Diels-Alder Reaction of Cyclopentadiene and Maleic Anhydride

Experimental Principle

Norbornene-5,6 cis-dicarboxylic anhydride is a white columnar crystal, slightly soluble in petroleum ether, soluble in benzene, toluene, acetone, carbon tetrachloride, chloroform, ethanol, ethyl acetate. It can be used as a raw material for polyester resin, alkyd resin, pesticides, urea-formaldehyde resin, melamine resin, turpentine resin, rubber vulcanization regulators, resin plasticizers, surfactants, and so on. Its diallyl ester can be used as a heat-resistant cross-linking agent for unsaturated polyester resin.

Norbornene-5,6-cis-dicarboxylic anhydride is prepared from cyclopentadiene and maleic anhydride through the Diels-Alder reaction. Dicyclopentadiene thermally decomposes on heating (reverse Diels-Alder reaction) to give cyclopentadiene. Cyclopentadiene undergoes a Diels-Alder reaction with maleic anhydride at room temperature to obtain endo-norbornene-5,6-cis-dicarboxylic anhydride.

Experimental Supplies

• Instruments

Round bottom flask, distillation head, thermometer, straight condensing tube, spherical condensing tube, liquid receiving tube, conical bottle, etc.

• Reagents

Cyclopentadiene dimer, maleic anhydride, ethyl acetate, etc.

Experimental Steps

20mL cyclopentadiene dimer was added to the 100mL round bottom flask, and the cyclopentadiene monomer was obtained by inverse Diels-Alder reaction pyrolysis and distillation in an oil bath at 170~190℃, keeping the outlet temperature of the fraction at 40~45℃.

8mL cyclopentadiene was added to the 100mL round bottom flask and the round bottom flask was cooled in an ice bath. Weigh 7.64g maleic anhydride accurately, add it to the conical bottle of 100mL, and add 30mL ethyl acetate to dissolve it. Transfer the ethyl acetate solution of maleic anhydride to a round bottom flask containing cyclopentadiene, take an ice water bath during the transfer process, and stir at room temperature until there is no more white precipitation. Then the round bottom flask is heated in a water bath at 50℃. After the precipitation is completely dissolved, it is cooled to room temperature and white needle-like crystals are precipitated. The product is obtained through reduced-pressure filtration and drying.

Precautions

• Maleic anhydride and its additional products are easy to hydrolyze into dicarboxylic acid, so all instruments, reagents, and solvents should be dried, and attention should be paid to prevent water or water vapor from entering the reaction system.
• Cyclopentadiene is easy to be polymerized into a cyclopentadiene dimer at room temperature, and all marketed cyclopentadiene are dimers. The dimer can be depolymerized to cyclopentadiene above 170℃. If the turbidity of cyclopentadiene obtained by such fractionation is caused by moisture invasion, it can be dried with anhydrous calcium chloride and can be sealed and placed in the refrigerator.
• The addition product norbornene-5,6-cis-dicarboxylic acid anhydride still retains double bonds in the molecule, but potassium permanganate solution or bromine-carbon tetrachloride solution fades. The product is easily hydrolyzed into the corresponding dicarboxylic acid when it encounters water or absorbs water vapor in the air, so it should be stored in a desiccator.