Reactions that result in
C-H bonds in the reactant being replaced by
C-O bonds in the product are classed as
oxidations.
Alcohols that have
hydrogen at the
carbon bearing oxygen react with chromic acid (H
2CrO
4 or Cr
2O
72–/H
+) to give organic products in which no C-C bonds are broken. This reaction also produces Cr
3+, and the colour of the solution changes from orange to green.
Rolling your mouse over the alcohol reactants below highlights that in these reactions 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 H
2CrO
4 may give either the aldehyde 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 H
2CrO
4.