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Dicarboxylic Anhydride

White solids, maleic anhydride (2. 45 g, 0. 025 mole) was dissolved in ethyl acetate (8mL) using steam as a source of heat. Hexane (8mL) was then added to the mixture and cooled using an ice bath. Cyclopentadiene, which is prepared by thermal cracking, was added to the solution. The mixture has turned into white solid form after it was swirled in an ice bath. The mixture has been heated on the steam bath until the solid particles was totally dissolved. The solution was then observed and it slowly crystallizes at room temperature.

White needle shapes of crystals are formed slowly in the solution. The solids compounds are norbeornene-2, 3-dicarboxylic anhydride; 2. 976 g, 18. 1 mmole, 72. 6 % yield, M. p=152? C-156? C (Lit2=165? C) Discussion Norbeornene-2, 3-dicarboxylic anhydride was obtained by Diels-Alder reaction between cyclopentadiene and maleic anhydride. Cyclopentadiene was a conjugated diene, which acted as a nucleophile. Maleic anhydride was a dienophile, which has a double bond conjugated with electron withdrawing group.

The reaction involved the redistribution of electrons and bonds, which occurred in one step of the reaction. Two double bonds have disappeared, two new single bonds were formed, and a double bond appeared between two atoms which formerly shared a single bond. Since cyclopentadiene is not available, the compound was prepared by thermal cracking of dicyclopentadiene. Cyclopentadiene has low boiling temperature that is why it was collected by distillation process.

The mixture has been slowly cooled in order prevent equilibrium which is being reversed and to minimize the loss of cyclopentadiene due to its high volatility. Ethyl acetate was used as a solvent to dissolve maleic anhydride. Hexane was added after all maleic anhydride was dissolved because it changes the polarity of the solvent to prevent dissolving maleic anhydride. Another reason of using hexane is to crystallize the desired product, norbeornene-2, 3-dicarboxylic anhydride, because ethyl acetate can dissolved the product.

Accumulation of water was prevented because of two reason; it can hydrate maleic anhydride to form maleic acid and it can hydrate the product, norbeornene-2, 3-dicarboxylic anhydride to form its dicarboxylic acid. Two different configurations, of the “exo” and the “endo” products are possible to be formed. The “endo” product was obtained because it is generally predominant in Diels Alder reactions due to ? stacking. The product yield of 72. 6 % has indicated that some of the products were lost during the experiment.

Loss of the reagent, cyclopentadiene thru evaporation possibly affects the product yield due to its high volatility. Also, some of the product has not crystallized into the solvent. The possibility, that the equilibrium has been reversed because the reaction favored the room temperature. The low and broader melting point, 152? C-156? C (Lit2=165? C) indicated that some impurities has existed in the product. Some of the solvent has remained in the product because it was dried over a relative short period of time.

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