Phenols/OC -II PCI Syllabus/preparation of Phenols/ Sources of Phenols/Qualitative tests of Phenols

Phenols/OC -II PCI Syllabus/preparation of Phenols/ Sources of Phenols/Qualitative tests of Phenols

Hi dear students, in this video I had explained about Phenols. I had tried to explain all the points by animations. So don't hasitate to study now, See this video and you will come to know the facts about acidity and basicity of organic compounds. After watching this video it will be very easy to answer the following questions,

What are phenols?
what about acidity of phenols?
Sources of phenols?
Naming of phenols?
qualitative tests of phenols?


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Acidity of Phenols : https://youtu.be/hOh8x_YCsHM

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1. Phenols

2. Introduction Shape Nomenclature Sources Preparation of phenols Physical properties Chemical properties Structure and uses Qualitative tests Contents

3. Compounds in which —OH group is directly attached with benzene ring are called as Phenols.

4. Phenols Phenol is also called as carbolic acid. Phenol is discovered by Runge Hofmann, another scientist, prepared it first from ‘coal tar’.

5. Shape

6. sp 2 - sp 2 ( C-C σ bond ) sp 3 - s ( O -H σ bond ) sp 2 – sp 3 (C- O σ bond ) sp 2 - s ( C-H σ bond ) Formation of sigma ( σ ) bonds in Phenol All ring carbon atoms also have a p orbital and these are perpendicular to the plane of the σ bonds of the ring. The lateral overlap of these p orbitals produces a delocalized π molecular orbital.

7. Adjacent p orbitals overlap to form the delocalized π molecular orbital.one of the lone pair electrons on the oxygen atom resides in sp 3 orbital and interacts with the delocalized π molecular orbital to form an extended π molecular orbital containing 8 electrons.

8. Nomenclature

9. 9 Phenols Examples are:

10. Sources

11. Sources Phenols occur widely in nature and have many industrial, pharmaceutical, and biological applications. phenol is a general disinfectant, commonly called carbolic acid. Poison ivy, which produces the phenol urushiol . Cloves contain the phenol eugenol .

12. Sources Peppers, a source of capsaicin, which is a phenol. Polyphenols are found in olive oil. Salicylic acid is a phenol that is used to treat acne.

13. Anthocyanins and flavonoids provide the bright colors in certain fruits and vegetables.

14. Physical properties Have higher boiling points than hydrocarbons of the same molecular weight Modest solubility in water Form strong intermolecular hydrogen bonds

15. Physical properties Figure : Hydrogen bonding in phenols. The weak attraction between a positively polarized _ OH hydrogen and a negatively polarized oxygen holds molecules together. Phenols and alcohols have unusually high boiling points because, like water, they form hydrogen bonds. These forces must be overcome for a molecule to break free from the liquid and enter the vapor, so the boiling temperature is raised.

16. Preparation of phenols

17. Dow process From diazonium salt From benzene sulphonate From salicylic acid from oxidation of cumene From benzene Preparation of phenols

18. Reaction of phenols

19. Nitration Halogenation Sulfonation Kolbe’s Reaction Claisen Rearrangement Fries Rearrangement Reimer - Tiemann Reaction Reaction with Neutral FeCl 3 Oxidation Reaction with Benzene diazonium chloride Reaction with Formaldehyde Reaction with Phthalic aanhydride Formation of salt Formation of Ether Formation of Ester

20. Reactions of Phenols Formation of salt Phenols are weak acids and react with strong bases, such as NaOH, to form water- soluble salts. Most phenol s do not react with weaker bases, such as sodium bicarbonate, and do not dissolve in aqueous sodium bicarbonate.

