Answers to SQ Ch. 29 Phenols

1. What phenol?

Phenols are aromatic hydroxy compounds. In phenols, one or more hydroxyl group is directly attached to the aromatic (benzene) nucleus.

2. How is phenol prepared using benzene?

Benzene is heated with excess of concentrated sulphuric acid at about 388 K to give benzene sulphonic acid. It is neutralized with sodium hydroxide solutio, when sodium benzene sulphonate is obtained. Dry sodium benzene sulphonate is next fused with excess of caustic soda at about 573 K when it yields sodium phenate (or sodium phenoxide). Sodium phenate is decomposed by dilute sulphuric acid to give phenol.

3. What is the action of Bromine water on phenol?

when phenol is treated with bromine water, it gets decolourised giving a white precipitate of 2,4,6, tribromophenol.

4.How is phenol prepared using benzene sulphonic acid?
It is neutralized with sodium hydroxide solutio, when sodium benzene sulphonate is obtained. Dry sodium benzene sulphonate is next fused with excess of caustic soda at about 573 K when it yields sodium phenate (or sodium phenoxide). Sodium phenate is decomposed by dilute sulphuric acid to give phenol.



5.What is the action of dilute nitirc acid on phenol?

a mixture of o-nitrophenol and p-nitrophenol is formed.

6. How is phenol prepared using chlorobenzene?

By (i) Dow's Process
(ii) Rasching process

7. What is the action of conc. nitric acid in the presence of conc. sulphuric acid on phenol?

2,4,6-trinitrophenol is formed. This is picric acid.

8. How is phenol prepared using cumene?

Air or oxygen is passed through a suspension of cumene in acqueous sodium carbonate solution in presence of cobalt or manganese naphthenate catalyst. The oxidation product is cumene hydroperoxide.

The hydroperoxide is then decomposed by hot dilute sulphuric acid when phenol is formed withliberation of acetone. Acetone is removed from phenol by distillation.


9. What is the action of Bromine in CS-2 on phenol?

o-Bromophenol + p-Bromophenol mixture is obtained. p-Bromophenol is the major product.

10. Give a test distinguish between phenol and ethanol?

Alcohol react with metal sodium to form alkoxide, liberating hydrogen. Phenol does not react with metal sodium.

11. What is the action of conc. sulphuric acid at different temperatures on phenol?
At low temperature about 288 to 293 K, o-phenol sulphonic acid is formed.

At high temperature about 373 K, p-phenol sulphonic acid is formed.

12. How will you obtain from carbolic acid, picric acid?

Phenol is also called carbolic acid.
When phenol is treated with concentrated nitric acid in the presence of concentrated sulhuric acid, 2,4,6-trinitrophenol is formed.


13. How do you use ferric chloride to distinguish between phenol and alcohol?
alcohol does not show any colouration with FeCl-3.
Phenol give violet colouration with ferric chlordie.

14. How will you obtain 2,4,6-tribromophenol from carbolic acid?

answer same as Q 12

15. What are the differences in physical properties among p-nitrophenol, o-nitrophenol and m-nitrophenol?

o-nitrophenol has a much lower boiling point, much lower solubility in water than its isomers.

These differences occur because o-nitrophenol involves intramolecular hydrogen bonding. the boiling point os o-nitrophenol is low because it exists as a monomolecule.

the solubility of m- and p- isomers is due to their ability to form hydrogen bonding with water.

The

16.What is williamson synthesis?

Phenols reacting with alkyl halides to yield ethers in alkaline medium.

17. what is Fries rearrangement?

When esters of phenols are heated with AlCl-3, the acyl group migrates from the phenolic oxygen to an ortho or para position of the ring producing a ketone.

18. What is the action of nitrous acid on phenol?

Nitrous acid converts phenol to nitrosophenol.

19. What is Reimer-Tiemann reaction?

When phenol is treated with cholorom and aqueous sodium hydroxide, a -CHO group is introduced in the ring.

20. What is Schotten-baumann reaction?

The reaction of phenol with benzoyl chloride.
This will produce phenylbenzoate.

21. What do phenols liberate when treated with sodium?

Phenols do not react with sodium.
22. Are phenols soluble in sodium bicarbonate solution?

Phenols are not soluble in sodium bicarbonate solution. There are soluble in sodium hydroxide solution.

23. what happens when phenol is exposed to air?
On exposure to air it turns to pink due to oxidation.
24. What is picric acid?

2,4,6-trinitrophenol

25. What is cresol?
The methylphenols are cresols. Both OH and NO-2 are attached to benzene.