Chemistry AMIDES
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AMIDES

Amides :

In the laboratory amides are prepared by the reaction of ammonia with acid chlorides or acid anhydrides. In industry they are often made by heating the ammonium salts of carboxylic acids.

Hydrolysis of Amides :

It involves nucleophilic substitution, in which the `NH_2` group is replaced by `- OH`. Under acidic conditions hydrolysis involves attack by water on the protonated amide. See fig.1.

Under alkaline conditions hydrolysis involves attack by the strongly nucleophilic hydroxide ion on the amide itself. See fig.2.

Basic Character of Amides :

Amides are very feebly basic and form unstable salts with strong inorganic acids. e.g. `RCONH_2HCl`. The structure of these salts may be `I` or `II`.

Acidic Character of Amides :

Amides are also feebly acidic; e.g. they dissolve mercuric oxide to form covalent mercury compound in which the mercury is probably linked to the nitrogen.

`2RCONH_2 + HgO -> (RCONH)_2 Hg + H_2O`

Reduction of Amides :

Amides are reduced by sodium ethanol, catalytically, or by lithium aluminium hydride to a primary amine.

`RCONH_2 + 4H overset(Na//C_2H_5OH)-> R- CH_2 -NH_2 + H_2O`

Reaction with Phosphorus Pentoxide :

When heated with `P_2O_5`, amides are dehydrated to alkyl cyanides.

`R - CONH_2 underset(-H_2O)overset(P_2O_5)-> R - CequivN`

Alkyl cyanides are also formed when the amides of the higher fatty acids are heated in the presence of ammonia.

`R- CO_2H + NH_3 -> RCO_2NH_4 overset(-H_2O)-> RCONH_2 overset(-H_2O)-> RCN`

Amides may also be converted into cyanides by phosphorus pentachloride.

`RCONH_2 overset(PCl_5)-> RC Cl_2NH_2 overset(HCl)-> R - C Cl = NH overset(-HCl) -> RCN`
 
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