practical 8

AIM:To prepare semicarbazone of the given compound.

MATERIAL REQUIRED:

Given compound ,Boiling tube, Test tubes, Ethyl methyl ketone (2ml), Semicarbazide hydrochloride (salt form),  Sodium acetate (salt form)

THEORY:

1.Equation: RCHO + NH2-NHCONH2HCI --------> RCH=N.NHCONH2

2.Mechanism:

RCHO + H^+ ----------> RCHOH^- + NH2-NHCONH2 ---------> RCOHNH2^+-NHCONH2 --------> RCOH-NH-NHCONH2 

------> RCH=N-NHCONH2

The semicarbazone formation is a type of condensation reaction, where the carbonyl compound (RCHO or RCOR') reacts with semicarbazide (NH2–NH–CO–NH2).

The carbonyl group (C=O) is nucleophilically attacked by the amine group (–NH2) of the semicarbazide, leading to the formation of an intermediate.

Water is eliminated as a byproduct, and a double bond forms between the carbon and nitrogen, resulting in a semicarbazone (RCH=N–NH–CO–NH2).

3.Properties of Semicarbazones:

Semicarbazones are typically crystalline solids with well defined melting points, making them useful for identifying unknown carbonyl compounds.

They are stable and can be purified easily, aiding in the confirmation of the structure of the parent carbonyl compound.

PROCEDURE :

1.)Make separate solution of semicarbazide hydrochloride and sodium acetate in minimum water.

2.) Add sodium acetate to neutralize the semicarbazide hydrochloride  solution and create a mildly basic environment, which facilitates the reaction.

3.)Mix the solution of the carbonyl compound with the semicarbazide solution.

4.)Stir the mixture at room temperature or slightly heat if needed.

5.)Allow the reaction to proceed until the semicarbazone precipitates.

6.)Filter the precipitate.

OBSERVATION:

A white crystalline solid of the semicarbazone will be formed.

PRECAUTIONS:

1.)Add the semicarbazide solution to the aldehyde or ketone dropwise to control the reaction.

2.)Ensure the reaction is conducted in an alkaline medium to facilitate the reaction.

3.)During filtration, ensure that the filter paper is clean and free from contaminating substances.