16. Organic synthesis
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What pieces of apparatus are needed to heat under reflux?
• pear-shaped flask • condenser • stand and clamp • heat source
What is added to the liquid before the flask is heated to make sure the content will boil smoothly?
Anti-bumping granules
What will happen when anti-bumping granules are not added to the liquid before the flask is heated?
• large bubbles will form at the bottom of the liquid • the glassware (玻璃器皿) will vibrate or jump violently
What should you never do when heating under reflux?
Never put a stopper in the top of the condenser
What pieces of apparatus are needed to do distillation?
• pear-shaped flask • condenser • stand and clamp • heat source • screw-cap adaptor • receiver adaptor • still head • thermometer
Which way must water enter and exit the condenser?
Water must enter from the bottom of the condenser and exit from the top of the condenser.
What piece of apparatus is used to remove an organic layer from an aqueous layer?
Separating funnel
How to identify the organic layer from an aqueous layer?
Add some water to the mixture. The layer that gets bigger is the aqueous layer.
What are the steps of purifying organic products?
• ensure the tap of separating funnel is closed • pour the mixture of liquids into the separating funnel • place a stopper in the top of the separating funnel • invert the separating funnel to mix the contents • allow the layers to settle • add some water to see which layer increases in volume to identify the aqueous layer • place a conical flask under the separating funnel • remove the stopper and open the tap until the whole of lower layer has left the funnel • place another conical flask under the separating funnel to collect the other layer • label both conical flasks and make sure not to mess up them
How to remove acid impurities?
Add aqueous sodium carbonate and shake the mixture in the separating funnel.
What are the common inorganic salts that are used to dry organic liquids?
• anhydrous calcium chloride (CaCl2) • anhydrous calcium sulfate (CaSO4) • anhydrous magnesium sulfate (MgSO4)
What is anhydrous calcium chloride (CaCl2) used to dry?
Hydrocarbons
What is anhydrous calcium sulfate (CaSO4) used to dry?
General organic liquids
What is anhydrous magnesium sulfate (MgSO4) used to dry?
General organic liquids
What are the steps of drying an organic liquid?
• add the organic liquid to a conical flask • add some drying agent to the liquid with a spatula • swirl the content gently to mix together • place a stopper on the flask to prevent the product from evaporating away • leave the content for 10 minutes • if the solid has all stuck together, that means there is still some water present • add more drying agent until some solid is disperse (分散) in the solution as powder • pour the liquid from the solid into another flask, if the liquid is dry it should be clear
Why do we sometimes do redistillation?
Because sometimes organic liquids have boiling points that are close together, and the sample might still contain some organic impurities.
How to do redistillation?
• clean and dry the distillation apparatus • set up again so that a second distillation can be carried out • only collect the product with the boiling point of compound you are trying to make • the narrower the boiling range, the purer the product • separate the product from any impurities
What is a target molecule?
The compound that the chemist is attempting to prepare by organic synthesis.
How to convert a starting molecule into a target molecule?
• identify the functional group in the starting and target molecule • identify the intermediate that links the starting and target molecule • state the reagents and conditions for each step