Terphenyl by the Diels-Alder Reaction

Prelab Exercise Why does the dicarboxylate, 5, undergo double decarboxylation to give terphenyl, while the diacid formed from the reaction of cyclopentadiene with maleic anhydride (Chapter 24) does not undergo decarboxylation under the same reaction conditions  

Caution Handle dimethyl acetylenedicarboxylate with care. 

Place 1.5 g of , -1,4-diphenyl-1,3-butadiene (from the Wittig reaction. Chapter 34) and 1.0 mL (1.1 g) of dimethyl acetylenedicarboxylate caution, skin irritant ) in a 25 x 150-mm test tube and rinse down the walls with 5 mL of triethylene glycol dimethyl ether (triglyme) (bp 222°C). Clamp the test tube in a vertical position, introduce a cold finger condenser, and reflux the mixture gently for 30 min. Alternatively, carry out the experiment in a 25-mL round-bottomed flask equipped with a reflux condenser. Cool the yellowish solution under the tap, pour into a separatory funnel, and rinse out the reaction vessel with a total of about 50 mL of ether. Extract twice with water (50-75 mL portions) to remove the high-boiling solvent, shake the ethereal solution with saturated sodium chloride solution, and dry the ether layer over anhydrous sodium sulfate. Filter or decant the ether solution into a tared 125-mL Erlenmeyer flask and evaporate the 

This ester is a powerful lachrymator (tear producer) and vesicant (blistering agent) and should be dispensed from a bottle provided with a pipette and a pipetter. Even a trace of ester on the skin should be washed off promptly with methanol, followed by soap and water. 

Caution Extinguish all flames before working with ether 

---