Module 4: Chapter 16 - Organic Synthesis Flashcards
What does a basic set of Quickfit apparatus consist of?
- Reound bottom (or pear shaped) flask
- Receiver
- Screw-cap adaptor
- Liebig Condenser
- Still head
What is heating under reflux?
The continual boiling and condensing of a reaction mixture back to the original container to ensure that the reaction takes place without the solvent, reactants, or products boiling off
Why is reflux used?
Many organic reactions occur slowly at room temperature. It is common for organic reactions to be heated to overcome the activation energy and increase the rate of reaction. Heating under reflux ensures the contents of the flask does not boil away whilst being heated
What apparatus do you need to heat under reflux?
- Round bottom flask
- Liebig Condenser
- Rubber tubing
- Stand and clamp
- Heat source
(and antibumping granules)
What are commonly used heat sources?
- Bunsen burner, tripod, and gauze
- Heating mantle
What is added to the contents of the flask during reflux?
Anti-bumping granules
Why are anti-bumping granules added to the flask during reflux?
anti-bumping granules ensure the contents of the flask boil smoothly, If the granules are not used, large bubbles form at the bottom of the liquid and make the glassware vibrate or jump violently
Why is a thin layer of grease applied to the ground glass joints on quickfit apparatus?
To ensure the apparatus easily comes apaart at the end of the experiment
What end of the condenser does water enter and exit and why?
Water enters at the bottom of the condenser adn exits at the top to ensure that the condenser is always full of water
What are the benefits of using reflux?
It allows the contents of the flask to be continually boiled whilst the reaction takes place. It prevents volatile components from escaping and the flask from boiling dry
How does reflux prevent contents boiling away?
The vapour from the mixture will rise 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 a method used to separate a pure liquid from its impurities?
Distillation
Why may refux be followed by distillation?
Reflux may be used during the reaction however distillation is used after to separate a pure liquid from its impurities
What apparatus is required for distillation?
- Round bottom flask
- Receiver
- Screw-cap adaptor
- Condenser
- Still head
- Rubber tubing
- Heat source
- Stand and clamp
- Thermometer
Why is a flask/beaker used to collect the distillate?
So that the apparatus is not completely airtight
Why shoulf quickfit apparatus not be airtight?
This would create a closed system and pressure would build up inside as the heated air expands. This could result in the appratus cracking or exploding.
What is the distillate?
a liquid product condensed from vapor during distillation
How does distillation work?
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. The 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
How can you separate an organic liquid from water (when the 2 liquids are immiscible)?
Once the organic layer has been identified, the 2 layers can be separated using a separating funnel:
1. Ensure that the tap of the separating funnel is closed.
2. Pour the mixture of liquids into the separating funnel, place a stopper in the top of the funnel, and invert to mix the contents
3. Allow the layers to settle
4. Add some water to see which layer increases in volume - this is the aqueous layer
5. 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
6. Place a second conical flask under the separating funnel to collect the other layer
7. You will now have one conical flask containing the organic layer and another containing the aquous layer
How can you dry the organic product, removing any traces of water that may remain?
Adding a drying agent to the organic liquid
What is a drying agent?
An anhydrous inorganic salt that readily takes up water to become hydrated
What are 3 common drying agents?
- Anhydrous calcium chloride
- Anhydrous calcium sulfate
- Anhydrous magnesium sulfate
What is Anhydrous calcium chloride used for?
drying hydrocarbons
Whay is anhydrous calcium sulfate used for?
general drying
What is anhydrous magnesium sulfate used for?
general drying
What is the procedure for drying an organic liquid?
- Add the organic liquid to a conical flask
- Using a spatula, add some of the drying agent to the liquid and gently swirl the contents to mix together
- Place a stopper on the flask to prevent your product from evaporating away. Leave for about 10 minutes.
