阅读说明：本技术 一种3-溴-5,5-二甲基-4,5-二氢异噁唑的合成方法 (Synthetic method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole ) 是由 姜正成 姜正金 于 2021-10-14 设计创作，主要内容包括：本发明公开了一种3-溴-5,5-二甲基-4,5-二氢异噁唑的合成方法,包括中间体二溴甲醛肟的连续合成及产物3-溴-5,5-二甲基-4,5-二氢异噁唑的合成。本发明通过对生产路线的改进,首先通过乙醛酸和盐酸羟胺经脱水缩合,得到的中间体无须出料,直接加入溴化试剂,在催化剂存在下一锅法反应生成二溴甲醛肟,再经溴化、1,3-偶极环加成反应生成目标产物,本发明通过对每个步骤不同条件的筛选,能够实现整个生产路线过程中目标产物整体收率的提高,降低副产物和三废的生成,还能够实现溶剂的回收再利用,中间产物乙醛酸肟无须出料减少了损失,操作简便,且整个过程所用原料和溶剂价格低,有利于控制成本,非常适合工业化生产。(The invention discloses a method for synthesizing 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole, which comprises the continuous synthesis of an intermediate dibromoformaldehyde oxime and the synthesis of a product 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole. According to the invention, through improvement on a production route, firstly, glyoxylic acid and hydroxylamine hydrochloride are subjected to dehydration condensation, an obtained intermediate does not need to be discharged, a bromination reagent is directly added, the one-pot reaction is carried out in the presence of a catalyst to generate dibromoformaldoxime, and then bromination and 1, 3-dipolar cycloaddition reaction are carried out to generate a target product.)

1. A synthetic method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole is characterized by comprising the following steps:

(1) continuous synthesis of dibromoformaldehyde oxime

At room temperature, performing dehydration condensation reaction on a glyoxylic acid solution and hydroxylamine hydrochloride, directly adding a catalyst and a brominating reagent in a system after the reaction is finished, performing a Hensbach-like reaction in the presence of the catalyst, and performing post-treatment after the reaction is finished to obtain dibromoformaldehyde oxime;

(2) synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

In an organic solvent, reacting the dibromoformaldehyde oxime obtained in the step (1) under an alkaline condition to generate a nitrile oxide intermediate, and performing 1, 3-dipolar cycloaddition reaction on the nitrile oxide intermediate and isobutene to generate the target compound 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole.

2. The synthesis method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the mass concentration of glyoxylic acid used in step (1) is 5-50%, and the molar ratio of glyoxylic acid to hydroxylamine hydrochloride is 1: 1-1.5, preferably 1: 1.

3. the synthesis method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the dehydration condensation reaction time in step (1) is 5-24 hours, and the temperature is-10-50 ℃, preferably 25 ℃.

4. The method for synthesizing 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the catalyst in step (1) is at least one of ZSM-5 molecular sieve, tributylmethylammonium chloride, MCM-41 mesoporous molecular sieve, MCM-22 catalyst, SBA-15 molecular sieve and SAPO-11.

5. The synthesis method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the brominating agent in step (1) is at least one of N-bromosuccinimide, liquid bromine, 1, 3-dibromo-5, 5-dimethylhydantoin, preferably liquid bromine, and the molar ratio of glyoxylic acid to brominating agent is 1: 1.5-2, preferably 1: 1.8; the brominating reagent is added in an ice-water bath condition when dripping is performed, and the reaction is performed at room temperature after dripping is completed.

6. The synthesis method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the post-treatment process in step (1) is to add an extractant for extraction, concentrate the organic phase to dryness, and recrystallize the obtained solid with a purification reagent, wherein the extractant is dichloromethane, ethyl acetate, petroleum ether, n-hexane, tetrahydrofuran or toluene, preferably dichloromethane; the adopted purification reagent is at least one of n-hexane, n-heptane, ethyl acetate, petroleum ether, diethyl ether and methyl tert-butyl ether.

7. The method for synthesizing 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the organic solvent in step (2) is at least one of methyl tert-butyl ether, ethyl acetate, dichloromethane, dichloroethane, toluene, tetrahydrofuran and dimethylformamide.

8. The method for synthesizing 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the alkaline substance used in step (2) is at least one reagent selected from sodium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

9. The synthesis method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the reaction temperature in step (2) is-30 ℃ to 50 ℃.

10. The synthesis method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole according to claim 1, characterized in that the molar ratio of dibromoformaldoxime to isobutylene in step (2) is 1: 2-2.5, preferably 1: 2.

Technical Field

The invention relates to the technical field of organic chemical synthesis, in particular to a synthetic method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole.

