C A U T I O N
When preparing and handling solutions of potassium
permanganate, it is advisable to wear rubber gloves to avoid contact of the
solution with your skin; it will cause unsightly stains on your hands for
several days. If this oxidant comes in contact with the skin. wash the affected
area thoroughly with soap and warm water.
Residues of manganese dioxide on glassware can be
difficult to remove. Rinsing the glassware with sodium bisulfite solution will
sometimes work. In more difficult cases, abrasive cleanser should be used (
Consult your Instructor ).
Equation:
C6H5CH2CH3 + 4KMnO4 + 4HCl ---> C6H5CO2H + CO2 + 4MnO2 + 4KCl + 4H2O
Table of Physical Constants
| Compound | MW | Density | mp | bp |
| C6H5CH2CH3 | 106.0 | 0.867 | -95 | 136 |
| C6H5COOH | 122.0 | ----- | 122 | 250 |
| KMnO4 | 158.0 | ----- | ----- | ----- |
Table of amounts of reactants used and of amounts of products theoretically possible
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C6H5CH2CH3 |
KMnO4 |
6M HCl |
C6H5CO2H |
KCl |
CO2 |
H2O |
MnO2 |
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MW |
106 |
158 |
36.5 |
122 |
84.5 |
44 |
18 |
87 |
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Moles |
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Grams |
1.7 |
11.2 |
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mL |
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Day 1
1. Bring your 250 mL RBF, wide-mouth funnel and cork ring over to a balance area.
2. Weigh out 11.2 gm. potassium permanganate into the flask.
3. Return to your hood workstation, and rinse the funnel and neck of the flask (wash bottle) until no purple color remains.
4. Add an additional 100 mL of water to the flask, and clamp it atop your hotplate/stirrer.
5. Add your magnetic stirring bar to the flask and turn on the stirrer so that the contents of
the flask is stirring vigorously - you should see a vortex at the center of the flask.
6. Add a plastic pipet full of 3 M Sodium Hydroxide, and two shots of ethylbenzene to the flask.
7. Place your reflux condenser in the flask.
8. Attach hoses to the condenser and gently run water through them. Water runs from bottom hose to top hose.
9. Turn on the heating portion of your hot plate/stirrer to a setting of “4". CAUTION: severe bumping occurs if heated too strongly.
10. Once a gentle reflux has been maintained for 15 mins., you are to finish your EAS product melting point determination.
11. At the end of a two hour reflux period turn off the heat.
12. Remove the flask from the hotplate and test the hot solution for unchanged permanganate by placing a drop of the reaction mixture on a piece of filter paper. Obtain the drop by removing the reflux condencer and dip your stirring rod into the mixture, then placing the drop, on the end of the stirring rod, onto the filter paper. If a purple ring appears around the brown spot of manganese dioxide, permanganate remains.
13. Destroy any excess permanganate by adding small amounts of solid sodium bisulfite to the mixture until the spot test is negative. Do not add a large excess of bisulfite.
14. Filter the hot mixture by vacuum filtration:
a. Connect a vacuum hose to the water/house vacuum.
b. Connect the other end of the vacuum hose to the side arm of your 500 mL filter flask.
c. Place your large Buchner Funnel assembly atop your filter flask.
d. Place a sheet of 7 cm. Whatman #1 filter paper into your Buchner Funnel.
e. Wet the filter paper using the water in your wash bottle.
f. Turn on the house vacuum.
g. Mix a heaping spoonfull of filter aid with 50 mL of water and pour it onto the filter paper.
h. Disconnect the vacuum hose from the filter flask.
i. Remove the funnel and pour the contents of the filter flask down the sink.
j. Re-connect the funnel.
k. Reconnect the vacuum hose to the filter flask.
l. Pour your HOT reaction mixture onto the filter paper and filter the solution.
15. Rinse the reaction flask and filter cake with two 10-mL portions of hot water. Dispose of the filter cake into the recovery jar at the front of the room.
16. Disconnect the vacuum hose from the filter flask slowly, then turn off the water/vacuum.
17. Pour the filtrate into your 600 mL beaker, add your magnetic stirrer and concentrate the filtrate to about 30 mL by evaporation. Set your hotplate no higher than 4 . If the concentrate is turbid. filter it by gravity; the filtrate should be clear.
18. Cool the concentrate to room temperature, then acidify with 10 mL of 6M hydrochloric acid.
19. Test this solution on blue litmus – if the paper turns red you are finished, if not add an additional 10 mL of 6M HCl. Record in your table the volume that you use.
20. Cool this mixture in an ice-water bath, and isolate the benzoic acid by vacuum filtration.
21. Wash the contents of the filter flask down the sink.
22. Recrystallize your crude product using between 25 and 50 mL of water as your solvent.
Place in your drawer on 11 cm filter paper supported by a big watch glass until next lab period. Make sure the solid is covered by another piece of 11 cm filter paper.
Day 2
Determine the yield, melting point and molecular weight of the pure benzoic acid obtained, and record them in the Results section of your lab report, complete with appropriate calculations. Identify the peaks on your IR and NMR.
NMR for Ethylbenzene
Assign. Shift(ppm)
A 1.22
B 2.63
C 7.0 to 7.45
IR for Ethylbenzene
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IR/NMR for Benzoic Acid
Assign. Shift(ppm)
A 12.09
B 8.12
C 7.62
D 7.45
IR/NMR for Benzoic Acid
