Written by Hannah
Ring expansion can be achieved through a cyclo addition reaction of a dinophile and a conjugated diene in a concerted reaction where all electrons move at the same time. The experiment takes place in a single step and therefore contamination would stem from overuse of the non-limiting reagent. Cyclohex-4-ene-1,2-cis-dicarboxcylic anhydride was prepared by placing butadiene sulfone (2.0g, 0.0169moles), the diene, with maleic anhydride (1.2g, 0.0122moles), the dinophile, while dissolved in the solvent xylene (.80mL, 0.0075moles) and applying heat to initiate the mobility of the electrons. The crude product was purified by filtering the solid with a Buchner funnel and the utilization of hexane affording only 46.53% yield. The product’s structure was confirmed using melting point (97C-103C) and H’NMR.
In order to synthesize the desired cyclohexane system, heat is utilized to excite electrons and allow the dinophile and diene to participate in a concerted reaction. The conjugated diene provides four electrons and the alkene (dinophile) provides the other two electrons to synthesize the cyclohexane. There are no competing reactions to be concerned with due to the one step concerted reaction that takes place between the compounds.
For this experiment, the concerted Diels-Alder reaction was established by synthesizing cyclohex-4-ene-1,2-dicarboxylic anhydride from butadiene sulfone and maleic anhydride.
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Weight 2.0g 1.2g .965g
Or Vol. ———- ———- ———-
Molec. Wt. 118.2 98.1 170
Or molarity ———– ———– ———–
0.0169 0.0122 0.00567
Moles ———– ———— ———–
Moles butadiene sulfone 0.00169 X ——————– = 0.0169 moles needed
needed to react with butadiene 1 mole butadiene (0.0122 used)
Therefore, maleic anhydride is the limiting reagent
1 mole cyclohex-4-ene, ect. 170
Theoretical yield = 0.0122 moles X —————————– X ——— = 2.074g
maleic anhydride 1 mole maleic anhydride 1 mole
Percentage yield = .965g/2.074g X 100 = 46.53%
Cyclohex-4-ene-1,2-dicarboxcylic anhydride was synthesized in 46.43% yield from the concerted Diels-Alder reaction of butadiene sulfone and maleic anhydride. The products were dissolved in xylene and heated to xylene’s boiling point in order to catalyze the reaction. The mixture was collected via Buchner funnel vacuum filtration. The only product isolated from the reaction was the desired concerted reaction of the two reagents.
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This suggests that the lack of percent yield was due to the use of the solvent xylene. Portions of the reagents and the xylene may have evaporated during the hour long reflux period. The heating of the reagents was necessary to conjugate butadiene sulfone into butadiene so that the electrons were available for reacting with maleic anhydride. The oxygen electron withdrawing groups enhanced the speed of the reaction greatly. Xylene was used in order to liquefy the reagents and allow heating them to occur more easily.
The identity of the product was determined by the use of melting point that which was between 82C and 84C. The melting point should have been between 97C and 103C. The H’NMR spectra showed correct spikes for the corresponding unique protons. This suggests that the melting point may have been contaminated by unreacted butadiene sulfone. This may have been caused by the butadiene remaining in the butadiene sulfone state rather than conjugating into the butadiene state and thus did not allow the necessary electrons to become available. However, another possibility was that the butadiene sulfone did not have enough maleic anhydride to react with and thus remained in the product.
Another possible reason that the percent yield was so low was the transfer methods used to remove the product from both the round bottom flask and the beaker it was later placed in. parts of the product more than likely remained upon transfer and thus lowered the percent yield collected in the final vial it was placed in.
The results of this experiment suggest that the concerted reaction of alkenes and cyclic compounds can be an easily done, general method to create cyclohexane systems. They also show that the use of maleic anhydride can be extremely useful in the creation of cyclohexane systems because of its electron withdrawing groups and its cyclic properties. It readily uses the electrons necessary for the Diels-Alder reaction.
2.048 grams of butadiene sulfone was combined with about 1.2 grams of maleic anhydride and .80mL of xylene in a 50mL round bottom flask. This was attached to a reflux condenser set up with water cooling agents before the mixture was heated with a sand bath. The heat remained on the reaction until the solid was dissolved before refluxing at 150C for an hour. Once the reaction completed reflux, it was removed and cooled for ten minutes before being placed in a dry beaker. The mixture was then allowed to solidify before 2mL of hexane was added to it. The solid lumps were broken with stirring and an additional 2mL was needed to completely detach the solid from the beaker. Once it was slushed, the product was collected on a Buchner funnel with two 2mL washes of hexane. About .965 grams of brown sugar colored crystals were collected.
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Molecular Weight Calculator.” Lenntech. Lenntech B.V, n.d. Web. 17 Apr 2013. http://www.lenntech.com/calculators/molecular/molecular-weight-calculator.htm
A Diels-Alder Reaction.” Washington Departments. N.p., n.d. Web. 17 Apr 2013. http://depts.washington.edu/chemcrs/bulkdisk/chem241A_spr07/handout_Diels_Alder.pdf.