Process for the synthesis of hydroxamic acids

Abstract

The present application belongs to the field of collector synthesis, and particularly relates to a method for economically and efficiently preparing hydroxamic acid compounds. The method comprises performing an oximation reaction of alkali, hydroxylamine salt and organic carboxylic acid ester in an ethylene glycol solvent system to prepare a hydroxamic acid salt product. Compared with the existing hydroxamic acid synthesis method, the oximation reaction of the organic acid ester in the ethylene glycol solvent is inhibited to a certain extent due to the solvent characteristics and the solvent effect, and a high hydroxamic acid yield is maintained at a low hydroxylamine dosage. In addition, the ethylene glycol solvent is simple and economical after filtration or centrifugal separation. Furthermore, the synthesis method has the characteristics of short reaction time, mild reaction condition, no wastewater discharge and direct use of the product as a flotation collector, which is beneficial to industrial production.

Description

Technical Field

[0001] This invention relates to a method for preparing isohydroxamic acid compounds, belonging to the field of flotation collector synthesis. Background Technology

[0002] In the field of froth flotation, hydroxamic acids are a class of chelating collectors that readily combine with metal ions and are widely used in the flotation of oxide ores. The synthesis methods of hydroxamic acids include the hydroxylamine method and the nitroalkane rearrangement method. Among these, the hydroxylamine method is a commonly used industrial production method for hydroxamic acid compounds, typically using carboxylic acid esters and hydroxylamine as raw materials to undergo a nucleophilic substitution reaction under alkaline conditions to prepare hydroxamic acids. The flotation application of hydroxamic acids was first developed by… It was proposed in 1940 and was granted a patent in Germany as a collecting agent (Froth flotation of ores, De700735, 1940).

[0003] Shchukina et al. (Shchukina NE, Ryaboi V I. Synthesis of alkylhydroxamicacids in an aqueous-alkaline medium. Chemical Abstracts, 1973(78):291-93m.) reported in 1973 the synthesis of C6-C ... 22 The oximation reaction of fatty acid methyl esters and hydroxylamine in aqueous solutions of higher alcohols and the emulsifier dioctyldimethylamine chloride can achieve a hydroxamic acid yield of up to 81% after 5 hours of reaction, and the product can be directly used for flotation. In addition, Shchukina et al. (Shchukina NE, Ryaboi V I. Laboratory and industrial methods for the production of alkylhydroxamic acids. Chemical Abstracts, 1974(80):95199k.) synthesized C7-C9 alkylhydroxamic acids in 1974 using water as the reaction medium, with product yields of 72-78%. Although using only water as a solvent avoids the use of methanol, the heterogeneous reaction system results in incomplete reaction between organic acid methyl esters and hydroxylamine, and easy hydrolysis of organic carboxylic acid esters, leading to low yields of hydroxamic acids or hydroxamic acid salts.

[0004] Hartlage et al. (James A. Hartlage. Method for preparation fatty hydroxamates. US3933872.) used dimethylamine instead of a base for the oximation reaction. The hydroxamic acid produced by the reaction was then neutralized with dimethylamine, filtered and dried to obtain the hydroxamic acid salt product, with a yield of about 75%.

[0005] In 2014, Liu Guangyi et al. (Liu Guangyi, Zhang Huili, Zhong Hong, Liu Sheng, Zhao Gang, Xiao Jingjing. A method for preparing isohydroxamic acid or isohydroxamic acid salt, CN201410189143.1, 2015.7.1) published a method for synthesizing hydroxamic acid or hydroxamic acid salt. In this process, the solvent methanol can be recycled to avoid the generation of wastewater, and the yield of hydroxamic acid or hydroxamic acid salt is relatively high.

[0006] When producing isohydroxamic acids using water as a solvent, organic carboxylic acid esters readily hydrolyze to form organic acid salts under strongly alkaline conditions, resulting in low isohydroxamic acid yields. Furthermore, when synthesizing isohydroxamic acids in solvents such as methanol, organic carboxylic acid esters also readily decompose into organic acid anions. To suppress OH-... - The reaction with organic carboxylic acid esters requires an increased amount of hydroxylamine, resulting in higher synthesis costs. Furthermore, to ensure sufficient mixing of the reactants, a large amount of methanol is required, leading to high energy consumption and a large recycling volume during distillation recovery. Summary of the Invention

[0007] The purpose of this invention is to provide an economical, efficient, mild method for synthesizing isohydroxamic acid, which allows for easy solvent recycling. This method is simple to operate, economical, efficient, and suitable for the industrial production of isohydroxamic acid.