Background

Isoxazole compounds are a very valuable class of organic compounds, and because of the N, O heteroatom contained in the isoxazole ring, the molecule has three carbon atoms, and groups which can cause molecular diversity can be introduced. Due to the unique structure and biological activity of isoxazole and derivatives thereof, the isoxazole and the derivatives thereof have important significance in the fields of organic synthesis, drug development, pesticide development, catalytic reaction, electrochemistry and the like, and some isoxazole compounds such as 3, 5-disubstituted isoxazole provide effective and convenient ways for synthesizing various compounds such as lead drugs, bactericides, herbicides, pesticides and the like. Therefore, the method has very important significance for quickly, simply and efficiently synthesizing the 3, 5-disubstituted isoxazole compounds.

International patent publication No. WO2006038657a1 discloses a method for synthesizing 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole using dibromoformaldoxime and isobutylene as raw materials and isopropyl ether as a solvent, wherein the isopropyl ether solvent used in the method is not suitable for industrial production due to high price, instability in light and air, easy formation of peroxide, low safety coefficient and the like; for the synthesis of the raw material dibromoformaldehyde oxime, the prior literature reports that the dibromoformaldehyde oxime is prepared by an indirect method, such as J. org. chem. 1990,55, 3045. 3051 and chem. Commun. 2010, 46, 8475. 8477 reports that the dibromoformaldehyde oxime and bromine are generated by reaction, the yield is 47% and 76% respectively, but the glyoxylic acid oxime has the defects of easy water absorption, large separation and purification loss in the preparation process, difficult long-time storage and the like, so that the total yield is lowered; there are also patents disclosing the use of a continuous process for the preparation of the raw material dibromoformaldehyde oxime such as WO2000006083, WO2006129199, WO2010127978, reacting glyoxylic acid aqueous solution with hydroxylamine hydrochloride for a period of time and then directly adding alkali to the system, and then slowly adding bromine to prepare the dibromoformaldehyde oxime, the reaction does not require discharging, but the yields are 28%, 18%, 22%, respectively, the yield is low, and the process is not suitable for industrial production.

Disclosure of Invention

Aiming at the problems in the prior art, the invention aims to provide a rapid, simple and continuous synthesis method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole, namely, the method uses cheap raw materials and solvents to react in the presence of a catalyst, the reaction process is easy to control, glyoxylic acid oxime does not need to be discharged in the reaction, so the loss is avoided, and the post-treatment is simple; by adding the catalyst, the yield of the dibromoformaldehyde oxime is improved, and the catalyst can be recycled, so that the cost is reduced; therefore, the method provided by the invention has the advantages of high overall yield, less environmental pollution, convenience in operation and the like, and is suitable for industrial production.

In order to achieve the purpose, the invention adopts the following technical scheme:

the invention discloses a synthesis method of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole, which is characterized by comprising the following steps:

(1) continuous synthesis of dibromoformaldehyde oxime

At room temperature, performing dehydration condensation reaction on a glyoxylic acid solution and hydroxylamine hydrochloride, directly adding a catalyst and a brominating agent into a system after the reaction is finished, performing Hensbach-like reaction in the presence of the catalyst, and performing post-treatment after the reaction is finished to obtain dibromoformaldehyde oxime, wherein the reaction equation is shown as follows:

；

(2) synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

In an organic solvent, reacting the dibromoformaldehyde oxime obtained in the step (1) under an alkaline condition to generate a nitrile oxide intermediate, and performing 1, 3-dipolar cycloaddition reaction on the nitrile oxide intermediate and isobutene to generate a target compound, namely 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole, wherein the reaction equation is as follows:

。

further, the invention also limits the mass concentration of the glyoxylic acid used in the step (1) to be 5-50%, and the molar ratio of the glyoxylic acid to the hydroxylamine hydrochloride to be 1: 1-1.5, preferably 1: 1.

further, the present invention also defines the dehydration condensation reaction time in the step (1) to be 5 to 24 hours, and the temperature to be-10 to 50 ℃, preferably 25 ℃.

Furthermore, the invention also limits the catalyst in the step (1) to be at least one of ZSM-5 molecular sieve, tributylmethylammonium chloride, MCM-41 mesoporous molecular sieve, MCM-22 catalyst, SBA-15 molecular sieve and SAPO-11.

Further, the invention also defines that the brominating reagent in the step (1) is at least one of N-bromosuccinimide, liquid bromine and 1, 3-dibromo-5, 5-dimethylhydantoin, preferably liquid bromine, and the molar ratio of glyoxylic acid to brominating reagent is 1: 1.5-2, preferably 1: 1.8; the brominating reagent is added in an ice-water bath condition when dripping is performed, and the reaction is performed at room temperature after dripping is completed.

