Ortho-substituted fluorine in 2, 4-difluorobenzoic acid was found to be regio-selectively replaced to hydroxide by solid sodium hydroxide in 1, 3-dimethyl-2-imidazolidinone, to afford 4-fluoro-2-hydroxybenzoic acid in high yield. Several multi-fluoro-substituted benzoic acid derivatives were effectively transformed to the corresponding salicylic acid derivatives under the similar conditions.