[0008] A method for synthesizing isohydroxamic acid compounds involves oximating a base, a hydroxylamine salt, and an organic carboxylic acid ester in an ethylene glycol solvent system to obtain isohydroxamic acid salt products.

[0009] Existing methods for synthesizing isohydroxamic acids suffer from low raw material utilization, unsatisfactory oxime conversion rates and selectivity, difficulty in recycling reaction solvents, and inconsistent product quality. To address these industry problems, this invention innovatively demonstrates that the unique physicochemical properties of ethylene glycol, along with its solvation effect, exhibit excellent synergistic effects with the oxime reaction. This significantly improves the conversion rate of the oxime reaction, achieving superior oxime conversion efficiency with lower raw material and solvent consumption. Furthermore, it possesses high oxime selectivity, effectively suppressing carboxylation side reactions. Moreover, the ethylene glycol used in the synthesis process can be effectively recycled after filtration or centrifugation, exhibiting excellent cycle quality stability.

[0010] The present invention is theoretically applicable to the oximation reaction of any organic carboxylic acid ester and hydroxylamine salt. For example, in a typical embodiment of the present invention, a base with the expression MOH, a hydroxylamine salt, and an organic carboxylic acid ester of formula 1 are subjected to an oximation reaction in an ethylene glycol solvent system to obtain an isohydroxyoxime salt product of formula 2;

[0011]

[0012]

[0013] R1 is C4-C 17 Alkyl, substituted alkyl, aryl or substituted aryl;

[0014] The substituted alkyl group is a group with a substituent on a carbon chain of C1 to C6; the substituted aryl group is a group with a substituent on an aromatic ring; the substituent is at least one of C1 to C6 alkyl, C1 to C6 alkoxy, hydroxyl, and halogen.

[0015] R2 is a C1-C4 alkyl group;

[0016] M is at least one of Na, K, and NH4.

[0017] In this invention, the aryl group (aromatic ring) can be any ring with an aromatic structure, for example, it can be a benzene ring, a five-membered heteroaryl group, or a six-membered heteroaryl group;

[0018] In this invention, R1 is C4-C 17 Alkyl, phenyl, or substituted phenyl, wherein the substituted phenyl is a hydroxyl, C1-C6 alkoxy, or halogen-substituted phenyl.

[0019] In this invention, the hydroxylamine salt is a hydrochloride salt and / or sulfate salt of hydroxylamine.

[0020] In this invention, the molar ratio of organic carboxylic acid ester: base: hydroxylamine can be controlled according to the conventional oxime reaction principle, for example, it can be 1:2 to 2.3:1 to 1.3. Considering the advantages of the preparation process of this invention in terms of conversion rate and oxime selectivity, the molar ratio of organic carboxylic acid ester: base: hydroxylamine can be further controlled at 1:2 to 2.2:1 to 1.1.

[0021] In this invention, ethylene glycol is used as an auxiliary agent and solvent, and its dosage can be adjusted as needed. Considering the processing cost, the molar ratio of ethylene glycol to organic carboxylic acid ester is above 1, preferably 5 to 13:1, and more preferably 5 to 10:1.

[0022] In this invention, the alkali is mixed with a hydroxylamine salt solution in ethylene glycol in batches under stirring, and then an organic carboxylic acid ester is added to carry out an oxime reaction.

[0023] Preferably, the temperature of the solution system during the alkali mixing process is controlled below 25°C.

[0024] In this invention, the oxime reaction temperature is 25–45°C.

[0025] Preferably, the oxime reaction takes 1 to 5 hours.

[0026] In this invention, after the oxime reaction, solid-liquid separation is performed to obtain isohydroxamic acid salt, which is then acidified and separated by filtration or centrifugation to obtain the isohydroxamic acid product solid of Formula 3.

[0027]

[0028] In Equation 3, the selection range of R1 is the same as in Equation 1.

[0029] In this invention, the acid used in the acidification process is hydrochloric acid.

[0030] In this invention, ethylene glycol is recovered during the preparation process and recycled as a solvent.

