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Module 6 Chemistry > Chapter 28 - Organic Synthesis > Flashcards

Chapter 28 - Organic Synthesis Flashcards

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1
Q

what are the 4 main ways to increase the length of a carbon chain

A
  1. reacting a haloalkane with ethanolic KCN
  2. reacting a carbonyl compound with HCN (acidified KCN)
  3. alkylation of benzene
  4. acylation of benzene
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2
Q

what is the reaction to increase the carbon chain length of a haloalkane, what are the conditions/reactants

A

Haloalkane + ethanolic KCN —> nitrile + KCl

ethanolic KCN
warmed

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3
Q

what reaction mechanism is the reaction to increase the carbon chain length of a haloalkane, describe it

A

it is nucleophilic substitution

  • the C-X bond on the haloalkane is polar with the carbon being delta(+ve)
  • the C(-)N ion is negative, it contains a lone pair on the carbon
  • the cyanide ion attacks the delta(+ve) carbon and donates an electron pair, acting as a nucleophile
  • the C-X bond breaks by heterolytic fission
  • the product is a C-CN group and a halogen ion
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4
Q

what is the reaction to increase the carbon chain length of carbonyl compounds, what are the conditions/reactants and what to note about one of the reactants

A

carbonyl compound + HCN —> Hydroxynitrile

  • the HCN comes from acidified KCN because it is too dangerous to use directly
  • heat under reflux
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5
Q

what is the mechanism for the reaction to increase the chain length of a carbonyl compound, describe it

A
  • nucleophilic addition
  • the C=O bond is polar where the carbon is delta(+ve)
  • the C(-)N ion is polar and contains a lone pair
  • the C(-)N ion attacks the delta(+ve) carbon forming a daitive covalent bond
  • the C=O pi bond breaks by heterolytic fission forming a negative intermediate
  • this negative intermediate is protonated by water
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6
Q

what is the reaction for the alkylation of benzene

A

benzene + haloalkane –(AlCl3)–> alkyl benzene + HX

  • react benzene with a haloalkane e.g. CH3Cl and a halogen carrier catalyst of AlCl3
  • they react in an electrophilic substitution reaction to form benzene with an alkyl group on, in this case methyl benzene and HCl or a different hydrogen halide
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7
Q

what is the reaction for the acylation of benzene

A

Benzene + acyl chloride –(AlCl3)–> Ketone + HCl

AlCl3 acts as a halogen carrier catalyst

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8
Q

why don’t we want the nitrile group and what two reactions can we do to remove it

A

1) reduction of nitriles

2) hydrolysis of hydroxynitriles

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9
Q

what occurs in the reduction of nitriles

A
  • nitriles are reduced to amines in a reaction with hydrogen and a nickel catalyst

e.g.
R - CN + 2H2 —(Ni)—> R-CH2-NH2

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10
Q

what occurs in the hydrolysis of nitriles/hydroxynitriles

A

R-CN + 2H2O + HCl(aq) —-> R-COOH + NH4Cl

heat with dilute aqueous acid under reflux

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11
Q

describe when we would use filtration under reduced pressure

A
  • when separating a solid product form a solvent or liquid reaction mixture
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12
Q

what is the apparatus required for filtration under reduced pressure

A
  • Buchner Flask
  • Buchner Funnel
  • Pressure tubing
  • Filter paper
  • Access to filter/vacuum pump
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13
Q

describe the method for filtration under reduced pressure

A

1) connect the end of the pressure tubing to vacuum outlet or filter pump and other end to Buchner flask
2) fit Buchner funnel to Buchner flask using rubber bung to ensure a tight fit
3) switch on vacuum pump or tap and check for good suction
4) place filter paper in funnel and dampen using the same solvent as was used in the preparation of the solution
5) slowly pour mixture into the centre of the funnel and rinse container
6) rinse crystals again using the solvent and leave to dry for a few mins

