CHEMICAL PROCESS

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 COOH, COH, COOR , 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; 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 process comprising reacting a compound of general formula II: wherein R¹, R² and R³ 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.