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EXP-3
CHEM 233L
Oxidation and Reduction
Introduction:
In this experiment, we study the difference between reduction and oxidation .We will
first convert benzophenone to benzhydrol (diphenylmethanol), a process that involves
reduction. In the second part of the experiment, we will reverse the process and oxidize
benzylhydrol back to benzophenone, the carbonyl group(Carbon-Oxygen double bond) gains
a pair of hydrogens(one hydrogen on carbon and one on oxygen). In part A, the reduction of
carbonyl compound (ketone) was practiced to synthesize alcohol product. Ketone was
reduced by a weak reducing agent, sodium borohydride (NaBH4). The hydrogen of this metal
hydride(hydrogen with a pair of electron) is reactive in (carbon position) carbonyl group
reductions. The reaction of reduction benzophenone to benzhydrol as following:
O
OH
NaBH3
CH3OH
In part B, alcohol (benzhydrol) was oxidized to the ketone (benzophenone) in glacial
acetic acid solution by potassium dichromate, K2Cr2O7. The reaction was:
OH
O
NaOCl
CH3COOH
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Table of Physical Properties:
Compound Name
O
Benzophenone
White crystal
OH
Molecular Melting
Weight
Point
(grams)
(0C)
182.2214
48.5
Boiling
Point
(0C)
305.4
Density
(g/ml)
Solubility
Precautions
1.11
Insoluble
(<0.1g/100ml
at 250C)
Irritants
avoid skin
contact
32.042
-98
64.6
0.791
miscible
flammable
37.8313
36
400
decompose
slowly
0.945
soluble
Corrosive
flammable
60.0524
16.6
117.9
1.0492
miscible
-
184.237
66
298
-
-
Irritants
avoid skin
contact
104.0558
-
-
1.48
soluble
Air
sensitive
294.17
398
500
2.676
-
-
74.44217
_
40
1.209
_
_
H
H
Methanol
H
Na
+
B
H
H
H
Sodium Borohydride
O
OH
Glacial acetic acid
OH
benzhydrol
O
S
HO
O
Sodium bisulfite
Potassium
dichromate
+
Na
-O
Cl
Clorox (NaOCl)
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Safety Notes:
Sodium Borohydride is a flammable solid. It is decomposed by protic solvents and may
produce flammable hydrogen as. Handle the chemical in the HOOD.
Procedure:
EXP-3A: REDUCTION OF BENZOPHENONE
1. Add about 1.00 gram of benzophenone and dissolve it in 20mL of methanol in a
125mL Erlenmeyer flask.
2. Add 600 mg of sodium borohydride little by little with the help of a clean and dry
spatula while the reaction mixture is in an ice-water bath.
3. Swirl the flask periodically and cover with a small beaker to avoid inhaling any fumes.
After complete addition of NaBH4, the reaction stood at room temperature with
occasional swirling for 20 minutes.
4. Pour the reaction mixture into a 100ml or 250ml beaker with 25mL of ice-water and
stir for 5 minutes with a glass rod. A solid should precipitate.
5. Collect the precipitate by vacuum filtration and air dry for 5 minutes.
6. Dissolve the solid again with a minimum amount of hot methanol and then add water
to the cloudy point. (The amount of water should be about the same as the amount of
methanol because it was a mixture of 50% methanol in water)
7. Collect the crystals by vacuum filtration and air-dry overnight. (Rinse the crystals
with a small amount of the same solvent).
8. Finally, take the IR and m.p during the next lab period.
EXP-3B: OXIDATION OF BENXHYDROL
1. Place 500 mg of benzhydrol and then 2 mL of glacial acetic acid in a 100-mL
Erlenmeyer flask.
2. Place the flask in an ice bath and use a Pasteur pipette. Add 10-mL of 5% NaOCl
solution (Clorox) dropwise, with occasional swirling, while keeping the temperature
at 30 to 35oC.
3. Swirl the mixture well and return to the ice bath. Add another 5- mL of 5% NaOCl
dropwise. At this point, the mixture should give a positive reaction with potassium
iodine-starch paper. If it does not, add more NaOCl solution (1 to 5mL) until a
positive reaction is obtained.
4. Let the mixture to stand for 30 minutes at room temperature. Add the saturated
sodium bisulfite solution until the mixture gives a negative potassium iodide-starch
test.
5. Pour the mixture in a 100 mL beaker with 20 mL of ice-water and stir for 5 minutes
with a glass rod. A solid should precipitate.
6. Collect the solid by vacuum filtration and air dry for 5 minutes.
7. Dissolve the solid again with a minimum amount of hot methanol and then add water
to the cloudy point. (The amount of water should be about the same as the amount of
methanol because it was a mixture of 50% methanol in water)
8. Collect the crystal by vacuum filtration and air-dry overnight. (Rinse the crystals with
a small amount of the same solvent).
9. Weigh the product, obtain the percent yield and take the IR and m.p.
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Reference:
www.chemfinder.com
http://ptcl.chem.ox.ac.uk/MSDS