Pyrazole Purification via Acid Salt Crystallization
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Solution Overview
Problem
Current methods for producing pyrazoles, such as 3,4-dimethylpyrazole, face challenges in separating by-products like 3-ethylpyrazole, resulting in reduced yields and purity issues due to complex purification processes.
Innovation Solution
A process involving the reaction of carbonyl compounds with formic acid esters and hydrazines, followed by the formation of acid addition salts through crystallization, which allows for direct continuation of reactions without intermediate separation, effectively precipitating out unwanted by-products and achieving high yields of pyrazoles as pure acid addition salts.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If distillation is used to separate 3-ethylpyrazole from 3,4-dimethylpyrazole, then purity is improved, but yield is greatly reduced and process complexity increases
Solution Approach 1:
The patent changes the physical-chemical parameters of the pyrazole compounds by converting them into acid addition salts. This transformation alters their solubility and crystallization behavior, enabling separation based on these parameter changes rather than relying on distillation. The salt formation process allows for selective crystallization of the desired pyrazole salt while leaving impurities in the mother liquor, thus achieving high purity without significant yield loss.
Solution Approach 2:
The patent utilizes phase transition phenomena, specifically crystallization from solution. By forming acid addition salts, the pyrazole compounds undergo a phase change from molecular form to ionic salt form, which then crystallizes selectively. This phase transition enables efficient separation of the desired product from by-products through controlled crystallization, avoiding the need for energy-intensive distillation processes.
2Manufacturing precision
If filtration of sodium salt is used to purify 2-methyl-3-oxobutanal, then 3-ethylpyrazole content is reduced, but overall yield of DMP drops sharply
Solution Approach 1:
The patent applies preliminary action by forming acid addition salts of the pyrazole compounds before separation. This preliminary salt formation step prepares the compounds for selective crystallization, allowing the desired pyrazole to be separated from impurities in a subsequent crystallization step. This approach avoids the need for filtration of sodium salts at intermediate stages, thereby preventing yield loss while achieving high purity.
3Manufacturing precision
If intermediate product is separated by filtration or centrifugation, then by-product content is reduced, but process complexity increases
Solution Approach 1:
The patent merges the purification step with the reaction process by directly reacting the intermediate product without prior separation. The acid addition salt formation and crystallization steps are integrated into the overall process flow, eliminating the need for separate filtration or centrifugation operations. This merging of operations achieves purification while reducing process complexity and equipment requirements.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This method enables the production of pyrazoles with significantly reduced by-product content, maintaining high yields and achieving purity ratios of 3,4-dimethylpyrazole to 3-ethylpyrazole greater than 95:5, thereby overcoming the limitations of previous purification methods.
Implementation Method 1
converting the pyrazoles into acid addition salts which are precipitated or crystallized from organic solvents
Implementation Method 2
converting the pyrazoles into acid addition salts which are precipitated or crystallized from organic solvents
Implementation Method 3
reacting the intermediate product formed with hydrazines
Data Source
AI summary
Pyrazoles of the general formula (I), where R1 and R2 independently are hydrogen, halogen, nitro, or C1-20 alkyl, C3-8 cycloalkyl, C6-12 aryl, C7-13 alkylaryl, or C7-13 aralkyl optionally substituted by C1-4 alkyl, halogen, and/or nitro and R3 is hydrogen or C1-20 alkyl, C3-8 cycloalkyl, C6-12 aryl, C7-13 alkylaryl, or C7-13 aralkyl optionally substituted by C1-4 alkyl, halogen, and/or nitro, are purified by dissolving the pyrazoles of the general formula (I) in water or an organic solvent, then reacting the solution with at least equimolar amounts of an inorganic mineral acid and/or an organic acid, and separating the obtained acid addition salts by means of crystallization.