[0031] Solvent recycling is a conventional approach in synthesis, but the challenge lies in maintaining the quality stability of the recycled product. In this invention, thanks to the unique physicochemical properties and solvation effect of ethylene glycol, as well as its special compatibility and synergistic effect with the oxime reaction, the ethylene glycol used in the preparation process can be recycled, exhibiting excellent cycle stability.

[0032] In this invention, ethylene glycol from the oxime reaction and / or acidification reaction is recovered and recycled. For example, a typical recycling method of this invention is to directly recycle the liquid obtained from the solid-liquid separation of the oxime reaction (such as the filtrate from filtration, the solution from centrifugation). Alternatively, another recycling method of this invention involves directly acidifying the oxime reaction system, followed by solid-liquid separation of the acidified reaction system, and recycling the resulting ethylene glycol solution.

[0033] The beneficial effects of this invention are:

[0034] Existing water-based methods for preparing hydroxamic acid yield approximately 82%. In this technology, the organic carboxylic ester readily undergoes side reactions in strongly alkaline aqueous solutions, forming organic acid salts and consuming the raw material organic carboxylic ester, resulting in a low hydroxamic acid yield. Simultaneously, the separation of the hydroxamic acid product generates a large amount of wastewater requiring treatment, leading to high production costs. Methanol-based synthesis methods can achieve hydroxamic acid yields of approximately 90%. However, in this technology, the organic carboxylic ester also readily decomposes into organic acid anions in strongly alkaline methanol solvent. To suppress OH-... - The reaction with organic carboxylic acid esters requires a large amount of hydroxylamine, resulting in high synthesis costs. Furthermore, in order to ensure sufficient mixing of the reaction materials, a large amount of methanol is also required, which leads to high energy consumption during distillation and recovery, large recycling volume, and high production costs.

[0035] This invention uses ethylene glycol as a solvent. During the oxime reaction, due to the inherent properties of ethylene glycol and its solvation effect, the side reaction of organic carboxylic acid esters decomposing into organic acids is suppressed to a certain extent. Even with low hydroxylamine dosage, a high yield of isohydroxamic acid (approximately 92%) is still achieved. Furthermore, the ethylene glycol solvent, after filtration or centrifugation, can be directly recycled to the next round of oxime reaction, avoiding wastewater discharge and making the process simple and economical. Additionally, the amount of ethylene glycol used is less than that of water or methanol, and considering potential explosiveness and toxicity, ethylene glycol is safer and more environmentally friendly than methanol. In conclusion, the ethylene glycol solvent method for synthesizing isohydroxamic acid is simple, efficient, economical, and environmentally friendly, making it highly suitable for industrial production. Detailed Implementation

[0036] The present invention is further illustrated by the following embodiments, but the scope of protection of the present invention is not limited to these embodiments. All parts and percentages in the embodiments refer to mass unless otherwise specified. Hydroxime acid content was detected using the ferric ion colorimetric method.

[0037] In this invention, the isohydroxamic acid compounds include isohydroxamic acids and their salts, which are compounds with a -CONHO- structure. For the synthesis of these compounds, this invention innovatively uses ethylene glycol as a solvent to carry out an oximation reaction of a base, hydroxylamine salt, and organic carboxylic acid ester in an ethylene glycol solvent system to obtain isohydroxamic acid salt products. These products can then be selectively acidified to obtain isohydroxamic acids.

[0038] This invention provides a typical, economical, and efficient method for preparing isohydroxamic acid compounds. Under stirring, an alkali is added in batches to an ethylene glycol solution of hydroxylamine salt at a temperature not exceeding 20°C. Then, an organic carboxylic acid ester having the structure of formula 1-A or formula 1-B is added. The reaction is carried out at 25–45°C for 1–5 hours. After the reaction is complete, the mixture is acidified, and after filtration or centrifugation, an isohydroxamic acid product having the structure of formula 3-A or formula 3-B is obtained. The filtrate is recycled as a solvent for the next round of oximation reaction.

[0039]

[0040]

[0041]

[0042]

[0043] Where R is C4-C 17 Alkyl group; X is a hydrogen atom, hydroxyl group, R 2 or R 2 O;R 2 It is a C1-C4 alkyl group.

[0044] The molar ratio of the organic carboxylic acid ester: base: hydroxylamine: ethylene glycol is 1:2-2.3:1-1.3:5-13.

