organic synthesis

• In a distillation setup, why is it necessary to have a continuous water flow around the condenser?

  so that the water remains cool in order for the mixture to be distilled
• What is the method that can be used to separate immiscible liquids?

  1 pour the mixture into a separating funnel and some distilled water

  2) add the stopper and invert the flask to mix the mixture

  3) equalise the pressure by opening the stopper as required

  4) continue shaking until there is no ‘whistle’ sound

  5) to collect the water in the lower layer, open the stopper and place a beaker under the spout

  6) use another beaker to collect the desired organic layer

  7) shake the liquid with some drying agent
• What are 2 drying agents?

  magnesium sulfate

  calcium chloride
• How do you use drying agents?

  1 add a selected drying agent to the organic product

  if the drying agent forms clumps add some more until they are moving freely

  use gravity filtration to collect the dry product

  filtrate is the product
• What is re-distillation?

  when a liquid i purified by using multiple distillations
• How can unsaturated hydrocarbon be tested, what are the observations?

  use bromine water

  add few drops of bromine water to the sample and mix well

  positive test- bromine water turns colourless
• What are the reagent used to test haloalkanes and what are the observations?

  reagents: silver nitrate, ethanol and water

  observations: chloro- white precipitate,

  bromo- cream precipitate, iodo- yellow precipitate
• What are the observations when acidified potassium dichromate reacts with ketones and aldehydes?

  aldehydes: turns from orange to green colour ketones: no change
• What are the reagents that can be used to test carboxylic acid, what are the corresponding observations?

  universal indicator - PH of weak acid

  reactive metal- hydrogen effervescence

  metal carbonate- carbon dioxide effervescence
• explain how you could obtain pure hex-1-ene from the mixture obtained after reflux?

  1 use of a separating funnel to separate organic and aqueous layers - collection of upper layer (which is less dense) from the separating funnel

  2) dry with anhydrous salt e.g cacl2 or mgso4

  3) distillation
• what are 2 drying agents?

  magnesium sulphate

  calcium chloride
• How do you use drying agents?


  add a selected drying agent to the organic product

  if the drying agent forms clumps add some more until they are moving freely

  use gravity filtration to collect the dry product
• What are the reagents used to test haloalkanes?

  reagents: silver nitrate, ethanol and water
• What is re-distillation?

  Re-distillation is the process of distilling a liquid multiple times to purify it
• What are the 3 reagents that can be used to test carbonyls?

  acidified potassium dichromate

  fehling's solution

  tollens' reagent
• What are the observations when acidified potassium dichromate reacts with aldehydes and ketones?

  ketones: remains orange/no change

  aldehydes: turns from orange to green
• What are the observations when Tollens' reagent is reacted with ketones and aldehydes?

  ketones: no silver mirror

  aldehydes: silver mirror
• What are the reagents that can be used to test carboxylic acids, what are the corresponding observations?

  universal indicator: PH of weak acid

  reactive metal: hydrogen effervescence

  metal carbonate: carbon dioxide effervescence
• when is a reflux apparatus used?

  to continually heat the contents of the flask to allow reactions such as the oxidation of primary alcohols to proceed all the way to the formation of carboxylic acids
• What is the condenser for in reflux?


  the condenser helps ensure that the vapours condense and return to the flask of further heating

  this ensures the product vapours can't escape
• When is a distillation apparatus used?

  to separate liquids with different boiling points
• Distillation:

  • the round-bottomed flask is heated and the liquid with the lower boiling point will evaporate first
  • it rises out of the flask and into the attached tubing which is surrounded by a condenser
  • the condenser causes the vapour to cool and condense back into a liquid, which is then collected in a separate flask
• When is a separating funnel used?

  to separate two liquids with different densities

  the mixture is added to the flask, and then you put a stop in the flask and invert several times to mix the contents

  wait for the liquids to separate into 2 layers

  then open the tap to collect the bottom, denser layer in one flask, then the less dense layer in a second flask

  usually these layers will be distinguished to be an aqueous and organic layer
• what is redistillation?

  when subsequent distillations are carried out to obtain a purer product
• boiling point determination:

  the purer the substance, the closer to the databook boiling point value it will be

  if a sample has a low purity, the melting/boiling point will occur over a range of temperatures

  to determine the BP the substance is packed into a thiele tube which has an inverted capillary tube in it

  the substance is heated to above its boiling point and allowed to cool

  when it condenses into a liquid it will be drawn into the capillary tube and the temperature at which this change occurs is taken to be the boiling point
• How can a compound be dried?

  by the addition of an anhydrous salt

  the anhydrous salt will absorb moisture and water present, thus drying and purifying the compound
• What are common anhydrous salts used for drying?

  magnesium sulphate

  calcium chloride
• What are synthetic routes?

  the routes which can be used to produce a certain product from a starting organic compound