AIM: To detect the presence of extra elements(like N,S,P,X) in a given organic compound.
APPARATUS REQUIRED: Given organic compound, Na piece ,ferrous sulphate, dil. sulphuric acid, dil. acetic acid, lead acetate, dil.nitric acid , silver nitrate , ignition tubes, tongs, bunsen burner, wire gauge, china dish, filter paper, funnel, glass rod, test tubes.
THEORY: The detection of extra elements in organic compounds is crucial in its investigation. Carbon is included in all organic molecules. Hydrogen is also found in most organic molecules (the few exceptions are the compounds such as CCl₄, CS₂, etc.). Other elements included in organic molecules include oxygen, nitrogen, sulfur, and halogens, in addition to carbon and hydrogen.
Because virtually all organic substances include carbon and hydrogen, procedures to identify them are frequently unnecessary, and their existence may be presumed without testing. The tests for detecting nitrogen, sulfur, and halogens will be discussed here.
What is the Lassaigne’s Test, and how does it work?
Lassaigne’s test can identify nitrogen, sulfur, and halogens organic molecules. A little bit of Na metal is heated with the organic compound in a fusion tube.
The idea is that Na changes all of the elements present into ionic form.
Na + C + N → NaCN
2Na + S → Na₂S
Na + X → NaX ( X= Cl, Br, or I)
By boiling the fused mixture with distilled water, the produced ionic salts are removed. Sodium fusion extract is what it’s called.
PROCEDURE:
Lassaigne’s Extract Preparation
In a fusion tube, place a little piece of dry sodium. Warm the line until it melts into a gleaming globule. A pinch of the organic substance should be added. First, heat it slowly to allow the chemical to react with sodium metal. Now bring it to a high temperature. Plunge the red hot tube into distilled water in a porcelain dish. Using a glass rod, crush the ingredients and bring to a boil.Filtration is used to remove the insoluble materials. Lassaigne’s extract is the name given to the filtrate.
Lassaigne’s extract is used to detect extra elements in organic compounds like nitrogen, sulfur, and halogens in an organic molecule.
Procedure for the Lassaigne Test
Lassaigne’s test, commonly known as the sodium fusion test, is used in elemental analysis for the subjective estimate of the presence of foreign components in an organic molecule or detection of extra elements in organic compounds, especially halogens, nitrogen, and sulphur.
L. Lassaigne created this method. By fusing the sample with pure sodium metal, the piece is roughly boiled in this experiment.
There have been many different sorts of techniques defined. The water aids the “fused” sample’s emergence inside it, and the typical conditional trials threat detection and response for the various probable components are carried out on the resultant solution.
Discuss the Lassaigne Test.
A process exists to detect extra elements in organic compounds if a halogen, nitrogen, or sulfur exists in an organic solution. Heat is used to simulate a model in a test tube containing sodium. The boiling tube is submerged in clear water, and the wreckage has fully adhered.
The presence of a halogen can be detected by using silver nitrate solution to precipitate it. The presence of nitrogen can be seen by forming a Prussian blue precipitate on the heated section of the solution with iron. The precipitation of Lead Ethanoate or Sodium Nitroprusside indicates the presence of sulfur.
Sulfur testing :-
To detect presence of sulphur in given organic compound.
Materials Required : lassaigne extract, test tubes, tongs, dil.acetic acid, lead acetate.
procedure:
take 1ml extract in test tube.
add 1ml dil. acetic acid for acidification.
now add lead acetate in the test tube.
what to observe:
if black ppt form then given organic compound contains sulphur as extra elements.
Halogens testing
To detect presence of halogen in given organic compound.
materials required:- lassaigne extract, test tubes, tongs, dil.nitric acid, silver nitrate.
procedure:-
take 1ml lassaigne extract in a test tube.
add 1 ml dil.nitric acid in a test tube.
now add little silver nitrate in the test tube.
What to Observe :-
if a white ppt is formed in test tube then halogen is present as extra element in given organic compound.
Nitrogen testing
To detect presence of nirogen in given organic compound.
Materials required:- lassaigne extract, test tube, tongs, dil.sulphuric acid, ferrous sulphate.
procedure:-
take 1 ml lassaigne extract in a test tube.
add one spatula ferrous sulphate in the test tube.
now, acidified the extract with dilute H₂SO₄ and heated it shortly.
let it be cool and observe the change of colour.
What to Observe:-
The appearance of Prussian blue colour in test tube which indicates the presence of nitrogen.
The following reactions occurs:-
6CN⁻ + Fe²⁺→ [Fe(CN)₆]⁴⁻
H⁺+ Fe²⁺ → e⁻ + Fe³⁺
4Fe³⁺ + Fe(CN)₆⁴⁻ → Fe₄Fe(CN)₆.H₂O
Ferrous ions are oxidized to ferric ions with the assistance of the acid. The production of ferriferous cyanide indicates the presence of nitrogen.
Combined test for nitrogen and sulphur:-
To detect presence of nitrogen and sulphur together in given organic compound.
Materials required:- lassaigne extract, test tube, tongs, dil.hcl,fecl3.
procedure:-
take 1 ml lessaigne extract in test tube.
add 1 ml of dil.hcl .
add fecl3 to the test tube.
observe carefully.
what to observe :-
observe blood red coloration in the test tube.
PRECAUTIONS:
Here are some precautions to consider when performing the Lassaigne's sodium fusion test:
1. Safety: Wear appropriate personal protective equipment, such as gloves and goggles, to protect yourself from any potential hazards.
2. Handling sodium: Sodium is a highly reactive metal that reacts violently with water. Handle sodium with caution, using dry forceps or spatula, and keep it away from moisture.
3. Fusion process: Carefully add a small amount of the organic compound to the fusion tube, followed by a small piece of sodium metal. Avoid adding excessive amounts of sodium, as it may lead to violent reactions.
4. Heating: Heat the fusion tube gently and gradually to avoid any sudden reactions or splattering. Use a Bunsen burner or a heating mantle for controlled heating