Question

Diels-Alder Reaction of cis-Butadiene with Maleic Anhydride Experiment:

Give the reaction conditions, ie. what apparatus, solvent, temperature and time will be used. How will the product be isolated from the reaction mixture and how will it be characterized?

Answer 1

Experimental Set-Up for Diels-Alder Reaction

The 25-mL round bottom flask contained 2.79 grams of 3-sulfolene, 1.63 grams of maleic anhydride, and 1.0 mL of xylene to dissolve the materials. The solution was lightly heated until the mixture fully dissolved, then the mixture was strongly heated until reflux. The reaction was conducted at reflux temperature for 30 minutes. After the round bottom flask was removed from the experimental set-up, 10 mL of xylene was added to the hot mixture and the reaction was stirred until all of the precipitate dissolved again. Then the mixture was transferred to an Erlenmeyer flask. About 5 mL of petroleum ether was added to precipitate the reaction product and that was filtered with vacuum filtration.

A small amount of the product, 4-cyclohexene-cis-1,2-dicarboxylic anhydride, was removed and tested for unsaturation with bromine and permanganate. The product tested positive for unsaturation by both tests. Another small amount of this product was set aside to air-dry in the lab locker for one week. After drying, the melting point was measured to be 920C. The remaining anhydride sample was separated for hydrolysis.

About 12 mL of deionized water was added to about 2 grams of anhydride in an Erlenmeyer flask. The flask was heated until all of the crystals dissolved, with occasional mixing by swirling the flask. Then the flask was cooled to room temperature and the side of the flask was scratched with a metal spatula to promote the growth of crystals. The crystals were removed from the water by vacuum filtration and set in the lab locker to air-dry for one week. Once the products was dry, unsaturation tests and melting point of the solid was conducted. The dicarboxylic acid product tested positive for both the bromine and permanganate unsaturation tests and the metling point was found to be 1670C. A mass of 1.90 grams of product was also recorded.

Observed Properties of Products:

4-cyclohexene-cis-1,2-dicarboxylic anhydride:

White solid

Observed Melting Point = 920C

2.26 grams recovered: Yield = 2.26 g/2.529 g = 89% yield

Positive unsaturation tests

4-cyclohexene-cis-1,2-dicarboxylic acid:

White solid

Observed Melting Point = 1670C

Adjusted Yield Calculations: 2.26 grams anhydride x = 0.01485 mol anhydride = 0.01485 mol acid x = 2.53 grams of acid predicted.

1.90 grams recovered: Yield = 1.90 g/2.53 g = 75% yield

Positive unsaturation tests

Side Reactions:

1. Anhydride product of Diels-Alder reaction could have possibly hydrated before extraction, causing it to be soluble in petroleum ether.

2. The 1,3-butadiene could have evaporated before it had a chance to react with the maleic anhydride.

Method of Purification: