Question

What is B in \[3R - OH + PX - 3 \to 3R - X + B\]?
A. Metaphosphoric acid
B. Phosphorous acid
C. Pyro phosphorous acid
D. Phosphoric acid

Answer 1

Hint: We need to know that the phosphoric acid can replace three hydrogen atoms, hence it is a tribasic acid. The phosphoric acid is also known as orthophosphoric acid which acts as an oxidizing agent. This is the main difference of the orthophosphoric acid from other phosphoric acid. The metaphosphoric acid is an inorganic compound having the formula \[HP{O_3}\]. And this acid is obtained by heating of orthophosphoric acid.

Complete answer:
The B in the given equation is not equal to metaphosphoric acid. This acid is a chemical compound having the formula, \[HP{O_3}\]. Hence, the option (A) is incorrect.
The phosphorus acid is a chemical compound having the formula, \[{H_3}P{O_3}\]. In this reaction the haloalkane is reacted with halide of phosphorus and there is a formation of haloalkane. This is done by the addition reaction of halide of phosphorus to the alcohol. Let’s see the reaction,
\[3R - OH + PX - 3 \to 3R - X + B\]
Here, three moles of alcohol are reacted with one mole of phosphorus halide and there is a formation of one mole of haloalkane with phosphorus acid. This haloalkane has high purity and the quantity is also very high. Therefore, we can say that, B in this reaction is phosphorous acid, \[{H_3}P{O_3}\]. Hence, option (B) is correct.
The pyro phosphorus acid is a chemical compound having the formula, \[{H_4}{O_5}{P_2}\]. And this is formed by the reaction of phosphorous acid. B in the given reaction is not pyro phosphorous acid. Hence, option (C) is incorrect.
The phosphoric acid is also known as orthophosphoric acid which acts as an oxidizing agent. And B in the given reaction is not phosphoric acid.

So, the correct answer is “Option B”.

Note:
 We need to know that the halides of phosphorus acids are free radical quenchers and it is more effective than the halogen acids. The phosphorus halide contains both halogen and phosphorus. When the phosphorus halide is reacted with alcohol, there is a formation of phosphorous acid with haloalkane. The alcohol is easily reacted with phosphorus halide at room temperature.