Question

What would be the final product of this reaction sequence?

Answer 1

Hint: To answer this question, we should recall the concept of nucleophilic substitution reactions. It is the type of reaction that involves the replacement of one atom or molecule of a compound with another atom or molecule.

Complete step by step answer:
- Reaction of the carboxylic acid with phosphorus chloride yields acyl chloride. With $PC{{l}_{5}}$, the reaction is quite simple utilizing a one-mole reactant and yielding products. The major advantage of this reaction is that there is only one side product i.e. phosphonic acid which is non-toxic, is easily removed by filtration whereas reaction with $PC{{l}_{5}}$ gives two side products making the reaction more volatile.

- Reaction of an acyl chloride with ammonia takes place in two stages. In the first stage, we initially get $HCl$, with the hydrogen atom coming from $N{{H}_{3}}$ group. Since ammonia and amines are basic, they react with $HCl$ to produce salt. Therefore, in the second stage, we get benzamide.

- Amides dehydrated with ${{P}_{4}}{{O}_{10}}$ yield cyanides. Since ${{P}_{4}}{{O}_{10}}$ is known to be a very strong dehydrating agent, it reacts itself with water molecules to form phosphoric acid. That enables it to remove free water molecules by a simple hydrolysis reaction. Amide reacts with it to give its substituted nitriles and Cyanide as a major product is formed.

Note: It is important to note that in each case, the nucleophile approaches the given substrate to the leaving group. The leaving group is pushed out of the transition state on the opposite side of the carbon-nucleophile bond, forming the required product.