Procedure to study Cannizarro's reaction of Benzaldehyde

1. CPP-1.5 (1.1) Practical Organic Chemistry
DOS & R in Organic Chemistry, TUT Page 1
Prepared By
Dr. Krishnaswamy G
Faculty
DOS & R in Organic Chemistry
Tumkur University
Tumakuru

2. CPP-1.5 (1.1) Practical Organic Chemistry
DOS & R in Organic Chemistry, TUT Page 2
Cannizaro’s Reaction: Benzaldehyde
AIM:
To study Cannizaro’s reaction of Benzaldehyde by solvent free
grindstone technique.
PRINCIPLE:
The disproportionation reaction (self oxidation and reduction) of non
enolizable aldehydes to corresponding carboxylic acid and alcohol in
presence of base is known as Cannizaro’s reaction.
In this experiment benzaldehyde underwent solvent free
disproprtionation reaction to benzoic acid and benzyl alcohol in
presence of sodium hydroxide.
CHEMICALS REQUIRED:
Benzaldehyde, NaOH, Ethyl acetate, Na2SO4, HCl.
APPARATUS:
Mortar and pestle, Beaker, Separating funnel, Funnel, Measuring
cylinder, Filter paper.
PROCEDURE:
• 1 g Benzaldehyde (0.0096 mol) was taken in a clean and dry
mortar. To this 0.75 g NaOH (0.0188 mol) was added and

3. CPP-1.5 (1.1) Practical Organic Chemistry
DOS & R in Organic Chemistry, TUT Page 3
grounded well together using pestle for 30 minutes at lab
temperature. The reaction proceeds exothermically.
• After 30 minutes of grinding (indicated by no smell of
benzaldehyde), pour 15 ml of cold water into the whole reaction
mass and neutralize the mixture with concentrated HCl till acidic
pH. The precipitated product (benzoic acid) was collected by
filtration and dried.
• The filtrate was extracted to 20 ml of organic layer (ethyl
acetate) and dried over anhydrous Na2SO4. The organic layer was
evaporated and benzyl alcohol was obtained.
• Weigh the product, calculate the yield and obtain melting point.
REACTION:
H
O
OH
O
2
OHNaOH
Grind, 30 min
Lab Temp.
H3O+
CALCULATIONS:
Compound Amount
Molecular
Weight
Moles Equivalent
Benzaldehyde 1 g
106.12
D = 1.04 g/cm3 0.0094 1
NaOH 0.75 g 40 0.0188 2
HCl 5 mL - - -
Ethylacetate 20 mL - - -

4. CPP-1.5 (1.1) Practical Organic Chemistry
DOS & R in Organic Chemistry, TUT Page 4
THEORETICAL CALCULATION:
Moles of benzaldehyde = 1/106.12 = 0.0094
Moles of benzoic acid = ½ X moles of Benzaldehyde
= ½ X 0.0094 = 0.0047
Moles of benzyl alcohol = ½ X moles of Benzaldehyde
= ½ X 0.0094 = 0.0047
% Yield of benzoic acid = (Practical mol) / (Theoretical mol) X 100
% Yield of benzyl alcohol = (Practical mol) / (Theoretical mol) X 100
MECHANISM:
H
O
OH H
O
OH
H
O
OH
O
O
H H
O
O
OH
H H
OH
O
Hydride shift
Proton transfer
H3O

5. CPP-1.5 (1.1) Practical Organic Chemistry
DOS & R in Organic Chemistry, TUT Page 5
CHEMICAL TESTS:
Odour
Benzaldehyde: Bitter almond
Benzoic acid: Slight pungent
Benzyl alcohol: Odourless
Reaction with NaHCO3
Benzaldehyde: No evolution of gas (-Ve)
Benzoic acid: Evolution of gas (+Ve)
Reaction with 2,4-DNP
Benzaldehyde: Orange precipitate (+Ve)
Benzyl alcohol: No Orange precipitate (-Ve)
REPORT:
Structure
and name
of the
compound
Theoretical
yield
Practical
yield
Percentage
yield
Theoretical
Melting
Point/
Boiling point
Experimental
Melting
point/
Boiling point
COOH
Benzoic acid
122oC

6. CPP-1.5 (1.1) Practical Organic Chemistry
DOS & R in Organic Chemistry, TUT Page 6
CH2OH
Benzyl alcohol
205 ± 3oC
REFERENCES:
1. Arabian journal of chemistry, 2016, 9, S1373-S1377.