Dicyclopentadiene → 4,5,6,7-Tetrahydro-4,7-methanoisobenzofuran-1,3-dione

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Mixed polybasic anhydride containing a plurality of 1,2 anhydrides is obtained by distilling, at 200° C., 66.10 gms. (1 mole) of cyclopentadiene directly from dicyclopentadiene into a reactor containing 98.06 gms. (1 mole) of maleic anhydride, heated to a temperature of 55° C. When the transfer is complete, the reaction mixture is heated to 100° C. for 2 hours. The reaction mixture is then stripped of any excess cyclopentadiene at 120° C. at 1 atmosphere. The resulting Diels-Adler adduct of cyclopentadiene and maleic anhydride is the anhydride of cis.-5-norbornene-2,3-dicarboxylic acid. The reaction mixture is cooled to 50° C., and 4.90 gms. (0.03 moles) of boron trifluoride etherate is added slowly with stirring. The reaction mixture exotherms to 65° C. after which it is heated to 125° C., to decompose the BF3OEt and then cooled. The reaction is quenched by mixing with 3 liters of 10% sodium bicarbonate. The mixture is then neutralized with dilute 5% hydrochloric acid. The mixed polybasic anhydride of norbornene-2,3-dicarboxylic acid anhydride is obtained as a fine tan power, Mp. 200° C., and used for foam preparation without further purification.

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