Experiment 8

AIM: To prepare semicarbazone of the given compound, recrystalize and found the melting point.

MATERIAL REQUIRED:

Given compound ,Boiling tube, Test tubes, Ethyl methyl ketone (2ml), Semicarbazide hydrochloride (salt form),  Sodium acetate (salt form),Semicarbazone compound (sample), alcohol, tripod stand, water bath, Kjeldahl Apparatus,Thermometer,Bunsen burner,Capillary tubes,Safety goggles and gloves

THEORY:

 Equation: 

RCHO + NH2-NHCONH2HCI --------> RCH=N.NHCONH2

Mechanism:

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

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

The carbonyl group (C=O) is nucleophilically attacked by the amine group (–NH2) of the semi carbazide, 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 semi carbazone (RCH=N–NH–CO–NH2).

Properties of Semi carbazones:

Semi carbazones 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:

Preparation:

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

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

3.) Mix the solution of the carbonyl compound with the semi carbazide solution.

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

5.) Allow the reaction to proceed until the semi carbazone precipitates.

6.) Filter the precipitate.

Recrystallization:

1. First take two spatula given organic compound in a beaker.

2. Add 50 ml alcohol in the beaker and stir it little.

3. Now take wire gauge and Bunsen burner, set it together and light up the burner.

4. Put the water bath on wire gauge and heat it up to the water starts boiling.

5. Now put beaker containing dissolved compound inside water bath using tongs.

6. Take precautions that flames of burner doesn't comes in contact with the dissolved compound ( otherwise it will catch fire ).

7. Now heat the beaker up to complete dissolution of solution.

8. During heating constantly stir it.

9. Take filter paper and set it inside funnel carefully ( ensure that there must be no space for filtrate  to get down without getting filter ).

10. Put china dish below funnel, now pour filtrate from beaker to china dish through funnel carrying filter paper.

11. When you get filtrate in china dish let it cool properly without disturbing for good crystals.

Melting point:

Weigh the Sample: Use a balance to weigh a small amount (a few milligrams) of the semi carbazone compound.

Sealing of capillary: Use Bunsen burner to seal one end of capillary.

Capillary Tube Method: Pack the sample tightly into one end of a thin-walled capillary tube. Tap it gently to ensure it settles.

Set Up the Melting Point Apparatus:

Adjusted Kjeldahl Apparatus in the stand and filled it with sulphuric acid.

Took thermometer, dipped it into sulphuric acid.

Attached capillary to the thermometer.

Moved thermometer slowly into the conical flask so that it could not touches surface of conical flask and could not move the capillary.

Heating:

Gradually heat the sample, ensured even heating all over the apparatus.

Monitored the temperature closely in the thermometer.

Observe the Melting Process:

As the temperature rises, first signs of melting showed (the compound changed to liquid).

Recorded the temperature at which the sample first begins to melt (this is the melting point).

Repeat:

For accuracy, I repeated the experiment 2-3 times with fresh samples to confirm the melting point.

Clean Up:

Dispose of the samples and clean your workspace according to safety guidelines.

OBSERVATION:

A white crystalline solid of the semi carbazone will be formed.

PRECAUTIONS:

1.) Add the semi carbazide 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.

4.) Wear safety goggles and gloves throughout the experiment.

5.) During heating sand bath must be present below bunsen burner as precaution.

6.) The capillary must be sealed completely for accurate melting point.