Microwave-Assisted Organic Synthesis of a Diels-Alder Reaction

I. Introduction

A. Objective

The purpose of this experiment is to perform a microwave assisted Diels-Alder reaction of 2,3-dimethyl-1,3-butadiene with maleimide. This reaction will take place inside a microwave reactor, which will assist the Diels-Alder reaction and make it happen much faster and more efficiently than it normally would.

B. Materials and Safety

C. Experimental Procedure

First, a microwave reaction vessel and small magnetic stirring bar will be obtained from the teaching assistant. The stir bar will be placed into the vessel. Next, 1.28 g of maleimide, 3.00 mL of 2,3-dimethyl-1,3-butadiene, and 3.75 mL of water will be added to the reaction vessel. The teaching assistant will fit the reaction vessel with the top and tighten it with a pre-set torque wrench. The teaching assistant will then help place the reaction vessel into a protective sleeve and into the microwave turntable. The position of the vessel in the turntable will be recorded. The teaching assistant will then turn the microwave reactor on, and the vessels will be heated for 10 total minutes. The reactor will be allowed to cool for 20 minutes after completion of heating. The vessel will then be removed from the reactor and brought to the work area under the hood. The cap of the vessel will be loosened and the vessel will be allowed to vent and cool to room temperature. The white solid inside the vessel will be collected via vacuum filtration. Once the product is dry, it will be weighed and its melting point will be determined using the Mel-Temp apparatus.

II. Experiment and Results

A. Data

First, a microwave reaction vessel and a small magnetic stirring bar were obtained. Then added to the vessel were 1.281 g of maleimide, about 3.75 mL of water, and 3.00 mL of 2,3-dimethyl-1,3-butadiene, in that order. The cap of the reaction vessel was fastened using a pre-set torque wrench and it was placed into the microwave reactor. The microwave reactor was then turned on a set to its programmed heating method, in which the temperature was increased to 110 ºC over a 5 minute period and was held at 110 ºC for 5 more minutes. The vessel was then allowed to cool in the reactor for about 25 minutes. The vessel was then brought to the work area and the cap was removed. The vessel was allowed to cool for a few more minutes, then the solid in the vessel was collected using vacuum filtration. The vessel was washed with cold water to help transfer the product to the filtration device. The product was allowed to air dry for two weeks, and was then weighed and its melting point was determined using a Mel-Temp device.

Moles of maleimide was calculated by dividing the weight by the molar weight. The molecular weight of the product was calculated by adding the molecular weight of the two reagents. The theoretical moles of product recovered is the same as the moles of maleimide, which is the limiting reagent. The theoretical weight of the product was found by multiplying the molecular weight by the number of moles. The percent recover was determined by dividing the actual weight recovered by the theoretical weight recovered and multiplying by 100.

III. Conclusions

This was a fairly straightforward lab. I expect the percent recovery to be very high because the microwave reactor is very efficient at speeding up chemical reactions. Microwaves do not produce a lot of excess waste from reactions, so this means most of the chemical reaction that we wanted to take place should have happened, which would result in a high percentage of desired product. The only things that would throw our results off are if we were not able to get all of the product out of the reaction vessel or if cold water was not used in washing it out. If warm water was used, the product would become soluble and it would wash away, leaving a low percent yield.