| 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 COOH, COH, 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; R 3 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: weight of pure compound of formula (1) .times. 100/weight of pure compound o f formula (I) + weight of solvent, and in that the temperature to which the solution is cooled for crystallisation is not greater than about 3 0 .degree. C.
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