Answer to Question #159325 in Organic Chemistry for hazel

Question

how are aldehydes made? how do you increase the yield and why might this be an important consideration in drug design?

Answer 1

Aldehydes are made by oxidising primary alcohols.

But when oxidizing, the aldehyde produced can be oxidised further to a carboxylic acid by the acidified potassium dichromate(VI) solution used as the oxidising agent. In order to produce only the aldehyde, this has to be prevented from happening.

To stop the oxidation at the aldehyde, use an excess of the alcohol. That means that there isn't enough oxidizing agent present to carry out the second stage and oxidize the aldehyde formed to a carboxylic acid.

distil off the aldehyde as soon as it forms. Removing the aldehyde as soon as it is formed means that it doesn't stay in the mixture to be oxidized further.

In order to maximise yield collected, only collect the distillate at the approximate boiling point of the desired aldehyde and not higher during the reaction. That way, the reactants are efficiently used and the maximum possible yield of the aldehyde is gotten before it has the chance to be further oxidised to carboxylic acid.