| 摘要 |
A process for the preparation 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 alk yl 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; the proce ss comprising reacting a compound of general formula (II), wherein R1, R2 and R3 are as defined for general formula (I) with a nitratin g agent comprising nitric and sulphuric acids in the presence of an organic solvent and in the presence of acetic anhydride, the molar ratio of acetic anhydride to compound of general formula (II) is from about 1:1 to 3:1 characterised in that the acids are added sequentially to t he reaction mixture.
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