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How to Form an Aldehyde

Chemists identify chemicals by certain functional groups. These are atoms or arrangements of atoms within a molecule that tend to take part in specific types of chemical reactions. By understanding the functional groups, chemists can predict and control the reactions of entire molecules. One functional group is an aldehyde. It̵7;s a carbon atom, single bonded to another carbon with one of its four bonds, single-bonded to a hydrogen with another, and double-bonded to oxygen. There are straightforward approaches to synthesizing aldehydes in the laboratory.

Things You'll Need

Primary alcohol
Oxidizing agent
Chemical glassware

Instructions

- 1
  Start with a primary alcohol. An alcohol is a chemical with an OH group attached to a carbon that is bonded only to other carbons or to hydrogen atoms. If that carbon is bonded to at least two hydrogen atoms, the chemical is a primary alcohol. If the carbon has only one hydrogen, it̵7;s a secondary alcohol. If the carbon with the OH group forms its three remaining bonds only with other carbons, that̵7;s a tertiary alcohol. Oxidizing primary alcohols yields aldehydes.
- 2
  Oxidize the alcohol. In organic chemistry, if a chemical loses hydrogen atoms, or gains oxygen atoms, it is said to be oxidized. A chemical capable of doing this is an oxidizer. When an oxidizer oxidizes another chemical, the oxidizer is reduced. You can oxidize a primary alcohol to form an aldehyde with a solution of sodium or potassium dichromate(VI) acidified with dilute sulfuric acid.
- 3
  Prevent further oxidation. The initial oxidation reaction will remove the hydrogen from the OH group and the one of the hydrogens from the carbon to which the OH group is attached, leaving an aldehyde. For example CH3-CH2-OH -> CH3-CH-O. The carbon that once was bonded to the OH group now is double-bonded to the oxygen, and single-bonded to another hydrogen.
- 4
  Observe that the oxidizing agent may oxidize the aldehyde further, leaving you with a carboxylic acid (in which a carbon is double-bonded to oxygen as well as to an OH group, and not to a hydrogen atom) instead of an aldehyde.
- 5
  Ensure partial oxidation to an aldehyde instead of full oxidation to a carboxylic acid by distilling off the aldehyde as it is formed, so it is not available for further oxidation, or you can begin with an excess of alcohol so that there is only enough oxidizing agent available for the first reaction.

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