Question

Write a short note on the following
Raschig–Hooker process.

Answer 1

Hint: As we know that Raschig–Hooker process is an organic synthesis used for the production of phenol. It is more preferable over Dow’s and Bayer’s process but this process takes place at very high temperatures in a very acidic medium or environment. So here we have to explain the Raschig–Hooker process.

Complete answer:
Let us discuss about Raschig–Hooker process as follows:-
-Raschig–Hooker process: It is a chemical process in organic chemistry which is used for the production of phenol. This process is mainly preferred in European countries. The main steps in this process are as follows:-
(a) Firstly we need to produce chlorobenzene from benzene by using hydrochloric acid (HCl) and oxygen gas. This step uses either a copper or iron chloride catalyst and also exposes these materials to air at 400$^{\circ }C$. This reaction is shown below:-

(b) Then chlorobenzene is introduced to steam or water vapour at 450$^{\circ }C$ over a silicon catalyst which hydrolyses the chlorobenzene. This hydrolysis of chlorobenzene yields phenol and hydrogen chloride which can be recycled back to get reused in the first step.

-This whole process takes place at a very high temperature in the acidic medium. The recycling of hydrogen chloride in the end of the process made it more preferable synthesis over Dow’s and Bayer’s process.

Note:
-Remember that there are two steps in the Raschig–Hooker process due to which it can be used to produce either chlorobenzene or phenol.
-Also the overall selectivity of the reaction is $70\%$ to $80\%$ as the second step shares the low conversion rate and the first step has a high selectivity rate.