Question

When phenol reacts with\[PC{l_5}\], the main product is
A.Chlorobenzene
\[
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;O \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;|| \\
  B.\;Ph - O - P - Cl \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;| \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;Cl \\
    \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;O \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;|| \\
  C.\;Ph - O - P - O - Ph \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;| \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;Cl \\
    \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;O \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;|| \\
  D.\;Ph - O - P - O - Ph \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;| \\
  \;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;\;OPh \\
\]

Answer 1

Hint: The chemical formula of phenol is\[{C_6}{H_5}OH\]. When phenol reacts with \[PC{l_5}\] two products are formed, one is major and the other one is a minor product. The –OH group of phenol is replaced by –Cl that gives chlorobenzene as a minor product and the major product formed is the ester of phosphoric acid.

Complete answer:
We came to know the chemical names of two products formed, now let us see how this reaction occurs and also the structures of the products formed. The reaction is as follows:
\[{C_6}{H_5}OH + PC{l_5} \to {C_6}{H_5}Cl + {\left( {{C_6}{H_5}} \right)_3}P{O_4}\]
In the above reaction, the –OH group attached to phenol gets replaced by –Cl present in \[PC{l_5}\] and the resultant product is chlorobenzene i.e. \[{C_6}H{}_5Cl\] which is a minor product because it is formed in very small amounts. The other product formed here is Triphenyl phosphate which is\[{\left( {{C_6}{H_5}} \right)_3}P{O_4}\] and it is a major product. The name itself indicates that there are three phenyl groups and one phosphate group in it. You are now confused in selecting the answer because both the products are given in the options, in such cases the product which is formed in bulk i.e. the major product should be selected as answer hence triphenyl phosphate could be the correct answer. If you are not aware of the structure of triphenyl, then look at the options which contain three phenyl groups in it. We can see that the compound given in the fourth option has three phenyl groups and that is triphenyl phosphate.

So, by the above explanation we can conclude that the correct option is D.

Note: In all the cases the reaction cannot take place. The reaction can occur only when there is excess phenol because the –OH group of phenol is strongly attached to the benzene ring to be replaced by –Cl unlike alcohols whereas in alcohols the –OH group can be easily replaced.