1. By Puan Azduwin Khasri 6th NOVEMBER 2012
ALCOHOL
By Puan Azduwin Khasri
6th NOVEMBER 2012

2. INTRODUCTION

3. Reaction of Alcohol Others OXIDATION SUBSTITUTION ELIMINATION
(DEHYDRATION)
OXIDATION
SUBSTITUTION
Others
ALKYL HALIDE
SULFONATE ESTER
KETONE
ALDEHIDE
CARBOXILIC ACID
ALKENE

4. Nucleophilic substitution of Alcohol
An alcohol has a strongly base leaving group (HO-) therefore alcohol cannot undergo a nucleophilic substitution reaction
Convert the strongly basic leaving group (OH–) into the good leaving group, H2O (a weaker base):

5. Primary, secondary, and tertiary alcohols all undergo
nucleophilic substitution reactions with HI, HBr, and HCl:

6. SN1 REACTION OF ALCOHOL
Secondary and tertiary alcohols undergo SN1 reactions
with hydrogen halides:

7. Look out for rearrangement product in the SN1 reaction of the secondary or tertiary alcohol:

8. SN2 REACTION OF ALCOHOL
Primary alcohols undergo SN2 reactions with hydrogen halides:

9. When HCl is used; SN2 reaction is slower, but the rate can be increased using ZnCl2 as catalyst .
ZnCl2 functions as a Lewis acid that complexes strongly with the lone-pair electrons on oxygen:

10. CLASS EXERCISE 1
Give the major product of each of the following reactions:

11. Other Methods for Converting Alcohols
into Alkyl Halides
Utilization of phosphorus tribromide:
PYRIDINE
Other phosphorus reagents can be used:
PBr3, phosphorus tribromide
PCl3, phosphorus trichloride
PCl5, phosphorus pentachloride
POCl3, phosphorus oxychloride

12. Activation by SOCl2
Pyridine is generally used as a solvent and also acts as a base:

14. Summary: Converting of Alcohols to Alkyl Halides
Recommended procedures:

15. Converting Alcohols into
Sulfonate Esters

16. Several sulfonyl chlorides are available to activate OH
groups:

17. ELIMINATION REACTION OF ALCOHOL (DEHYDRATION)
Dehydration of alcohol requires acid catalyst and heat
Dehydration of Secondary and Tertiary Alcohols by an E1 Pathway 17

18. Mechanism of E1 Dehydration of an Alcohol

19. The major product is the most stable alkene product:
The most stable alkene product has the most stable
transition state

20. The rate of dehydration reflects the ease with which the
carbocation is formed:

21. Look out for carbocation rearrangement:

22. Pinicol Rearrangement
Protonate alcohol:
Eliminate water:
Rearrange carbocation:
Deprotonate:
Resonance-stabilized
oxocarbocation

23. Ring Expansion and Contraction
Mechanism for this reaction:
Protonate the alcohol.
Eliminate water.
Rearrange carbocation to afford the more stable cyclohexane ring.
Deprotonate.

24. Primary Alcohols Undergo Dehydration by an E2 Pathway

25. A Milder Way to Dehydrate an Alcohol

26. Oxidation of Alcohols Oxidation by chromic acid:
Secondary alcohols are oxidized to ketones

27. Primary alcohols are oxidized to aldehydes and eventually carboxylic acids:
Mechanism:

28. The oxidation of aldehydes to acids requires the presence of water:
In the absence of water, the oxidation stops at the aldehyde:
PCC, a methylene chloride–soluble reagent:
No water present

29. A tertiary alcohol cannot be oxidized and is converted to a stable chromate ester instead:
No hydrogen on this carbon
Di-tert-Butyl Chromate

30. ETHER

31. Nucleophilic substitution reaction of Ether
Ethers, like alcohols, can be activated by protonation:
Ether can undergo nucleophilic substitution with HBr and HI only (HCl cannot be used because Cl- too poor nucleophile

32. Ether cleavage: an SN1 reaction:

33. Reagents such as SOCl2 and PCl3 can activate alcohols but not ethers
Ethers are frequently used as solvents because only they
react with hydrogen halides

34. Nucleophilic Substitution
Reactions of Epoxides
Acidic condition;
HBr:
Aqueous acid:

35. Reaction of an epoxide in different substituent
Regioselectivity:
Mechanism:

36. Neutral or Basic condition:
When a nucleophile attacks an unprotonated epoxide,
the reaction is a pure SN2 reaction:
Therefore:

37. Epoxides Are Synthetically
Useful Reagents
Enantiomers

38. CLASS EXERCISE 2
Give the major product of the following reactions:

39. THE END