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14
Q

when would we use recrystallisation and what is the principle on which it works

A
  • after filtration, the solid product will still have impurities, these can be removed via recrystallisation
  • it works by the desired product and the impurities having different solubilities in the chosen solvent
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15
Q

describe the method for recrystallisation

A

1) pour a quantity of solvent into a conical flask, heat either in a water bath or over a Bunsen burner depending on its volatility
2) pour the impure sample into a clean conical flask/beaker
3) add the minimum amount of solvent required to dissolve the impure sample
4) once the solid has dissolved, allow to cool, wait for crystals to stop forming then filter crystals again under reduced pressure and leave to dry

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16
Q

why may we use melting point determination

A

melting points can be used for:
- purity checks, pure substances have a sharp melting point, impure substances melt over a range of temperatures (usually lower temperatures)

  • identification, you can compare experimental values to standard values to identify a substance
17
Q

independent of the technique being used, what are always the first few steps of finding a melting point

A

1) ensure the solid is completely dry and free-flowing
2) hold the end of a glass capillary tube in the flame of a Bunsen burner, rotate until the end of the tube is sealed
3) let the capillary tube cool and fill to about 3mm with the crystals, tap the side of the tube to make sure the crystals reach the bottom

18
Q

what are the two specific techniques for finding melting point

A
  • using electrically heated apparatus

- using an oil bath or Thiele tube

19
Q

how can we find the melting point of a substance by using electrically heated apparatus

A

1) place capillary tube into sample hole and a 0-300 degree celcius thermometer into the thermometer hole
2) use rapid heating setting, observe the sample through the window
3) record melting point when it is seen to melt
4) repeat process but heat slowly when near to the melting point recorded in the first run
5) record an accurate result

20
Q

what is the method for finding melting point when using an oil bath/Thiele tube

A

1) set up oil bath or Thiele tube
2) attach capillary tube to thermometer using a rubber band
3) attach capillary tube such that the end of the thermometer and tube are just submerged in the water/oil
4) heat oil/water, record melting point
5) repeat to obtain an accurate result

21
Q

what should you do with the purified solid after the filtration stage of recrystallisation

A

rinse with cold water/solvent and leave to dry

22
Q

define reflux

A

the continuous evaporation and condensation of a substance through strong heating such that the most volatile components cannot escape

23
Q

define distillation

A

the evaporation and condensation of a substance when heated such that only the most volatile component escapes/is collected

24
Q

what is the general method for purifying an organic liquid

A

1) pour the distillate of the organic product into a separating funnel
2) wash product by adding
- sodium hydrogencarbonate to remove any unreacted acid, shake and release CO2 from funnel
- add saturated sodium chloride solution to the solution to help separate layers
3) run the organic layer into a clean conical flask and add 3 spatula loads of drying agent e.g. anhydrous sodium sulfate
4) decant liquid into distillation flask and distill to obtain a pure sample

25
Q

what to do after having produced an ester to purify

A

1) rearrange the apparatus to a distillation setup, distill off the crude ester
2) place distillate in a separating funnel and add 30% sodium carbonate solution to react with the conc. H2SO4 catalyst added for esterification
3) add calcium chloride solution to remove unwanted alcohol
4) pour into a clean conical flask and add anhydrous calcium chloride
5) distil again

26
Q

what is the detailed method for nitration/things to remember

A
  • dissolve benzene/ methyl benzoate in conc. H2SO4 at < 10 degrees celcius
  • prepare the nitrating mixture by adding Conc H2SO4 to HNO3 slowly at < 10 degrees celcius
  • mix, keeping the mixture cold
  • recrystallise
27
Q

what is an important thing to remember when naming molecules

A
  • if the numbers are such that they are the same either way round e.g. 3 bromo 2 chlorobutane or 2 bromo 3 chlorobutane
    then the one which comes first takes the lower number

Module 6 Chemistry (6 decks)

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