Alcohols - Reactions replacing H atoms

• Alcohols are organic compounds containing the functional group -OH.
• In many reactions, the hydroxyl (OH) group can be replaced by another atom or group of atoms.
• Such reactions are known as reactions replacing H atoms.

Types of reactions replacing H atoms:

1. Dehydration Reactions
   • Alcohols can undergo dehydration reactions to eliminate a molecule of water and form an alkene.
   • Example: CH₃CH₂OH → CH₂=CH₂ + H₂O

2. Substitution Reactions
   • The hydroxyl group (-OH) in alcohols can be replaced by halogens (Cl, Br, I) or other nucleophiles.
   • Example: CH₃CH₂OH + HBr → CH₃CH₂Br + H₂O

3. Oxidation Reactions
   • Primary and secondary alcohols can undergo oxidation reactions to form aldehydes and ketones, respectively.
   • Example: CH₃CH₂CH₂OH → CH₃CH₂CHO + H₂O

4. Esterification Reactions
   • Alcohols can react with carboxylic acids to form esters and water.
   • Example: CH₃CH₂OH + CH₃COOH → CH₃CH₂COOCH₃ + H₂O

5. Ether Formation Reactions
   • Alcohols can undergo reactions to form ethers by reacting with another alcohol or alkyl halide.
   • Example: CH₃CH₂OH + CH₃CH₂Br → CH₃CH₂OCH₂CH₃ + HBr

6. Decarboxylation Reactions
   • Beta-keto acids can undergo decarboxylation reactions in the presence of heat or catalysts to form ketones.
   • Example: CH₃COCH₂COOH → CH₃COCH₃ + CO₂

11. Dehydration Reactions

• Alcohols can undergo dehydration reactions to eliminate a molecule of water and form an alkene.
• The reaction is catalyzed by acids or heat.
• Example: CH₃CH₂OH → CH₂=CH₂ + H₂O

12. Substitution Reactions

• The hydroxyl group (-OH) in alcohols can be replaced by halogens (Cl, Br, I) or other nucleophiles.
• This reaction is known as a nucleophilic substitution reaction.
• Example: CH₃CH₂OH + HBr → CH₃CH₂Br + H₂O

13. Oxidation Reactions

• Primary and secondary alcohols can undergo oxidation reactions to form aldehydes and ketones, respectively.
• Oxidation is typically carried out using oxidizing agents like potassium permanganate (KMnO₄) or potassium dichromate (K₂Cr₂O₇).
• Example: CH₃CH₂CH₂OH → CH₃CH₂CHO + H₂O

14. Esterification Reactions

• Alcohols can react with carboxylic acids to form esters and water.
• This reaction is catalyzed by an acid like concentrated sulfuric acid (H₂SO₄).
• Example: CH₃CH₂OH + CH₃COOH → CH₃CH₂COOCH₃ + H₂O

15. Ether Formation Reactions

• Alcohols can undergo reactions to form ethers by reacting with another alcohol or alkyl halide.
• This reaction is known as Williamson ether synthesis.
• Example: CH₃CH₂OH + CH₃CH₂Br → CH₃CH₂OCH₂CH₃ + HBr

16. Decarboxylation Reactions

• Beta-keto acids can undergo decarboxylation reactions in the presence of heat or catalysts to form ketones.
• The carboxyl (-COOH) group is eliminated as carbon dioxide (CO₂).
• Example: CH₃COCH₂COOH → CH₃COCH₃ + CO₂

17. Dehydration Reaction Mechanism

• Dehydration reactions proceed through the E1 or E2 mechanism.
• E1 mechanism: Unimolecular elimination reaction involving a carbocation intermediate.
• E2 mechanism: Bimolecular elimination reaction involving a concerted process.
• Example: CH₃CH₂OH + H₂O → CH₂=CH₂ + H₃O⁺ + OH^- CH₂=CH₂ + H₃O⁺ → CH₃CH₂OH + H₂O

