Question

In the following reaction $ C{{H}_{3}}-COOH\to C{{H}_{3}}COCl $
Here, the reagent is_______________
(A) $ CHC{{l}_{3}} $
(B) $ \text{Red P+C}{{\text{l}}_{\text{2}}} $
(C) $ CHC{{l}_{3}} $
(D) $ PC{{l}_{5}} $

Answer 1

Hint: We need the reactant that converts carboxylic acid to acid chloride. This question requires the concepts of organic chemistry. The reagent involved is a Lewis acid and contains an empty d orbital.

Complete step by step solution:
We already know that,
A carboxylic acid is converted to acid chloride by using various reagents.
But as given from the following examples:
Phosphorus pentachloride converts carboxylic acid to acid chloride.
The reaction is as follows:
 $ C{{H}_{3}}COOH+PC{{l}_{5}}\to C{{H}_{3}}COCl+POC{{l}_{3}}+HCl $
The bi-products are phosphoryl chloride and hydrochloric acid.
So, we need to select the correct option.
The correct option is D.

Note:
Phosphorus pentachloride is a greenish-yellow crystalline solid with an irritating odour. It is decomposed by water to form hydrochloric and phosphoric acid and heat. Phosphorus pentachloride is a phosphorus halide. It is used as a chlorinating reagent in the manufacturing of antibiotics. Also, for the manufacturing of electrolytes for lithium-ion batteries. According to Lewis concept, acid is the substance with empty orbital in the valence shell so that it can accept electron pairs. It contains an empty d orbital in a valence shell. Hence it can act as Lewis acid.
Also, Phosphorus pentachloride, the central Phosphorus atom is $ s{{p}^{3}}{{d}^{2}} $ hybridised. It acquires such a shape so as to minimize the interelectronic repulsion between the Cl atoms. Hence it is fairly stable.
About the bi-product, we can say that phosphoryl chloride (commonly called phosphorus oxychloride) is a colourless liquid with the formula $ POC{{l}_{3}} $ . It hydrolyses in moist air releasing phosphoric acid and fumes of hydrogen chloride. Phosphorus oxychloride is a commonly used dehydrating agent in chemical laboratories. It is used as a dehydrating agent in the preparation of nitriles from primary amides. It is also used as a dehydrating agent in the Bischler-Napieralski reaction.