Lab 2 Diels-Alder PDF

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Lab 2 Diels-Alder...

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Retro and Forward Diels-Alder Reaction Introduction: The purpose of this lab is to execute a forward Diels-Alder reaction to form a cyclohexene ring with no intermediates, and to also execute the microscopic reverse of it is the Retro Diels-Alder reaction. This experiment involves both reactions back to back, no intermediates are formed, thus it is a concerted reaction. Heat initiates the reaction and high temperatures will favor the retro Diels-Alder reaction. A faster reaction will result when there are one or more electron withdrawing groups adjacent to the alkene or alkyne of the dienophile. A successful reaction involves the diene adopting the s-cis geometry. Addition of electron donating groups to the diene helps to increase rate and the efficiency of the reaction. One of four possible dienophiles will be given to form a bicyclic Diels-Alder product. The new technique used will be microwave distillation and the previous techniques used are reflux, FTIR spectroscopy, and H NMR spectroscopy. Balanced Reaction:

Reaction Mechanism:

(The R1 and R2 are the opposite sides of the dienophiles. So, the compound containing the Rs could be DMAD, DEAD, DPAD, or DIAD) Table of Reagents: Name

Structure

Molecula r Weight g/mol

Dicyclopentadiene

132.2

Melting Point Degree C 32.5

Cyclopentadiene

66.1

-

Boiling Point Degree C 170

Densit y

40.8

786 kg/ m³

-

Dimethyl Acetylenedicarboxylate (DMAD)

142.11

-

195198

1.16 g/ cm³

Diethyl Acetylenedicarboxylate (DEAD)

170.16

-

107110

1.063 g/mL

Diisopropyl Acetylenedicarboxylate (DIAD)

198.22

-

273.11

1.074 g/cm^3

Dipropyl Acetylenedicarboxylate (DPAD)

198.22

-

285.8

1.109 g/mL

Safety: General: Safety Glasses and lab gloves must always be worn. Make sure the snorkels are

positioned properly, turned on, and are functioning properly before dispensing liquids. Avoid breathing fumes or allowing liquid to meet skin. Any vapor or liquid exposure should be reported to the TA immediately. Dispose of all liquid and solid waste in the appropriately labeled bottle in the lab hood. Chemical: Dicyclopentadiene: Flammable liquid and vapor. Harmful if swallowed. Causes skin irritation. Causes serious eye irritation. Fatal if inhaled. May cause respiratory irritation. Toxic to aquatic life with long lasting effects. Cyclopentadiene: Flammable liquids. Flammable liquid and vapor. Dimethyl Acetylenedicarboxylate (DMAD): Combustible liquid. Harmful if swallowed. Causes severe skin burns and eye damage. Diethyl Acetylenedicarboxylate (DEAD): Combustible liquid. Serious eye damage. Causes severe skin burns and eye damage. Causes serious eye damage. Skin corrosion. Diisopropyl Acetylenedicarboxylate (DIAD): Serious eye damage. Causes severe skin burns and eye damage. Causes serious eye damage. Skin corrosive. Combustible liquid. Dipropyl Acetylenedicarboxylate (DPAD): Serious eye damage. Causes severe skin burns and eye damage. Causes serious eye damage. Skin corrosive.

Microwave Distillation Set up Experimental Procedure: Retro Diels-Alder reactionAdd around 300 mL of dicyclopentadiene to a 500 mL microwave round bottom flask. Place two microwave absorbing chips plus a stir bar into the flask. Attach the fiber optic thermal detector to the side arm. Construct a distillation apparatus set-up trough the microwave. Set the microwave program to the temperature profile from 0-200 Degrees Celsius. Start the program and collect the cracked cyclopentadiene in a round bottom flask sitting in an ice bath. Ramp for 10 minutes until reactant temperature reaches 168 degrees Celsius. Keep the temperature at 168 Celsius for 30 minutes. Forward Diels-Alder Reaction: Add 1.5 mL of dienophile assigned by the TA and place a spin vane into a 10 mL round bottom flask a place it on an aluminum block. Place a clamp to secure the flask. Add 2.0 mL of cold cyclopentadiene dropwise into the flask while stirring for 30 seconds. Place a lid loosely. Stir for 20 minutes at room temperature. Take the lid off from the round bottom flask. Turn the heat up to 140 Celsius and boil off the excess cyclopentadiene still stirring. Do not exceed 150 Celsius! This process should not take longer than 25 minutes. Characterization of the Product Obtain an IR spectrum and an H NMR spectrum.

Forward and Retro Diels-Alder Data Sheet Unknown dienophile code: 51B426P8 Initial Volume of dienophile: 1.5 mL Initial Volume of cyclopentadiene: 2.0 mL The final weight of the Diels-Alder product: 2.131 g Time spent boiling off starting material: 30 mins Miscellaneous Experimental Observations: Cyclopentadiene was clear, pungent liquid. Dienophile was a clear, yellow liquid. The product was dark brown liquid. Product:

Limiting reagent and percent yield: (1.50 mL _dienophile_)*

1.16 g DMAD 1 mL D M AD

2 08.21 g Diels alder product 1 mol Diels− Alder product

*

¿ 2.55 g

1 mol D M AD ∗1 mol Diels− Alder product 1 42.11 g D M AD * 1 mol D M AD

(2.00 mL

cyclopentadiene )*

0.852 g cyclopentadiene * 1mL cyclopentadiene

1 mol cyclopentadiene ∗1 mol Diels− Alder product 2 08.21 g Diels alder product * ¿ 66.1 g cyclopentadiene 1 mol Diels− Alder product 1 mol cyclopentadiene 5.37 g 2.131 g Diels− Alder product = 83.6 % yield of Diels-Alder Product. 2.55 g Diels −Alder Product Conclusion/Discussion: The percent yield of the experiment was 83.6% which is very good because having a high yield means that the experiment was properly executed and that there were not many errors. The limiting reagent for this experiment was the dienophile. From the IR spectra, we can determine that there will be a C=O and a C-O. The presence of IR absorption bands can help identify the compound by the sp3 (CH3) carbons, sp2 (CH2) carbons, and the C-O bonds around the 1500 range of the IR, but this is not the most accurate way to decide what product was formed. The most accurate way to identify the product formed would be by HNMR and from that, we can determine the structure and hybridization of the Hydrogens. Also, the HNMR shows us the splitting pattern of the hydrogens so we can easily figure out where hydrogens need to be placed in the product that will lead us to the identification of the dienophile used. On the HNMR, you can see a 6 singlet meaning the c

H’s are CH3’s, the singlet means that there are no other hydrogens around. Thus, there is not any CH2 on the right side of the product meaning the dienophile that was used was Dimethyl acetylenedicarboxylate. Post Lab questions: 1. 5-methyl furan-2(5H)-one is an alcohol/water sensitive compound. IN the presence of alcohol, it undergoes a process known as transesterification. Draw the structure of the transesterified 5-methyl furan-2(5h)-one:

2. If the reaction vessel were exposed to methanol during reflux, would a Diels-alder reaction also take place with the transesterified dienophile from question 1? Why or why not? Draw the structure of the product formed if the transesterified 5-methyl furan-2(5h)one were to undergo a Diels-Alder reaction with cyclopentadiene: Yes a reaction would take place. Because cyclopentadiene would be present

3. Provide the appropriate products for each of the following Diels-Alder reactions. Your answers must be stereospecific:

4. Provide the appropriate starting materials for the following Diels-Alder reactions:...