Further, the invention also defines the post-treatment process in the step (1) as adding an extracting agent for extraction, concentrating the organic phase to dryness, and recrystallizing the obtained solid by using a purification reagent, wherein the extracting agent is dichloromethane, ethyl acetate, petroleum ether, n-hexane, tetrahydrofuran or toluene, preferably dichloromethane; the adopted purification reagent is at least one of n-hexane, n-heptane, ethyl acetate, petroleum ether, diethyl ether and methyl tert-butyl ether.

Further, the invention also defines that the organic solvent in the step (2) is at least one of methyl tert-butyl ether, ethyl acetate, dichloromethane, dichloroethane, toluene, tetrahydrofuran and dimethylformamide.

Further, the invention also limits that the alkaline substance adopted in the step (2) is at least one reagent of sodium hydroxide, sodium bicarbonate, potassium bicarbonate, sodium carbonate, potassium carbonate, dipotassium hydrogen phosphate and potassium dihydrogen phosphate.

Furthermore, the invention also limits the reaction temperature in the step (2) to be-30-50 ℃, and the nitrile oxide intermediate is generated under the alkaline condition to illustrate the reaction mechanism, which is equivalent to the starting of the reaction.

Further, the invention also defines that the mol ratio of the dibromoformaldoxime to the isobutene in the step (2) is 1: 2-2.5, preferably 1: 2.

compared with the prior art, the invention has the following excellent beneficial effects:

the invention provides a method for quickly synthesizing 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole by improving a production route, firstly, glyoxylic acid and hydroxylamine hydrochloride are dehydrated and condensed to obtain an intermediate, a brominating reagent is directly added without discharging, the intermediate is reacted in a one-pot method in the presence of a catalyst to generate dibromoformaldehyde oxime, and then the dibromoformaldehyde oxime is brominated and subjected to 1, 3-dipolar cycloaddition reaction to generate a target product. Is very suitable for industrial production.

Drawings

FIG. 1 shows the preparation of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole¹HNMR spectrogram;

FIG. 2 is a schematic representation of the product 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole¹³CNMR spectrogram.

Detailed Description

The technical features of the technical solutions provided by the present invention are further clearly and completely described below with reference to the embodiments, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.

EXAMPLE 13 Synthesis of bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

(1) Synthesis of dibromoformaldoxime

Adding 74g (0.5 mol) of 50% glyoxylic acid solution into 111ml of water to prepare a 20% glyoxylic acid solution, mixing the glyoxylic acid solution with 34.75g (0.5 mol, 1 eq) of hydroxylamine hydrochloride at room temperature, fully stirring for 12 hours, adding 1g of SBA-15 molecular sieve catalyst, dropwise adding 50ml (0.9 mol) of liquid bromine in an ice water bath, removing the ice water bath after dropwise adding, continuing to react for 3 hours, adding 250ml of dichloromethane after the reaction is finished, extracting, concentrating to be dry, recrystallizing the obtained solid by using n-hexane to obtain 71.85g of white solid, namely dibromoformaldehyde oxime, wherein the yield is 70.85%;

(2) synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

50.71g (0.25 mol) of dibromoformaldoxime prepared in the step (1) is dissolved in 100ml of ethyl acetate to prepare a solution; dissolving 25g of sodium bicarbonate in 100ml of water, adding 500ml of ethyl acetate, introducing 28.1g (0.5 mol) of isobutene gas in an ice-water bath, dropwise adding the prepared ethyl dibromoformaldoxime acetate solution at 0-8 ℃ in the dropwise adding process, fully reacting for 2 hours in the ice-water bath after the dropwise adding is finished, stirring for 3 hours at room temperature, separating an organic phase, drying with anhydrous sodium sulfate, concentrating under reduced pressure to obtain a light yellow liquid, distilling and purifying to obtain 39.4g of colorless transparent liquid with the yield of 88.54 percent, wherein a hydrogen spectrum chart and a carbon spectrum chart of the product are shown in figures 1 and 2,

¹H-NMR (500 MHz, CDCl₃) δ 2.94 (s, 2H), 1.42 (s, 6H)；

¹³C-NMR (126 MHz, CDCl₃) δ 136.25, 86.29, 52.98, 27.04。

example 23 Synthesis of bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

(1) Synthesis of dibromoformaldoxime

Mixing 74g (0.5 mol) of 50% glyoxylic acid solution with 34.75g (0.5 mol, 1 eq) of hydroxylamine hydrochloride at room temperature, fully stirring for 12 hours, adding 1g of ZSM-5 molecular sieve catalyst, dropwise adding 50ml (0.9 mol) of liquid bromine in an ice water bath, removing the ice water bath after dropwise adding is finished, reacting for 3 hours, stopping the reaction, extracting with 250ml of dichloromethane, concentrating to be dry, recrystallizing the obtained solid with n-hexane to obtain 65.32g of white solid, namely dibromomethylaldoxime, wherein the yield is 64.42%;