[0045] The carboxylic acid ester is preferably a methyl ester of valeric acid, hexanoic acid, heptanoic acid, octanoic acid, nonanoic acid, decanoic acid, undecanoic acid, dodecanoic acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, palmitic acid, heptadecanoic acid, stearic acid, oleic acid, cyclohexanoic acid, benzoic acid, methylbenzoic acid, methoxybenzoic acid, salicylic acid, or a mixture thereof.

[0046] The alkali is sodium hydroxide or potassium hydroxide; the hydroxylamine salt is hydroxylamine hydrochloride or hydroxylamine sulfate; and the acid used for acidification is hydrochloric acid.

[0047] The alkali is added in batches to a mixture containing hydroxylamine salt and ethylene glycol, and the temperature during alkali addition is less than 20°C, more preferably 5-15°C.

[0048] The oximeting temperature is 25–45°C, and the reaction time is 1–5 hours.

[0049] Comparative Example 1

[0050] Synthesis of benzohydroxyxamic acid in an alkaline aqueous medium:

[0051] 7.62 g of hydroxylamine hydrochloride and 13.6 g of methyl benzoate were sequentially added to a three-necked flask containing 60 mL of water. An aqueous solution of sodium hydroxide containing 8.4 g of sodium hydroxide and 14 mL of water was added dropwise over 2 hours, with the temperature not exceeding 15°C. The mixture was then heated to 30°C and reacted for 3 hours. After the reaction was complete, a sample was taken and analyzed using a ferric ion colorimetric reaction. The yield of benzohydroxyxamic acid was 89.1%. The mixture was then acidified with 8.5 mL of hydrochloric acid and filtered below 15°C to obtain a solid product of benzohydroxyxamic acid with a yield of 81.9%.

[0052] Comparative Example 2

[0053] Synthesis of benzohydroxyoxime acid via alkaline methanol medium:

[0054] Benzyl hydroxamic acid was prepared according to the method of invention patent CN201410189143.1 (Liu Guangyi, Zhang Huili, Zhong Hong, Liu Sheng, Zhao Gang, Xiao Jingjing. A method for preparing isohydroxamic acid or isohydroxamic acid salt. CN201410189143.1, 2015.7.1).

[0055] 8.34 g of hydroxylamine hydrochloride was added to a three-necked flask containing 140 mL of methanol. 8.8 g of sodium hydroxide was added in three batches (3.50 g, 3.40 g, and 1.9 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide was added, the temperature was raised to 30°C, and 13.6 g of methyl benzoate was added dropwise over 2 hours, followed by a 6-hour reaction. After the reaction was complete, a sample was taken and analyzed using a ferric ion colorimetric reaction. The yield of benzohydroxyxamic acid was 91.6%. Then, 8.5 mL of hydrochloric acid was added for acidification, and methanol was distilled under reduced pressure to obtain the solid product of benzohydroxyxamic acid, with a yield of 91.5%.

[0056] Example 1

[0057] 7.62 g of hydroxylamine hydrochloride was added to a three-necked flask containing 40 mL of ethylene glycol. 8.4 g of sodium hydroxide was added in three batches (3.50 g, 3.40 g, and 1.5 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide was added, the temperature was raised to 30°C, and 13.6 g of methyl benzoate was added dropwise over 2 hours, followed by a further 4 hours of reaction. After the reaction was complete, samples were taken and analyzed using a ferric ion colorimetric reaction. The yield of benzohydroxyxamic acid was 93.8%.

[0058] It is evident that the present invention can achieve better yields with lower material usage.

[0059] Example 2

[0060] 7.62 g of hydroxylamine hydrochloride was added to a three-necked flask containing 40 mL of ethylene glycol. 8.4 g of sodium hydroxide was added in three batches (3.50 g, 3.40 g, and 1.5 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide was added, the temperature was raised to 40°C, and 13.6 g of methyl benzoate was added dropwise over 2 hours, followed by a further 4 hours of reaction. After the reaction was complete, samples were taken and analyzed using a ferric ion colorimetric reaction. The yield of benzohydroxyxamic acid was 93.2%.

[0061] Example 3

[0062] 7.62 g of hydroxylamine hydrochloride was added to a three-necked flask containing 30 mL of ethylene glycol. 8.56 g of sodium hydroxide was added in three batches (3.5 g, 3.5 g, and 1.56 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide had been added, the temperature was raised to 30°C, and 13.6 g of methyl benzoate was added dropwise over 2 hours, followed by a further 4 hours of reaction. After the reaction was complete, samples were taken and analyzed using a ferric ion colorimetric reaction. The yield of benzohydroxyoxime acid was 93.4%.

