Question
Question: In the following reaction \( C{{H}_{3}}-COOH\to C{{H}_{3}}COCl \) Here, the reagent is___________...
In the following reaction CH3−COOH→CH3COCl
Here, the reagent is_______________
(A) CHCl3
(B) Red P+Cl2
(C) CHCl3
(D) PCl5
Solution
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:
CH3COOH+PCl5→CH3COCl+POCl3+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 sp3d2 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 POCl3 . 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.