Question

The boiling points of acetic anhydride (I), propionic anhydride (II) and butyric anhydride (III) follow the order.
(A) $ I < II < III $
(B) $ III < II < I $
(C) $ I < III < II $
(D) $ II < III < I $

Answer 1

Hint : We know that the anhydride is the chemical compound which is obtained, either in principle or in practice, by the elimination of water from any other compound. An example of inorganic anhydrides is given as sulfur trioxide, which has been derived from the sulfuric acid, and the calcium oxide, derived from calcium hydroxide.

Complete Step By Step Answer:
The most important compound of the organic anhydrides is acetic anhydride, with the chemical formula $ {{\left( C{{H}_{3}}CO \right)}_{2}}O. $ It can be prepared industrially in either two ways: and from acetic acid by the reaction with ketene or acetylene or by acetaldehyde's atmospheric oxidation in the presence of metal acetate. Other organic anhydrides are prepared from the carboxylic acids by reaction with ketene, acetic anhydride, isopropenyl acetate or methoxy-acetylene.
Acid Anhydride is the molecule capable of forming acidic solutions in water. An acid anhydride is defined as a non-metal oxide capable of creating an acidic solution when reacted with water. In organic chemistry, an Anhydride is a functional group having two acyl groups combined together by an Oxygen atom. Only the non-metals capable of reacting with water are called Acid anhydrides, and non-metals that do not react with water don't come under acid anhydrides. Acetic anhydride can be employed in cellulose acetate manufacturing, which is widely used as a base for the magnetic tape and in textile fibre manufacturing. Also, it can be heated with salicylic acid to form the medicinal chemical acetylsalicylic acid (which is called aspirin). Butyric anhydride's boiling point is at 140°C. This is only because it is a fairly big polar molecule, and so has both dipole-dipole attractions and van der Waals dispersion forces. However, it doesn't form hydrogen bonds. It means that the boiling point is not as high as that of a carboxylic acid of a similar size. For example, acetic acid (one of the most similarly sized acids) boiling point is at $ 186{}^\circ C. $
Therefore, the correct answer is option B.

Note :
Remember that anhydrides can be produced when acyl halides react with carboxylic acid and pyridine or acetic anhydride. The organic anhydrides can be used to introduce the acyl group $ \left( RCO \right) $ in organic synthesis. They react with water to produce carboxylic acids, either with alcohols or phenols to form esters and with ammonia and amines to form amides.