[0063] Example 4

[0064] Ethylene glycol cycling test

[0065] 7.62 g of hydroxylamine hydrochloride was added to a three-necked flask containing 40 mL of ethylene glycol. 8.88 g of sodium hydroxide was added in three batches (3.5 g, 3.5 g, and 1.88 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide was added, the temperature was raised to 30°C, and 13.6 g of methyl benzoate was added dropwise over 2 hours, followed by a further 4 hours of reaction. After the reaction was complete, a sample was taken and analyzed using a ferric ion colorimetric reaction. The yield of benzohydroxyoxime acid was 93.1%. Then, after acidification with 9.4 mL of concentrated hydrochloric acid and filtration, solid benzohydroxyoxime acid product was obtained, with a yield of 37.2%.

[0066] The filtrate obtained above was transferred to a three-necked flask, and then 7.62 g of hydroxylamine hydrochloride was added. 8.88 g of sodium hydroxide was added in three batches (3.5 g, 3.5 g, and 1.88 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide was added, the temperature was raised to 30°C, and 13.6 g of methyl benzoate was added dropwise over 2 hours, followed by a 4-hour reaction. After the reaction was complete, a sample was taken and analyzed using a ferric ion colorimetric reaction. The original benzoyl hydroxamic acid in the filtrate was subtracted, and the actual yield of benzoyl hydroxamic acid was calculated based on the newly added methyl benzoate, resulting in a yield of 92.7%. Then, 9.4 mL of concentrated hydrochloric acid was added for acidification, followed by filtration to obtain a solid benzoyl hydroxamic acid product with a yield of 80.7%.

[0067] The filtrate obtained from the previous filtration was used for the next synthesis, and the actual yield and solid product yield of benzohydroxyxamic acid are shown in Table 1.

[0068] Table 1. Synthesis results of benzohydroxyxamic acid when ethylene glycol solvent is recycled.

[0069]

[0070] Table 1 shows that the synthesis yield (actual yield) of benzohydroxyxamic acid is about 92%. At the beginning of the cycle, the yield of the solid benzohydroxyxamic acid product obtained by acidification is lower than its synthesis yield, and some benzohydroxyxamic acid dissolves in ethylene glycol solvent. As the cycle proceeds, the yield of the solid benzohydroxyxamic acid product gradually approaches its synthesis yield, indicating that the synthesis and separation steps have gradually reached equilibrium.

[0071] In this invention, the oxime reaction system can be subjected to solid-liquid separation, and the resulting ethylene glycol-containing solvent can be recycled. Alternatively, the oxime reaction system can be directly acidified followed by solid-liquid separation, and the resulting ethylene glycol solution can be recycled. This invention also demonstrates that when recycling the ethylene glycol solvent after oxime-acidification, using hydrochloric acid in the acidification stage provides better compatibility and synergistic effects with the ethylene glycol and preparation system of this invention, resulting in superior recycling operation and quality stability.

[0072] Example 5

[0073] 7.62 g of hydroxylamine hydrochloride was added to a three-necked flask containing 45 mL of ethylene glycol. 8.56 g of sodium hydroxide was added in three batches (3.5 g, 3.5 g, and 1.56 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide was added, the temperature was raised to 30°C, and 15.2 g of methyl salicylate was added dropwise over 2 hours, followed by a further 3 hours of reaction. After the reaction was complete, samples were taken and analyzed using a ferric ion colorimetric reaction. The yield of salicylic acid hydroxyxamic acid was 90.9%.

[0074] Example 6

[0075] 7.62 g of hydroxylamine hydrochloride was added to a three-necked flask containing 45 mL of ethylene glycol. 8.56 g of sodium hydroxide was added in three batches (3.5 g, 3.5 g, and 1.56 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide had been added, the temperature was raised to 30°C, and 15.8 g of methyl octanoate was added dropwise over 2 hours, followed by a further 4 hours of reaction. After the reaction was complete, samples were taken and analyzed using a ferric ion colorimetric reaction. The yield of octyl hydroxamic acid was 94.9%.

