Introduction

A Diels-Alder reaction is a reaction in which a conjugated diene bonds with an alkane to produce a cyclohexane molecule. This reaction works best with dienes that are electron rich and dienophiles that are electron poor. For this experiment, our dicyclopentadiene is the diene and the maleic acid is our dienophile.

In a Diels-Alder reaction, sigma bonds are formed from pi bonds. For this particular experiment, cyclopentadiene and maleic anhydride react via Diels-Alder in order to produce an endo-bicyclic product: cis-5-norbornene-endo-2,3-dicarboxylic anhydride. This product is a six-membered ring alkene with two sigma bonds.

Materials and Methods

Materials Used

* 3 g maleic anhydride * 5 mL dicyclopentadiene * 8 mL ethyl acetate * 3 mL cyclopentadiene (from distillation)

Method

1) A total of ____________ of maleic anhydride was measured out into a 125 mL Erlenmeyer flask 2) Approximately ____________ of ethyl acetate was measured out to dissolve the anhydride. This mixture was then placed on a hot plate. 3) Once heated, ____________ of hexanes was added to the mixture, and then allowed to cool in an ice bath. 4) A total of ____________ of distilled, dry cyclopentadiene was then added and mixed with the ice-cold maleic anhydride solution. 5) The mixture was then swirled in the ice bath until the exothermic reaction ended and we saw a white solid precipitate. 6) Recrystallization was then carried out to purify our final product (the cis-norbornene-5,6-endo-dicarboxylic anhydride). This was done by carrying out the steps entailed below: a. The solid we collected was heated on a hot plate until the solid completely dissolved. b. After dissolving, the solution was removed and allowed to cool to room temperature. c. The product was then filtered using a Buchner funnel. d. The solid crystals were then washed with cold hexanes. e. The crystals were allowed to dry for a week.

Results

The lab group collected the solid crystals and allowed it to dry in a clam shell apparatus for approximately one week. After the week had passed, the sample was then weighed out to determine how much was collected. The lab group also obtained the melting point temperatures of the final product using a Mel-Temp Melting Point Apparatus. The results are tabulated below.

Final weight of product plus clamshell holding device including product: 10.160 g

Clamshell apparatus weight with filter paper and no product: 5.897 g

Total weight of product: 10.160 g – 5.897 g = 4.263 g of product

Melting points of final product (carried out three times):
- Literature value melting point of cis-norbornene-5,6-endo-dicarboxylic anhydride: 165 C * 160 – 164 C * 161 – 163 C * 161 – 163 C

Discussion

For this lab experiment, a Diels-Alder reaction was carried out in order to obtain cis-norbornene-5,6-endo-dicarboxylic anhydride. The steps entailed in the lab were followed as precisely as possible. After the experiment and once the product was allowed to dry, a total of 4.26 g of cis-norbornene-5,6-endo-dicarboxylic anhydride was obtained. However, our theoretical value that should have been obtained was 5.02 g.

Our melting point measurements were incredibly precise (see data given under “Results” section) and accurate. Even though we did not obtain as much product as we should have, we can assume that we collected a fairly pure product, seeing as how we were incredibly close to literature melting point value.

In order to have obtained more product, better transferring of chemicals to different vessels would be on top of the list. Although it’s nearly impossible to get every drop of the product, it is important to be as precise and streamlined as possible. Had we done this, I believe we would have obtained a percent yield closer to the value given.