2-Chloro-4-Fluoro-5-Nitrobenzoic Acid Nitration for Isomer Separation
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Solution Overview
Problem
The existing synthesis of Saflufenacil involves a mixture of isomers, primarily 2-chloro-4-fluoro-5-nitrobenzoic acid and 2-chloro-4-fluoro-3-nitrobenzoic acid, which are difficult to separate efficiently, leading to low yields and purity issues.
Innovation Solution
A modified nitration process is employed to favor di-nitration of the undesired isomer, resulting in a 3,5-dinitro-2-chloro-4-fluorobenzoic acid side product with increased solubility, allowing for easy separation and purification of the desired isomer through crystallization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If conventional nitration conditions are used to produce 2-chloro-4-fluoro-5-nitrobenzoic acid, then the desired isomer is formed, but the undesired isomer (2-chloro-4-fluoro-3-nitrobenzoic acid) is also formed in significant amounts (10-15%), and these isomers are difficult to separate
Solution Approach 1:
The patent converts the harmful effect of forming undesired isomer into a beneficial outcome by allowing the undesired isomer to undergo further di-nitration reaction. This transforms the difficult-to-separate undesired isomer into an easily separable dinitro side product with different solubility characteristics, enabling efficient purification of the desired mononitro isomer through crystallization
Solution Approach 2:
The patent modifies the nitration reaction parameters, specifically using excess nitric acid (1.25-2.0 equivalents) and controlling reaction temperature (55-70°C) for extended time (3-7 hours), to promote di-nitration of the undesired isomer. This parameter optimization balances the formation of desired mononitro isomer with conversion of undesired isomer to separable dinitro product
2Manufacturing precision
If multiple crystallization steps are used to purify the desired isomer from the isomeric mixture, then purity may be improved, but the process becomes complex and requires unacceptably large proportions of solvent and product
Solution Approach 1:
By promoting di-nitration of the undesired isomer to form dinitro side product, the patent creates a substantial solubility difference between desired and undesired components. This single chemical transformation enables simple one-step crystallization to achieve high purity, eliminating the need for multiple complex crystallization steps
3Productivity
If excess nitric acid is used to promote di-nitration of the undesired isomer, then separation efficiency improves, but the yield of the desired isomer decreases due to over-nitration
Solution Approach 1:
The patent optimizes nitric acid quantity to 1.25-2.0 equivalents and controls reaction temperature (55-70°C) and time (3-7 hours) to achieve optimal balance. These parameter settings ensure sufficient di-nitration of undesired isomer for easy separation while limiting over-nitration of desired isomer, maintaining acceptable yield
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
The process achieves high purity (>99.5%) 2-chloro-4-fluoro-5-nitrobenzoic acid, suitable for herbicide synthesis, by balancing mononitration and di-nitration reactions and utilizing specific solvents for efficient crystallization.
Implementation Method 1
reacting 2-chloro-4-fluorobenzoic acid with a nitrating agent; purifying the crude reaction product; and obtaining 2-chloro-4-fluoro-5-nitrobenzoic acid in an essentially pure form
Implementation Method 2
the 3,5-dinitro side product can be easily separated from the crude product by crystallization, as opposed to the undesired isomer, which is difficult to remove
Data Source
AI summary
The present invention relates to a novel nitration process of 2- chloro -4- fluorobenzoic acid to 2-chloro-4- fluoro-5-nitrobenzoic acid, 2-chloro-4- f luoro-3 -nitrobenzoic acid and 3, 5-dinitro-2-chloro-4- fluorobenzoic acid; purifying the crude reaction product; and recovering 2-chloro-4- fluoro-5-nitrobenzoic acid in an essentially pure form, which can be used in the synthesis of the herbicide saflufenacil.