(2) synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

50.71g (0.25 mol) of dibromoformaldoxime produced in step (1) were dissolved in 100ml of tetrahydrofuran to prepare a solution. Dissolving 25g of sodium bicarbonate in 100ml of water, adding 500ml of tetrahydrofuran, introducing 28.1g (0.5 mol) of isobutene gas in an ice-water bath, dropwise adding the prepared dibromoformaldoxime tetrahydrofuran solution after the completion of the dropwise adding process, controlling the temperature to be 0-8 ℃, fully reacting for 2 hours in the ice-water bath after the completion of the dropwise adding process, stirring for 4 hours at room temperature, separating an organic phase, drying with anhydrous sodium sulfate, concentrating under reduced pressure to obtain a light yellow liquid, and distilling and purifying to obtain 35.76g of colorless transparent liquid, wherein the yield is 80.36%.

Example 33 Synthesis of bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

(1) Synthesis of dibromoformaldoxime

Adding 74g (0.5 mol) of 50% glyoxylic acid solution into 111ml of water to prepare a 20% glyoxylic acid solution, mixing the glyoxylic acid solution with 34.75g (0.5 mol, 1 eq) of hydroxylamine hydrochloride at room temperature, fully stirring for 12 hours, adding 1g of ZSM-5 molecular sieve catalyst, dropwise adding 50ml (0.9 mol) of liquid bromine under an ice water bath, and removing the ice water bath after dropwise adding to react for 3 hours. Stopping the reaction, extracting with 250ml of dichloromethane, concentrating to dryness, recrystallizing the obtained solid with diethyl ether to obtain 67.32g of white solid, namely dibromoformaldehyde oxime with the yield of 66.39%;

(2) synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

50.71g (0.25 mol) of dibromoformaldoxime produced in step (1) were dissolved in 100ml of methylene chloride to prepare a solution. Dissolving 25g of sodium bicarbonate in 100ml of water, adding 500ml of dichloromethane, introducing 28.1g (0.5 mol) of isobutene gas in an ice-water bath, dropwise adding the prepared dibromoformaldoxime dichloromethane solution after the completion of the dropwise adding process, controlling the temperature to be 0-8 ℃, fully reacting for 2 hours in the ice-water bath after the completion of the dropwise adding process, stirring for 3 hours at room temperature, separating an organic phase, drying with anhydrous sodium sulfate, concentrating under reduced pressure to obtain a light yellow liquid, and distilling and purifying to obtain 30.72g of colorless transparent liquid with the yield of 69.03%.

Example 4

Synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

(1) Synthesis of dibromoformaldoxime

Adding 74g (0.5 mol) of 50% glyoxylic acid solution into 111ml of water to prepare a 20% glyoxylic acid solution, mixing the glyoxylic acid solution with 34.75g (0.5 mol, 1 eq) of hydroxylamine hydrochloride at room temperature, fully stirring for 12 hours, adding 1g of ZSM-5 molecular sieve catalyst, dropwise adding 55.6ml (1 mol) of liquid bromine in an ice-water bath, and removing the ice-water bath after dropwise adding to react for 3 hours. Stopping the reaction, extracting with 250ml of dichloromethane, concentrating to dryness, recrystallizing the obtained solid with n-hexane to obtain 67.41g of white solid, namely dibromoformaldehyde oxime with the yield of 66.48%;

(2) synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

50.71g (0.25 mol) of dibromoformaldoxime produced in step (1) was dissolved in 100ml of toluene to prepare a solution. Dissolving 25g of sodium bicarbonate in 100ml of water, adding 500ml of toluene, introducing 28.1g (0.5 mol) of isobutene gas in an ice-water bath, dropwise adding the prepared dibromoformaldehyde oxime toluene solution after the completion of the dropwise adding process, controlling the temperature to be 0-8 ℃, fully reacting for 2 hours in the ice-water bath after the completion of the dropwise adding process, stirring for 3 hours at room temperature, separating an organic phase, drying with anhydrous sodium sulfate, concentrating under reduced pressure to obtain a light yellow liquid, and distilling and purifying to obtain 31.5g of colorless transparent liquid, wherein the yield is 70.79%.

