Oxidation reaction
Reactions that result in C-H bonds in the reactant being replaced by C-O bonds in the product are classed as oxidations.
Traditionally reactions with oxygen are referred to as oxidations. Thus combustion reactions are oxidations, and C-H bonds in the reactant are replaced by C-O bonds in the product CO2.
CH3CH3(g) + 7/2O2(g)
2CO2(g) + 3H2O(g)
Alcohols that have hydrogen at the carbon bearing oxygen react with chromic acid (H2CrO4 or Cr2O72–/H+) to give organic products in which no C-C bonds are broken. This reaction also produces Cr3+, and the colour of the solution changes from orange to green.
Rolling your mouse over/tapping the alcohol reactants below highlights that C-H bonds are replaced by C-O bonds.
Because aldehydes have a hydrogen attached to the carbon bearing oxygen, they can be further oxidised. Reaction of a primary alcohol with H2CrO4 may give either the aldehyde or the carboxylic acid. The aldehyde can be isolated by distilling it out of the reaction mixture as it is formed because the aldehyde has a lower boiling point than either the alcohol or the carboxylic acid.
The ketone product from a secondary alcohol has no hydrogen at the carbon bearing oxygen, and these do not react further.
Tertiary alcohols have no hydrogen at the carbon bearing oxygen, and they do not react with H2CrO4.
Traditionally reactions with oxygen are referred to as oxidations. Thus combustion reactions are oxidations, and C-H bonds in the reactant are replaced by C-O bonds in the product CO2.
CH3CH3(g) + 7/2O2(g)
2CO2(g) + 3H2O(g)Alcohols that have hydrogen at the carbon bearing oxygen react with chromic acid (H2CrO4 or Cr2O72–/H+) to give organic products in which no C-C bonds are broken. This reaction also produces Cr3+, and the colour of the solution changes from orange to green.
Rolling your mouse over/tapping the alcohol reactants below highlights that C-H bonds are replaced by C-O bonds. | ||||
| primary alcohol | aldehyde | carboxylic acid | ||
Because aldehydes have a hydrogen attached to the carbon bearing oxygen, they can be further oxidised. Reaction of a primary alcohol with H2CrO4 may give either the aldehyde or the carboxylic acid. The aldehyde can be isolated by distilling it out of the reaction mixture as it is formed because the aldehyde has a lower boiling point than either the alcohol or the carboxylic acid.
 | ||
| secondary alcohol | ketone | |
The ketone product from a secondary alcohol has no hydrogen at the carbon bearing oxygen, and these do not react further.
 | H2CrO4 | no reaction |
| tertiary alcohol | ||
Tertiary alcohols have no hydrogen at the carbon bearing oxygen, and they do not react with H2CrO4.