6.2.10: Practical skills for organic synthesis Flashcards
what is a Quickfit apparatus?
-A selection of heat-resistant glassware with connectors that connectors that can easily be fixed in a variety of arrangements.
What is the purpose of distillation and outline the steps.
- Distillation is used to separate an organic product from the reaction mixture.
- Each connector is carefully greased or held with a plastic clip o ensure it fits well.
- The bottom of the condenser is connected to he cold water supply an the top connector is connected to a hose that drains water into the sink.
- A few anti-bumping granules are added to the distillation flask to ensure smooth boiling.
- To complete the distillation, the mixture is heated.
- As the product is collected, the thermometer on the can be used to identify the chemical.
What doe heating under reflux mean and what is the purpose of this technique?
- Heating under reflux is a technique used in organic synthesis to ensure that volatile compounds are not lost from the reaction mixture.
- Volatile reagents are returned to the reaction mixture, rather than escaping before they react.
Organic solids will often crystallise out of solution after an organic synthesis. What is one way of collecting the product?
filtration under reduced pressure.
- Connect thick-walled rubber tubing to the vacuum, check that there is suction.
- Put Buchner funnel on top of a filter flask (Hirsch funnel for smaller quantities)
- Connect the tubing from the vacuum pump to the side arm of the clamped filter flask and start the suction.
- Place a piece of filer paper on top of the funnel.
- Dampen the filter paper using distilled water.
- Slowly pour reaction mixture into he centre of the funnel.
- Wash out the reaction vessel with the solvent and add this to the funnel.
- Rinse the collected solid with more solvent and maintain the suction for a minute after all the washing have been added.
- Turn off suction by removing the rubber tube from the side arm of the filtration flask.
- Invert the funnel onto a watch glass to collect the organic solid.
What is the purpose of recrystalisation?
- In organic synthesis, often a mixture of different organic chemicals is produced.
- Recrystalisation is a technique which allows an organic product to be purified from unreacted starting materials. catalysts and unwanted side products.
What are the three stages of recrysalisation?
Step 1:
- Crude product is dissolved in the minimum volume of hot solvent.
- Hot solvent is used as the solubility of solids is higher. If the product id coloured.
- activated charcoal can be heated with the mixture to remove the coloured impurities.
What are the three stages of recrysalisation?
Step 1:
-Crude product is dissolved in the minimum volume of hot solvent.
-Hot solvent is used as the solubility of solids is higher. If the product id coloured.
-activated charcoal can be heated with the mixture to remove the coloured impurities.
Step 2:
- The hot solution should then quickly undergo gravity filtration using fluted filter paper.
- The residue of the used activated charcoal and insoluble impurities can be disposed of.
- the hot filtrate should be allowed to cool.
- This reduces solubility and crystals of the product will form.
- Any soluble impurities should remain dissolved.
What are the three stages of recrysalisation?
Step 2:
-The hot solution should then quickly undergo gravity filtration using fluted filter paper.
-The residue of the used activated charcoal and insoluble impurities can be disposed of.
-the hot filtrate should be allowed to cool.
-This reduces solubility and crystals of the product will form.
-Any soluble impurities should remain dissolved.
Step 3:
- The purified organic product can be collected by vacuum filtration.
- The crystals should be washed with a small amount of cold solvent to remove any of the filtrate which contains dissolved impurities.
In step 2 of recrystalisation, what can you do if no crystals seem to be forming?
- Scratching the sides of the conical flask with a clean glass rod can form nucleation sites and aid crystallisation.
- Crash cooling the mixture in an ice bath can also be used to speed up this stage.
How can melting and boiling points be used to identify a chemical?
- All pure chemicals have distinct melting and boiling points.
- By measuring these values and comparing them to information in a data book or database, the chemical can be identified.
How can melting and boiling points be used to determine the purity of a chemical?
- By measuring the melting point of a known chemical, the purity can be determined.
- The pure chemical will have the exact chemical melting point as listed in a trusted source.
- However, he more impure the product is, the greater the range of the melting point will be.
What are the two methods for measuring melting point?
- Melting point apparatus.
- Thiele tube
how would you measure melting point with melting point apparatus?
- In a sealed capillary tube, put a few grains of the organic solid.
- Gently insert the tube into the melting point machine and add an accurate thermometer with a suitable range.
- Switch on the machine and turn the heating dial to about 4.
- Look through the lens and carefully watch the crystals.
- When they start to fall away from the sides of the capillary tube, melting has begun.
- record this temperature.
- Continue until the sample has liquefied and note new temperature
- These two values give your melting point range.
how would you measure melting point with a Thiele tube?
- In a sealed capillary tube, put a few grains of the organic solid.
- Using a small rubber band, attach the tube to a thermometer.
- Submerge the thermometer into the oil of Thiele tube, ensuring that the rubber band is above the oil line.
- Using a microburner with a small gentle flame, heat the side arm of the Thiele tube.
- Note the temperature range of when the organic solid starts and finishes melting.