Example 5

Synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

(1) Synthesis of dibromoformaldoxime

Adding 74g (0.5 mol) of 50% glyoxylic acid solution into 111ml of water to prepare a 20% glyoxylic acid solution, mixing the glyoxylic acid solution with 34.75g (0.5 mol, 1 eq) of hydroxylamine hydrochloride at room temperature, fully stirring for 12 hours, adding 1g of ZSM-5 molecular sieve catalyst, dropwise adding 50ml (0.9 mol) of liquid bromine under an ice water bath, and removing the ice water bath after dropwise adding to react for 3 hours. Stopping the reaction, extracting with 250ml of dichloromethane, concentrating to dryness, recrystallizing the obtained solid with n-hexane to obtain 61.15g of white solid, namely dibromoformaldehyde oxime with the yield of 60.31%;

(2) synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

50.71g (0.25 mol) of dibromoformaldoxime produced in step (1) were dissolved in 100ml of methyl t-butyl ether to prepare a solution. Dissolving 25g of sodium bicarbonate in 100ml of water, adding 500ml of methyl tert-butyl ether, introducing 28.1g (0.5 mol) of isobutene gas in an ice-water bath, dropwise adding the prepared dibromoformaldoxime methyl tert-butyl ether solution at 0-8 ℃ in the dropwise adding process, fully reacting for 2 hours in the ice-water bath after the dropwise adding is finished, stirring for 3 hours at room temperature, separating an organic phase, drying with anhydrous sodium sulfate, concentrating under reduced pressure to obtain a light yellow liquid, and distilling and purifying to obtain 33.47g of colorless transparent liquid with the yield of 75.21%.

Example 6

Synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

(1) Synthesis of dibromoformaldoxime

Adding 74g (0.5 mol) of 50% glyoxylic acid solution into 111ml of water to prepare a 20% glyoxylic acid solution, mixing the glyoxylic acid solution with 34.75g (0.5 mol, 1 eq) of hydroxylamine hydrochloride at room temperature, fully stirring for 8 hours, adding 1g of ZSM-5 molecular sieve catalyst, dropwise adding 50ml (0.9 mol) of liquid bromine under an ice water bath, and removing the ice water bath after dropwise adding to react for 3 hours. Stopping the reaction, extracting with 250ml of dichloromethane, concentrating to dryness, recrystallizing the obtained solid with n-hexane to obtain 66.28g of white solid, namely dibromoformaldehyde oxime with the yield of 65.11%;

(2) synthesis of 3-bromo-5, 5-dimethyl-4, 5-dihydroisoxazole

50.71g (0.25 mol) of dibromoformaldoxime produced in step (1) was dissolved in 100ml of ethyl acetate to prepare a solution. Dissolving 25g of sodium bicarbonate in 100ml of water, adding 500ml of ethyl acetate, introducing 28.1g (0.5 mol) of isobutene gas in an ice-water bath, dropwise adding the prepared ethyl dibromoformaldoxime acetate solution at 0-8 ℃ in the dropwise adding process, removing the ice-water bath after the dropwise adding is finished, stirring for 5 hours at room temperature, separating an organic phase, drying with anhydrous sodium sulfate, concentrating under reduced pressure to obtain a light yellow liquid, and distilling and purifying to obtain 34.27g of colorless transparent liquid with the yield of 77.01%.

Comparative example

Preparation of intermediate dibromocarbaldehyde oxime using an indirect process

(1) Synthesis of glyoxylic acid oxime

74g (0.5 mol) of 50% glyoxylic acid solution is added into 111ml of water to prepare a glyoxylic acid solution with the concentration of 20%, the glyoxylic acid solution is mixed with 34.75g (0.5 mol, 1 eq) of hydroxylamine hydrochloride at room temperature, the mixture is fully stirred for 12 hours, the reaction is finished, the mixture is frozen and crystallized, filtered, and the filtrate is washed by ice water and then dried in vacuum, 34.8g of white solid, namely glyoxylic acid oxime is obtained, and the yield is 78.20%. m.p. 139.8-142.2 ℃;

(2) synthesis of dibromoformaldoxime

26.7g (0.3 mol) of glyoxylic acid oxime solid prepared in the step (1) is dissolved in 300ml of water, 30ml (0.54 mol) of liquid bromine is added dropwise in an ice-water bath, an appropriate amount of SBA-15 molecular sieve catalyst is added, and then the ice-water bath is removed for reaction for 3 hours. The reaction was stopped, 150ml of dichloromethane was extracted, concentrated to dryness, and the obtained solid was recrystallized from n-hexane to obtain 32.53g of a white solid, namely dibromocarbaldehyde oxime, with a yield of 53.47%.