Question

Which of the following is an anhydride ?
(A)
   
(B)

(C)

(D)

Answer 1

Hint : We can define an anhydride compound as a compound that is formed from another compound by dehydration or elimination of water. Anhydrides have functional groups which used to be derivatives of either acid or bases. Basic anhydrides have a different pattern from acid anhydrides. Anhydrides can be organic and inorganic both.

Complete step by step solution:
> In organic chemistry acid anhydrides contain the functional group \[R\left( {CO} \right)O\left( {CO} \right)R'\]. Hence an acid anhydride compound contains two acyl groups bonded to the same oxygen atom. A common example of acid anhydride is carboxylic anhydride whose parent acid is a carboxylic acid. The organic anhydrides introduces the acyl group $(RCO)$ in organic synthesis. Anhydrides reacts with water and produces carboxylic acids.
> In the options all are organic compounds. In the given organic compounds we have to identify the functional group \[R\left( {CO} \right)O\left( {CO} \right)R'\]. If in the given compounds we consider $C{H_3} - $ group as $R - $ group then analysis will become easy. In the first option we have found this compound satisfy the formula\[R\left( {CO} \right)O\left( {CO} \right)R'\] of anhydride compounds where $R = R' = C{H_3}$, hence this is a symmetric type of anhydride. The rest of the option does not satisfy the chemical formula of anhydrides so they are not anhydrides.

So here option A is the correct answer to this question. Compound ( A) is acetic anhydride.

Note : Anhydrides produces ester when it reacts with alcohol or phenol and with ammonia and amines it produces amides. Symmetric acid anhydrides can be prepared easily and have a wide range of applications. These are used in synthesis of other useful organic compounds and used as reagents for amines.