- If the solid has all stuck together in a lump, there is still some water present. Add more drying agent until some solid is dispersed in the solution as a fine powder
- Decant the liquid from the solid into another flask. If the liquid is dry it should be clear
What is redistillation?
Redistillation is when a second distillation is carried out, however, this time only collect the product with the boiling point of the compound you are intending to make. When the thermomemter shows the temperature is changing, put another flask at the end of the condenser as a different liquid is about to be delivered. The narrower the boiling range the purer the product.
How can a solution be heated strongly?
Reflux
How do you produce an alkene from an alcohol?
React it with concentrated sulfuric acid
What happens when an alcohol react with concentrated sulfuric acid?
An alkene is produced
How do you produce an alcohol from an alkene?
React it with steam (H2O gas) in the presence of a phosphoric acid catalyst
What happens when an Alkene reacts with steam in the presence of a phosphoric acid catalyst
An alcohol is produced
How do you produce a carboxylic acid from a primary alcohol?
Reflux it with acidified pottassium dichromate
What happens if you reflux a primary alcohol with acidified pottassium dichromate
you produce a carboxylic acid
How do you produce an aldehyde from a primary alcohol?
Distil it with acified potassium dichromate
What happens if you distil a primary alcohol with acified potassium dichromate?
You produce an aldehyde
How do you produce a ketone from a secondary alcohol?
Reflux it with acidified potassium dichromate
What happens if you reflux a secondary alcohol with acidified potassium dichromate?
You produce a ketone
What happens if you react an alcohol with a sodium halide and sulfuric acid?
you produce a haloalkane
How do you produce a haloalkane from an alcohol?
React it with a sodium halide and sulfuric acid
How do you produce an alkane from an alkene?
React it with hydrogen in the presence of a nickel catalyst
What happens if you react an alkene with hydrogen in the presence of a nickel catalyst?
You produce an alkane
How do you produce a haloalkane from an alkene?
React it with a hydrogen halide
What happens if you react an alkene with a hydrogen halide?
You produce a haloalkane
How do you produce a haloalkane from an alkane?
React it with a halogen in the presence of UV light
What happens if you react an alkane with a halogen in the presence of UV light?
You produce a haloalkane
How do you produce an alcohol from a haloalkane?
Reflux it with aqueous sodium hydroxide
What happens if you reflux a haloalkane with aqueous sodium hydroxide?
You produce an alcohol
What is the formula for potassium dichromate?
K₂Cr₂O₇
What is organic synthesis?
The preparation of complex molecules from simpole starting molecules
What is the AS organic synthesis flowchart?
How can you predict the properties and reactions of complex molecules you have not seen before?
- Draw out the structure and identify the functional groups
- The molecule will have all the reactions of the functional groups it contains
What is a target molecule?
The compound that the chemist is attempting to prepare through organic synthesis
Why do most organic synthesis’ require multiple steps?
Sometimes it may be possible to obtain the target molecule through a single reaction, however it often requires many steps to change the functional groups or add carbon atoms to the chain length in order to obtain the target molecule
How do you solve a 2 step synthesis?
- Identify the functional groups in your starting and target molecules
- Identify the intermediate molecule that links the starting and target molecule (using flowchart)
- State the reagents and conditions for each step
State the reagents and conditions for the 2-stage synthesis of propanal from 1-chloropropane
Stage 1: Reagents: NaOH(aq), conditions: reflux
Stage 2: Reagents: Potassium dichromate and sulfuric acid, conditions: distil
State the reagents and conditions for the 2-stage synthesis of butanone from butan-2-ene
Stage 1: Reagents: Steam, conditions: Phosphoric acid catalyst
Stage 2: Reagents: potassium dichromate, conditions: reflux
What are the reagents and conditions for each step?
Step 1: Reagents: Hydrogen, conditions: Nickel catalyst
Step 2: Reagents: NaOH(aq) Conditions: reflux
Step 3: Reagents: Potassium dichromate and sulfuric acid, Conditions: reflux
