Is Acetamide base or acid? | Preparation | Properties

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Preparation of Acetamide

Laboratory Method

Ammonia acetate is heated in the presence of glacial acetic acid to make Acetamide in the laboratory.

CH₃COONH₄ → CH₃CONH₂ + H₂O

Glacial acetic acid is used to prevent side reaction.

CH₃COONH₄ ⇌ CH₃COOH + NH₃

In the presence of glacial acetic acid, the forward reaction is not effective due to the high velocity of the opposite reaction and the main product is acetamide produce when ammonium acetate is heated.

Chemistry Notes

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Method: Approximately equal amounts of dry ammonium acetate and glacial acetic acid are taken in a round-bottomed flask. A long and direct air condenser is attached to the flask. Put the flask on a wire mesh and heat it for about 4 hours.

Partial dehydration of ammonium acetate occurs and the water formed in the reaction exits the air condenser. After this, the flask mixture is poured into a distillation flask.

A thermometer and air candenser are placed in the distillation flask. Attaches the air condenser to the receiver. Heats the flask and collects the distilled fluid in the receiver.

Above in 200°C temperature they collect the distilled fluid in another receiver. It contains acetamide. When cooled it converts into a solid form. Pure acetamide is obtained after its ether or alcohol is crystallized.

Methyl Cyanide

Acetic acid is obtained from complete water decomposition of methyl cyanide and acetamide is obtained from partial water decomposition of methyl cyanide. Partial water decomposition of methyl cyanide is done in two ways.

Alkaline hydrogen peroxide
Dissolved in concentrated sulfuric acid and poured into cold water

CH₃-C≡N + H₂O → CH₃CONH₂

Acetamide can also be made by the reaction of ammonia solution concentrated on acetyl chloride, acetic anhydride or ethyl acetate.

CH₃COCl + 2NH₃ → CH₃CONH₂ + NH₄Cl

(CH₃CO)₂O + 2NH₃ → CH₃CONH₂ + CH₃COONH₄

CH₃COOC₂H₅ + NH₃ → CH₃CONH₂ + C₂H₅OH

Acetamide Physical Properties

It is colorless, needle-shaped and crystalline solids. It is soluble in water, alcohol and ether. In pure state it is odorless but in impure state it smells like rat. Its melting point is 82°C and the boiling point is 222°C.

Acetamide Chemical Properties

Water decomposition: It is slowly decomposed by water and quickly by dilute acids.

CH₃CONH₂ + H₂O → CH₃COOH + NH₃

It is more rapidly decomposed by dilute bases. Sodium acetate and ammonia are formed in this reaction. This reaction is used to test amide group.

CH₃CONH₂ + NaOH → CH₃COONa + NH₃

Amphoteric Properties: It reacts with intense acids to form temporary salts which exhibit its alkaline properties.

CH₃CONH₂ + HCl(Base) → CH₃CONH₂.HCl(acetamide hydrochloride)

It reacts with sodium metal to form a salt called sodium acetamide which exhibits its acidic properties.

2CH₃CONH₂ + 2Na → 2CH₃CONH.Na(sodium acetamide) + H₂

It is Amphoteric due to exhibiting both acidic and alkaline properties.

Reduction: This H₂/Ni. Sodium ethanol is reduced by LiAlH₄ or NaBH₄ to form ethyl amine.

CH₃CONH₂+ LiAlH₄ → CH₃CH₂NH₂ + H₂O

Action of nitrous acid: It reacts with nitrous acid to make acetic acid and nitrogen gas is free.

NaNO₂ + HCl → NaCl + NHO₂

CH₃CONH₂ + NHO₂ → CH₃COOH + H₂O + N₂

Dehydration: On heating acetamide with phosphorus pentoxide, one molecule of water is released from one of its segments and forms methyl cyanide.

CH₃CONH₂ + P₂O₅ → CH₃CN + H₂O

Hoffmann bromamide Reaction: Methyl amine is obtained when acetamide is heated with bromine and caustic potash solution. Here are the reactions:

CH₃CONH₂ + Br₂ → CH₃CONHBr + HBr

KOH + HBr → KBr + H₂O

CH₃CONHBr + KOH → CH₃NCO + KBr + H₂O

CH₃NCO + 2KOH → CH₃NH₂ + K₂CO₃

The complete reaction can be represented by the following equation.

CH₃CONH₂ + Br₂ + 4KOH → CH₃NH₂ + 2KBr + K₂CO₃ + 2H₂O

With the help of this reaction amide group (-CONH₂) can be converted into amino group (-NH₂). This reaction is very important and is used to obtain a lower member from a higher member of a homogeneous category.

What is acetamide used for?

Being hygienic, it is used in softening the fabrics etc.
Used in making methyl amine.
It is used in making diethyl bromo bromoacetamide. Which is used as a sleeping medicine called neuronal.