A process of preparing the crystalline modification II of the anhydrate of boscalid comprising: reacting 2-chloro-nicatinoyl chloride with 4'-chloro-biphenyl-2-ylamine in a solvent system while removing from the reaction mixture hydrogen chloride formed during the reaction; and recovering the crystalline modification II of the anhydrate of boscalid from the reaction mixture. Preferably 4'-chloro-biphenyl-2-ylamine is present in the reaction mixture in excess and the solvent system comprises a polar organic solvent and/or an aromatic solvent. For example the solvent system may comprise iso-propanol, acetonitrile, benzene, toluene or dichloromethane. Preferably the hydrogen chloride produced is removed by adsorption using an adsorbent, preferably activated alumina and an alkali metal promoter. Also preferably the reaction is conducted at a temperature of 20-80°C, and the reaction mixture is subsequently cooled to 5-20°C to allow boscalid to crystallize from the reaction mixture.
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