CHEM 343 - Expt 9 - Acid-Catalyzed Hydration of Norbornene PDF

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Example of an organic chemistry lab report for the Acid-Catalyzed Hydration of Norbornene....

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CHEM 343-06 November 14, 2019 Acid-Catalyzed Hydration of Norbornene Objective: The goal of this experiment was to hydrate norbornene and determine if the reaction is stereoselective. The lab completed an acid-catalyzed hydration of norbornene which included the overall reaction and mechanisms, purification via sublimation, and acquiring a melting point using a sealed capillary tube.

Stoichiometry Table: Compound

Norbornene

Molar Mass

Density (in

(in g/mol)

g/mL)

mg or mL

mmol

Molar Equiv.

94.16

1.005

300 mg

3.2

1

98.08

1.840

1 mL

5.54

Catalyst

18.02

0.997

0.5 mL

27.7

8.1

(Limiting Reagent) Sulfuric Acid (18M) Water

Procedure and Observations:

Procedure: 1. Pipet 500 µL of water into a 10 mL RB flask with a stir bar over an ice

Observations: Mixture was a rusty orange color probably due to impurities

bath. 2. Carefully add 1 mL of 18M sulfuric acid dropwise and continuously be swirling. 3. Once the addition is complete, remove the flask from the ice bath. 4. Add 300 mg of norbornene and sur the reaction for 15 minutes or until all of the solid has dissolved. 5. Once fully dissolved, return the flask to the ice bath and neutralize the

After the addition of NaOH, the mixture became clear with a cloudy, white precipitate

reaction by adding approximately 5 mL of 6M NaOH dropwise in the fume hood. Be sure to continuously test the pH. 6. Remove the stir bar and transfer the solution to a small separatory funnel. 7. Rinse the flask with 2-3 mL of water and add that to the separatory funnel.

Top layer: Aqueous Bottom layer: Organic

8. Extract your product two times with 34 mL portions of dichloromethane (DCM). Be sure to shake and vent. 9. Combine the organic extracts in a 25 mL E. flask and dry over anhydrous sodium sulfate while stirring or swirling occasionally. 10. Stopper the flask with a neoprene stopper and evaporate the DCM. You may need to place the flask in a warm water or sand bath to help the evaporation process. 11. Weigh the residue and calculate the crude yield of your product. 12. Purify by sublimation from the same filter flask. 13. Use the apparatus that uses a coldfinger inserted in a side arm flask. 14. Weigh your final product and calculate final yield. 15. Obtain the melting point.

Weight of E. flask: 57.4904 g Weight of flask + solid: 57.6952 g Weight of solid: 0.2048 g Melting Point: 121℃-124℃

Results: Theoretical yield = mmol norbornene x molar mass of the product (exo norboeneol) 1 mol

= 3.2 mmol norbornene x 1000 mmol x experimental−theoretical

% yield = |

theoretical

0.2048g−0.3589 g

| x 100% = |

Melting Range: 121℃-124℃

Overall Reaction and Mechanisms:

112.17 g exo norborneol mol

0.3589 g

= 0.3589 g

| x 100% = 42.9%

Discussion: The objective of this experiment was to hydrate norbornene via an acid catalyst and determine if the reaction is stereoselective. Sulfuric acid was used as the catalyst in this experiment. In this particular experiment, the yielding product was exo-norborneol which was confirmed via melting point (121℃-124℃). The low yield could be due to product not fully scraped from the coldfinger or an excess amount of impurities. The pi-bonds in norbornene are broken by an addition reaction which formed norborneol through the addition of H+ and OH- to the subsequent carbons. How this occurs is the norborneol cation was formed when the norbornene picked up an H+ from the solvent, sulfuric acid. Then, water can attack the norborneol cation from two different directions: if the water attacks from the bottom, the OH- functional group attaches in the axial position which results in endo-norborneol; if the water attacks from the top, the OH- functional group attaches in the equatorial position which results in exo-norborneol. Through this, two different stereoisomers can form: endonorborneol and exo-norborneol. Both have different melting points (endo-norborneol: 149℃151℃; exo-norborneol: 124℃-126℃). In this lab, sublimation is used as the purification technique to help rid the product of impurities. Once the product has been vacuum-filtered, all impurities are left at the bottom of the flask along with the product. If we stopped right here, we would acquire a melting point which would be very inaccurate. By using sublimation, the product can escape the impurities and begin to evaporate due to the decreased pressure. The product, now in a gaseous state, hits the coldfinger apparatus and begins to recrystallize. From here, we weigh the product and obtain a melting point to determine which stereoisomer we was formed.

Post-Lab Questions: 1. There are only two stereoisomers (the left pair). The stereoisomers are cis/trans, and when you rotate them, they become identical to each other. 2. Connecting or disconnecting the vacuum can change the pressure within the flask resulting in the product being sucked out. 3. Since the reaction is in equilibrium, all you have to do is remove the water which will form a more concentrated sulfuric acid to favor the formation of norbornene over norborneol. This is based on the Le Chatelier’s Principle. 4. The temperature of the water was probably too high so the dichloromethane (DCM) evaporated quickly, and since he wasn’t watching when it did, the vacuum probably sucked up the product....