Phenols

The class of organic compounds characterized by hydroxyl (-OH) group attached to an aromatic ring. Phenol is commonly known as carbolic acid. Phenols are aromatic components which contain one or more hydroxyl groups that are attached to an aromatic ring. Phenol is a benzene derivative and it consists of a phenyl bonded to a hydroxyl (-OH) group. General chemical formula of phenol is C6H5OH and molecular formula C6H6O.
Phenol is a monohydroxy derivative of benzene prepared by the replacing of one of the hydrogen of benzene by hydroxyl group. Phenol contain two part one part is aryl group (phenyl) and other is hydroxyl group.
On the basis of number of hydroxyl group bonded to benzene. It can be classified into di, tri, tetra hydroxyls benzene.

1. Phenols P.M. Jadhav Assistant Professor Dept. of Chemistry M.S.P. Mandals, Shri Muktanand college, Gangapur, Dist : Aurangabad.

2. Phenol The class of organic compounds characterized by hydroxyl (-OH) group attached to an aromatic ring. Phenol is commonly known as carbolic acid. Phenols are aromatic components which contain one or more hydroxyl groups that are attached to an aromatic ring. Phenol is a benzene derivative and it consists of a phenyl bonded to a hydroxyl (-OH) group. General chemical formula of phenol is C 6 H 5 OH and molecular formula C 6 H 6 O.

3. Nomenclature of Phenol Phenol is a monohydroxy derivative of benzene prepared by the replacing of one of the hydrogen of benzene by hydroxyl group. Phenol contain two part one part is aryl group (phenyl) and other is hydroxyl group. On the basis of number of hydroxyl group bonded to benzene. It can be classified into di, tri, tetra hydroxyls benzene . In case of substituted phenol, the relative position is indicated by word Ortho (1, 2), Meta (1, 3) or Para (1, 4 ). However numbers are used if more than two substituents are present on ring.

4. Preparation Methods 1. From Aryl Halides (Dow’s Process): Chlorobenzene when heated with dilute solution of sodium hydroxide at about 300-400 C under 200 atm. pressure in presence of copper salt as catalyst to forms a sodium phenoxide which on treated with dil. HCl to give product phenol. This method is called Dows process. 2 . Benzene sulphonic acid: Benzene sulphonic acid when treated with NaOH to give sodium salt of benzene sulphonic acid (sodium benzene sulphonate ). The sodium benzene sulphonate when fused with NaOH gives sodium phenoxide , which on hydrolysis with dilute H 2 SO 4 give product Phenol .

5. 3. From Cumene : Cumene oxidised by air in presence of cobalt naphthenate in alkaline medium to form cumene hydroperoxide , which on heating in presence of dil. Sulphuric acid form phenol and acetone . 4 . From diazonium salts: Hydrolysis of diazonium salts in the acidic condition to forms corresponding phenols.

6. Physical Properties of Phenol Molecular formula C 6 H 6 O Molar mass 94.11 g/mole Appearance Colorless, Crystalline solid Density 1.07 g/cm 3 Melting point 41°C Boiling point 182°C Solubility in water Soluble in water

7. Acidic Nature of Phenol Phenols are much more acidic than alcohols. Since phenols are acidic in nature, they are soluble in dilute sodium hydroxide . The greater acidity of phenols can be attributed to the resonance stabilization of the phenoxide ion. The resonance structures of phenoxide ion are shown

8. Electrophilic Substitution Reactions The hydroxyl group is a activating group and hence it readily undergo electrophilic substitution reactions. Phenol is ortho and para director as the ortho and para positions of the phenol are electron rich, the substitution takes place at these positions. 1.Friedel-Crafts Acetylation : The reaction in which treatment of phenol with acylating agents like acid chloride, carboxylic acid, acetic anhydride in presence of Lewis acid (AlCl 3 ) or mineral acid to give product phenyl acetate . 2 . Friedel -Crafts Alkylation: The reaction in which treatment of phenol with alkyl halide in presence of Lewis acid (AlCl 3 ) or mineral acid to gives product o/p alkyl phenol.

9. 3. Nitration: Nitration is electrophilic substitution reaction in which hydrogen atom of phenyl ring is replaced by nitro group (-NO 2 ). The reaction in which the treatment of phenol with the dilute HNO 3 at low temperature to gives products o- nitrophenol and p- nitrophenol . 4. Sulphonation : Sulphonation is electrophilic substitution reaction in which hydrogen atom of phenyl ring is replaced by sulphonic acid group (-SO 3 H). Phenols react with conc. H 2 SO 4 to form o - and p- sulphonic acid derivatives. At lower temperature (15-25 C) major product is o-isomer.

10. 5. Kolbe Reaction: Kolbe Reaction is a electrophilic substitution reaction in which hydrogen atom of phenyl ring is replaced by carboxyl group (-COOH). The formation of aromatic carboxylic acid by the reaction of phenoxide with carbon dioxide at 120 C under pressure to gives product salicylic acid . 6. Reimer- Tiemann Reaction: Phenols when react with chloroform in the presence of sodium hydroxide or potassium hydroxide to give hydroxy aldehydes, this formylation reaction is called as Reimer- Tiemann reaction.

11. 7. Gattermann synthesis: This reaction is an electrophilic substitution reaction in which hydrogen atom of phenyl ring is replaced by carbonyl group (C=O ). Phenol when react with hydrogen cyanide or alkyl cyanide and HCl in presence of Lewis acid (AlCl 3 , ZnCl 2 ) as catalyst to give hydroxy aldehyde or ketone. 8. Claisen Rearrangement: The alkyl ether of phenol when heated at higher temperature to give an ortho or para allyl phenol, this sigma tropic rearrangement is known as Claisen Rearrangement. The allyl group migrates from oxygen to the phenyl ring preferably at ortho position.

12. 9. Fries Rearrangement: The rearrangement reaction in which phenyl ester is converted into an ortho and para hydroxy aryl ketone in presence of Lewis acid catalyst followed by an aqueous this reaction is known as Fries rearrangement . 10 . Reduction : Phenols undergo reduction with zinc dust distillation to form the aromatic hydrocarbon benzene.

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