EXP-7
CHEM 233L
THE CANNIZZARO REACTION
Introduction:
The Cannizzaro reaction is that of aldehydes that do not contain alpha hydrogens
to give carboxylic acids and alcohols (alpha hydrogens cause an Aldol reaction to take
place). This occurs in the presence of a strong base. Benzaldehyde, which does not
contain alpha hydrogens, was used for this reaction.
The refulx technique will be used in order to allow for a complete reaction
between all the components. On completion of the reaction, the extraction technique will
enable the separation of benzoic acid and benzyl alcohol. This will be achieved by the
ionization of Benzoic acid which will separate from the organic benzyl alcohol.
Reacidification will reform the Benzoic acid.
The analysis of the benzyl alcohol will be done by completing a series of
qualitative tests: the Jone’s test, Tollen’s test, and 2,4-DNP test. The Jones’ test will
check for the presence of an aldehyde or a 1o and 2o alcohol. This result can be confirmed
by the Tollen’s test which checks for the presence of an aldehyde. 2,4-DNP test will
verify the presence of an aldehyde or a ketone. These tests will permit one to determine if
benzyl alcohol was indeed produced.
Main reaction:
O
O
H
+
O
OH
KOH
H
OH
+
CH3OH
H
H
Reflux
Benzoic acid
The Cannizzaro reaction was discovered in 1853 by the Italian chemist Stanislao
Cannizaro (1826-1910).
Benzyl alcohol
Table of Physical Data:
Compound Name Molecular Melting Boiling Density Solubility Precautions
Weight
point
point
(g/ml)
o
o
(grams)
( C)
( C)
O
H
106.124
-26
179
1.045
32.042
-98
64.6
0.791
56.097
--
--
2.044
84.933
-96.7
39.8
1.326
18.0152
0
100
0.995
122.123
122.2
249
1.08
108.139
-15.3
205
1.045
Benzaldehyde
OH
H
H
H
Methanol solvent
10 M KOH
H
H
Cl
Cl
CH2Cl2
Extraction solvent
H2 O
Extraction solvent
O
OH
Benzoic acid
OH
H
H
Benzyl alcohol
Safety Notes:
 Benzaldehyde is toxic and flammable. Avoid contact with skin, eyes, and clothing
and dispense it under the hood condition.
 Potassium hydroxide and hydrochloric acid are corrosive
Procedures:
Exp 7A:
1. Place about 3.0 ml of benzaldehyde, 15 ml of methanol and 2 ml of aqueous 10 M
KOH in a 100 ml round bottom flask; add a couple of boiling chips finally.
2. Attach a reflux condenser and heat the reaction mixture to the boiling point of
methanol for 1 hour.
3. Allow the mixture to cool down and place in an ice bath.
4. Transfer the mixture carefully to a separatory funnel with the help of 15ml of CH2Cl2
and addition of 10 ml of water.
5. Shake the separatory funnel and separate the layers. The benzoic acid (as potassium
benzoate) will stay in the water phase, while the benzyl alcohol and benzaldehyde
will remain in the lower organic phase.
6. Extract the organic phase with 10 ml of water and combine the water with the first
aqueous phase.
7. Back-extract the combined aqueous phase 2 times with 5 ml of CH2Cl2.
8. Save the organic layer as well as the aqueous layer for the next lab.
Exp 7B:
Organic Phase Work-up:
1. Dry the combined CH2Cl2 phase over by anhydrous MgSO4. Add enough drying
agent so, the solution appears clear as opposed as cloudy.
2. Remove MgSO4 by filtration. Rinse the MgSO4 with 5 ml of CH2Cl2 drop wise using
a pipette.
3. In the hood, evaporate the CH2Cl2 by using a hot plate and a water bath to gauge the
temperature. Keep the hot plate around 30-40 0C.
4. Dissolve the oily residue in 2 ml of CH2Cl2 and transfer the solution to a tarred vial.
5. Evaporate the CH2Cl2 completely again, over a hot plate kept at low heat
(30-40 oC).
6. Use the flask with water and a thermometer to gauge the temperature.
7. Determine the yield of the oily residue. Perform some qualitative tests and then take
the IR of your product and submit the rest.
Reference:
www.chemfinder.com