chem practical (organic synthesis)

Question 1

considerations when using a synthesis method

Answer 1

• product of yield
• ease of separating the desired product from by-products or excess reactants
• cost & availability of reactants
• simplicity of experimental set-up
• types of catalyst used
• selective reaction of polyfunctional reactants
• stereochemical control (?????)

Question 2

when to use heat under reflux

Answer 2

when organic solvents have low bp but needs to heat higher than its low bp, to prevent loss of reactants or solvent during prolonged heating

any vapour is immediately condensed back

Question 3

reflux system: hot plate

Answer 3

is replaced by direct heating using a bunsen burner cuz organic solvents/reacants are highly flammable -> can create high [] vapour in air-> can easily ignite when exposed to spark/flame

Question 4

reflux system: oil bath/heating mantle

Answer 4

oil bath used instead of water bath cuz some heating is higher than 100C (bp of water)

heating mantle -> more versatile and easier to handle but need to find appropriate size to fit RBF

Question 5

reflux system: round bottom flask (RBF)

Answer 5

RBF: allows even heat distribution. 2 to 3-neck RBF provide versatility.

can attach:
- condenser => must be clamped vertically above RBF. water flow in water jacket from lower end to upper end to carry away heat of vapourisation released by vapour. upper end of condenser open to air to prevent pressure build-up in system
- dropping funnel => introduce liquids dropwise
- temperature probe => measure temperature of rxn

inside RBF:
- boiling chips => make boiling more even
- magnetic stirrer => ensure reaction is homogeneous. rate of stirring controlled by hot plate

Question 6

when to use gravity filteration?

Answer 6

if i want LIQUID rom solid-liquid mixture

Question 7

when to use vacuum filteration?

Answer 7

if i want SOLID from solid-liquid mixture

Question 8

things to take note for gravity filteration:

Answer 8

fluted filter paper:
- faster filtering
- prevent more loss of liquid product.
- if we filter hot organic mixture, hot liquids may form crystals if filtration too slow until mixture cooled down and crystalise liao

Question 9

things to take note for vacuum filteration:

Answer 9

Buchner funnel: need to have filter paper w appropriate dimensions to cover all drainage holes. moisted w appropriate solvent so that it remains fixed onto base of funnel when vacuum is on

• the soild we want is on top of Buchner funnel
• cold trap => used to prevent low bp from condensing into vacuum pump

Question 10

things to take note for liquid-liquid extraction:

Answer 10

• mixture needs to shake and left to stand

Question 11

recrystallisation: to get pure solids

Answer 11

1. dissolve impure solid organic product in min quanitites by gradually adding small vol of hot solvent to get SATURATED SOLN
   *** need to choose solvent that is soluble in high temp but insoluble in low temp