| 摘要 |
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 together with one or more isomers or di-nitrated analogues thereof; the process comprising dissolving the mixture in a suitable crystallisation solvent and recrystallising the product from the resulting crystallisation solution;characterised in that the crystallisation solution contains not more than 25% loading of the compound of general formula I wherein loading is defined as:and in that the temperature to which the solution is cooled for crystallisation is not greater than about 30° C.
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