Question

2. When using the separatory funnel you may have observed a oily emulsion between the aqueous and DCM layers. What components of tea are responsible for this emulsion? How can one minimize the size of the emulsion layer? 3. How does adding the anhydrous sodium sulfate to the dichloromethane solution remove water? 4. If the above step was omitted in the isolation procedure, how would this be reflected in the yield of caffeine? 5. A student used 8.23 g of tea leaves in the experiment. How much caffeine is expected, assuming all the caffeine is extracted? Assume tea leaves are 5% caffeine by mass.

Answer 1

2) Saponins present in the tea are responsible for the formation of an emulsion. These molecules commonly contain hydrophilic glycoside moieties along with hydrophobic triterpenes and steroids. This amphipathic nature makes them behave like a soap in the water to form an emulsion.

It is advisable to avoid the formation of an emulsion by not shaking the separatory funnel vigorously as we do it in general extraction, instead, we can invert the s. funnel and gently several times.
If the emulsion is formed then we can break by washing organic and emulsion layer with a saturated solution of NaCl (called as brine solution). By adding NaCl solution we are reducing surface tension and hence that breaks the emulsion.

3) Anhydrous sodium sulfate is a hygroscopic compound. Hence when we add it to DCM layer it absorbs the traces amount of water present in the DCM layer.
Na2SO4(anhydrous) + 10 H2O -------> Na2SO4.10H2O(s)

4) If we do not dry the DCM layer over anhydrous Na2SO4 then it would lead an excess of water mass along with caffeine and hence yield will be exceptionally high.

5) Given 5% of caffeine is present.

then 100 g of leaves contains 5 g of caffeine.

So, 8.23 g of leaves contains = (8.23*5)/100 = 0.41 g of caffeine.

We can expect 0.41 g of caffeine to be extracted.