Diels-alder Reaction

Objective

The objective is to react a dienophile in the form of maleic anhydride with a diene in the form of cyclopentadiene to produce a Diels-Alder product, cis-Norbornene-5,6-endo-dicarboxylic anhydride. The product will be formed as crystals through filtration and the melting point will be noted to determine purity as well as the percent yield.

Procedure

Note: Cyclopentadiene will be prepared fresh before each lab through distillation because it readily goes through Diels-Alder reactions with other cyclopentadienes.

·         Add 0.405 g of maleic anhydride and 1ml of ethyl acetate to a test tube and dissolve by stirring with a spatula. If dissolving does not occur through warming, add an extra 0.5ml ethyl acetate.

·         Once all the maleic anhydride has dissolved, add 2ml of hexane.

·         Add 0.4ml of cyclopentadiene (20 drops from a Pasteur Pipette) to the maleic anhydride under the hood and mix with a spatula.

·         Allow the test tube to cool down to room temperature for 5 minutes, and then place the test tube in an ice water bath for 2 minutes to complete the crystallization process.

·         Weight the dry filter and filter paper and set up the aspirator for suction filtration.

·         Use a pipette to break up the crystals and decant the crystals into the filter.

·         If any crystals are remaining in the test tube, rinse with 3 ml of hexane and pour the mixture into the filter.

·         Allow the crystals to dry in the filter for two minutes as the suction pulls air over the crystals.

·         Reweigh the filter, filter paper and crystals. Note the yield.

Collect crystals and find the melting point and melting point range to determine the purity.

Data and Results

0.405 grams maleic anhydride

1 ml ethyl acetate

2 ml hexane

0.4 ml cyclopentadiene

Calculations

            Finding the Limiting Reagent

·         0.4ml cyclopentadiene (0.8g/1ml)(1mol/66g) = 4.485E-3 moles cyclopentadiene

·         0.405 g maleic anhydride (1mol/98g) = 4.13E-3 moles maleic anhydride

SO since the reaction is 1:1 for the reagents maleic anhydride is the limiting reagent.

            Percent Yield

·         0.405 g maleic anhydride (1mol/98g)(1mol maleic anhydride/1mol cis-Nornornene-5,6-endo-dicardoxylic anhydride) =   4.13E-3 moles cis-Nornornene-5,6-endo-dicardoxylic anhydride Theoretical Yield

·         Product Crystals = 8.231g-7.612g= .619g cis-Nornornene-5,6-endo-dicardoxylic anhydride Crystals

·         .619g cis-Nornornene-5,6-endo-dicardoxylic anhydride (1mol/164g) = 3.77E-3 mol cis-Nornornene-5,6-endo-dicardoxylic anhydride

·         (3.77E-3 mol observed/4.13E-3 mol expected)*100 = 91.4% yield

Conclusions

For the experimental yield the percent yield of cis-Nornornene-5,6-endo-dicardoxylic anhydride was 91.4 % yield. This is a very good yield for the reaction and is only slightly lower than 100% because not all of the crystals were able to be obtained from the test tube, although most were obtained. The product crystals then had their melting points taken. The crystals began to melt at 140°C and were fully melted at 142°C. The melting range of the crystals was only 2°C meaning that the crystals were rather pure. The melting point of the crystals was around 20°C lower than the theoretical melting point of 165°C. Although the crystals were fairly pure, there was probably some cyclopentadiene and maleic anhydride left over that would have lowered the melting point.