Butadienoic Acid from Allenyllithium

Apparatus 21 round-bottomed, three-necked flask, provided with an inlet tube (for C02), a mechanical stirrer and a combination of thermometer and gas outlet. 

The experimental conditions for the carboxylation of allenyllithium are governed by the consideration that introduction of the COOLi group renders the allenic protons more acidic (resonance stabilization). If the normal order addition is used (introduction of C02 into the solution of allenyllithium), the allenic carboxylate primarily formed may easily be deprotonated by the strongly basic allenyllithium. The new species (either LiCH=C=CHCOOLi or H2C=C=C(Li)COOLi) may react also with C02. To avoid this situation the solution of allenyllithium is gradually added to a strongly cooled solution of carbon dioxide in THF. As usual, liberation of the acid occurs by adding mineral acid. In view of the possibility of an acid-catalyzed cyclization to a lactone too strongly acidic conditions should be avoided  

THF (200 ml) is cooled to —90 °C (occasional cooling with liquid nitrogen, care being taken that no solid is formed on the bottom of the flask, Note 1). A vigorous stream of carbon dioxide (about 1 1/min) is introduced for 5 min with efficient stirring, while keeping the temperature between —80 and —95 °C. The thermometer-outlet combination is then removed and a solution of 0.20 mol of 

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