3.2. Reaction with ferric chloride (III).

Take 4-5 drops of 0,1% α-tocopherol spirit solution, place it into a dry test tube, add 0,5 ml of ferric chloride (III) and mix properly. The solution is turning red when heated as a result of tocopherol oxidation by ferric chloride (III).

Experiment 4. Qualitative reaction to vitamin K (vicasol).

Add 5 drops of aniline to 0,5 ml of 0,2% vicasol solution in ethanol and mix. The mixture will get red coloring.

Experiment 5. Reaction of vitamin В₁ (thiamine) oxidation into thiochrome.

Pour 5-6 drops of 5% К₃[Fe(CN)₆] solution and 1 ml of 30% sodium hydroxide to 0,5 ml of thiamine solution and mix. Then add 1 ml of isobutyl alcohol and shake intensively during 1-2 minutes. You can observe blue fluorescence in UV rays in the upper spirit layer. Heat the mixture in the test tube in a water bath, stirring. You will observe yellow coloring appearance. The fluorescence and the yellow coloring are caused by thiochrome formation:



Thiamine chloride

Thiochrome

Experiment 6. Qualitative reaction to vitamin В₂ (riboflavin).

Pour 10 drops of concentrated hydrochloric acid and add a piece of zinc metal to 0,5ml of riboflavin solution. Hydrogen bubbling is beginning and the liquid is gradually getting pink and then it is decolorizing. The reaction is caused by riboflavin reduction first into rhodoflavin of red coloring and then into colorless leucoflavin. When the bleached solution is shaken, the leuco compound is again oxidized by aerial oxygen into riboflavin:

Riboflavin Leucoflavin

Experiment 7. Reaction of vitamin В₆ (pyridoxine) with iron chloride (III).

Pyridoxine is a general definition for a group of chemical compounds that possess the activity of vitamin В₆:

Pyridoxol (pyridoxine) pyridoxal pyridoxamine

Pour 5-10 drops of 5% vitamin В₆ water solution into a test tube, add 1-2 drops of 5% iron chloride solution. After shaking the mixture there will be a red-colored liquid. A complex compound of iron phenolate type is formed.

Experiment 8. Qualitative reaction to vitamin РР (nicotinamide, nicotinic acid).

Dissolve 5-10 mg of nicotinic acid in 10-20 drops of 10% acetic acid solution and heat. Add the equal volume of 5% copper acetate solution to the solution heated up to boiling. The liquid becomes blue, and when left to stand undisturbed, the blue colored sediment of copper salt of nicotinic acid settles down.

Experiment 9. Qualitative reaction to vitamin С (ascorbic acid).

9.1. Interaction of vitamin С with К₃[Fe(CN)₆]. Add some drops of 5% potassium hydroxide solution and 10% К₃[Fe(CN)₆] solution to 5 ml of 0,02% vitamin C solution and mix, then add 2-3 drops of 10% hydrochloric acid solution and 1-2 drops of 10% iron chloride (III) solution. You will see blue-green coloring and gradually settling down blue sediment of Berlin blue (ferric ferrocyanide) - Fe₄[Fe(CN)₆]₃.

L- ascorbic acid L- dehydroascorbic acid

3K₄[Fe(CN)₆] + 4FeCl₃ → Fe₄[Fe(CN)₆]₃ ↓ + 12KCl