106.0 g of 3,5-difluorophenylhydroxyacetohydrazide (B2) are dissolved in 820 ml of N,N-dimethylformamide. 104.9 g of 2-ethyl-4-methoxy-3-methylbenzoic acid (B1), 153.9 g of N-3-dimethylaminopropyl-N′-ethylcarbodiimide hydrochloride (DAPECI) and 42.8 g of hydroxybenzotriazole (HOBt) are subsequently added. The reaction mixture is cooled in an ice bath during the addition of the compounds enumerated above. The solution is then stirred at room temperature for 24 hours. For work-up, the reaction mixture is diluted with 3.5 litres of water. The resultant suspension is stirred for one hour, subsequently filtered off and washed with additional water. The filter cake is recrystallised from 2.5 litres of methanol, giving 129.0 g of the title compound as colourless solid having a melting point of 197.1° C. (MS: 401 (MNa+)).
