Question: Oxidation of primary alcohol to an aldehyde usually gives some over-oxidation to the carboxylic acid. Assume you have used PCC to oxidize pentan-1-ol to pentanal.

1. Show how you would use acid-base extraction to purify the pentanal.
2. Which of the expected impurities cannot be removed from pentanal by acid-base extractions? How would you remove this impurity?

A complex mixture is converted into organic acids, organic bases, and other molecules in acid-base extraction.Two different layers are formed: one is organic, and the other is an aqueous layer.

When pentanal, pentanoic acid, pentan-1-ol, and pyridine are shaken with aq. NaOH, pentanoic acid converts into ${\text{CH}}_{\text{3}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{CH}}_{\text{2}}{\text{COO}}^{\text{-}}{\text{Na}}^{\text{+}}$; the rest remains the same.

Now, pentanal, pentan-1-ol, and pyridine are shaken with aq. HCl; pyridinium cation is formed; pentanal and pentan-1-ol remain the same. After evaporating ether and then distilling, two pure compounds, pentanal and pentan-1-ol, are formed.

Acid-base extraction to purify the pentanal

Distillation is one of the separation methods used for separating liquids by converting liquid into vapors, and then again, it is condensed into a liquid form. It involves different boiling points of liquids.

(b) Pentan-1-ol cannot be removed from pentanal in acid-base extraction. So, these two can be separated by the process of distillation. The boiling point for pentan-1-ol is higher than pentanal because of hydrogen bonding.