Module I Oxidation Reactions - NPTel

NPTEL – Chemistry – Reagents and Organic reactions
Me OH
MeO 2C
O
N
N
O
CrO 3 • (pyridine) 2
CH 2Cl 2
O
OH
CrO3 • (pyridine) 2
CH2Cl2 Me
H
OH
OH
n-Am
OTHP
CrO 3 • (pyridine) 2
CH 2Cl 2
1.3.5 Collins-Ratcliff Oxidation
CrO 3 • (pyridine) 2
CH 2Cl 2, C
Scheme 6
Me H
MeO 2C
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N
N
O
O
Me
H
H
O
O
n-Am
OTHP
A 1:2 mixture of CrO3 and pyridine in dichloromethane (DCM) is known as Collins
reagent or Collin-Ratcliff reagent. It also oxidizes the primary alcohols and
secondary alcohols to aldehydes and ketones, respectively (Scheme 6). This
reaction works under mild reaction condition without affecting other functional
groups and the only disadvantage is the excess use of the reagent.
1.3.6 Pyridinium Dichromate (PDC) Oxidation
Pyridinium dichromate (PDC), (C5H5NH + )2Cr2O7 2- , oxidizes alcohols under
neutral condition without affecting other functional groups (Scheme 7). Primary
alcohols are oxidized to aldehydes with excellent yield. Allylic alcohol can be
-unsaturated carbonyl compounds. Excellent yields are obtained
by the oxidation of secondary alcohols by using trimethyl silyl peroxide and PDC
(Scheme 8).
O
O
H
O