[0076] Example 7

[0077] 7.62 g of hydroxylamine hydrochloride was added to a three-necked flask containing 40 mL of ethylene glycol. 8.56 g of sodium hydroxide was added in three batches (3.5 g, 3.5 g, and 1.56 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide was added, the temperature was raised to 30°C, and 14.2 g of methyl cyclohexane was added dropwise over 2 hours, followed by a further 4 hours of reaction. After the reaction was complete, samples were taken and analyzed using a ferric ion colorimetric reaction. The yield of cyclohexylmethylhydroxamic acid was 92.2%.

[0078] Example 8

[0079] 7.62 g of hydroxylamine hydrochloride was added to a three-necked flask containing 50 mL of ethylene glycol. 8.56 g of sodium hydroxide was added in three batches (3.5 g, 3.5 g, and 1.56 g), maintaining the addition temperature below 15°C. After all the sodium hydroxide was added, the temperature was raised to 30°C, and 19.3 g of methyl p-tert-butylbenzoate was added dropwise over 2 hours, followed by a further 4 hours of reaction. After the reaction was complete, samples were taken and analyzed using a ferric ion colorimetric reaction. The yield of p-tert-butylbenzoic acid was 90.1%.

[0080] Comparative Example 3

[0081] Compared to Example 1, the only difference is that ethylene glycol was replaced with an equimolar amount of glycerol; all other operations and parameters were the same as in Example 1. The yield of benzohydroxyxamic acid was 78.3%.

Claims

1. A method for synthesizing a hydroxamic acid compound, characterized by, Under stirring, the base with the expression MOH was mixed in batches with an ethylene glycol solution of hydroxylamine salt, and then an organic carboxylic acid ester of formula 1 was added to carry out an oximation reaction to obtain the isohydroxyoxime salt product of formula 2. Formula 1 Formula 2 R1is C4-C 17 alkyl, substituted alkyl, aryl, or substituted aryl; The substituted alkyl group is a group with a substituent on a C1-C6 carbon chain; the substituted aryl group is a group with a substituent on an aromatic ring; the substituent is at least one of a C1-C6 alkyl group, a C1-C6 alkoxy group, a hydroxyl group, and a halogen group; the aryl group is a benzene ring, a five-membered heteroaryl group, or a six-membered heteroaryl group. R2 is a C1-C4 alkyl group; M is at least one of Na and K; The molar ratio of organic carboxylic acid ester: base: hydroxylamine is 1:2~2.3:1~1.3; The molar ratio of ethylene glycol to organic carboxylic acid ester is 5~13:

1.

2. The method for synthesizing isohydroxamic acid compounds as described in claim 1, characterized in that, R1 is C4-C 17 alkyl, phenyl or substituted phenyl, the substituted phenyl being hydroxy, C1-C6alkoxy, halogen substituted phenyl.

3. The method for synthesizing isohydroxamic acid compounds as described in claim 1, characterized in that, The hydroxylamine salt is a hydrochloride and / or sulfate of hydroxylamine.

4. The method for synthesizing isohydroxamic acid compounds as described in claim 1, characterized in that, The molar ratio of organic carboxylic acid ester: base: hydroxylamine is 1:2~2.2:1~1.1; The molar ratio of ethylene glycol to organic carboxylic acid ester is 5~10:

1.

5. The method of claim 1, wherein the hydroxamic acid compound is ###00003### 5 The temperature of the solution system during the alkali mixing process is controlled below 25℃.

6. The method for synthesizing isohydroxamic acid compounds as described in claim 1, characterized in that, The oxime reaction occurs at temperatures ranging from 25 to 45°C.

7. The method for synthesizing isohydroxamic acid compounds as described in claim 6, characterized in that, The oxime reaction takes 1 to 5 hours.

8. The method for synthesizing isohydroxamic acid compounds as described in claim 1, characterized in that, After the oxime reaction, isohydroxamic acid salt is obtained, which is then acidified and separated into solid and liquid components by filtration or centrifugation to obtain the isohydroxamic acid solid product of formula 3. Formula 3 In Equation 3, the selection range of R1 is the same as in Equation 1.

9. The method for synthesizing isohydroxamic acid compounds as described in claim 8, characterized in that, The acid used in the acidification process is hydrochloric acid.

10. The method of synthesis of hydroxamic acids according to any one of claims 1 to 9, wherein Ethylene glycol generated during the preparation process is recovered and recycled as a solvent.

11. The method for synthesizing isohydroxamic acid compounds as described in claim 10, characterized in that, Ethylene glycol from oxime and / or acidification reactions is recovered and recycled.

Images