Patent ID: 8063253

Claim:
A semi-continuous crystallization process for preparing the Form 1 polymorph of mesotrione, said process comprising a) initially charging a crystallizer with an aqueous slurry containing at least 5% by weight mesotrione crystals, wherein at least 80% by weight of the mesotrione crystals present in the slurry are of Form 1; b) feeding a mesotrione solution at a pH greater than 7 to the crystallizer at a controlled rate while maintaining the pH in the crystallizer between 2.5 and 4.0 by addition of an acid; c) stopping the feed of the mesotrione solution when the level in the crystallizer reaches an upper limit; d) removing the mesotrione slurry from the crystallizer until the volume reaches a lower limit of the crystallizer capacity; and optionally e) restarting the mesotrione solution feed of b).