2130- Lab 5 Diels-Alder PDF

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Lab 5 Diels-Alder Worksheet YouTube video link: https://www.youtube.com/watch?v=HdvrTQpzfjc 1. Purpose of the experiment: (1 point) The purpose of this lab is to perform a 4+2 cycloaddition Diels-Alder reaction to produce a polycyclic product under reflux conditions. 2. Reagents Table: (4 points) Name of reagent

M.W. g/mL

M.P. ºC

B.P. ºC

Density g/mL

Hazards

Anthracene

178.23

215

339.9

1.25

Irritant, health hazard

Maleic anhydride

98.06

52.8

202

1.43

Corrosive, irritant, health hazard

Xylene

318.5

13.2

144

0.864

Flammable, irritant

3. Procedure: (5 points)      

Place 1.0g anthracene and 0.5gmaleic anhydride in 100 mL round bottom flask. Add 15 mL xylene and 1-2 boiling chips and attach reflux condenser to flask (don’t forget to grease joints) Run cool eater through condenser to prevent any escaping vapors and heat mixture under reflux for 30 minutes. At the end of reflux, cool flask to room temperature and then keep flask in ice bath for 10 minutes to completely crystallize the product. Collect crystals by vacuum filtration using Büchner funnel and wash the solid with 15-20 mL ice cold xylene and keep vacuum on for 8-10 minutes. Dry products on filter paper for a further 10 minutes and record wright of products and calculate percent yield of reaction.

4. Mechanism: (5 points)

Observations: 1. 1.02g anthracene and 0.52g maleic anhydride were added to round bottom flask 2. 15mL xylene and 1 boiling chip were added to flask and attached to reflux condenser 3. Transformer was set to 4 and once close to reflux was reduced to 3.5 4. Reflux began, and ran for 30 minutes 5. 16mL of xylene was chilled on ice. Was reflux finished, flask was cooled to room temperature and on ice for 10 minutes. Dark yellow forms as crystals develop 6. 20mL was used to filter product and Büchner funnel set for 10 minutes (product weight  0.97g) Results:

5. Calculate the % yield if 1.1g of anthracene reacts with 1.17g of maleic anhydride to give 0.8g of 9,10-Dihydro-9,10-ethanoanthracene-11,12- Dicarboxylic Anhydride product. Show the calculations. (5 points)

6.

Discussion: (6 points)

The purpose of this lab was to perform a 4+2 cycloaddition Diels-Alder reaction to produce a polycyclic product under reflux conditions. The addition of anthracene and maleic anhydride with xylene as the solvent was subjected under reflux conditions to produce the polycyclic product from Diels-Alder at a faster rate due to the constant conversion of vapor back to the liquid form through a condenser. Xylene was used instead of water, as the maleic anhydride is more reactive in water which affect the results of the experiment. The limiting reagent was determined to be maleic anhydride due to the mole to molecular weight ratio expressed. The mass of the product was filtered and vacuumed through the Büchner funnel to produce 0.97g of product. The mass of product resulting from Diels-Alder reaction (actual yield) was divided by the limiting reagent product mass (theoretical yield) to get the percent yield. With the percent yield being 66.21%, this is fairly accurate in regard to the yield produced but could be improved. The percent yield will never truly reach 100% as side products are formed during the reaction. Possible reasons for error include some of the product falling off of the watch glass before being weighed.

7.

Conclusion: (6 points)

Reflux involves heating the reaction/reactants over a specified time and using a condenser to cool and convert vapor back into liquid form. This allows the reaction to proceed at a faster rate. Through this process, Diels Alder reactions can take place in a time efficient manner

and allow for synthesis of a polycyclic product to be expressed throughout the experiment. The 4π e- anthracene (diene) reacted with the 2π e- of maleic anhydride (dienophile) to form the polycyclic product. This type of reaction is also used in the production of vitamin B6.

POSTLAB QUESTIONS: (2 points each) a.Explain why a 0.4 M solution of maleic anhydride is made in xylene and not in water. Show the reaction between maleic anhydride and water. The maleic anhydride is reactive in water, so the xylene is used instead. Xylene is also a high boiling point solvent which allows for the reaction to be conducted in a faster and more efficient way in comparison to water.

A

c. Give structures for the major Diels-Alder product of the following reactions: 1,3cyclohexadiene and tetrachloroethene 1,3-cylcohexadiene and fumaric acid, the trans isomer of maleic acid

d....