16 Organic synthesis

Question 1

What is the practical method for heating under reflux?

Ethanol

Answer 1

1. Add the pre-weighed 4.0 g sodium dichromate(VI)-2-water to the pear-shaped/round-bottomed flask using the funnel.
2. Slowly add 20 cm3 3.0 mol dm-3 sulfuric(VI) acid into the pear-shaped/round-bottomed flask using the funnel.
3. Add a few anti-bumping granules and swirl the flask to dissolve the solid.
4. Cool the solution by swirling the flask in an ice water bath for 2-3 minutes, until the solution is ice cold
5. Carefully add 0.5 cm3 ethanol to the flask dropwise with swirling in the ice-water.
6. Continue to swirl the mixture in the ice-water, monitoring the temperature of the reaction with a thermometer – you will observe an increase in temperature.
7. When a maximum temperature has been reached, repeat steps 4-6 with a second 0.5 cm3 ethanol.
8. Clamp the flask by the neck, position in your heating apparatus and arrange the condenser above the flask in a reflux setup. Turn on the condenser water flow.
9. Heat the reaction mixture under reflux for about 20 minutes.
10. Allow the apparatus to cool for 5 minutes.

Question 2

How can you purify organic products?

Answer 2

1) Ensure that the tap of the separating funnel is closed.
2) Pour the mixture of liquids into the separating funnel, place a stopper in the top of the funnel, and invert to mix the contents.
3) Allow the layers to settle.
4) Add some water to see which layer increases in volume-this is the aqueous layer.
5) Place a conical flask under the separating funnel, remove the stopper and open the tap until the whole of the lower layer has left the funnel.
6) Place a second conical flask under the separating funnel to collect the other layer.

Question 3

How can you dry the organic product?

Answer 3

1) Add the organic liquid to a conical flask.
2) Using a spatula, add some of the drying agent (anhydrous salt e.g CaCl2) and gently swirl the contents to mix together.
3) Place a stopper on the flask to prevent your product from evaporating away. Leave for about ten minutes.
4) If the solid has all stuck together in a lump, there is still some water present. Add more drying agent until some solid is dispersed into the solution as a fine powder.
5) Decant the liquid from the solid into another flask. If the liquid is dry it should be clear.