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11 Dec 2019

What is the most likely reaction that would be competing with the desired elimination (E1) reaction? Draw the mechanism of this reaction and the expected product. Why is the formation of this product not an issue in the experiment you performed?

Laboratory Procedure

1. Set up a fractional distillation apparatus so that the receiving flask can be cooled in a ice water bath.
2. In your distillation flask (50mL flask if possible) place 15 mL of t-pentyl alcohol(2-methyl-2-butanol) and slowly mix in 8 mL of 9 M sulfuric acid.
3. Collect all products with a temperature below 90 oC. During the distillation the temperature should stay below 80 oC for most of the reaction. Stop when 90 oC or about 10 mL remains in the reaction flask.
4. Transfer the crude product to an Erlenmeyer flask and dry with a small amount of anhydrous potassium carbonate. If the product remains cloudy after a few minutes add another small portion of carbonate.
5. Transfer the clear liquid organic product into a fresh DRY 25 mL round bottom flask and simple distill the organic alkenes into a chilled receiver.
6. Determine boiling point from this simple distillation and record the yield of the purified material collected.
7. Add a few drops of bromine test solution to check for the presence of alkenes. Record your observations. Did the color change? Did the bromine solution (brown/orange) react with your product?

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For the lab below, what is the separation scheme?

Elimination of 1-octanol.

Apparatus Assembly:

Set up a distillation apparatus.

Using a preweighed 50-mL round-bottom flask as the distilling flask, add 7.5 mL of 1-octanol and weigh it again to determine the exact amount added. Add 2.0 mL of 85% phosphoric acid and 30 drops of concentrated sulfuric acid. Add a magnetic stir bar.

Use a 25 mL round-bottom flask as the receiving flask. Be prepared to immerse it into an ice bath to ensure that no octene vapors will escape into the lab; however, do not add the ice until after the distillation is underway or you will have extra water in your product (from condensation). Even more effectively, you can ice your condenser circulator, but don't do that until after distillation commences either.

Dehydration:

Ensure that the water is flowing in your condenser and begin to heat the distilling flask on the appropriate insert of your heater/stirrer.

The heating should be regulated because ideal time of the distillation should be 30 minutes. Too fast of a distillation will cause an incomplete reaction and isolation of the starting material. The temperature registered by your thermometer will rise very slowly at first, but when the refluxing (soon to be distilling) vapors hit the thermometer, the temperature will rise quickly. It should stabilize as the first condensate begins to form in the distillation condenser; from that point to the end of the distillation, record the range of temperatures: this is your boiling-point range (although in this experiment, the broad distribution of products may cause a broad range of temperatures).

Ideally, you do not want to collect distillate until the temperature is at least 110Â°C (as the distillate, below this temperature, is mostly water); however, since you will have to remove water anyway, this is not critical. However, you don't want to collect product at temperatures much above the boiling point of the octenes since that will increase contamination of your product with unreacted 1-octanol and S_N1 ether byproduct.

Continue the distillation until no more liquid is collected or until tar begins to form; if tar begins to form, stop the distillation. Be sure to not distill the reactants completely, as you will be left with a thick residual tar that will be nearly impossible to remove from the flask.

Isolation and Drying of the Product:

Transfer the distillate to a separate container (flask or separatory funnel) with the aid of an approx. equal quantity of saturated sodium chloride solution (brine). Allow the layers to separate; remove the bottom aqueous layer (using a Pasteur pipet if you chose a flask) and discard it.

Transfer the organic layer (using a dry Pasteur pipet if you chose a flask) in the container to a small round-bottom flask and add a small amount of anhydrous sodium sulfate. Stopper the flask and allow it to sit for 10-15 minutes.

When the product is dry, transfer it to a pre-weighed screw-cap vial (preferably with a Teflon liner) and obtain its mass. Then filter a solution of dichloromethane and product into a GC vial, properly label it, and submit it to the GC vial collection box. The proper ratio of product in dichloromethane is 1 drop in 1-1.2 mL DCM: one drop in a full syringe of DCM.

For this experiment, you will also be required to set up the GC-MS to run your sample by adding your run to the instrument sequence. Follow the instructor's instructions with regard to this task.

Hydration of Cyclohexene to Cyclohexanol Lab

As you have seen, dehydration and hydration are relatively reversible processes as the change in Gibbs Energy (?G) is small. Consider the form of Gibbs Energy equation (?G = ?H â T?S) ??? and address the following:

1. Consider the nature of the bonds broken and formed (?- vs ?-) and intuit the sign of the change in enthalpy ?H as positive or negative. (Or look it up.) Is it endothermic or exothermic?

2. Consider the number of moles of reagent vs product and intuit the sign of the change in entropy ?S as positive or negative. (Or look it up.) How is the position of equilibrium affected by temperature and concentration of acid?

