Nitrogen insertion reaction of maleic anhydrideNitrogen insertion reaction of maleic anhydride
SyntheticPage 707
Published Dec 05, 2013
A 50 ml 3 neck round bottom flask, equipped with water condenser, water bath, stirring hot plate,dropping funnel, nitrogen inlet, magnetic stirrer, and calcium chloride drying tube, was charged under nitrogen with 4.90 g (0.059 mole) maleic anhydride and 14 ml (~ 0.1 mole) trimethylsilyl azide. A rubber tube exiting the water condenser lead to a one liter water filled inverted graduate cylinder in a water trough, allowing for easy monitoring of nitrogen evolution. Stirring was commenced and the solution was warmed to ~ 40oC with the water bath, upon which the maleic anhydride dissolved. The reaction was gently exothermic at this point with gas evolution into the inverted graduate cylinder. External heating was discontinued. Gas evolution became moderate at ~ 55-60oC. The mixture was alternatively heated and cooled with the water bath to maintain a temperature range of ~ 55-60oC. After 3 h nitrogen gas evolution had ceased. The solution was cooled to room temperature in ice water and 30 ml chloroform was added with stirring. Addition of 2.5 ml absolute ethanol (0.054 mole) and cooling in an icebath to ~ 0oC gave a copious white precipitate which TLC (silica gel, ethyl acetate eluent) showed to be essentially pure "oxauracil". The precipitate was suction filtered, and washed with diethyl ether, yielding 3.2 g (57%), of material. Mother liquor concentration gave a second crop, 1.2g ( total 78%). The product is sufficiently pure for most purposes but may be recrystallized from ethyl acetate. Yields are typically in the 60-80% range.