Oxidation of alcohols to aldehydes and ketones, HYPERVALENT IODINE REAGENTS, Dess – Martin periodinane, DMP, Oxidation Mechanism, IBX 2-iodoxybenzoic acid, DMSO BASED REAGENTS, DMSO – dimethyl sulfoxide, Swern Oxidation, Corey-Kim oxidation, DMSO – dimethyl sulfoxide, Aluminium based reagents, Aluminium isopropoxide, Dicyclohexyl carbodiimide (DCC)

1. UNIT IV – OXIDATION AND REDUCTION
4.1.2 Oxidation of alcohols to aldehydes and ketones
SP | MSc – I | Oct 23rd

2. HYPERVALENT IODINE REAGENTS

3. Dess – Martin periodinane
 IUPAC: 3-oxo-1,2-benziodoxole-1,1,1-triyl triacetate I(V)
 Nature: Electrophilic, slightly acidic
 Oxidation: Primary alcohol to aldehyde and secondary
alcohol to ketone
 G.R.

4. Oxidation
mechanism:
Step I: Substitution
Step II: I - O bond cleavage
aldehyde
intermediate
DMP alcohol

5. Examples:
DMP

6. Advantages of DMP:
a) milder reaction conditions
b) avoids use of toxic Chromium reagents
c) does not require excess of co-oxidants
d) high chemo selectivity & yield
e) reaction proceeds at R.T.
DMP

7. IBX
 IUPAC: 2-iodoxybenzoic acid
 Oxidation: Primary alcohol to
aldehyde and secondary alcohol
to ketone
 Characteristics: mild oxidant,
non-toxic, poor solubility in
organic solvents except DMSO
 G.R.

8. Oxidation
mechanism:
• Mechanism is similar to that of DMP
IBX aldehyde

9. Examples:

10. DMSO BASED REAGENTS

11. DMSO – dimethyl sulfoxide
• Non-metal based oxidizing
reagent
• Also used as a solvent
• Mech. of activated DMSO
with an electrophile
• Base deprotonates the
alcohol
• Oxidation reactions
involving DMSO:
a) Swern
b) Corey-Kim
c) Pfitzner-Moffatt
E+ : SOCl2, Cl2, NCS, (COCl)2, Ac2O
Nu- : ROH, PhOH, PhNh2, R2C=N-OH

12. Swern oxidation
 Reagents: Oxalyl chloride + DMSO + Triethylamine (base) +
dichloromethane (solvent)
 Oxidation: Primary alcohol to aldehyde and secondary alcohol to ketone
 Convenient method for the production of DMS-chlorine intermediate
without using dimethyl sulphide and chlorine
 G.R. (occurs at -78oC)

13. Oxidation
mechanism:
DMSO intermediate
intermediate
ketone

14. Examples:
 For cyclic compounds
 Oxidation occurs in the presence of disulphide, sulphur does not get oxidized
 Alipatic long chain can be oxidized

15. Importance of base:
• Cl- is a good nucleophile but a weak base

16. Corey – Kim Oxidation
 Reagents: Dimethyl sulphide + NCS + Triethylamine (base)
 Here DMS is activated with N-chlorosuccinimide
 Conversion: Primary alcohol to aldehyde and secondary alcohol
to ketone
 Advantage over Swern oxidation: can be carried out at - 25oC
(Swern occurs at -78oC)
 Limitations: has issues with selectivity in substrates susceptible
to chlorination by NCS
 G.R.

17. Oxidation
mechanism:
• Exception: In this mechanism, reactive oxidative species is not generated (which
occurs by rxn of DMSO with E+ )
• Without base: Chlorides are easily formed.

18. Examples:
”
”

19. Pfitzner – Moffatt Oxidation
• Reagents: Dicyclohexyl carbodiimide (DCC) + DMSO +
proton source (acid catalyser)
• Oxidation: Primary alcohol to aldehyde and secondary
alcohol to ketone
• Acid catalyser: Phosphoric acid or pyridinium
trifluoroacetate – activates DCC
• G.R.

20. Oxidation
mechanism:
• It is critical that the conjugate base of the acid is basic enough to effect the last step of the reaction
Dicyclohexyl carbodiimide
DMSO intermediate
dicyclohexyl urea
aldehyde

21. Examples:

22. Al BASED REAGENTS

23. Oppenauer Oxidation
 Reagents: Aluminium isopropoxide + Acetone
 Oxidation: Secondary alcohol to ketone in the presence of
acetone as they are oxidized much faster than primary
alcohols
• Acetone acts as a hydrogen acceptor
• Excess of acetone drives the reaction in forward direction
• Reaction generally done in benzene/acetone mixtures
 G.R.

24. Oxidation
mechanism:
Step I: Alcohol – intermediate formed
Step II: 6 – membered transition state
isopropanol
ketone isopropanol