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10 Nov 2019

1. Discuss what the TLC indicated about the reactiontime and product yield.

2. Melting Point characterization ofproduct. Compare to the literature value and comment.m.p. 55-57

3. Compare the IR spectra of the student products(posted to Blackboard) with the IR spectra of pure benzophenone andbenhydrol samples shown below in appendix II; do the student spectra showproduct? Are the student products very pure or is it amixture of reactant and product?

Discuss what the TLC indicated about the reaction time and product yield. Melting Point characterization of product. Compare to the literature value and comment. m.p. 55-57 Compare the IR spectra of the student products (posted to Blackboard) with the IR spectra of pure benzophenone and benhydrol samples shown below in appendix II; do the student spectra show product? Are the student products very pure or is it a mixture of reactant and product?

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Related questions

1. what gaseous product evolved during the reaction and how isit formed (hint: an excess of BH4 is used so what else might it beable to react with)?

2. What absorption is diagnostic of benzophenone and not presentin benzhydrol (give frequency and functional group); and whatabsorption is diagnostic of benzhydrol and not present inbenzophenone

3. compare the IR spectra of the student products (posted toBlackboard) with the IR spectra of pure benzophenone and benhydrolsamples shown below in Figure 2,3,4; do thestudent spectra show product? Are the student products very pure oris it a mixture of reactant and product? P.S Please referFigure 1

4. comment on whether the product melted quickly (< 3 0Ctemperature range) or slowly (> 3 0C temperature range)? Whatdoes this observation tell you about the compound purity? P.S mymelting point was range of 65~67

Figure 1

Figure 2,3

Figure 4

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.

Procedure:

In a 5-mL round bottom flask, add 120 mg of 4-aminobenzoic acid (often called PABA for p- aminobenzoic acid), 1.5 mL of absolute ethanol (absolute ethanol is completely free of water and can be found on the hooded shevles), and 3 boiling chips. Heat this mixture on a sand bath until all the solid dissolves. Cool in ice and then add 0.25 mL of concentrated sulfuric acid dropwise. (One drop at a time.) A large amount of precipitate will form when the sulfuric acid is added, but this will dissolve during the reflux that follows. Attach an air condenser from the microscale kit, and reflux gently for 60- 75 min. Check periodically to be sure that the mixture is refluxing gently, and that the ring of condensation of solvent lies somewhere along the inner surface of the air condenser; loss of solvent will cause overheating and a significant decrease in yield. Detach the air condenser from the reaction tube and allow the reaction mixture to cool to room temperature. Using a Pasteur pipet, transfer the reaction solution to a 10-mL Erlenmeyer flask and add 3 mL of distilled water. Dropwise, add saturated sodium bicarbonate (about 3 mL, approximately 10% or 1 M) to neutralize the excess sulfuric acid and the ammonium sulfate salt form of the amino ester (making it neutral and insoluble in water). After each addition of the sodium bicarbonate, agitate the solution to mix thoroughly. Extensive CO2 evolution (gas) and frothing will be observed until the mixture is nearly neutralized. As the pH increases, a white precipitate of benzocaine is produced. When gas no longer evolves as you add a drop of sodium bicarbonate, check the pH of the solution with "Alkacid" pH paper and, if it is less than 8, add further portions of saturated sodium bicarbonate solution. Collect the benzocaine by vacuum filtration using a Hirsch funnel. Use three 1-mL portions of cold water to wash the product crystals from the flask onto the funnel. Make sure the product is rinsed thoroughly with cold water water. After the product has dried thoroughly by leaving it in an open container until the next lab period, weigh it, calculate the % yield, and determine its melting point. The m.p. of pure benzocaine is 92Â°C.

Benzocaine Data Sheet

1) Draw the reaction scheme

2) Find the limiting reactant, and calculate the theoretical yield: 2.41g

3) Provide the mass of recovered product, and calculate the percent yield: 200 F

4) Provide the melting point and melting point range of your product. Compare it to the literature value

5) Below is the structure of benzocaine. Correlate each proton to the corresponding peak in the 1H NMR spectrum