Module 6.2.5 - Organic synthesis

• 3 steps in purifying a solid

  -filtration under reduced pressure

  -recrystallisation

  -measurement of melting points
• Summary of purifying a solid

  -Filter reaction mixture under reduced pressure

  -(recrystallisation) Dissolve impure product in minimum volume of hot solvent

  -Leave to cool and allow crystals to form

  -Filter crystals under reduced pressure again

  -Rinse them with ice

  -cold distilled water

  -Leave them to dry on a dish

  -Decant

  -Record the melting point if you want to identify the product
• Apparatus needed for filtration under pressure

  -Buchner flask

  -Buchner funnel

  -pressure tubing

  -filter paper

  -access to the filter or vacuum pump

  See diagram!

  
• Filtration under reduced pressure steps

  -pour the mixture of solid and liquid into Buchner funnel containing filter paper

  -attach vacuum pump to the side arm of the Buchner flask and switch it on

  -this reduced pressure in the flask forces the liquid through the funnel, leaving the solid on the filter paper

  -rinse beaker with solvent so all solid crystals collect in the Buchner funnel

  
• Recrystallisation method

  -dissolve impure product in minimum amount of hot solvent

  -once solid has dissolved, allow solution to cool

  -crystals will begin to start forming

  -once finished, filter crystals under reduced pressure again
• Preparing a sample to take its melting point

  -take a capillary tube and hold one end to a hot flame of a Bunsen burner

  -this seals the capillary tube and allow it to cool

  -fill the tube with crystals to about 3mm depth
• Using electrically heated melting point apparatus

  -place tube with sample in the sample hole

  -heat up by increasing the temperature and observe through magnifying window

  -once the solid begins to melt, record its melting point

  
• Using an oil bath or Thiele tube method

  -attach capillary tube to thermometer using a rubber band

  -insert the thermometer through a hole in the cork (Thiele tube) or clamp thermometer (oil bath)

  -using a micro-burner, heat the side arm of the Thiele tube or oil bath whilst observing the liquid

  -record the temperature when solid begins to melt

  
• Synthetic routes map of the main functional groups

  
• Reactions of benzene and its derivatives

  
• Reactions of phenol and its derivatives