18. Substitution Reaction Mechanism

• Substitution reactions can proceed via SN1 or SN2 mechanism.
• SN1 mechanism: Unimolecular nucleophilic substitution involving formation of a carbocation.
• SN2 mechanism: Bimolecular nucleophilic substitution involving a concerted process.
• Example: CH₃CH₂OH + HBr → CH₃CH₂Br + H₂O

19. Oxidation Reaction Mechanism

• Oxidation of alcohols involves loss of hydrogen and gain of oxygen.
• Primary alcohols are oxidized to aldehydes, which further oxidize to carboxylic acids.
• Secondary alcohols are oxidized to ketones.
• Example: CH₃CH₂CH₂OH → CH₃CH₂CHO + H₂O CH₃CH(OH)R → CH₃C(O)R + H₂O

20. Esterification Reaction Mechanism

• Esterification reactions involve the condensation of an alcohol and a carboxylic acid to form an ester.
• The reaction is catalyzed by an acid like concentrated sulfuric acid (H₂SO₄).
• Example: CH₃CH₂OH + CH₃COOH → CH₃CH₂COOCH₃ + H₂O

21. Ether Formation Reaction Mechanism

• Ether formation reactions follow the Williamson ether synthesis mechanism.
• The reaction involves the nucleophilic substitution of an alkoxide ion with an alkyl halide.
• Example: CH₃CH₂OH + CH₃CH₂Br → CH₃CH₂OCH₂CH₃ + HBr

22. Decarboxylation Reaction Mechanism

• Decarboxylation reactions occur in beta-keto acids through decarboxylation of the carboxyl group.
• The reaction is facilitated by heat or catalysts like acid or base.
• Example: CH₃COCH₂COOH → CH₃COCH₃ + CO₂

23. Dehydration of 2-Methyl-2-Butanol

• 2-Methyl-2-butanol can undergo dehydration to form 2-methyl-2-butene.
• This reaction proceeds via an E1 mechanism.
• Example: (CH₃)₂CHCH₂OH → (CH₃)₂CHCH=CH₂ + H₂O

24. Substitution of Ethanol with Sodium

• Ethanol can undergo substitution reaction with sodium to form sodium ethoxide and hydrogen gas.
• Example: CH₃CH₂OH + Na → CH₃CH₂O^-Na⁺ + 1/2H₂

25. Oxidation of Ethanol to Ethanal

• Ethanol can be oxidized to ethanal (acetaldehyde) using oxidizing agents like potassium dichromate (K₂Cr₂O₇).
• Example: CH₃CH₂OH → CH₃CHO + H₂O

26. Oxidation of Ethanol to Ethanoic Acid

• Ethanol can be further oxidized to form ethanoic acid (acetic acid) using stronger oxidizing agents like potassium permanganate (KMnO₄).
• Example: CH₃CH₂OH → CH₃COOH + H₂O

27. Esterification of Ethanol with Acetic Acid

• Ethanol can react with acetic acid to form ethyl acetate and water.
• This reaction is carried out in the presence of concentrated sulfuric acid as a catalyst.
• Example: CH₃CH₂OH + CH₃COOH → CH₃CH₂COOCH₃ + H₂O

28. Ether Formation from Alcohol and Alkyl Halide

• Alcohols can react with alkyl halides to produce ethers.
• This reaction is an example of nucleophilic substitution.
• Example: CH₃CH₂OH + CH₃CH₂Br → CH₃CH₂OCH₂CH₃ + HBr

29. Acid-Catalyzed Dehydration of Ethanol

• Ethanol can undergo acid-catalyzed dehydration to form ethene (ethylene) and water.
• Example: CH₃CH₂OH → CH₂=CH₂ + H₂O

30. Mechanism of Acid-Catalyzed Dehydration of Ethanol

• The acid-catalyzed dehydration of ethanol follows an E1 mechanism.
• The reaction involves the formation of an intermediate carbocation.
• Example: Step 1: CH₃CH₂OH + H⁺ → CH₃CH₂O⁺ + H₂O Step 2: CH₃CH₂O⁺ → CH₂=CH₂ + H⁺