21. Formation of Ether (Williamson’s Ether Synthesis) Phenols reacts with alkyl halides in alkali solution to form phenyl ethers. the alkali first forms phenoxide ion which then reacts with alky halide

22. Formation of Ester Phenols reacts with acyl halides in alkali solution to form phenyl esters. the alkali first forms phenoxide ion which then reacts with alky halide

23. Formation of Ester Phenols reacts with anhydrides in alkali solution to form phenyl esters. the alkali first forms phenoxide ion which then reacts with alky halide

24. Resonance in phenol and phenoxide ion: It is evident from the above structures that — OH group of phenol is o- and p-directing, as these are electron richer places; so electrophiles attack at these positions. Phenoxide ion is resonance stabilized. That is why phenol shows acidic character. The hydroxyl oxygen is less basic, and the hydroxyl proton is more acidic in phenol than in alcohol. Reactions of Benzene ring of Phenols

25. Electrophilic aromatic substitution

26. The hydroxyl group is a powerful activating group—and an ortho–para director in electrophilic aromatic substitutions. Monobromination of phenol can be achieved by carrying out the reaction in CS 2 at a low temperature, conditions that reduce the electrophilic reactivity of bromine. The major product is the para isomer Halogenation

27. Nitration Phenol reacts with dilute nitric acid to yield a mixture of o- and p- n itrophenol . Although the yield is relatively low (becaus e of oxidation of the ri ng), the ortho and para isomers can be separated by steam distillation.

28. o- nitrophenol and p - nitrophenol can be separated by steam distillation More Volatile Less Volatile Due to intramolecular H - bonding Due to intermolecular H - bonding Low B.P. High B.P. Nitration

29. With concentrated HNO 3 , phenol is converted to 2,4,6 – trinitrophenol ( Picric acid ). The yield of reaction product is poor. Nitration Nowadays picric acid is prepared by treatin g phenol first with concentrated sulphuric acid which converts it to phenol-2,4-disulphonic acid, and then with concentrated nitric acid to get 2,4,6-trinitrophenol.

30. Sulfonation Phenol reacts with concentrated sulfuric acid to yield mainly the ortho- sulfonated produc t if the reaction is carried out at 25 o C and mainly the para- sulfonated product at 100 o C.

31. Kolbe’s Reaction Phenoxide ion is even more susceptible to S E Ar than phenol. The Kolbe–Schmitt reaction or Kolbe process is a carboxylation chemical reaction that proceeds by heating sodium phenoxide with carbon dioxide under pressure, then treating the product with sulfuric acid.

32. Kolbe’s Reaction

33. Claisen Rearrangement Heating allyl phenyl ether to 200 c effects an intramolecular reaction to generate o - allylphenol . Mechanism:

34. Claisen Rearrangement When the ortho position is occupied, attack take place on para position.

35. Fries Rearrangement Phenolic esters of aliphatic and aromatic carboxylic acids, when treated with a Lewis acid as catalyst, do undergo a rearrangement reaction to yield ortho- and para- acylphenols respectively.

36. Reimer- Tiemann reaction On treating phenol with chloroform in the presence of sodium hydroxide, a –CHO group is introduced at ortho position of benzene ring. This reaction is known as Reimer - Tiemann reaction.The intermediate substituted benzal chloride is hydrolysed in the presence of alkali to produce salicylaldehyde .

37. H

38. Reaction with Benzene diazonium chloride Benzene diazonium chloride Phenol p - Hydroxyazobenzene Phenols couples with Benzene diazonium chloride in an alkaline solution to form p - Hydroxyazobenzene

39. Reaction with Phthalic anhydride Phenols reacts with phthalic anhydride in the presence of sulfuric acid to fom phenolphthalein. Phthalic anhydride phenolphthalein Phenol Phenol

40. Reaction with Formaldehyde Phenol o and p - Hydroxyazobenzyl alcohol Phenols is treated with an alkaline solution of formaldehyde, a mixture of o- and p - Hydroxybenzyl alcohol is formed.

41. Reaction with Formaldehyde If the reaction is carried at high temperature and in excess of formaldehyde, hard thermosetting plastic Bakelite is formed.

42. Oxidation p- Benzoquinone Phenols undergoes oxidation with air or chromic acid to form p- Benzoquinone

43. Structure and uses

44. BHT ( Butylated Hydroxytoluene ) Antioxidant Disinfectant

45. Qualitative tests for Phenols

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