A boiling solution of maleic anhydride (128) (196.2 g, 2.0 mol) in AcOH (200 mL) was added dropwise over 1 hour to a boiling solution of 2-aminopyridine (129) (94.1 g, 1.0 mol) in AcOH (200 mL). A strong CO2 evolution was observed. The mixture was heated under reflux for 2.5 hours, and then acetic acid was distilled off through a Claisen bridge. After adding 2 M H2SO4 (600 mL), the mixture was stirred under reflux for 2 hours. After cooling, the precipitated crystals were filtered off and washed with 2 M H2SO4 (3 x 50 mL) and H2O (2 x 50 mL). Light brown flakes (obtained after 24 hours in a desiccator (P2O5)) were sublimated at 60 °C and 0.02 mbar.
Yield: 68.0 g (0.54 mmol, 54%) colorless crystals of 2,3-dimethylmaleic anhydride, Rf(SiO2) = 0.46 (c-hexane/EA 1:1). mp 91-92°C (95°C).
Figure 2,3-Dimethylmaleic Anhydride Synthetic Route
