Question

Find A,B,C,D in the given reaction.

${C_6}{H_5}COOH\xrightarrow{{SOC{l_2}}}A\xrightarrow{{N{H_3}}}B\xrightarrow[{KOH}]{{B{r_2}}}C\xrightarrow{{HN{O_2}}}D$

Answer 1

Hint: In organic chemistry, this type of question is the conversion of organic compounds to certain compounds using some suitable reagents and get the final product. $SOC{l_2}$ which is also known as thionyl chloride is a reagent used in organic reactions. It acts as a chlorinating agent. It is a toxic reagent. It is controlled under the Chemical Weapons Convention for its toxic nature.

Complete step by step answer:
The complete reaction is written below:

(A) (B) (C) (D)

In the first step benzoic acid reacts in presence of $SOC{l_2}$ (thionyl chloride) to give the product (A) which is Benzoyl chloride.

In the second step, product (A) which is benzoyl chloride reacts in presence of $N{H_3}$ (ammonia) to give product (B) which is an aromatic amide commonly known as Benzamide.

In the third step, product (B) which is benzamide on treatment with bromine and potassium hydroxide undergoes Hofmann rearrangement to give product (C) which is an aromatic amine commonly known as Aniline.

In the last step, the product (C) which is aniline reacts with $HN{O_2}$(nitrous acid) in presence of $HCl$ (hydrochloric acid) at 273 K to give the product (D) which is a diazonium salt and commonly known as Benzene diazonium chloride. The reaction is called the diazotization.

At ${50^ \circ }C$ aniline reacts with nitrous acid to give phenol

                     

Note: Benzene diazonium is an organic compound with a chemical formula${C_6}{H_5}N_2^ + C{l^ - }$. It is a salt of diazonium cation and chlorine which is widely used in organic chemistry.
The diazo group in the benzene diazonium chloride can be replaced by many other groups.
There are many organic named reactions where benzene diazonium chloride is involved. Such reactions are Sandmeyer’s reaction, Schiemann's reaction, Gomberg-Bachmann's reaction.