ANALAB Wk 2

• Organic compounds are isolated either from natural sources or from reaction mixtures
• Organic compounds are seldom pure and are usually contaminated with small amounts of other similar compounds, which are found to exist together or formed during the reaction
• In order to characterize them, it is important to purify them
• Steps involved in the characterization of organic compounds

  • Purification
  • Qualitative Analysis
  • Determination of molecular mass
  • Calculation of empirical formula and molecular formula
  • Elucidation of the structure by various methods including chemical methods
• The common techniques used for the purification of a particular compound are based on its nature and on the nature of the impurities present in it
• Extraction


  A useful technique for separating compounds that have different polarities
• Extraction


  1. Compounds to be separated are treated with a mixture of a polar and non-polar solvent

  2. Technique is also used to extract solutes from a solid
• Purification techniques for organic compounds

  • Filtration
  • Centrifugation
  • Crystallization
  • Solvent extraction
  • Distillation
  • Fractional distillation
  • Sublimation
  • Chromatography
  • Steam distillation

  
• Filtration


  To separate an insoluble solid from a liquid particularly when the solid is suspended throughout the liquid

  
• Suspension


  • Solid/liquid mixture
• Filtration


  1. Liquid containing suspended solid is passed through a filter paper

  2. Small particles of solvent and dissolved solutes pass through as filtrate

  3. Larger insoluble particles are retained on the filter paper as residue

  
• Centrifugation


  Used when there is only a small amount of suspension, or when much faster separation is required
• Centrifugation


  1. Liquid containing undissolved solids is put in a centrifuge tube

  2. Tubes are spun around at a very high rate and thrown outwards

  3. Denser solid is collected as a lump at the bottom of the tube with the clear liquid above

  
• Crystals


  Solids that have a definite regular shape, smooth flat faces and straight edges
• Crystallization


  The process of forming crystals
• Crystallization by cooling a hot concentrated solution

  1. Solution is gently heated to make it more concentrated

  2. Solution is allowed to cool at room conditions

  3. Solubility of most solids increases with temperature, so when cooled the solution cannot hold all the dissolved solutes and they separate out as crystals

  
• Crystallization by evaporating a cold solution at room temperature

  1. As the solvent in a solution evaporates, the remaining solution becomes more concentrated

  2. Eventually the solution becomes saturated and further evaporation causes crystallization to occur

  3. If a solution is allowed to stand at room temperature, evaporation will be slow and it may take days or weeks for crystals to form
• Solvent extraction


  Involves extracting a component from a mixture with a suitable solvent
• Solvent extraction


  1. Water is used to extract salts from a mixture containing salts and sand

  2. Non-aqueous solvents (e.g. 1,1,1-trichloroethane and diethyl ether) can be used to extract organic products

  3. Often involves the use of a separating funnel, where the organic product in an aqueous solution dissolves into the ether layer
• Distillation


  A method used to separate a solvent from a solution containing non-volatile solutes
• Distillation


  1. When a solution is boiled, only the solvent vaporizes and the hot vapour condenses to liquid again on a cold surface

  2. Anti-bumping granules are added to prevent vigorous movement of the liquid called bumping during heating

  
• Fractional distillation


  A method used to separate a mixture of two or more miscible liquids
• Fractional distillation


  1. A fractionating column packed with glass beads is attached vertically between the flask and the condenser

  2. The temperature of the escaping vapour is measured using a thermometer

  3. Fractions with different boiling points can be collected separately
• Sublimation


  The direct change of a solid to vapour on heating, or a vapour to solid on cooling without going through the liquid state
• Sublimation


  A mixture of two compounds is heated in an evaporating dish, one compound changes from solid to vapour directly and the vapour changes back to solid on a cold surface, while the other compound remains in the evaporating dish
• Distillation is among the most important and widely used separation process in industrial operations today, with about 95% of all separation processes carried out using more than 40,000 distillation systems
• Sublimation is used to create freeze-dried substances like tea, soup, and drugs
• Steam distillation is employed in industry for the recovery of various essential oils from plants and flowers
• Crystallization helps to increase physical stability, bioavailability, and sustained release of chemicals