Google

Demonstration of Microscale Projection Experiments - Chemistry en miniature

Test for Vitamin A in Cod-liver-oil

Peter Keusch




German version



Material:
cod-liver-oil
Vitamin A (Retinol)


Chemicals:
chloroform
antimony chloride


Hazards and safety precautions:

Chloroform causes cancer in laboratory animals, and is IARC listed as a probable human carcinogen. Inhalation and ingestion are harmful and may be fatal. May cause reproductive damage. Irritant. Exposure to alcohol may increase toxic effects. Prolonged or repeated skin contact may cause dermatitis
Antimony chloride is harmful by ingestion, inhalation or through skin contact. Corrosive - causes serious burns.

Safety glasses and gloves must be worn. Effective ventilation required. The experiment should be carried out in a portable fume hood giving all-round visibility!


Experimental procedure:

Two test tubes are set up as shown in the following below.

Test tube 1   1.5 mL of chloroform / 0.3 g of antimony chloride    2 drops cod-liver-oil  
Test tube 2 1.5 mL of chloroform / 0.3 g of antimony chloride    2 drops of Vitamin A


The two experiments must be carried rapidly out one after the other, because very rapidly an intense coloration occurs that cannot be projected on a screen.


Results:

Blue 'schlieren' are formed immediately in the antimony chloride solutions.










Photo
Photo



Discussion:

·   Antimony tri chloride forms with vitamin A a blue colored complex.


The first step is the conversion of retinol to a carbenium ion by SbCl3. The carbenium ion is converted to anhydrovitamin with elimination of a proton. The addition of the Lewis acid SbCl3 to the terminal C = C double bond (C15) leads to the formation of a complex with the absorption maximum l max = 619 nm. On the other hand a complex with the absorption maximum l max = 586 nm is produced by addition of SbCl3 to the endocyclic C = C double bond (C4). The strong inductive effect of the chlorine atoms produces a charge separation over the molecule.




Antimony trichloride is a reagent for detecting vitamin A and related carotenoids in the Carr-Price test. The brilliant blue complex can be measured by colorimetry.


The equation above are taken from Seminar Medizinische Chemie (Uni Mainz) - Biochemisches Grundpraktikum 'Therapie des trockenen Auges'


General experimental instructions and index of experiments






Site Meter