Fluorination of Pyrazole Carbonyl Chlorides Using PEG Solvent
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Solution Overview
Problem
Current processes for preparing 5-fluoro-1,3-dialkyl-1H-pyrazole-4-carbonyl fluorides suffer from low space-time yield, high reaction temperatures, long reaction times, and difficulty in removing solvents like sulpholane, making industrial-scale production challenging.
Innovation Solution
The process involves fluorinating 5-chloro-1,3-dialkyl-1H-pyrazole-4-carbonyl chlorides with potassium fluoride in the presence of a phase transfer catalyst, such as quaternary phosphonium or amidophosphonium salts, and a protic compound like sulpholane or water, at temperatures between 140° C to 190° C in polyethylene glycol dimethyl ether, which enhances yield and allows direct distillation of the product.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If fluorination is performed with potassium fluoride in the presence of sulpholane as a diluent, then the reaction can proceed, but the space-time yield is low and the process is difficult to realize on an industrial scale
Solution Approach 1:
The patent changes the solvent parameter from sulpholane to polyethylene glycol dimethyl ether (PEG), and adjusts the temperature parameter to 140-190°C. This parameter change enables the reaction to proceed with high space-time yield while maintaining industrial scalability, as PEG allows for easier product isolation and higher reaction efficiency
Solution Approach 2:
The patent introduces a phase transfer catalyst as an intermediary substance that facilitates the fluorination reaction between potassium fluoride and the pyrazole carbonyl chloride. The phase transfer catalyst enables efficient ion transfer between phases, significantly improving the reaction rate and space-time yield while maintaining industrial feasibility
2Reliability
If fluorination is performed at high temperatures for extended periods, then the reaction can complete, but the reaction temperature becomes high and reaction time becomes long
Solution Approach 1:
The phase transfer catalyst acts as an intermediary that lowers the activation energy barrier for the fluorination reaction. This enables the reaction to proceed reliably at moderate temperatures (140-190°C) rather than requiring high temperatures, thus reducing energy consumption while maintaining reaction completion
Solution Approach 2:
The patent optimizes the temperature parameter to the range of 140-190°C and controls reaction time to 1-24 hours. This parameter optimization allows the reaction to complete reliably without requiring excessively high temperatures or prolonged heating, improving energy efficiency while maintaining product formation
3Quantity of substance
If conventional phase transfer catalysts are used, then some improvement is achieved, but the yield only increases to 30% and the process remains complex
Solution Approach 1:
The patent optimizes multiple parameters simultaneously: using polyethylene glycol dimethyl ether as solvent, controlling water content to 0.01-1%, adjusting temperature to 140-190°C, and using specific phase transfer catalysts. These coordinated parameter changes achieve high yields (70-90%) while keeping the process manageable through systematic optimization rather than complex multi-component systems
Solution Approach 2:
The patent applies local quality control by carefully managing the water content parameter (0.01-1%) and selecting specific catalyst structures. This localized optimization of critical parameters enables high yield while avoiding the need for complex process adjustments, as the key factors are controlled in specific local conditions rather than requiring system-wide complexity
4Productivity
If water is present in the reaction mixture, then the fluorination can proceed, but the acid chloride group may undergo hydrolysis
Solution Approach 1:
The patent precisely controls the water content parameter to the range of 0.01-1% in the reaction mixture. This parameter control allows sufficient water to be present for the fluorination reaction to proceed at acceptable rates, while limiting water to levels that prevent significant hydrolysis of the acid chloride group, thus balancing reaction productivity with preventing harmful side reactions
Solution Approach 2:
The patent employs feedback control by monitoring and adjusting water content within the narrow range of 0.01-1%. This feedback mechanism ensures that enough water is present to facilitate the fluorination reaction, but not so much as to cause hydrolysis, allowing the process to self-regulate and maintain optimal conditions without requiring complex additional control systems
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 achieves high-purity 5-fluoro-1,3-dialkyl-1H-pyrazole-4-carbonyl fluorides with improved yields and selectivity, enabling their production at lower temperatures and shorter reaction times, facilitating industrial-scale production without the need for solvent removal.
Implementation Method 1
The addition of phase transfer catalysts (PTC) such as quaternary alkylammonium, alkylphosphonium, pyridinium, amidophosphonium, 2-azaallenium, carbophosphazenium and diphosphazenium salts brought only slight improvement (30% yield).
Implementation Method 2
in the presence of catalytic amounts of a protic compound from the group of sulpholane, dimethyl sulphoxide (DMSO), dimethylacetamide, dimethylformamide (DMF), N-methylpyrrolidone (NMP), 1,3-dimethylimidazolinone, HF, water, dichloromethane, chloroform, dichloroethane or trichloroethane; ketones such as acetone, butanone, methyl isobutyl ketone or cyclohexanone
Implementation Method 3
For these purposes, azeotropic drying in the presence of toluene or chlorobenzene is utilized in production. This is particularly important in the case of fluorination of acid chlorides, in order to prevent the hydrolysis of the acid chloride group.
Implementation Method 4
The fluorination of 5-chloro-1,3-dialkyl-1H-pyrazole-4-carbonyl chlorides in polyethylene glycol dimethyl ether (PEG) with a boiling point of over 250° C. could be highly advantageous, since the product would be distillable directly out of the reaction mixture.
Data Source
AI summary
The present invention relates to a novel process for preparing known 5-fluoro-1,3-dialkyl-1H-pyrazole-4-carbonyl fluorides which can be used as starting materials for active fungicidal ingredients by a halex reaction.