PROCESS FOR THE PURIFICATION OF DIPHENYL ETHER COMPOUNDS

摘要

A process for the purification of a compound of general formula (I), wherein R<1> 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, COOR<4>, COR<6>, CONR<4>R<5> or CONHSO2R<4>; R<4> and R<5> are each independently hydrogen or C1-C4 alkyl optionally substituted with one or more halogen atoms; R<6> is a halogen atom or a group R<4>; R<2> 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 (I) x 100/weight of pure compound of formula (I) + weight of solvent, and in that the temperature to which the solution is cooled for crystallisation is not greater than about 30 DEG C.