Carboxylic Acid to Aldehyde
Carboxylic acids to aldehyde is an organic conversion and carboxylic acid should have been reduced to an aldehyde from several reactions. A primary alcohol is produced in the process before aldehyde is formed.
Carboxylic acid to aldehyde is a two step conversion
- Reduction of carboxylic acid to primary alcohol by LiAlH4
- Oxidation of primary alcohol by PCC
Reduction of carboxylic acid to primary alcohol by LiAlH4
Carboxylic acids are reduced by lithium aluminum hydride (LiAlH4). As the product, a primary alcohol is given.
- LiAlH4 is dissolved in ether compound to protect from water. First, LiAlH4 in the ether is added to carboxylic acid at room temperature.
- Then, dilute sulfuric acid is added added to take primary alcohol.
Oxidation of primary alcohol by PCC
Produced primary alcohol is oxidized to an aldehyde by a weak oxidizing agent, Pyridinium chlorochromate (PCC). You cannot use strong oxidizing agents like acidic potassium permanganate to oxidize primary alcohols because primary alcohols will be oxidized to back to carboxylic acid. Therefore, you have to use weak oxidizing agents such as PCC.
Examples of carboxylic acid to aldehyde
Ethanoic acid (acetic acid) to ethanal
- LiAlH4 is added to ethanoic acid. Then add dilute sulfuric acid. Then, you will get ethanol.
- Then, as the next step, ethanol is oxidized to ethanal by PCC.
 to ethanal.jpg "ethanoic acid (acetic acid) to ethanal")