Methods of Preparation of Phenols Preparation and Properties

Methods of Preparation of Phenols Preparation and Properties

Laboratory Methods :

→ From Benzene Diazonium SaIt : An aqueous solution of benzene diazonium salt on boiling gives phenol.

→ From Haloarenes : When chiorobenzene is heated or fused with NaOH at 623 K and 320 atmospheric pressure then sodium phenoxide is obtained. Phenol is obtained by acidification of sodium phenoxide.

→ From Benzenesulphonlc Acid : Benzene is suiphonated with oleum then benzene suiphonic acid is obtained. On heating it with sodium hydroxide, sodium phenoxide forms. Acidification of the sodium salt gives phenol.

→ From Salicylic AcId : On heating salicylic acid with soda lime (NaOH + CaO), sodium phenoxide forms. On acidic hydrolysis it forms phenol.

→ From Grignard Reagent : Phenyl magnesium bromide reacts with O₂ in the presence of light. The product thus obtained on hydrolysis gives phenol.

Commercial Preparation :

→ From Cumene : Phenol is prepared commercially from cumene. Isopropyl benzene is known as cumene. In the presence of air cumene is oxidised to cumene hydro peroxide. On reaction with dii. acid it converts into phenol and acetone. Acetone is obtained as byproduct in this reaction, which is an important reagent for industrial purpose.

→ From Coaltar : Middle oil fraction is obtained by fractional distillation of coaltar. It contains mainly phenol and napthalene etc., When this fraction reacts with NaOH, sodium phenoxide forms, which is dicomposed by CO₂ and phenol is obtained.

→ By Oxidation of Benzene It is modern method for the preparation of phenol. When mixture of benzene and air are passed over hot vanadium pentaoxide (V₂O₅) at 583 K, phenol is formed.

→ Rasching’s Process : In this process firstly chiorobenzene is prepared from benzene, then it reacts with red hot silica and steam to give phenol.

→ Dow’s Process : Chiorobenzene prepared from Rasching’s process is hydrolysed with sodium hydroxide (NaOH) and sodium carbonate (Na₂CO₃) solution at about 623 K under 300 atmospheres and in the presence of CuCl₂ to form phenol.

Chemistry Notes