Aldehyde and Ketone

Aromatic aldehyde and ketone

Preparation of benzaldehyde from toluene

Preparation of acetophenone by Friedel-Craft acylation

Physical properties of benzaldehyde

1. It is colourless liquid with bitter almond odour.
2. It is insoluble in water.
3. It’s boiling point is 179°C.

Chemical properties

Cannizzaro reaction

Perkin reaction

Benzaldehyde is heated with acetic anhydride in presence of sodium acetate to give α, β- unsaturated acid (cinnamic acid).

Benzoin condensation

Benzaldehyde is heated with an alcoholic solution of KCN gives benzoin.

Electrophilic substitution reaction

From the above resonating structure, it is clear that the -CHO group decreases the electron density at ortho and para positions. Consequently, incoming electrophile prefers to attack at the meta position. So, -CHO group is a meta directing group.

1. Chlorination

2. Nitration

3. Sulphonation

Some Important Questions

1. Write any three methods of preparation of
   i. Acetaldehyde ii. Propionaldehyde iii. Iso butyraldehyde iv. Acetone v. Ethyl methyl ketone
2. How can you distinguish
   i. Methanal and Ethanal ii. Ethanal and Benzaldehyde
   iii. Propanal and propanone iv. Benzaldehyde and acetophenone
3. How can you convert
   i. Methanal to ethanal ii. Ethanal to methanal
   iii. Ethanal to propanone iv. Ethanal to propanal
   v. Propane to 2-hydroxy 2-methyl propanoic acid
4. Give the example each of
   i. Rosenmund reduction ii. Ozonolysis
   iii. Clemmenson reduction iv. Wolff-Kishner reduction
   v. Aldol reaction vi. Cannizaro reaction
   vii. Tollen’s test viii. Fehling’s test
5. An organic compound C₂H₄O gives a red precipitate with Fehling’s solution. It also undergoes aldol reaction. Write the IUPAC name of the compound.
6. An organic compound A(C₄H₈O) forms phenyl hydrazone with phenyl hydrazine and reduce Fehling’s solution. It has negative iodoform test. Identify the compound.
7. Write the structure and one use of the main product obtained by the reaction of formaldehyde with ammonia.