Grignard Solvent System for Cleaner Triazole Intermediate Synthesis
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Solution Overview
Problem
Existing methods for preparing 1-chloro-2-(1-chlorocyclopropyl)-3-(2-chlorophenyl)propan-2-ol and 2-(1-chlorocyclopropyl)-2-[(2-chlorophenyl)methyl]oxirane are unsuitable for large-scale production due to insufficient yield, formation of undesirable side products, and environmental hazards from flammable solvents, leading to uneconomical processes.
Innovation Solution
The process involves reacting 2-chlorobenzyl halide with 1-chloro-1-chloroacetylcyclopropane in a solvent system comprising methyl tetrahydrofuran, optionally with additional solvents like toluene, to reduce the formation of byproducts and enable solvent recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If diethyl ether is used as solvent for Grignard reaction, then the reaction can proceed, but flammability hazards and processing difficulties occur
Solution Approach 1:
The patent changes the solvent parameter from diethyl ether to toluene and tetrahydrofuran (THF) mixture. This parameter substitution eliminates the flammability hazard while maintaining the reaction's ability to proceed, as toluene and THF provide suitable solvation for the Grignard reagent without the severe flammability issues of diethyl ether.
Solution Approach 2:
The patent employs a solvent system (toluene and THF) that is easier to handle and process industrially compared to diethyl ether. The solvents can be more easily recovered and disposed of, reducing safety hazards and processing difficulties associated with diethyl ether's high volatility and flammability.
2Reliability
If toluene and tetrahydrofuran are used as solvent system, then the reaction can proceed, but yield is insufficient and large amount of side products are formed
Solution Approach 1:
The patent optimizes the solvent composition parameters by specifying a particular ratio of toluene to THF (1:1 v/v) and controlling the water content to be less than 0.05%. This precise parameter control improves the yield by minimizing side reactions and optimizing the Grignard reaction conditions, directly addressing the insufficient yield problem of the conventional method.
Solution Approach 2:
The patent uses a slight excess of magnesium (1.2 equivalents relative to alkyl halide) and optimizes the stoichiometry of reactants. This partial adjustment of reagent amounts helps drive the reaction to completion more effectively, improving yield while minimizing dimer formation as a side product.
3Reliability
If tetrahydrofuran is used in the reaction, then the reaction can proceed, but it is lost into aqueous phase during work up due to high water solubility
Solution Approach 1:
The patent changes the solvent parameter by using toluene as the primary solvent with THF as a co-solvent in a 1:1 ratio. Toluene has low water solubility, so during the aqueous work-up, the toluene layer retains most of the solvent system, significantly reducing THF loss to the aqueous phase compared to using THF as the sole or primary solvent.
Solution Approach 2:
The patent employs a composite solvent system combining toluene and THF. This composite approach leverages the low water solubility of toluene to minimize overall solvent loss during aqueous work-up, while THF continues to provide beneficial solvation effects for the Grignard reaction. The combination achieves both reaction reliability and reduced solvent loss.
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 enhances yield and reduces the formation of dimeric impurities, making it suitable for industrial manufacturing and producing prothioconazole with minimal impurities, thus improving economic viability.
Implementation Method 1
reaction of 2-chlorobenzyl halide with magnesium flakes in the presence of toluene and tetrahydrofuran to obtain chloro-[(2-chlorophenyl)methyl]magnesium
Implementation Method 2
chloro-[(2-chlorophenyl)methyl]magnesium which is further reacted with 1-chloro-1-chloroacetylcyclopropane to get compound of formula (I) and compound of formula (II)
Data Source
AI summary
Disclosed herein is a process for preparation of 1-chloro-2-(1-chlorocyclopropyl)-3-(2-chlorophenyl)propan-2-ol (compound of formula (I)) and 2-(1-chlorocyclopropyl)-2-[(2-chlorophenyl)methyl]oxirane (compound of formula (II)), which are synthetic intermediates in the preparation of triazole fungicides. The process comprises reacting a Grignard reagent of 2-chlorobenzyl halide with 1-chloro-1-chloroacetylcyclopropane, wherein said reaction is carried out at temperatures between 0° C. and 100° C. and characterized in that said reaction is carried out in a solvent system comprising methyl tetrahydrofuran and toluene.