Organic Synthesis Practical Skills Flashcards
What is the quick fit apparatus?
Round-bottomed flask, condenser, pear-shaped flask, dropping funnel, separating funnel.
What is reflux?
Continuous process of evaporating and condensation to prevent volatile substances escaping.
What is distillation?
Used to separate an organic product with a lower boiling point from reactants/products with a higher boiling point.
Why is the water filled in the way it is during distillation/reflux?
To ensure the condenser is filled with water.
Why are anti-bumping granules added?
To ensure smooth boiling.
When purifying an organic liquid how and why is a separating funnel used?
To separate organic and aqueous layer and remove water soluble impurities. Add water to organic product in a separating funnel, put stopper in, shake, invert, open tap (to equalise pressure), repeat, remove stopper, open tap and allow lower (more dense) aqueous layer to run off. Repeat process again.
How does drying work when purifying an organic liquid?
Add anhydrous MgSO4 or CaCl2 to organic layer, shake and keep adding until solid is free flowing. Filter or decant of the dry organic layer.
How does redistillation work?
Multiple distillations until the pure product is collected. If impurities are present the boiling point will be lower than expected and the product will be collected over a wide temperature range.
When purifying an organic solid how does filtering under pressure work?
To separate a solid organic product from the reaction mixture. Use a Buchner funnel or Hirsch funnel, connect side arm of filter flask to pump, dampen filter paper with solvent, filter mixture.
How recrystallisation work when purifying an organic solid?
Dissolve in minimum amount of hot solvent. Filter quickly under gravity to remove any insoluble impurities. Cool the hot filtrate until crystals start to form (scratch sides of flask if necessary). Soluble impurities remain in the cool solution. Filter under reduced pressure to collect pure crystals. Wash with a little, cold solvent. Dry.
How can checking the melting point help you in the purification of an organic solid?
If pure, the substance will have an exact melting point. Comparison to database can be used to identify the substance. Impure samples tend to gave a lower melting point and tend to have a wider range.
Why should you add reagents slowly?
To avoid reactions getting too hot which could be dangerous and result in side reactions.
Why may the yield not be 100%?
Due to side reactions, incomplete reactions, loss of product in washing/transferring/distilling/recrystallising or impure starting materials.
