxazole herbicide with the chemical name 3-[5-(difluoromethoxy)-1-methyl-3-(trifluoromethyl)pyrazole-4 -ylmethylsulfonyl]-4,5-dihydro-5,5-dimethyl-1,2-isoxazole, the molecular formula is C 12 h 14 f 5 N 3 o 4 S, the molecular weight is 391.32, and the CAS accession number is 447399-55-5. Metraclofenazole is mainly used as a pre-emergence sealing treatment agent, supplemented by blocking broad-leaved grasses, which are mainly grasses, and has many advantages: it is suitable for a wide range of crops, and can be used for wheat, corn, peanuts, rice, soybeans, cotton and other crops; It is safe for the environment, and it is safe for the current crops and the next crops; the effective peri...

AI Technical Summary

Problems solved by technology

[0007] The disadvantages of this method are: (1) the bromination reaction needs to adjust the pH value with sodium bicarbonate while adding liquid bromine dropwise, and impurities will be generated when the pH value is too high or too low, which makes the bromination reaction more difficult to control, and the product Both the purity and the reaction yield are unsatisfactory; (2) carbon dioxide is also produced during the addition of sodium bicarbonate, and carbon dioxide is easy to bring out a large amount of liquid bromine, which is not only environmentally unfriendly, but also has poor safety and is not suitable for industrial production ; (3) The final product has more impurities, which need to be removed by rectification, resulting in a lower yield