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Oxidation of Alkenes Chemistry Tutorial

Key Concepts

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Oxidation of Alkenes Under Mild Oxidizing Conditions Examples

Mild oxidising conditions are present when the oxidising agent is a cold (room temperature), alkaline solution (OH-(aq)) of potassium permanganate (KMnO4)

The mild oxidation of alkanes produces an alkane-1,2-diol (often just referred to as a diol).

The examples below show the mild oxidation of:

Because the mild oxidation of alkenes results in two hydroxyl (OH) groups adding across the double bond, these reactions are also commonly referred to as hydroxylation reactions.

Example of Mild Oxidation of Alkene: Hydroxylation of ethene (ethylene)

Hydroxylation of ethene (ethylene), CH2=CH2, using cold, alkaline potassium permanganate solution produces ethane-1,2-diol (ethylene glycol).

This synthesis of ethane-1,2,-diol from ethene is shown below:

ethene
(ethylene)
  intermediate
(cyclic inorganic ester)
  ethane-1,2-diol
(ethylene glycol)
manganese dioxide
(solid)
  H
|
  H
|
 
H- C = C -H
         
MnO4-

25oC
  H
|
  H
|
 
H- C - C -H
  |
O
  |
O
 
  \ /
Mn
// \
 
  O   O  
OH-

  H
|
  H
|
 
H- C - C -H
  |
OH
  |
OH
 
+ MnO2(s)
colourless
reactant
purple
reagent
    colourless
organic product
brown
by-product

Example of Mild Oxidation of Alkene: Hydroxylation of but-2-ene (2-butene)

Hydroxylation of but-2-ene (2-butene), CH3-CH=CH-CH3, using cold, alkaline potassium permanganate solution produces butane-2,3-diol (2,3-butanediol).

This synthesis of butane-2,3-diol from but-2-ene is shown below:

but-2-ene
(2-butene)
  intermediate
  butane-2,3-diol
(2,3-butanediol)
manganese dioxide
(solid)
  H
|
  H
|
  H
|
  H
|
 
H- C - C = C - C -H
  |
H
          |
H
 
MnO4-

25oC
  H
|
  H
|
  H
|
  H
|
 
H- C - C - C - C -H
  |
H
  |
O
  |
O
  |
H
 
  \ /
Mn
// \
 
  O   O  
OH-

  H
|
  H
|
  H
|
  H
|
 
H- C - C - C - C -H
  |
H
  |
OH
  |
OH
  |
H
 
+ MnO2(s)
colourless
reactant
purple
reagent
    colourless
organic product
brown
by-product

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Oxidation of Alkenes Under Strong Oxidizing Conditions

Strong oxidising conditions are represented by the use of hot, concentrated potassium permangante solution (KMnO4(aq)).

Under these conditions, the double bond (C=C) in the alkene breaks.

The products of the strong oxidation of alkenes can include carbon dioxide, water, alkanones (ketones) and alkanoic acids (carboxylic acids) depending on the location of the double bond within the alkene molecule.

The examples below shown the strong oxidation of

Example of Strong Oxidation of Alkene: Strong Oxidation of Ethene (ethylene)

Oxidation of ethene (ethylene), CH2=CH2, using hot, concentrated potassium permanganate solution produces carbon dioxide and water.

The synthesis of carbon dioxide and water from the strong oxidation of ethene is shown below:

ethene
(ethylene)
  intermediate
(2 × formic acid)
(2 × methanoic acid)
  intermediate
(2 × carbonic acid)
  carbon dioxide
+ water
  H
|
  H
|
 
H- C = C -H
         
conc. MnO4-

heat
  H
|
  H
|
 
HO- C   +   C -OH
  ||
O
  ||
O
 
conc. MnO4-

heat
  OH
|
  OH
|
 
HO- C   +   C -OH
  ||
O
  ||
O
 
conc. MnO4-

heat
CO2 + H2O
colourless
reactant
purple
reagent
        colourless
products

Example of Strong Oxidation of Alkene: Strong Oxidation of Propene (propylene)

Oxidation of propene (propylene), CH2=CH-CH3, using hot concentrated potassium permangante solution produces carbon dioxide, water and acetic acid (ethanoic acid).

This synthesis of acetic acid (ethanoic acid) from propene (propylene) is shown below:

propene
(propylene)
  intermediate
(acetaldehye)
(ethanal)
+ intermediate
(formaldehyde)
(methanal)
  H
|
  H
|
  H
|
 
H- C - C = C -H
  |
H
         
conc. MnO4-

heat
  H
|
  H
|
 
H- C - C =O
  |
H
     
+
  H
|
 
O= C -H
     
    MnO4-   MnO4-
    product: acetic acid
(ethanoic acid)
  intermediate: formic acid
(methanoic acid)
   
  H
|
  OH
|
 
H- C - C =O
  |
H
     
 
  OH
|
 
O= C- H
     
        MnO4-
        intermediate (carbonic acid)
       
  OH
|
 
O= C- OH
     
        MnO4-
        products (carbon dioxide and water)
CO2 + H2O

Example of Strong Oxidation of Alkene: Strong Oxidation of 2-methylpropene

Oxidation of 2-methylpropene, CH3-C(CH3)=CH2, using hot, concentrated potassium permanganate solution produces acetone (propan-2-one), carbon dioxide and water.

This synthesis of acetone (propan-2-one) from 2-methylpropene is shown below:

2-methylpropene   product: acetone
(propanone)
+ intermediate: formaldehyde
(methanal)
  H
|
  CH3
|
H
|
 
H- C - C= C -H
  |
H
   
conc. MnO4-

heat
  H
|
  CH3
|
H- C - C=O
  |
H
   
+
  H
|
 
O= C -H
     
        MnO4-
    acetone (propanone) can also
be written as:
  intermediate: formic acid
(methanoic acid)
   
  O
||
   
CH3- C - CH3
       
 
  OH
|
 
O= C- H
     
        MnO4-
        intermediate (carbonic acid)
       
  OH
|
 
O= C- OH
     
        MnO4-
        products: carbon dioxide and water
CO2 + H2O

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