Organic Synthesis (16) Flashcards
What is reflux?
Reflux is a practical technique where a substance can be boiled continuously and condenses back into the flask
Why do we use reflux?
We use reflux to make sure that any volatile substances that evaporate easily aren’t lost. Using reflux, they continuously evaporate and condense back into the mixture which gives time for the reaction to occur.
Describe how reflux works using terms for equipment.
- Prepare your heating mantle or flame
- Add your solution to a pear-shaped flask
- Add antibumping granules to the flask too
- Clamp your condenser and then grease the end of it and place it into your flask
- Add rubber tubing to the inlet and outlet of the condenser, the inlet should be connected to the tap, the outlet should go in the sink, this keeps the flow of water
- Now heat your solution and give enough time for the reaction to take place
What heat source is best for reflux?
It is best to use a bunsen burner however, for flammable liquids use a heating mantle as naked flames cannot be present or it will ignite
Why are anti-bumping granules added?
They allow the mixture to boil smoothly so that no large bubbles are formed and the container doesn’t shake violently
What must you never put on the apparatus?
You must never put a stopper in the top of the Liebig condenser as the pressure will build up and the apparatus will explode
What is distillation?
It’s when you heat a mixture to a certain boiling point of your desired product. It then evaporates and condenses into another flask so you have separated out the mixture.
Why do we use distillation?
We use it to separate substances with different boiling points or to separate a pure substance from its impurities.
Describe how distillation works using terms for equipment.
- Prepare your bunsen burner
- Clamp your round-bottomed flask and fit it with a still head a screw cap adaptor
- Put a thermometer in your screw cap adaptor
- Clamp your receiver adaptor to support the structure and then attach your condenser to your still head.
- Place a conical flask at the bottom of the receiver
- Add tubing to the inlet and outlet of the condenser
- Start heating your liquid and wait until the substance with the lowest boiling point evaporates and condenses into the conical flask
What happens if the substance you need has the highest boiling point?
Redistillation can happen so you repeat the process after cleaning all the apparatus and closely monitor the boiling points until you end up with your final pure substance. The narrow the range of the boiling point, the purer the product.
What can happen when you form an organic product?
You can result in a mixture with the organic product and water. You will see two clear layers because most organic products are insoluble in water.
How can you tell which layer is organic?
Sometimes it can be difficult to tell, so you add more water to the mixture. The layer that gets bigger is your water layer and this will help you know which one to throw away once you separate them.
How do you separate organic products from water?
You use a separating funnel
Explain the steps for separating organic products from water
- Ensure the tap of the separating funnel is closed
- Pour your mixture into the separating funnel
- Put a stopper in the top of the funnel and invert it to mix the solution
- Allow the layers to settle
- Add water to see which layer increases in volume, so identify the water
- Open the tap and allow the entire lower layer to drip into a conical flask, label it
- Place a second flask under the tap and allow the remaining layer to drip into it, label it.
- Sometimes there may be H2SO4 also present in your reaction and this will interact with the drying agent to form CO2. You can get rid of this by tipping the separating funnel upside down and opening the tap slowly to release this gas.
Why might this still not be completely accurate?
There may still be traces of water left in the organic product from separating them using the funnel
How can you remove all water from the organic product?
You need to add a drying agent like an anhydrous inorganic salt which can take up the water to become hydrated. Examples are anhydrous magnesium sulphate or calcium sulphate. This process is called drying an organic product
Name the steps in drying an organic compound
- Add your organic liquid to a conical flask
- Using a spatula, add some drying agent to the liquid
- Gently swirl the contents together
- Place a stopper on the flask to prevent the product from evaporating away
- Wait ten minutes
- If the solid clumps up, there is still water so add more drying agent and repeat. If the solid is dispersed as a fine powder, it is ready to be separated.
- Decant the liquid from the solid and the liquid should be clear if it is pure.
Alkane -> Haloalkane
Free radical substitution
UV light condition
Alkene –> Alkane
Hydrogenation (addition)
Nickel catalyst
150 degrees temp
Alkene –> Haloalkane
Addition of a hydrogen halide
Gaseous hydrogen halide
Room temperature
Alkene –> Dihaloalkane
Halogenation (addition)
Room temperature
Alkene –> Alcohol
Hydration
H3PO4 catalyst
Steam
300-degree temp
Alcohol –> Aldehyde
Oxidation of primary alcohol
Acidified potassium dichromate
Distillation
Orange to green
Alcohol –> Carboxylic acid
Oxidation of primary alcohol (second)
Acidified potassium dichromate
Reflux
Orange to green
Alcohol –> Ketone
Oxidation of a secondary alcohol
Acidified potassium dichromate
Reflux
Orange to green
Alcohol –> Alkene
Dehydration (elimination)
H3PO4 catalyst
Reflux
Alcohol –> Haloalkane
Substitution of sodium halide
H2SO4 catalyst
Reflux
Alcohol –> Ester
Addition of carboxylic acid
Haloalkane –> Alcohol
Hydrolysis (substitution)
Reflux
Warm NaOH
What is a target molecule?
A target molecule is a compound that a chemist is trying to prepare
How do you work out the target molecule in a 2 stage synthesis?
- You work out the functional groups in the starting and target molecule
- You then work out the intermediate molecules
- State reagents for each step
How can you separate a solid product from a solvent or liquid mixture?
You filter under reduced pressure with vacuum filtration
What do you need for vacuum filtration?
- A Buchner funnel
- A Buchner flask
- pressure tubing
- filter paper
- Access to a vacuum pump
Explain vacuum filtration
- Connect one end of the tubing to the vacuum pump and the other end to the Buchner flask
- Fit the Buchner funnels inside to the Buchner flask, using a rubber bung to make sure it’s airtight
- Switch on your pump or the tap and check to see if there is good suction
- Moisten some filter paper with your solvent and place it on your porous plate in the Buchner funnel. You should see it being sucked against the holes
- Add your mixture slowly onto the filter paper and then rinse out your beaker with the solvent to make sure all of the solid collects in the Buchner funnel
- Rinse the crystals in the Buchner funnel with more solvent and let them dry under suction
