Patent ID: 6342630
Filing Date: 2002-01-29
Classification: C07C

Abstract:
A process for the purification of a compound of general formula I: wherein:R1 is hydrogen or C1-C6 alkyl, C2-C6 alkenyl or C2-C6 alkynyl (any of which may optionally be substituted with one or more substituents selected from halogen and OH) or COOR4, COR6, CONR4R5 or CONHSO2R4; R4 and R5 are each independently hydrogen or C1-C4 alkyl optionally substituted with one or more halogen atoms; R6 is a halogen atom or a group R4; R2 is hydrogen or halo; R3 is C1-C4 alkyl, C2-C4 alkenyl or C2-C4 alkynyl, any of which may optionally be substituted with one or more halogen atoms, or halo; or, where appropriate, a salt thereof; from a mixture containing the compound of general formula I prepared by the nitration of a compound of formula (II) wherein R1, R2 and R3 are as defined for general formula I, together with one or more isomers or di-nitrated analogues thereof; the process comprising dissolving the mixture in a suitable crystallisation solvent; recrystallising the product from the resulting crystallisation solution; holding the mixture after crystallization from about 1 hour to 2 hours before separating the compound of general formula I; and separating the compound of general formula I; wherein the crystallisation solution contains not more than 25% loading of the compound of general formula I, loading is defined as: weight&it;â€ƒ&it;of&it;â€ƒ&it;pure&it;â€ƒ&it;compound&it;â€ƒ&it;of&it;â€ƒ&it;formula&it;â€ƒ&it;IÃ—100weight&it;â€ƒ&it;of&it;â€ƒ&it;pure&it;â€ƒ&it;compound&it;â€ƒ&it;of&it;â€ƒ&it;formula&it;â€ƒ&it;I+weight&it;â€ƒ&it;of&it;â€ƒ&it;solventâ€ƒand the temperature to which the solution is cooled for crystallisation is not greater than about 30Â° C.