1: 72 percent / chromium trioxide / acetic acid / 12 h / Ambient temperature 2: 42 percent / p-toluenesulphonic acid / benzene / 18 h / Heating 3: 70 percent / H2O / 2 h / 190 - 200 °C / sealed tube 4: 58 percent / sodium borohydride / pyridine / 12 h / Heating 5: 48percent HBr / Heating View Scheme