Preparation of Phenols-From haloarenes, benzene sulphonic acid, diazonium salts, cumene, FAQs

Alcohols and phenols are formed when a hydrogen atom in an aliphatic or aromatic hydrocarbon is replaced by a –OH group. These classes of compounds have a wide range of applications in industry as well as in everyday life. Sugar, the cotton used in fabrics, and writing paper are all composed of compounds containing –OH groups. Consider life without paper: no notebooks, books, newspapers, currency notes, cheques, certificates, and so on. Magazines with beautiful photographs and interesting stories would vanish from our lives. 

Alcohol contains one or more hydroxyl (OH) groups directly attached to an aliphatic hydrocarbon atom (CH₃OH), whereas a phenol contains –OH group which is directly attached to an aromatic hydrocarbon atom (C₆H₅OH).

Examples are 

Alcohols:

• CH3 – OH                         –        Methyl alcohol
• CH3 – CH(OH) – CH3       –        Isopropyl alcohol

Phenol:

• C6H5-OH                       –           Phenol

Ether:

• CH3OCH3                      –            Dimethyl ether
• C2H5OC2H5                  –            Diethyl ether

Preparation of Phenols

Phenol is now commercially produced synthetically. In the lab, phenols are synthesized from benzene derivatives using one of the following methods:

From haloarenes

At 623K and 320-atmosphere pressure, chlorobenzene is fused with NaOH. The acidification of the resulting sodium phenoxide yields phenol.

From benzene sulphonic acid

When benzene is sulphonated with oleum, the resulting benzene sulphonic acid is heated with molten sodium hydroxide and converted to sodium phenoxide. Phenol is produced by acidifying sodium salt.

From diazonium salts

At 273-278 K, an aromatic primary amine is treated with nitrous acid (NaNO2 + HCl) to form a diazonium salt. Diazonium salts are hydrolyzed to phenols by heating them in water or treating them with dilute acids.

From cumene

Cumene, a hydrocarbon, is used to make phenol. In the presence of air, cumene (isopropyl benzene) is oxidized to cumene hydroperoxide. It is converted to phenol and acetone after being treated with dilute acid. This method also produces a significant amount of acetone as a byproduct of the reaction.

 

Solved Questions(FAQs)

Question 1: Write the structure of the following compounds-

• 2,6-Dimethylphenol
• ortho-Cresol
• Catechol

Answer:

Question 2: Write IUPAC name of the following compounds-

Answer:

1. 2 – Methylbutan – 2 – ol
2. 1 – Phenylpropan – 2 – ol
3. 1 – Ethoxypropane

Question 3: Which is more acidic ethanol (CH3-CH2-OH) or phenol (C6H5-OH)?

Answer:

Phenol (C6H5-OH) is more acidic than ethanol (CH3-CH2-OH) because when phenol loses H+ ion, phenoxide ion is formed, which is more stable due to negative charge delocalization.

Question 4: Give one reaction that shows the acidic nature of phenol?

Answer:

When phenol reacts with sodium hydroxide, sodium phenoxide and water are produced as products which show acidic nature of phenol.

Question 5: Give chemical reaction of phenol when it is treated with dilute HNO3?

Answer:

When phenol is treated with dilute HNO₃ than para-Nitrophenol and ortho-Nitrophenol is formed as a product-