Nitrobenzoic Acid Nitration Using Oleum for Isomer Selectivity
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Solution Overview
Problem
Existing methods for synthesizing 2-chloro-4-fluoro-5-nitrobenzoic acid result in a significant mixture of undesired isomers, making purification difficult and inefficient, with low yields of the desired isomer.
Innovation Solution
The use of oleum and nitric acid as a nitrating agent under controlled conditions, including specific temperature and stoichiometric ratios, to promote mononitration towards the desired isomer, followed by solvent recrystallization for high-purity recovery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional nitration method using sulfuric acid and nitric acid is used, then the reaction can proceed, but a significant mixture of undesired isomers (10-15%) is produced making purification difficult
Solution Approach 1:
The patent changes the chemical composition parameter of the nitrating agent by using oleum (fuming sulfuric acid) instead of conventional sulfuric acid. This parameter change fundamentally alters the reaction selectivity, producing the desired 5-nitro isomer in 94:6 ratio compared to the conventional method's 85-90:10-15 ratio, thereby resolving the isomer selectivity issue without requiring complex purification steps
Solution Approach 2:
The patent introduces oleum as an intermediary substance that mediates the nitration reaction. The oleum acts as a stronger sulfonating agent that directs the nitration to the desired position on the aromatic ring, serving as a selective mediator that prevents formation of undesired isomers while maintaining reaction efficiency
2Manufacturing precision
If multistep crystallization is used to purify the desired isomer, then some purification is achieved, but the process becomes complex and requires unacceptably large proportions of solvent and product
Solution Approach 1:
The patent applies preliminary action by using oleum in the nitration step to pre-establish high isomer selectivity (94:6 ratio) before purification is needed. This preliminary selective action eliminates the need for complex multistep crystallization processes, as the desired isomer is already formed in high purity from the outset
3Productivity
If conventional nitration conditions are used, then the reaction proceeds, but the yield of desired isomer is reduced due to low selectivity and purification losses
Solution Approach 1:
The patent changes the nitrating agent parameter to oleum, which fundamentally improves reaction selectivity to 94:6 ratio. This parameter change minimizes the formation of undesired isomers that would require purification removal, thereby reducing product loss and maximizing the yield of the desired 5-nitro isomer
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
Achieves a high yield of the desired isomer with purity levels exceeding 97%, effectively reducing the undesired isomer to less than 3%, enhancing the efficiency and yield of the purification process.
Implementation Method 1
reacting 2-chloro-4-fluorobenzoic acid with a nitrating agent prepared from oleum and nitric acid or its salt
Implementation Method 2
separation of the crude reaction product
Implementation Method 3
recovering 2-chloro-4-fluoro-5-nitrobenzoic acid in an essentially pure form
Data Source
AI summary
The present invention relates to a novel nitration process of 2-chloro-4-fluorobenzoic acid or alkyl 2-chloro-4-fluorobenzoate, using oleum and nitric acid, to obtain 2-chloro-4-fluoro-5-nitrobenzoic acid or alkyl 2-chloro-4-fluoro-5-nitrobenzoates; purifying the crude reaction product; and recovering 2-chloro-4-fluoro-5-nitrobenzoic acid or alkyl 2-chloro-4-fluoro-5-nitrobenzoates in an essentially pure form, which can be used in the synthesis of the herbicide saflufenacil.