| 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 hydroxy; or COOR4, COR6, CONR4R5 or CONHSO2R4; R4 and R5 independently represent 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; and 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 analogs thereof; the process comprising dissolving the mixture in a suitable crystallization solvent and recrystallizing the product from the resulting crystallization solution wherein the crystallization solution contains not more than 25% loading of the compound of general formula I, loading being defined as: and wherein the temperature to which the solution is cooled for crystallization is not greater than about 30 DEG C.; wherein, after the addition of the crystallizing solvent but before recrystallization, the crystallization solution is subjected to at least one wash with an aqueous solution having an acid pH. The process is particularly useful for purifying acifluorfen produced via a route starting with m-cresol.
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