Fipronil Synthesis Using Hydrogen Peroxide Oxidation
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Solution Overview
Problem
Current methods for synthesizing fipronil face challenges such as corrosion of industrial vessels due to the use of trifluoroacetic acid and hydrogen peroxide, high costs, and inconsistency in yield and quality, particularly due to the use of phase transfer catalysts and oxidant degradation in sulfuric acid media.
Innovation Solution
A process involving the oxidation of 5-amino-1-(2,6-dichloro-4-trifluoromethylphenyl)-3-cyano-4-trifluoromethylthio pyrazole using hydrogen peroxide and concentrated sulfuric acid in specific solvent systems without phase transfer catalysts, followed by quenching, separation, neutralization, and crystallization, which avoids corrosion and oxidant degradation, and allows for cost-effective and consistent production.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If trifluoroacetic acid and hydrogen peroxide mixture is used for oxidation, then selectivity and yield are improved, but corrosion of glass linings occurs due to hydrogen fluoride formation
Solution Approach 1:
The patent replaces expensive trifluoroacetic acid with cheaper alternatives like acetic acid or formic acid that can be used in larger quantities without causing corrosion problems, effectively using disposable-like chemicals that don't require recovery
Solution Approach 2:
The patent changes the chemical composition parameters by substituting fluorinated acids with non-fluorinated carboxylic acids, thereby eliminating hydrogen fluoride formation while maintaining oxidation capability through alternative mechanisms
2Manufacturing precision
If trifluoroacetic acid is used as solvent, then oxidation selectivity is improved, but process cost increases due to need for recovery
Solution Approach 1:
The patent employs inexpensive carboxylic acids like acetic acid or formic acid as reaction media that can be used in stoichiometric or excess amounts without requiring costly recovery systems, replacing the need to recycle expensive trifluoroacetic acid
Solution Approach 2:
The patent modifies the solvent system by transitioning from fluorinated to non-fluorinated carboxylic acids, changing the chemical environment to achieve similar oxidation outcomes without the economic burden of solvent recovery
3Productivity
If phase transfer catalyst is used in sulfuric acid medium, then oxidation proceeds, but oxidant degradation occurs leading to inconsistent yield and quality
Solution Approach 1:
The patent removes the phase transfer catalyst component from the reaction system entirely, eliminating the source of oxidant degradation and the associated inconsistencies in yield and product quality
Solution Approach 2:
The patent uses sulfuric acid itself as the reaction medium and catalyst, eliminating the need for additional phase transfer catalysts that cause oxidant degradation, thereby simplifying the system and improving reliability
4Productivity
If meta-chloroperbenzoic acid is used for oxidation, then fipronil is produced, but sulfone compound is co-formed which is difficult to remove
Solution Approach 1:
The patent changes the oxidizing agent from meta-chloroperbenzoic acid to hydrogen peroxide in carboxylic acid medium, altering the reaction pathway to achieve selective oxidation that prevents sulfone formation while maintaining efficient production rates
Data Source
AI summary
A process for preparation of Fipronil (i.e. 5-amino-l-(2, 6-dichloro-4-trifluoromethylphenyl)-3-cyano-4-trifluoromethylsulphinyl-pyrazole) is provided, which comprises oxidizing 5-amino-l-(2, 6-dichloro-4-trifluoromethylphenyl)-3-cyano-4-trifluoromethylthio-pyrazole with sulfuric acid and hydrogen peroxide as oxidizing agent in the presence of a solvent such as ethylene dichloride, chlorobenzene.