Properties & Reactions of Amides | chemca

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Properties and Reactions of Amides

Structure, Hydrolysis, Hoffmann Degradation, and Reduction.

By chemca Team • Updated Jan 2026

Amides ($R-CONH_2$) are the least reactive of the acid derivatives towards nucleophilic substitution due to strong resonance stabilization. They exhibit amphoteric character and undergo important reactions like Hoffmann degradation.

1. Physical Properties

• State: Most amides are solids at room temperature (except Formamide which is liquid).
• Boiling Point: Primary and secondary amides have very high boiling points (higher than corresponding acids) due to extensive intermolecular Hydrogen bonding.
• Solubility: Lower aliphatic amides are soluble in water due to H-bonding capability.

2. Amphoteric Character

Weak Bases

Amides are very weak bases because the lone pair on nitrogen is involved in resonance with the carbonyl group, making it less available for protonation.

$$ R-C(=O)-NH_2 \leftrightarrow R-C(O^-)=NH_2^+ $$

They dissolve in strong mineral acids to form salts: $RCONH_2 + HCl \rightarrow [RCONH_3]^+Cl^-$.

Weak Acids:

They also act as weak acids, reacting with reactive metals like Sodium or Mercury(II) oxide to form salts.

$$ 2RCONH_2 + HgO \rightarrow (RCONH)_2Hg + H_2O $$

3. Hydrolysis

Acidic and Alkaline

Amides hydrolyze slowly compared to other acid derivatives.

A. Acidic Hydrolysis: Yields Carboxylic Acid and Ammonium salt.

$$ RCONH_2 + H_2O + HCl \xrightarrow{\Delta} RCOOH + NH_4Cl $$

B. Alkaline Hydrolysis: Yields Salt of Carboxylic Acid and Ammonia gas.

$$ RCONH_2 + NaOH \xrightarrow{\Delta} RCOONa + NH_3 \uparrow $$

4. Hoffmann Bromamide Degradation

Step-Down Reaction

Reaction with Bromine and Ethanolic KOH converts a primary amide into a primary amine with one less carbon atom.

$$ R-CONH_2 + Br_2 + 4KOH \rightarrow \underset{1^\circ \text{ Amine}}{R-NH_2} + K_2CO_3 + 2KBr + 2H_2O $$

Mechanism Highlight: The migration of the alkyl group ($R$) from Carbon to Nitrogen is the rate-determining step. It involves the formation of an Isocyanate intermediate ($R-N=C=O$).

5. Dehydration and Reduction

A. Dehydration to Nitriles

Heating with strong dehydrating agents like $P_2O_5$, $SOCl_2$, or $POCl_3$ removes a water molecule to form Cyanides (Nitriles).

$$ R-CONH_2 \xrightarrow{P_2O_5, \Delta} R-C \equiv N + H_2O $$

B. Reduction to Amines

Strong reducing agents like Lithium Aluminium Hydride ($LiAlH_4$) reduce the carbonyl group $>C=O$ to a methylene group $>CH_2$, forming amines with the same number of carbon atoms.

$$ R-CONH_2 \xrightarrow{1. LiAlH_4, 2. H_2O} R-CH_2-NH_2 $$

Compare this with Hoffmann degradation where one carbon is lost.

6. Reaction with Nitrous Acid ($HNO_2$)

Amides react with Nitrous Acid ($NaNO_2 + HCl$) to liberate Nitrogen gas and form Carboxylic Acids.

$$ RCONH_2 + HNO_2 \rightarrow RCOOH + N_2 \uparrow + H_2O $$

This reaction is used to quantitatively estimate amides by measuring the volume of $N_2$ evolved.

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