| 摘要 |
A process for the preparation 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; the process comprising reacting a compound of general formula II: wherein R<1>, R<2 >and R<3 >are as defined for general formula I; with a nitrating agent comprising nitric acid or a mixture of nitric and sulphuric acids in the presence of an organic solvent and in the presence of acetic anhydride, characterised in that the molar ratio of acetic anhydride to compound of general formula I is from about 1:1 to 3:1. |
