Mesotrione Crystallization via Seed-Induced Polymorph Control
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Solution Overview
Problem
The commercial manufacture of mesotrione herbicide faces challenges in producing the thermodynamically stable Form 1 polymorph, as Form 2 is often formed during recrystallization in aqueous solutions, leading to instability and increased production costs due to the need for solvent use and disposal, and inefficient batch processes.
Innovation Solution
A semi-continuous or continuous crystallization process is employed, using a high concentration of Form 1 seed crystals and controlling the pH to ≤4.0, which allows for reliable production of Form 1 mesotrione crystals without solvents, enabling efficient conversion of Form 2 to Form 1 and reducing production losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If batch crystallization is used to produce mesotrione, then the process is simple to operate, but Form 2 crystals are formed which are thermodynamically unstable and require milling
Solution Approach 1:
The patent changes the crystallization parameters by using a continuous process instead of batch process, controlling pH to ≤4.0, and using high concentration of Form 1 seed crystals to shift the polymorph formation from unstable Form 2 to stable Form 1
Solution Approach 2:
The patent implements continuous crystallization where mesotrione solution and seed crystals are continuously fed into the crystallizer, and product is continuously removed, maintaining steady-state conditions that favor Form 1 formation throughout the process
2Manufacturing precision
If solvents are used during crystallization to avoid Form 2 formation, then polymorph control is improved, but manufacturing costs increase due to solvent recovery or disposal
Solution Approach 1:
The patent removes the solvent component from the crystallization system entirely, achieving polymorph control through pH control and continuous processing with seed crystals, thereby eliminating solvent recovery or disposal requirements
Solution Approach 2:
The system uses high concentration of Form 1 seed crystals (at least 5% by weight) to self-nucleate and guide crystal formation, eliminating the need for external solvents to control polymorph formation
3Quantity of substance
If Form 2 crystals are produced during recrystallization, then the crystals are fine and difficult to harvest, but conversion to Form 1 is not possible without solvent use
Solution Approach 1:
The patent performs preliminary action by adding high concentration of Form 1 seed crystals before crystallization begins, pre-establishing the desired crystal form and preventing Form 2 formation entirely, thus avoiding harvesting difficulties later
4Reliability
If continuous crystallization with high seed crystal concentration is used, then Form 1 polymorph is reliably produced without solvents, but the process complexity increases
Solution Approach 1:
The patent establishes specific parameter thresholds (pH ≤4.0, seed crystal concentration ≥5% by weight) that, when maintained, reliably produce Form 1 crystals. The continuous process design with these controlled parameters achieves polymorph consistency without requiring complex additional equipment
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 process ensures the production of mesotrione with the desired crystal morphology, reducing instability issues and manufacturing costs by maintaining Form 1 polymorph stability and eliminating the need for solvent recovery, thereby enhancing production efficiency.
Implementation Method 1
Crystallization of mesotrione is carried out by a pH shift in a predominantly aqueous solution whereby the soluble salt is converted to the insoluble free acid resulting in high yield
Implementation Method 2
WO 2005/035487 discloses a process for the purification of mesotrione by dissolving the mesotrione in an aqueous solvent, purifying the solution and crystallising the mesotrione out of solution
Implementation Method 3
using a semi-continuous or continuous crystallization process, wherein the aqueous mesotrione solution is introduced to a crystallizer containing at least 5% by weight mesotrione seed crystals wherein at least 80% by weight of the mesotrione crystals in the aqueous slurry are of Form 1
Implementation Method 4
the aqueous mesotrione solution is introduced to a crystallizer containing at least 5% by weight mesotrione seed crystals wherein at least 80% by weight of the mesotrione crystals in the aqueous slurry are of Form 1
Data Source
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AI summary
The invention relates to a process for selectively controlling the crystallisation mesotrione [2-(4-methylsulphonyl-2-nitrobenzoyl)cyclohexane-1 ,3-dione] from aqueous solution in which the aqueous mesotrione solution is introduced to a crystalliser containing seed crystals predominantly of the thermodynamically stable polymorph ("Form 1") in a semi-continuous or continuous manner. The invention further relates to a process for converting the metastable polymorph ("Form 2") of mesotrione to Form 1 by introducing an aqueous solution containing the former form to a crystalliser containing seed crystals predominantly of the latter form.