4.2.3 Organic synthesis

Definitions

Term	Definition
Fractional distillation	The separation of components in a liquid mixture by their different boiling points into fractions with different compositions
Drying agent	An anhydrous solid that readily absorbs water from the mixture to become hydrated

To prepare organic products without boiling off solvent, reactants or products
Ensures that the reaction goes to completion
Water bath can be used rather than Bunsen if can be carried out below 100°C
Heating mantle can be used for flammable liquids
Anti-bumping granules added to liquid so it boils smoothly
- Otherwise large bubbles will form at bottom so the glassware vibrate / jump
Glass joints greased lightly so apparatus comes apart easily after experiment
Condensers should be clamped loosely as the outer jacket is very fragile + kept in upright position
Never put stopper in top-closed system or pressure would build up and the apparatus would explode
Rubber tubing used to connect the inlet of condenser to tap and outlet to the sink (water always enters the condenser at the bottom and leaves at the top)

Separates a pure liquid from impurities
Flask clamped by neck
Still head connected to the flask
Condenser connected to rubber tubing for water (water enters at the bottom)
Flask used to collect the distillate so the apparatus is not airtight
Heat the mixture gently (make sure the temperature doesn't reach the boiling point of the less volatile compound)

When there are two layers inside the collection flask: one organic layer, one aqueous / water layer
Ensure tap of the separating funnel is closed
Pour in mixture and place a stopper in the top of the funnel + invert to mix the contents
Allow layers to settle
Can't tell the layers: add water to the mixture, the layer that increase in volume is the aqueous layer
Place conical flask under the separating funnel
Remove stopper + open the tap until whole lower layer has left the funnel
If the top layer is accidentally poured then pour the content in the first conical flask back into the separating funnel and restart
Repeat this several times until the bottom layer is almost completely removed

Organic compounds may have relatively close boiling points so the sample may still have some impurities left over
Carry out a second distillation (or more)
Only collect product with the exact boiling point of the target compound
Try to not overheat the mixture
Narrower boiling point range = purer product

There may be water left in the organic product
Add organic liquid to conical flask
Add some drying agent with spatula + swirl the contents
- e.g. \(CaCl_2\) for drying hydrocarbons, \(CaSO_4 / MgSO_4\) for general drying
Put a stopper on to prevent product from evaporating away
Leave for about 10 minutes
If the solid stuck in a lump water is still present so add more drying agent until it becomes a fine powder
After all the water is absorbed the organic mixture can be separated by filtration / simply decanting the liquid

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