Chapter 16 Organic Synthesis Flashcards
What is reflux used for?
The procedure is often used to prepare an organic liquid without boiling off the solvent, reactant or products.
Name the pieces of apparatus required for reflux
Round-bottom or pear-shaped flask
Condenser
Rubber tubing
Stand and clamp
Heat source
What is a safety precaution used when heating flammable liquids under reflux?
A heating mantle or water bath can be used so no naked flame is present.
Describe the procedure for setting up reflux
-The reaction mixture is placed into a pear shaped flask
-Anti-bumping granules are then added to promote smooth boiling
-The flask can be placed into a heating mantle or immersed within a water bath
-Quickfit apparatus with the condenser being clamped vertically upright, the joints of the apparatus are greased together creating a seal
-Rubber tubing is attached to the condenser allowing water to pass through the ‘water jacket’, the water enters at the bottom and is removed from the top pf the condenser
-The heating mantle is turned on and the reaction mixture is left to boil
-The mantle is turned off and the mixture is then left to cool back to room temperature
What is the use of anti-bumping granules?
To allow for smooth boiling as if granules are not used, large bubbles can form at the bottom of the liquid and make the glassware vibrate.
What is distillation used for?
Distillation is used to separate a pure liquid from its impurities, this is because some reactions may not go to completion or there are other chemicals produced alongside the desired product.
Name the pieces of apparatus used during distillation
Round bottom or pear shaped flask
Condenser
Rubber tubing
Heat source
Stand and clamp
Screw cap adaptor
Receiver adaptor
Still head
Thermometer
Describe the procedure of distillation
-Add the reaction mixture to the pear shaped flask
-Anti-bumping granules are then added alongside the reaction mixture to promote smooth boiling
-Quickfit apparatus is set up, including a still head which has two joints, one connected to the condenser and then other connected to the screw cap adaptor
-A receiver adaptor is also joined to the end of the condenser with a flask placed underneath for the collection of the distillate
-The joints of the Quickfit apparatus have a thin layer of grease for a better seal
-The thermometer bulb is placed to sit where the vapours will pass into the condenser
-Rubber tubing provides a constant stream of water from the tap to the water jacket. It enters at the bottom (near the receiver) and leaves at the top.
-The reaction mixture is then heated using a heating mantle or water bath
-The distillate formed in the condenser drips into the receiving vessel, when collected it should be within +/- 2 C of the boiling point of the desired product.
What is the use of a separating funnel?
A separating funnel is used to separate the organic liquid from water. This is because when organic products are being prepared, water can often from an aqueous layer alongside the organic layer.
How can the organic and aqueous later be identified before separation?
Adding water to the mixture will show which layer is aqueous and which is the organic product. The layer that increases in volume can be identified as water.
Describe the procedure of using a separating funnel
-Ensure the tap of the separating funnel is closed
-The reaction mixture is then transferred into the separating funnel and a stopper is added.
-The apparatus is then inverted to mix the contents
-The two layers are then allowed to settle
-Add some water to identify the aqueous and organic layer
-Place a conical flask under the separating funnel, remove the stopper and open the tap allowing the lower layer to leave
-Place a second conical flask under the separating funnel to collect the other layer.
How can some organic reactions be prepared before purification using a separating funnel?
Sodium carbonate can be added to the separating funnel to neutralise any acid impurities within the organic reaction.
Any acid present will react with the Sodium carbonate producing carbon dioxide gas, which needs to be released by holding the stoppered apparatus upside down and slowly opening the tap releasing the pressure.
What is the use of drying agents?
Drying agents are anhydrous inorganic salts that remove traces of water from the organic product to become hydrated.
What drying agent is used to dry hydrocarbons?
Anhydrous calcium chloride
What drying agents are general purpose?
Anhydrous calcium or magnesium sulfate
