Chapter 16: Organic Synthesis Flashcards
To carry out an organic preparation you will need to use Quickfit apparatus. State what this includes.
- round-bottom or pear-shaped flask
- receiver
- screw-tap adaptor
- condenser
- still head
- Why are organic reactions heated?
- What does heating under reflux mean?
- What apparatus do you need to heat under reflux?
- Many organic reactions occur slowly at room temperature. Organic reactions are heated to overcome the activation energy and increase the rate of reaction.
- Heating under reflux is a common procedure used to prepare and organic liquid without boiling off the solvent, reactants or products.
- To heat under reflux, you will need:
- round-bottom or pear-shaped flask
- condenser
- rubber tubing
- stand and clamp
- heat source (usually a Bunsen burner, tripod, and gauze, or heating mantle).
Show the experimental setup for a reflux experiment using a Bunsen burner to heat the reaction mixture.
Describe and explain the setup of apparatus and the method for a typical organic reaction that involves heating under reflux.
- The flask is clamped by its neck. Before fitting the condenser, reaction micture and anti-bumping granules are added to the flask.
- Anti-bumping granules are added to the liquid before the flask is heated so that the contents will boil smoothly. If the granles are not used, large bubble form at the bottom of the liquid and make the glassware vibrate or jump violently.
- Finally, apply a thin layer of grease to the ground-glass joint on the condenser. Place the condenser carefully into the flask and gently rotate the condenser back and forth to provide a good seal and ensure that the apparatus comes apart easily at the end of the experiment.
- During reflux the condenser is kept in the upright position. Condensersshould be clamped only loosely as the glass outer jacket is very fragile and is easily broken. Never put a stopper in the top of the condenser. Otherwise you would have a closed system and pressure would build up inside as the heated air expanded. This could result in the appartus exploding!
- Rubber tubing is used to connect the inlet of the condenser to the tap and the outlet to the sink. Water always enters the condenser at the bottom and leaves at the top to ensure that the outer jacket is full.
- Heating under reflux enables a liquid to e continually boiled whilst the reaction is taking place. This prevents volatile components from escaping and the flask from boiling dry.
- The vapour from the mixture rises up the inner tube of the condenser until it meets the outer jacket containing cold water. The vapour then condenses and drips back into the flask.
- What is distillation? Explain when this is used.
- Chemical reactions may not go to completion or may produce by-products as well as the desired product. Once reflux is complete the crude liquid or solid product dependant in the flask needs to be purified to remove any by-products and remaining reactants. Distillation is a common method used to separate a pure liquid from its impurities.
What apparatus is needed to carry out a distillation?
- round-bottom or pear-shaped flask
- condenser
- rubber tubing
- heat source
- stand and clamp
- screw-cap adaptor
- receiver adaptor
- still head
- thermometer
Show the apparatus set-up for distillation.
Describe the setup of the apparatus for distillation.
The flask is clamped by its neck and the still head is connected to the flask. The still-head adaptor is T shaped and has two ground-glass joints, one to fit the screw-cap adaptor and one to fit the condenser. You should grease the joints so that the apparatus comes apart easily after the experiment.
A second clamp is placed round the receiver adaptor at the point at which it is attached to the condenser. This removes the need to clamp the condenser, as it will be supported sufficiently at both ends.
As with reflux, rubber tubing is used to connect the inlet of the condenser to the tap and the outlet to the sink. Water always enters the condenser at the lowest point. For distillation, this is the closest point to the receiver adaptor.
A flask is used to collect the distillate so that the distillation apparatus is not completely airtight.
Once the apparatus is set up, the flask is heated and the mixture in the flask will start to boil. The different liquids in the mixture will have different boiling points. The liquid with the lowest boiling point is the most volatile and will boil first.
he vapour moves out of the flask up into the other parts of the apparatus, leaving behind the less volatile components of the mixture. When the vapours reach the cold condenser, they condense and become a liquid. This liquid then drips into the collecting flask.
Describe the need for and the process involving the purification or organic products.
When preparing samples of organic liquids, water may be obtained along with the product. The two layers are separated using a separating funnel.
- Ensure the tap of the separating funnel is closed.
- Pour the mixture of liquids into the separating funnel, place a stopper in the top of the funnel and invert to mix the contents.
- Allow the layers to settle.
- Add some wayer to see which layer increases in volume – this is the aqueous layer.
- 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.
- Place a second conical flask under the separating funnel to collect the other layer.
Describe the purification of impure organic products whose preparation involved acids.
In preparation using acids, your impure product may contain acid impurities. These can be removed by adding aqueous sodium carbonate and shaking the mixture in the separating funnel. Any acid present will react with sodium carbonate releasing carbon dioxide gas. The tap needs to be slowly opened, holding the stoppered separating funnel upside down to release any gas pressure that may build up.
Finally the aqueous sodium carbonate layer is removed and the organic layer washed with water before running both layers off into separate flasks.
Describe the process of removing traces of water from an organic product by the use of a drying agent.
- What is organic synthesis?
- What is the use of organic synthesis?
- Organic synthesis is the preparation of complex molecules from simple starting materials.
- With organic synthesis, chemists can make entirely new structures that can be investigated for their uses. For example, the manufacture of modern medicnes targeted at diseases uses organic synthesis.
Show the displayed formulae for the following functional groups:
- alkene
- alcohol
- haloalkane
- aldehyde
- ketone
- carboxylic acid
- ester
- amine
- acyl chloride
- nitrile
Describe the connections between functional groups in a flowchart. This can be useful for predicting reactions and in solving synthesis problems.
What is a target molecule?
The term target molecule is used to describe the compound that the chemist is attempting to prepare by organic synthesis.
Describe two-stage synthesis.
State the reagents and conditions for the two-stage synthesis of propanal from 1-chloropropane.
State the reagents and conditions for the two-stage synthesis of butanone for but-2-ene. Show the skeletal formula throughout and give equations for each stage.
