Advices For Studying Organic Chemistry

12.4 OXIDATION OF ALCOHOLS

12.4A OXIDATION OF PRIMARY ALCOHOLS TO ALDEHYDES:

RCH 2 OH → RCHO

1. 1° alcohols can be oxidized to aldehydes and carboxylic acids.

R CH 2 OH C

O

H C

O

R R OH

[O] [O]

1° Alcohol Aldehyde Carboxylic acid

2. The oxidation of aldehydes to carboxylic acids in aqueous solutions usually takes
   place with less powerful agents than those required to oxidize 1° alcohols to
   aldehydes ⇒ it is difficult to stop the oxidation at the aldehyde stage.

1. Dehydrogenation of an organic compound corresponds to oxidation, whereas
   hydrogenation corresponds to reduction.

3. A variety of oxidizing agents are available to prepare aldehydes from 1° alcohols
   such as pyridinium chlorochromate (PCC) and pyridinium dichromate
   (PDC).

1. PCC is prepared by dissolving CrO 3 in hydrochloric acid and then treated with
   pyridine.

CrO 3 + HCl + N N+ HCrO 3 Cl−

Pyridine Pyridinium chlorochromate
(C 5 H 5 N) (PCC)

H 2 + NN++ H Cr 2 O 72 −

2

Cr 2 O 7

Pyridine Pyridinium dichromate (PDC)
2) PCC does not attack double bonds.

(C 2 H 5 ) 2 C CH 2 OH CH

CH 3 O

PCC (C 2 H 5 ) 2 C

CH CH^3
2 Cl 2

• 25 oC
  2-Ethyl-2-methyl-1-butanol 2-Ethyl-2-methylbutanal