Organic Synthesis Flashcards
Describe how to carry out steam distillation.
- Steam is passed into the mixture
- The mixture evaporates and condenses - product distills off with water
- Use a separating funnel is layers form
What method can you use to separate an organic product from an inorganic substance?
Solvent extraction.
- A solvent is added to the mixture (it is immiscible in the liquid containing the solute)
- The two immiscible liquids are vigorously shaken together so the solute migrates to the added solvent
- Dry the solute with anhydrous calcium chloride, then leave and filter product.
What is the basis of recrystallisation?Describe how recrystallisation can be used to produce a pure organic product.
Based on the idea that solubility of a solid increases with temperature.
- Dissolve the solid in a minimum volume of hot ethanol
- Filter while hot - removes impurities that are insoluble at high temps
- Cool filtrate - so crystals can form
- Filter under reduced pressure (suction filtration) - soluble impurities are removed by cold filtration
- Wash with cold ethanol and leave to dry
- Find melting point and compare with known values
In complete combustion, why is dry oxygen used?
a) What can be used to absorb the carbon dioxide?
b) What can be used to absorb the water?
So only the water formed is absorbed by the substance that absorbs water, or else the mass would be too high.
a) Soda lime or potassium hydroxide
b) Anhydrous calcium chloride
What is a separating funnel and how is it used?
It is a funnel used to separate two immiscible liquids.
- The mixture of liquids is placed in the funnel and the lower density liquid floats on top (organic layer).
- The tap is opened to allow the higher density liquid (aqueous layer with unreacted salts) to flow out.
- The organic layer is kept and dried with CaCl2.
Briefly describe how combinatorial chemistry works, stating the type of bonding involved.
- Small compounds are attached to polymer beads
- Reaction occurs with plastic resin and products bonded to beads
- Excess reactants are washed away
Covalent bonding is involved.
What are the advantages of combinatorial chemistry?
- It speeds up the synthesis of new compounds - allows huge numbers of similar compounds to be made at once
- It is carried out quickly and accurately
- It saves companies money - drugs reach market faster
- Compounds are stored for use as medicines
What is the difference between a hazard and a risk?
Hazard: the potential to cause harm
Risk: the likelihood of harm
Why must risk assessments be carried out?
To avoid dangerous situations in synthesis. The hazards of reactants should be considered so safer, alternative routes and chemicals can be used.
State the main hazard and precaution that must be taken with the following reagents:
a) Sodium hydroxide
b) Methanol
c) Chromium compounds
a) Corrosive - wear gloves and safety goggles
b) Flammable - do not expose to naked flames (use a water bath)
c) Carcinogenic - use a fume cupboard (don’t inhale fumes)
How do you calculate the empirical formula from percentage by mass?
- Find the mass of each element
- Convert the masses to moles
- Find the simplest ratio by dividing by the smallest
- Round the mole ratios to the nearest whole number
Why is steam distillation used?
It works on the basis that immiscible liquids when mixed together can lower the boiling points of each other.
Steam is used to distil compounds with high boiling points that may decompose with normal distillation.
What is the difference between fractional distillation and normal distillation?
Fractional distillation is used to separate liquids with slight differences in boiling point and have the same intermolecular forces. Is more efficient.
Normal distillation is used to separate liquids which differ in boiling temperature considerably.
