Chemical experience - we get fluorescein

Fluorescein is a bright chemical dye that glows in ultraviolet rays. This material is devoted to obtaining this particular chemical substance, which will certainly be informative and will interest lovers of chemistry and beautiful chemical experiments.

Let's start the experiment by watching the video



So what we need:
- phthalic anhydride;
- resorcinol;
- metal crucible;
- sand bath;
- gas-burner;
- anhydrous zinc chloride;
- hydrochloric acid.

First of all, weighed into a metal crucible 3 g. phthalic anhydride.

Then sprinkle with 4.5 g. resorcinol.

We mix these substances and put in a sand bath, after which we light a gas burner, with which we heat the mixture to its melting point, that is, about 180 degrees Celsius.

Heating is necessary so that the mixture of phthalic anhydride and resorcinol melts.

After melting the mixture, add two 2.1 g to it. anhydrous zinc chloride. When this component is added, a condensation reaction occurs during which two resorcinol molecules and one phthalic anhydride molecule combine into a large fluorescein molecule. In this case, two water molecules are also released. Zinc chloride is a catalyst and takes care of the resulting water.

After adding zinc chloride, the temperature must be raised to 220 degrees Celsius and heat the mixture for another 15 minutes.

After 15 minutes of heating, the resulting fluorescein is removed from the heat and set to cool so that it hardens.

After the fluorescein has hardened, it must be picked out from the metal crucible. You can use a chisel for this.

All fluorescein is picked out from a metal crucible, so that you can proceed to the next step, namely grinding into small mortars to break all the large crystals.

After grinding, fluorescein must be washed off the residues of zinc chloride. To do this, pour it into 10% hydrochloric acid and heat to a boil with stirring.

We filter the washed fluorescein through vacuum filtration.

It is also necessary to wash the remaining hydrochloric acid with plain water.

After successful filtration, we received fluorescein. It remains to dry it. The fluorescein solution has a very bright green color. I use it for tinting ponds or for some decorative purposes. The solubility of this substance in water is very low. To increase it, alkali is added to the solution. Dissolution is also promoted by heating. The saturated fluorescein solution is red.