Question

Provide chemical equations for reactions such as Aldol Condensation, Cross Aldol Condensation, Wurtz Reaction, Fittig Reaction, and Hoffmann Bromamide Reaction.

Hint:

Hofmann bromamide reaction shortens the carbon chain by one carbon — a key exam point.

Answer 1

Step 1: Aldol Condensation.
Aldol condensation occurs when two molecules of an aldehyde or ketone containing at least one α-hydrogen react in the presence of a dilute base to form a β-hydroxy aldehyde or ketone (aldol), which may further dehydrate to give an α,β-unsaturated compound.

Example (Acetaldehyde):
2CH₃CHO → CH₃CH(OH)CH₂CHO (in presence of dil. NaOH)

On heating:
CH₃CH(OH)CH₂CHO → CH₃CH=CHCHO + H₂O

Step 2: Cross Aldol Condensation.
Cross aldol condensation occurs between two different carbonyl compounds. If one compound does not contain α-hydrogen, a single product is formed.

Example (Benzaldehyde and Acetaldehyde):
C₆H₅CHO + CH₃CHO → C₆H₅CH(OH)CH₂CHO (dil. NaOH)

On heating:
C₆H₅CH(OH)CH₂CHO → C₆H₅CH=CHCHO + H₂O

Step 3: Wurtz Reaction.
In Wurtz reaction, two molecules of alkyl halides react with sodium metal in dry ether to form a higher alkane.

2R–X + 2Na → R–R + 2NaX

Example:
2CH₃Br + 2Na → C₂H₆ + 2NaBr

Step 4: Fittig Reaction.
In Fittig reaction, two molecules of aryl halides react with sodium metal in dry ether to form a biaryl compound.

2Ar–X + 2Na → Ar–Ar + 2NaX

Example:
2C₆H₅Cl + 2Na → C₆H₅–C₆H₅ + 2NaCl

Step 5: Hoffmann Bromamide Reaction.
In Hoffmann bromamide reaction, an amide reacts with bromine in the presence of aqueous alkali to form a primary amine containing one carbon less than the parent amide.

RCONH₂ + Br₂ + 4NaOH → RNH₂ + Na₂CO₃ + 2NaBr + 2H₂O

Example:
CH₃CONH₂ + Br₂ + 4NaOH → CH₃NH₂ + Na₂CO₃ + 2NaBr + 2H₂O

Conclusion.
These reactions are important name reactions in organic chemistry and are widely used for carbon–carbon bond formation, chain extension, and preparation of amines.