Thermodynamic properties:

Cyclohexanol Thermodynamic Properties:

Question: For the following two experiments I have been asked to find at least 1 procedural change for each that could be made to improve the yield of my product. Please review the experiments and aid me in determining what this change might be. Thanks in advance!

Reduction of Benzophenone

1. In a 50 mL Erlenmeyer flask, dissolve 2.0 g benzophenone in 10 mL of methanol. Also add a stirbar to magnetically stir the solution.

2. Place your solution in an ice bath until the temperature has dropped to 10 C.

3. While your flask is in the ice bath, add 0.42 g of sodium borohydride, in small portions, over a 5 min period. The addition of sodium borohydride is exothermic, so you must take care to add it slowly to keep the temperature under control. This means adding the hydride in 5-6 portions, with about 1 min in between additions.

4. Once the addition of NaBH4 is complete and the vigorous bubbling has ceased, allow the solution to stir at room temperature for 10 minutes.

5. Carefully clamp the Erlenmeyer flask into a 80Â°C water bath and allow it to sit in the hot water bath for 2 minutes.

6. Remove the solution from the hot water bath and allow it to cool to room temperature and then cool it in an ice bath.

7. SLOWLY add 30 mL of cold water and then SLOWLY(dropwise) add 1.4 mL of 6M HCl. Use litmus paper to confirm that your solution is acidic. If your solution is not acidic, add more HCl until it is acidic. You should see the formation of a white precipitate at this point.

8. After adding the HCl, remove your solution from the ice bath and let it stir at room temperature for 20 minutes.

9. Collect the product by suction filtration, washing with 10-25 mL of cold water.

10. Allow the product to completely dry under suction and then record the crude weight.

11. Analyze the purity of your crude product by running a TLC. Dissolve a very small sample of your crude product and the benzophenone starting material in diethyl ether. Spot these samples on two separate lanes of your TLC place and develop the TLC pate with 9:1 petroleum ether: ethyl acetate.

12. If you are convinced that your crude sample is pure diphenylmethanol, record the final mass and run a melting point.

13. If you think some impurities are still present in your crude mixture, recrystallize your product with a minimal amount of hot hexanes. Review your notes from earlier in the semester if you donât remember the steps to run a recrystallization.

14. Record the mass and melting point of your purified diphenylmethanol and place it in a labeled vial to turn in to your instructor.

Oxidation of Diphenylmethanol

1. Place approximately 300-mL of hot (from the tap) water in a 400-mL beaker, add a boiling stone, and place it on a hot plate. Heat the water until it is 90-95 oC. It is important to keep the temperature just below 100 oC; thermal decomposition of the permanganate may occur at higher temperatures resulting in the release of toxic fumes.

2. While your water bath is heating, place 4.82 mmol of diphenylmethanol in a 10- or 25- mL round-bottomed flask.

3. Weigh out approximately 4 grams of the oxidant mixture of KMnO4/CuSO4â¢5H2O.

4. If the temperature of your water bath has reached 90-95 oC, combine the oxidant with the diphenylmethanol in your round-bottomed flask.

5. Vigorously stir the mixture with a microspatula for 5-10 min until the flask is warm to the touch. A color change from purple-blue to brown/black should be observed as you are stirring the solids. This is an indication that a reaction is occurring.

6. When the flask is warm, equip the reaction vessel with an air condenser and clamp it in the hot water bath. Be sure that the solid reaction mixture is below the surface of the water.

7. Heat the reaction for 1 h. Continue to monitor the temperature of the water; if the temperature increases close to 100 deg C, add a bit of cold water to keep the temperature 90-95 deg C and lower the heat setting on your hot plate.

8. After 1 h of heating, remove the flask from the hot water and allow it to cool to room temperature. Remove the reflux condenser.

9. Add 10 mL of hexanes to the solid and stir to mix. Remove the hexanes with a pipette and place it into a 25-mL Erlenmeyer flask. Repeat and combine the extracts.

10. Dry the combined hexane extracts with Na2SO4; decant/filter the hexanes into a preweighed 25-mL Erlenmeyer flask; and evaporate the hexanes using a gentle stream of air.

11. Analyze the purity of your crude product by running a TLC. Make samples of the following for TLC: stock benzophenone, crude benzophenone, and benzhydrol. Spot these samples on three separate lanes of your TLC place and develop the TLC pate with 5:1 hexane/ethyl acetate.

12. If you are convinced that your crude sample is pure benzophenone, record the final mass and run a melting point.

13. If you think some impurities are still present in your crude mixture OR if your product is not a solid, recrystallize your product with a minimal amount of hot methanol or methanol/water. Review your notes from earlier in the semester if you donât remember the steps to run a recrystallization.

14. Record the mass and melting point of your purified benzophenone and place it in a labeled vial to turn in to your instructor.

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