1: With sulfuric acid; water T=80°C; 3 h; 2: With sodium hydroxide in water 3: With hydrogenchloride in water pH=2 - 3;

1.1: hydroxylamine-o-sulphonic acid / water / 0.5 h / 90 °C 1.2: 20 °C 2.1: potassium carbonate; oxygen / N,N-dimethyl-formamide / 2 h / 20 °C 3.1: water; sulfuric acid / 3 h / 80 °C 3.3: pH 2 - 3 View Scheme