Question

Write the chemical equations when:
(a) Ethanal is treated with 2,4-dinitrophenylhydrazine?
(b) Propanone is treated with Zn(Hg) and conc. HCl?

Hint:

- The 2,4-DNPH test is a qualitative test for detecting aldehydes and ketones. - Clemmensen reduction is useful in removing carbonyl functional groups while retaining other sensitive groups.

Answer 1

(a) Reaction of Ethanal with 2,4-Dinitrophenylhydrazine (DNPH): Ethanal (\( CH_3CHO \)) reacts with 2,4-dinitrophenylhydrazine (\( H_2N-NH\)-Ar-\( NO_2 \)) to form a hydrazone derivative.

This reaction is used to detect the presence of carbonyl groups (aldehydes and ketones).

(b) Reduction of Propanone using Zn(Hg) and Conc. HCl (Clemmensen Reduction): Propanone (\( CH_3COCH_3 \)) undergoes Clemmensen reduction in the presence of zinc amalgam (Zn-Hg) and conc. HCl, reducing the carbonyl group to an alkane.

This method is commonly used to convert ketones into alkanes.