Reactions
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Reactions

There is somewhat of a problem in trying to make aldehydes by oxidizing a primary alcohol.

Equation for oxidation of alcohol to aldehyde. [63rxn20.JPG]
The problem is that aldehydes themselves are very easy to oxidize and if you leave them in contact with the oxidizing agent, they will be oxidized into carboxylic acids, as is shown here. The mechanism for the reaction is more involved than what is shown here, but the net result is that one oxygen atom is added to the molecule. Since oxygen is added, this is called an oxidation reaction.

Equation for oxidation of aldehyde to carboxylic acid. [63rxn21.JPG]

 

Oxidation

The equation for a specific aldehyde, butanal, is shown here (and in Example 19 in your workbook).

H H H O
| | | ||
H-C-C-C-C-H
| | | 
H H H  		oxidation
¾¾¾¾¾¾®		 H H H O 
| | | ||
H-C-C-C-C-OH
| | |  
H H H  

 

 

Reduction

Another reaction of aldehydes involves the reverse of their formation from primary alcohols. That is, aldehydes can be reduced to primary alcohols by adding hydrogen to the carbonyl double bond. This is shown below (and also in Example 20 in your workbook). This is the same kind of reaction as the reduction of ketones to secondary alcohols except that the carbonyl group is in a different place in the carbon chain.

H H H O
| | | ||
H-C-C-C-C-H
| | | 
H H H  		reduction
¾¾¾¾¾¾®		  H H H OH
| | | |
H-C-C-C-C-H
| | | |
H H H H

 

Other Reactions

Aldehydes can also undergo other kinds of addition reactions across the double bond between the carbon and oxygen, besides adding hydrogen. One of those will come up when you study the different forms of sugar molecules in a later lesson.

 

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