16 - Organic synthesis

• label the diagram

  A) condenser

  B) water out

  C) water in

  D) anti-bumping granules

  E) reaction mixture

  F) heat

  G) reflux

  
• reflux - a technique of boiling volatile reactants over a prolonged period :

  • uses a vertical condenser
  • prevents loss of reactant and products as gaseous vapours
  • any vapour formed is condensed back into a liquid and returned to the pear-shaped flask
  • anti-bumping granules prevent the mixture from rising out of the flask
• label this diagram

  A) thermometer

  B) water out

  C) water in

  D) condenser

  E) pure liquid

  F) distillate

  G) pear-shaped flask

  H) impure liquid

  I) anti-bumping granules

  J) heat

  K) distillation

  
• distillation - separation of a mixture of miscible liquids:

  • each component has a unique boiling point
  • the bulb of the thermometer must be positioned in line with the condenser to ensure an accurate reading of the boiling point of each liquid as it is collected
  • the water supply must come from the bottom of the condenser to make sure that an effective cooling system is maintained
  • anti-bumping granules are required to prevent the mixture from boiling over without separating
• redistillation - organic compounds that have relatively close boiling points can be separated

  • second distillation is carried out
  • the narrower the boiling point range, the purer the product
• label this diagram

  A) stopper

  B) separating funnel

  C) upper layer

  D) less dense

  E) lower layer

  F) more dense

  
• separating funnel - purifies an organic product after it has been synthesised

  • the organic product will form a separate layer from any aqueous liquids (the denser will be lower)
  • allow the layers to settle and then run off the lower layer – discard the aqueous layer
  • to neutralise any acidic impurities, sodium carbonate solution is added
  • allow the new layers to separate and discard the unwanted aqueous layer. (For alkaline impurities add a dilute acid)
  • wash the organic layer by adding distilled water. remove the aqueous layer
  • the product must be dried to remove any last traces of water
• common drying agents:

  1. anhydrous calcium chloride - drying hydrocarbons
  2. anhydrous calcium sulfate - general drying
  3. anhydrous magnesium sulfate - general drying
• drying agents:

  • add drying agent to the organic liquid using a spatula
  • place a stopper on the flask to prevent evaporation of the product
  • if clumps form, keep adding drying agent until powder forms
  • or until the liquid is clear
  • decant the liquid into a specimen tube
• label the diagram

  A) dihaloalkane

  B) poly(alkene)

  C) alkene

  D) alkane

  E) alcohol

  F) haloalkane

  G) ketone

  H) aldehyde

  I) carboxylic acid

  
• label the diagram

  A) hydrogen halide

  B) halogen

  C) UV

  D) H2

  E) Ni catalyst

  F) reflux

  G) NaOH (aq)

  H) sodium halide

  I) H2SO4

  J) reflux

  K) cH2SO4

  L) cH3PO4

  M) reflux

  N) steam

  O) H3PO4 catalyst

  P) K2Cr2O7

  Q) H2SO4

  R) reflux

  S) distil

  T) reflux

  
• label the diagram

  A) haloalkane

  B) alkane

  C) alkene

  D) alcohol

  E) primary

  F) secondary

  G) carboxylic acid

  H) aldehyde

  I) ketone

  
• alkene -> alkane

  • + H2
  • Ni catalyst
• alkane -> haloalkane

  • + halogen
  • UV light
• alkene -> haloalkane

  • + hydrogen halide
• haloalkane -> alcohol

  • + NaOH (aq)
  • reflux
• alcohol -> haloalkane

  • + sodium halide
  • + H2SO4
  • reflux
• alkene -> alcohol

  • + steam (H2O (g))
  • H3PO4 catalyst
• alcohol -> alkene

  • + concentrated H2SO4 or H3PO4
  • reflux
• primary alcohol -> carboxylic acid

  • + 2(O)
  • + K2Cr2O7/H2SO4
  • reflux
• primary alcohol -> aldehyde

  • + (O)
  • + K2Cr2O7/H2SO4
  • distil
• secondary alcohol -> ketone

  • + (O)
  • + K2Cr2O7/H2SO4
  • reflux
• target molecule - the compound that the chemist is attempting to synthesise
• two-stage synthesis steps

  1. identify the functional groups in starting and target molecules
  2. identify the intermediate that links the starting and target molecules
  3. state the reagents and conditions for each step
• haloalkane -> ? -> aldehyde

  
  

  intermediate = primary alcohol

  1. haloalkane + NaOH (reflux) -> primary alcohol + (NaCl)
  2. primary alcohol + (O) + K2Cr2O7/H2SO4 (distil) -> aldehyde + (H2O)

  1 = hydrolysis

  2 = oxidation
• complete the table

  A) alkene

  B) alcohol

  C) haloalkane

  D) aldehyde

  E) ketone

  F) carboxylic acid