Phenol

Phenol is often referred to as carbolic acid, and phenolic acid is an aromatic organic compound with the molecular formula C₆H₅OH. In it, a phenyl group ( -C₆H₅) is bonded with the hydroxyl group (OH) by a covalent bond. It is acidic in nature and can cause skin burns.

Physical Properties of Phenol

Phenol is a colourless white crystalline solid. Due to the acidic characteristics of phenols, it is often referred to as carbolic acid and phenolic acid. It is a volatile liquid and catches fire quickly. Due to the formation of hydrogen bonding, it is soluble in water. 

Name of the compound	Phenol
Molecular Formula	C6H6O
Structure
Molecular Weight/Molar Mass	94.11 gmol -1
Density	1.07 gcm -3
Melting Point	40.5 °C
Boiling Point	181.7 °C

Nomenclature of Phenol

Phenol is an organic compound with a hydroxyl (OH) substituent attached to the phenyl group ( -C₆H₅). We can classify phenols into three groups based on the number of hydroxyl groups attached to the benzene ring.

1. Monohydric phenol: Monohydric phenol consists of one hydroxyl group. Example: Phenol (C₆H₅OH).

2. Dihydric phenol: Dihydric phenol consists of two hydroxyl groups. Example: Quinol [C₆H₄(OH)₂].

3. Trihydric phenol: Trihydric phenol consists of three hydroxyl groups. Example: Pyrogallol [C₆H₃(OH)₃].

Synthesis of Phenol

1. Oxidation of benzene and toluene: Benzene and toluene oxidised to form phenol.

C₆H₆ + O → C₆H₅OH

C₆H₅CH₃ + 2 O₂ → C₆H₅OH + CO₂ + H₂O

2. Hydrolysis of benzene sulfonic acid: Benzene sulfonic acid hydrolysed to form phenol. Bayer and Monsanto discovered it.

C₆H₅SO₃H + 2 NaOH → C₆H₅OH + Na₂SO₃ + H₂O

3. Hydrolysis of chlorobenzene: Chlorobenzene in the presence of an alkali or steam hydrolyse to form phenol.

When the reaction proceeds in the presence of an alkali, it is known as Dow’s process.

C₆H₅Cl + NaOH → C₆H₅OH + NaCl

When the reaction proceeds in the presence of steam, it is known as the Raschig Hooker process.

C₆H₅Cl + H₂O → C₆H₅OH + HCl

Chemical Properties of Phenol

1. Reaction with a base: Phenols are acidic in nature. They react with a base to give a neutralisation reaction to form salt and water. 

C₆H₅OH + NaOH → C₆H₅Na + H₂O

2. Schotten–Baumann reaction: Phenol reacts with an acyl chloride in the presence of a mild alkali to form phenyl benzoate.

C₆H₅COCl + C₆H₅OH → C₆H₅COOC₆H₅ + HCl

3. Reduction with zinc dust: Phenol gets reduced to benzene when treated with zinc dust at 400 °C.

C₆H₅OH + Zn → C₆H₆ + ZnO

Applications of Phenol

Phenol is a universal precursor to an extensive array of drugs. Phenols are used in nylon production and are used as an antiseptic. Phenol is used to preserve vaccines and is used in oral analgesics. It is also used in plastic synthesis and synthesising detergents and carbonates. Derivatives of phenols are used in the cosmetic industry. It is one of the components of the extraction technique used in molecular biology to synthesise nucleic acid. We can also extract DNA and RNA from the body by using phenol.

Phenol is affordable and is used as one of the components of the industrial paint strippers. It is also used in the aviation industry to remove polyurethane, epoxy and other chemical coatings.

Cyclohexanone synthesis from phenol is used as a precursor to synthesise nylon.