Diels-Alder Reactions Experiment

Abstract

A Diels Alder reaction was done during this experiment between anthracene and maleic anhydride via to yield 9, 10-dihydroanthracene-9, 10-α, β-succinic anhydride. Anthracene was the diene and maleic anhydride was the dienophile. Following recrystallization of the product using xylene and vacuum filtration, a percent yield of 39.9% was calculated for the recrystallized product that was collected. The yield may have been low due to several of the crystals being stuck to flask and not going into the funnel, and there may have been other sources of error. The percent recovery from recrystallization was 56%. The melting point of the recrystallized product was 260 – 264°C, while the literature melting point of 262 – 264°C. Comparing these values shows that the product was indeed and that recrystallization yielded a purer product. Upon examination of an infrared spectrum of the product and of anthracene and maleic anhydride spectra, the data showed that the product spectrum had similarities with both spectrums for anthracene and the maleic anhydride. This indicated that 9, 10-dihydroanthracene-9, 10-α, β-succinic anhydride was a product of both anthracene and maleic anhydride, and thus that the experiment was successful.

Figure 1: Reaction scheme of 9,10 dihydroanthracene-9, 10- α, ß-succinic anhydride

Introduction

The 1950, Otto Paul Hermann Diels and Kurt Alder were awarded Nobel Prize in chemistry for their work on the discovery and development of [4+2] cycloaddition reactions. Diels-Alder reactions are used to synthesize new carbon-carbon bonds, more commonly they form six-membered cyclic compounds. The Diels-Alder reaction is categorized as a pericyclic reaction, which involves the overlap of spatial orbitals as well as the hybridization and delocalization of the molecules.1 The Diels-Alder reaction is a member of a class of reactions called cycloadditions, which are under pericyclic reactions. Usually, the reaction involves three π bonds, two from the diene and one from the dienophile in the reaction to form a six-membered ring.Since this reaction involves four π electrons in the diene and two π electrons from the dienophile, it is sometimes referred to as a 4π + 2π cycloaddition. Various chiral auxiliaries and catalysts for asymmetric Diels-Alder chemistry have been developed that allow the cycloaddition to proceed with very high levels of selectivity.3 The use of chiral Lewis acid catalysts and high pressure to enhance the selectivity and rate of these [4π + 2π]-cycloadditions have further extended the scope of this remarkable reaction.1,2 Diels-Alder reactions are normally favored by electron donating groups on the diene and electron withdrawing groups on the dienophile. The diene must be able to achieve a s-cis conformation to generate the cis double bond in the cyclohexene product.3 Acyclic dienes may rotate around a single bond, but dienes locked in the s-trans conformation do not react.3 The purpose of this experiment is to yield 9,10-dihydroanthracene-9,10-α, β-succinic anhydride via a Diels Alder reaction between anthracene and maleic anhydride, as shown in figure 1. Anthracene acts as the diene and maleic anhydride functions as the dienophile. Xylene is used as a high boiling temperature solvent so that the reaction will proceed quickly. A key characteristic of these reactions is their stereospecificity.3 Based on the interaction between a cyclic diene and a dienophile, different stereoisomeric compounds are formed. Stereochemistry represents a major component of the Diels-Alder reaction.2 Due to the interaction and arrangement between the conjugated diene and dienophile, an endo and exo product could be formed, which can characterize the reaction as stereo- and/or regioselective.

Experimental

Instruments used: The instruments that were used were the Thomas Hoover Melting, and a Nicolet IR 100 FT-IR were used in this experiment.

Procedure and Observations: A reflux apparatus was assembled. Xylene (6 mL), anthracene (0.5 g), and maleic anhydride (0.25 g) were added to a round bottom flask (25 mL). The solution turned a yellow color when the reactants were added together. The reflux was then started, and once it began to boil, it was boiled for 30 minutes. A watch glass was weighed (35.55 g), which the product would later be transferred to. After reflux, the solution was cooled to room temperature, and then xylene (6 mL) was added to a test tube and laced into an ice bath. The solution appeared to be a golden yellow color after the reflux. Next, xylene (15 mL) was added to a beaker (50 mL), and then a vacuum apparatus was assembled. The solution was placed chilled for 5 minutes, and it became cloudy and crystals began to form. The solution was filtered through a Buchner funnel on the vacuum filtration. After the vacuum filtration, the crude product were light yellowish-brown crystals. Xylene (15 mL) was boiled, and was then added to the crude product, just enough to cover it, and was heated. The crystals began to dissolve the hot xylene was added, and as it dissolved the color became lighter and clearer. Once dissolved, the solution was then placed into an ice bath, after being cooled to room temperature. It was then put through the vacuum filtration; the recrystallized product was allowed to dry, and then weighed (0.28 g). Finally, the product was analyzed using IR and the melting point apparatus.

References

C. Oliver Kappe, S. Shaun Murphree, Albert Padwa, “Synthetic applications of furan Diels-Alder chemistry”, Tetrahedron, Volume 53, Issue 42, 1997, Pages 14179-14233, ISSN 0040-4020.

Wade, L.G., Jr. “The Diels-Alder Reaction of Anthracene and Maleic Anhydride” (1998).

Simek, Jan William., and L. G. Wade. Solutions Manual Organic Chemistry, Eighth Edition L.G. Wade, Jr. Boston: Pearson, Boston, 2013. Print.