RP 10 - preparation of organic solids and liquids (aspirin)

Question 1

what are the 4 general steps to synthesising an organic product and purifying it

Answer 1

• preparation
• seperating the product from the reaction mixture
• purifying the product
• testing the purity

Question 2

1 . Preparation

Answer 2

react suitable quantities of the reactants to produce the product

Question 3

2 . Seperation of the crude (impure) product

how is it carried out for a liquid product vs solid product

Answer 3

for a liquid product:
- collected by distillation

for a solid product:
- the sample is usually collected by filtration from the reaction mixture
- sometimes the product forms a solid in the reaction but sometimes cold water has to be added to cause the product to formk a solid from solution
- the solid is then seperated by filtration under reduced pressure using buchner apparatus

Question 4

3 . Purification

for liquids vs solid products

Answer 4

liquids - seperating funnel and then distillation
solids- recrystalisation

Question 5

4 . Testing the purity

Answer 5

liquids- boiling point
solids- melting point

Question 6

What is reflux and why do we do it?

Answer 6

Reflux involves the cotinuous boiling and condensing of a reaction mixture
We do it to allow the reaction mixture to be heated without loosing any reactants or products

Question 7

1. Preparation (of organic solid- in this case aspirin)

what are the reactants to make aspirin?

Answer 7

2-hydroxybenzoic acid (salycilic acid) and ethanoic anhydride (with phosphoric acid)

Question 8

method of preparing aspirin (also seperating it-how?)

Answer 8

1. add 2g of 2-hydroxybenzoic acid to a 5cm3 pear shaped flask and add 4cm3 of ethanoic anhydride
2. add 5 drops of phosphoric acid and swirl to mix
3. fit the flask with a reflux condenser and heat the mixture on a boiling water bath for 5 minutes
4. without cooling add 2cm3 of water down the condenser
5. when the vigorous reaction has ended, our in 40cm3 of cold water and induce crystallisation
6. collect by suction filtration (seperation) and wash it with water

Question 9

what is the IPUAC name of aspirin

Answer 9

2-acetoxybenzoic acid

Question 10

what is the type of reaction that makes aspirin
And what’s the mechanism

Answer 10

esterification
nucleophillc adddition - elimination

Question 11

what functional groups does aspirin possess

Answer 11

aromatic, ester, carboxyllic acid

Question 12

Equation of reaction to produce aspirin

molceular formula and displayed formula

Answer 12

C7H6O3 + (CH3CO)2O –> C9H8O4 + C2H4O2

Question 13

what kind of mechanism is it

Answer 13

nucleophillic addition-elimination

Question 14

why is ethanoic anhydride used instead of acyl chloride?

Answer 14

• cheaper
• less vulnerable to hydrolysis
• less dangerous to use

Question 15

Buchner flask diagram

Question 16

How do you purify an organic solid like aspirin?

Answer 16

Recrysalization

Question 17

Breifly DESCRIBE recrystalisation

Answer 17

the product is dissolved in a small amount of hot solvent
any insoluble impurities are removed by filtration of this solution while hot
as the filtrate cools, the product crystalises out of solution but any soluble impurities remain dissolved. further filtration seperates the product from the soluble impurities.

Question 18

method recrysalisation

Answer 18

1) The impure solid is dissolved in a minimum volume of hot solvent
2) (If there are any insoluble impurities then they are removed in a) fast, hot filtration. Hot glassware is used.
3) Allow to cool slowly &// cool by inserting beaker in ice
4) Sucction filtration with Buchner flask (and washed with cold solvent)
5) Product is dried (in oven)

Question 19

recrysalisation

Why is the solid dissolved in a minimum volume of hot solvent?

Answer 19

To obtain a saturatedsolution and enable crystalisation upon cooling

(we use a minimum volume so that as much crystalises out as possible as it cools.)

Question 20

recrysalisation

what makes a good (min.hot.) solvent for recrystalisation?

Answer 20

one which will dissolve both the compound and its impurities when hot AND one in which the compound itself does not dissolve in when cold.

Question 21

recrysalisation

how does hot filtration remove insoluble impurities

Answer 21

the solvent is picked out so that the organic (solid) product is soluble in the solvent when hot, many impurities will be insoluble in the solvent still when it is hot, so filtration (with filter paper) is used to remove them, what gets through the filter paper will contain the product (soluble ) in the solvent.
it is done with hot glassware to prevent the prouct from crystalising out prematurly as it would then also get stuck in the filter and yield would decrease

Question 22

recrysalisation

Why is the solution cooled off (to RT//ice bath) before being filtered under reduced pressure?

Answer 22

This is when the crystals of organic product will form as it is much less soluble in the solevnt when the solvent is cool, any soluble impurities will hopefully remain in solution, so the crystals forming are our organic product
we leave it to do this so that yield is increased, solubility is higher at higher temperatures, so leaving it to cool to RTP for a while or on ice allows for as much product to crystalise out as possible

Question 23

recrysalisation

When suction filtration happens, the crystals are compressed on the aparatus - why?

Answer 23

to allow for better drying- air can pass through the sample and not just around it

Question 24

recrysalisation

Why do we filter under reduced pressure (buchner funnel) and when we do this why do we wash it through with a little cold solvent? (ie water)

Answer 24

the soluble impurities can be seperated from the product
we wash it through to remove any remaing soluble impurities

Question 25

# recrysalisation Why do we dry the product in a low temperature oven?

Answer 25

to remove excess water

Question 26

# recrysalisation what does it mean if yielf is over 100%

Answer 26

impurities remain- most likely water

Question 27

# purifying an organic solid (recrysalisation) Possible reasons for loss of yield

Answer 27

- crystals lost when filtering or washing - some of product stays in solution after recrystalisation (maybe temp was still too high- so still soluble) - other side reactions occur

Question 28

How do you purify the product - organic liquid?

Answer 28

Seperating funnel

Question 29

# purifying an organic liquid seperating funnel method | to remove acids or any kind

Answer 29

- the organic layer is shaken in the seperating funnel with an aqueous solution of sodium carbonate - the acid forms a salt, which dissolves in the aqueous layer. co2 is also formed (causes pressure to increase so tap should be opened frequently to relive pressure) - layers are allowed to seperate - the organic layer is decanted and washed with distilled water instead of sodium carbonate solution to remove soluble impurities

Question 30

# purifying an organic liquid how is the organic liquid dried?

Answer 30

poured into a conical flask and solid drying agent is added, the solution should become clear when it is dry anyhydrous calcium chloride is typically used. these drying agents will not dissolve in or react with the organic layer.