OXIDATION OF ALCOHOLS

AS Chemistry

Oxidised to aldehydes and acids

OXIDATION OF ALCOHOLS

for PRIMARY alcohols

for SECONDARY alcohols

NOT SIGNIFICANT for TERTIARY

alcohols!

NB Oxidant = hot acidified Cr2O72-

[O]

Orange Cr2O72- reduced to green Cr3+

or ketones

Oxidant is represented by :

[dichromate(VI)] ion]

Provided by mixture of potassium dichromate(VI), K2Cr2O7, and excess dilute sulphuric acid, H2SO4.

-CH2OH -C-CH(OH)-C-

    

   

C HC

H

OH

PRIMARY SECONDARY TERTIARY

+ [O] + [O] + [O]

C

O

H

C C

O

C

C

+ H2O + H2O

NO SIGNIFICANT OXIDATION

- no C–H bond

Aldehyde Ketone

+ [O]

C

O

OH

CAcid

+ [O]

NO FURTHER OXIDATION - no C – H bond

C CC

C

OH

C HC

C

OH

Any oxidation that does

occur involves breaking C-C bonds loss

of original structure.

What are the oxidation products of : 

1. Ethanol? 2.  Methyl-propan-2-ol? 3.  Butan-2-ol ?

Primary

CH3CH2OH

CH3CHO + H2O

CH3C(CH3)(OH)CH3 CH3CH2CH(OH)CH3

Tertiary Secondary

2. No significant oxidation

1. CH3CH2OH + [O]

CH3CHO + [O] CH3COOH

Ethanal

Ethanoic acid

CH3CH2COCH3 + H2O3. CH3CH2CH(OH)CH3 + [O]

Butanone

To Maximise the Production of an ALDEHYDE

To Maximise the Production of an ACID or a KETONE

Controlling Oxidation Products

This is PARTIAL oxidation This is FURTHER oxidation

Use only molar proportions of dichromate and acid

Use excess of dichromate and acid

Use minimum contact time between alcohol and oxidant by use of immediate distillation

Use maximum contact time between alcohol and oxidant by use of reflux

Click here for Distillation and Reflux Apparatus

Add acidified dichromate to the alcohol to avoid the presence of excess oxidant

Pre-mix acidified dichromate and alcohol to ensure excess oxidant at all times

Methanal Methanoic acid Methanone None

Propanal Propanoic acid Propanone None

Propanal Propanoic acid Propanone None

Pentan-3-al Pentan-3-oic acid Pentan-3-one None

2-Methylbutanal 2-Methylbutanoic acid

2-Methylbutanone None

Click on the options to select the possible oxidation products (MAY BE MORE THAN ONE) derived from :

Methanol

Propan-2-ol

Propan-1-ol

Pentan-3-ol

2-Methyl-butan-2-ol

The End

Distillation Reflux