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Formation
Oxidation of Aldehydes
| As was pointed out in the previous lesson, carboxylic acids can be formed
from the oxidation of aldehydes, as is shown here (and in Example 3-a in
your workbook). |
O
//
R¾C
\
H |
oxidation
¾¾¾¾¾® |
O
//
R¾C
\
OH |
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Oxidation of Primary Alcohols
| Carboxylic acids can also be formed by the oxidation of primary alcohols
(also shown in Example 3-b). I like to think of this as strong oxidation
-- mild oxidation changes the alcohol into an aldehyde and strong oxidation takes it all
the way to carboxylic acid. But perhaps continued oxidation would be a
better phrase. Aldehydes are very easily oxidized. So if an aldehyde is created by the
oxidation of a primary alcohol and some of the oxidizing agent is still there after the
aldehyde has been formed, the aldehyde will react with it, becoming a carboxylic acid. |
H
½
R¾C¾OH
½
H |
oxidation
¾¾¾¾¾® |
O
//
R¾C
\
OH |
|
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So, actually, making an aldehyde from a primary alcohol is the tricky reaction. The
conditions have to be just right. Usually this is done by carrying out the reaction at a
temperature high enough to boil off the aldehyde as it forms. This is possible because
alcohols have hydrogen bonding between molecules which gives them higher boiling points
than the corresponding aldehydes, which have weaker dipole-dipole intermolecular bonds.
| Now let's get back to the formation of carboxylic acids. I think you can
see from this equation that the oxidation of an aldehyde involves the addition of
one oxygen atom to the molecule in order to make the acid. |
O
//
R¾C
\
H |
oxidation
¾¾¾¾¾® |
O
//
R¾C
\
OH |
|
|
| In this equation you can see that the oxidation of a primary alcohol to
give an acid involves two steps: two H's have to be removed and
an oxygen added. Therefore, it takes a continued oxidation for that reaction to
happen. |
H
½
R¾C¾OH
½
H |
oxidation
¾¾¾¾¾® |
O
//
R¾C
\
OH |
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E-mail instructor:
Sue Eggling
Clackamas Community College
©2001, 2003 Clackamas Community College, Hal Bender
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