1: With sulfuric acid 2 h; Heating / reflux; 2: With anhydrous trisodium citrate in propan-1-ol; water T=0 - 4°C; pH=4; 1.5 h; 3: With 4-methyl-morpholine; sodium hydrogencarbonate in water T=0 - 4°C; pH=6 - 7; 4 h;