Esterification of Monoethyl Fumarate – DMAP as Catalyst

B. Neises and W. Steglich , Org. Synth. 63, 183 (1985)

1. A solution of monoethyl fumarate (28.83 g, 0.20 mol), dry dichloromethane (200 mL), tert-butyl alcohol (44.47 g, 0.60 mol), and DMAP (2.00 g, 0.16 mol) is prepared.  Keeping the reaction mixture dry, the stirred solution is cooled to 0°C and dicyclohexylcarbodiimide (45.59 g, 0.22 mol) is added over 5 min.
2. After stirring for a further 5 min. at 0°C, the reaction mixture is allowed to warm to ambient temperature and stirred for a further 3 h.
3. The precipitated dicyclohexylurea is removed by filtration and the filtrate is washed with 0.5 N hydrochloric acid (2 x 50 mL) and satruated sodium bicarbonate solution (2 x 50 mL).  Additional dicyclohexylurea is precipitated and removed by filtration of both layers to facilitate their separation.  The organic phase is dried over anhydrous sodium sulfate, filtered and concentrated.  The concentrate is distilled under reduced pressure affording tert-butyl ethyl fumarate (30.5-32.5 g, 76-81%, b.p. 105-107°C at 12 mm).