Question

Preparation of phenol from benzene sulphonic acid

Answer 1

There are four llmethods to convert Benzene to Phenol. They are as follows:-

Method I

First do chlorination of Benzene by reacting it with Chlorine gas in presence of either Ferric chloride or anhydrous Aluminium chloride or red Phosphorus to get chlorobenzene

C6H6+Cl2−→−−−−an.AlCl3C6H5Cl+HClC6H6+Cl2→an.AlCl3C6H5Cl+HCl

Then heat the chlorobenzene with steam at 698K using calcium phosphate or silica to get required Phenol

C6H5Cl+H2O−→−−−−−−−−−Ca3(PO4)2/698KC6H5OH+HClC6H5Cl+H2O→Ca3(PO4)2/698KC6H5OH+HCl

Method II

First do chlorination of Benzene by above-mentioned reaction, then react this chlorobenzene with Sodium hydroxide at 613K under 300atm pressure to get Sodium phenoxide

C6H5Cl+2NaOH−→−−−−−−−613K/300atmC6H5ONa+NaCl+H2OC6H5Cl+2NaOH→613K/300atmC6H5ONa+NaCl+H2O

React this Sodium phenoxide with Hydrochloric acid to get required Phenol

C6H5ONa+HCl→C6H5OH+NaOHC6H5ONa+HCl→C6H5OH+NaOH

Method III

First react Benzene with isopropyl chloride in presence of anhydrous Aluminium chloride to get isopropyl benzene (cumene)

C6H6+(CH3)2CHCl−→−−−−an.AlCl3C6H5CH(CH3)2C6H6+(CH3)2CHCl→an.AlCl3C6H5CH(CH3)2

Then oxidize this cumene by passing air/oxygen over it in presence of cobalt naphthenate & alkaline medium at 423K to get cumene hydroperoxide

C6H5CH(CH3)2+O2−→−−−−−−−−−−−−cobalt napthenate/423KC6H5C(CH3)2−O−OHC6H5CH(CH3)2+O2→cobalt napthenate/423KC6H5C(CH3)2−O−OH

Heat this cumene hydroperoxide with dilute sulphuric acid to get required Phenol & acetone

C6H5CH(CH3)2+O2−→−−−−−dil.H2SO4C6H5OH+(CH3)2C=OC6H5CH(CH3)2+O2→dil.H2SO4C6H5OH+(CH3)2C=O

Method IV

First react benzene with oleum (concentrated sulphuric acid) to get benzene sulphonic acid

C6H6+HO−SO3H→C6H5SO3H+H2OC6H6+HO−SO3H→C6H5SO3H+H2O

Neutralize this benzene sulphonic acid by reacting it with caustic soda (sodium hydroxide) to get Sodium benzene sulphonate

C6H5SO3H+NaOH→C6H5SO3Na+H2OC6H5SO3H+NaOH→C6H5SO3Na+H2O

Fuse this sodium benzene sulphonate with excess of caustic soda to get sodium phenoxide

C6H5SO3Na+2NaOH−→−−fused573KC6H5ONa+Na2SO3+H2OC6H5SO3Na+2NaOH573K→fusedC6H5ONa+Na2SO3+H2O

Treat this sodium phenoxide with dilute sulphuric acid to get required Phenol

C6H5ONa+H2SO4−→ΔΔC6H5OH+NaC6H5ONa+H2SO4→∆∆C6H5OH+Na

Answer 2

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Pyrolysis of sodium benzene sulfonate

In this process, benzene sulfonic acid is reacted with aqueous sodium hydroxide. The resulting salt is mixed with solid sodium hydroxide and fused at a high temperature. The product of this reaction is sodium phenoxide, which is acidified with aqueous acid to yield phenol.