Question

Which of the following reagents can be used to oxidise primary alcohols to aldehydes?

(i) $$\mathrm{CrO}{\phantom{A}}_3$$ in anhydrous medium.

(ii) $$\mathrm{KMnO}{\phantom{A}}_4$$ in acidic medium.

(iii) Pyridinium chlorochromate.

(iv) Heat in the presence of Cu at 573 K.

Answer 1

(i) $$\mathrm{CrO}{\phantom{A}}_3$$ in anhydrous medium.

(iii) Pyridinium chlorochromate.

(iv) Heat in the presence of Cu at 573 K.

Explanation:

Strong oxidising agents such as acidified potassium permanganate are used for getting carboxylic acids from alcohols directly. $$\mathrm{CrO}{\phantom{A}}_3$$ in anhydrous medium is used as the oxidising agent for the isolation of aldehydes.

$$\mathrm{RCH}{\phantom{A}}_2\mathrm{OH}\stackrel{\mathrm{CrO}{\phantom{A}}_3}{\to }\mathrm{RCHO}$$

A better reagent for the oxidation of primary alcohols to aldehydes in good yield is pyridinium chlorochromate (PCC), a complex for chromium trioxide with pyridine and HCl.