Preparation of Acetamide
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.
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.
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.