Diels alder reaction experiment

Experiment #4-3: Diels-Alder Reaction INTRODUCTION In1928 two German chemists, Otto Diels and Kurt Alder, developed a [4+2]π-cycloaddition reaction of dienes that has since come to bear their names. The reaction proved to be one of such great versatility and synthetic utility that Diels and Alder were awarded the Nobel Prize in chemistry in 1950. In general terms, the reaction is one between a conjugated diene (a 4πelectron system) and a compound containing a double bond (a 2π-electron system) called dienophile. In the Diels-Alder reaction, two new σ bonds are formed at the expense of two π bonds of the diene and dienophile. The product contains a new six membered ring with a double bond. In this experiment cis-4-cyclohexene-1,2-dicarboxylic anhydride will be synthesized from 3-sulfolene and maleic anhydride by Diels-Alder reaction as shown below mechanism. O S O 3-sulfolene 140 oC xylene + SO2 (g) 1,3-butadiene (diene) Scheme 1. Formation of 1,3-butadiene. O O O oC 140 xylene O maleic 1,3-butadiene anhydride (diene) (dienophile) O O cis-4-cyclohexene-1,2-dicarboxylic anhydride Scheme 2. Formation of the product cis-4-cyclohexene-1,2-dicarboxylic anhydride First, 1,3-butadiene is generated by heating 3-sulfolene at 140 °C in xylene because the physical state of 1,3-butadiene is gas. As soon as 1,3-butadiene is formed in the reaction flask, it reacts with maleic anhydride to yield the product (cis-4-cyclohexene-1,2-dicarboxylic anhydride). PROCEDURE Part A. Formation of the product 1. Place 1.0 mmol (0.098 g) of maleic anhydride and 2.2 mmol (0.260 g) of 3-sulfolene in a 3 mL conical vial with a boiling chip. Note: Whenever you measure reagents on a balance, you should always record the measured mass in your notebook because you will use it in the theoretical calculation. 2. Add 15 drops of xylene in to the conical vial. 3. Place the conical vial on a hotplate with an aluminum block. 1 4. Attach the condenser (using a clamp) and connect it to the tap water as shown in demo by your instructor. 5. Clamp a thermometer and place it on the hotplate through the small hole of the aluminum block. Note: Make sure the thermometer bulb is not touching the surface of the hotplate. 6. Turn on the tap water and make sure the outlet water hose is placed in the sink. 7. Heat the mixture to boiling and continue heating for additional 20 minutes (this heating method is called “reflux”). 8. Cool down the reaction mixture after 20 – 30 minutes of reflux. 9. Transfer the solution from the conical vial to a Craig tube and add 10 – 20 drops of toluene. Part B. Recrystallization 1. Place the Craig tube in a hot water bath until all solids dissolve. 2. Allow the Craig tube cool down slowly. You should see crystallization in the Craig tube. If not, add hexane to the Craig tube dropwise while tapping or stirring the solution until any precipitate forms, and then dissolve the precipitate in the hot water bath.