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• Caffeine

  • A member of the class of compounds called alkaloids
  • Systematic name: 1,3,7-trimethyxanthine
  • Molecular formula: C8H10N4O2
  • Constructed from the purine ring system, one of the nucleic acid components
  • Found in common beverages like tea, coffee, and soft drinks
  • Naturally found in various plants like tea beans, tea leaves, cacao (chocolate), guarana berries
  • Acts as a natural pesticide, deterring insects from its bitter taste
  • A white crystalline powder with a bitter taste
• Alkaloids


  Nitrogen-containing compounds in plants that usually taste bitter and are often physiologically active
• Composition of tea leaves

  • Cellulose
  • Organic acid
  • Caffeine
• Cellulose

  A major component of plant cell walls, water-insoluble
• Organic acids


  • Water soluble
  • Tannins yield gallic acid and glucose upon hydrolysis, acidic in nature
  • When exposed to water and heat, they break down into simpler compounds - glucose (a type of sugar) and gallic acid (an organic acid)
• Caffeine


  • Water soluble, due to the positive charge on the Nitrogen atom and its ability to easily form hydrogen bonds with water molecules
  • Tea leaves contain about 5% by weight of caffeine
  • An alkaloid, a naturally occurring base
  • A diuretic, cardiac, respiratory, and psychic stimulant
• Extraction

  1. Separating an organic compound from a mixture of compounds by selectively dissolving one or more of the mixture of compounds into a suitable solvent

  2. Basis is the difference in solubility
• Solid-liquid extraction

  1. Allows the separation of caffeine into water-insoluble components of tea leaves

  2. Extraction solvent is boiling dH2O (distilled water) as caffeine is highly soluble in boiling water
• Boiling the mixture

  Increases the solubility of caffeine, ensuring maximum yield
• Addition of Na2CO3

  Creates an alkaline or basic atmosphere, converting tannins and gallic acids into their CH2Cl2 (dichloromethane) insoluble salts
• Addition of salt

  Increases the polarity of the aqueous layer, 'salting out' the caffeine from the water solution and forcing it into the organic layer
• Liquid-liquid extraction

  Extraction solvent is dichloromethane, as it has a high affinity for caffeine and is immiscible with water
• Shaking


  Hastens the transfer of organic soluble compounds into the organic layer
• Distribution coefficient (Kd)


  Governs the amount of caffeine transferred, calculated as the ratio of caffeine solubility in organic layer to aqueous layer at a given temperature
• Solubility of caffeine: 1.0 g caffeine/ 46.0 mL water, 1.0 g caffeine/ 5.5 DCM, Kd at 25°C = 8.36
• Two-step extraction was done to increase efficiency
• Emulsion

  Dispersion of slightly miscible liquids, may be due to vigorous shaking or extraction while the mixture is still hot
• Handling emulsion

  Breaking using a stirring rod or by salting-out (addition of salt to lower the solubility of the organic compound in water)
• Pressure build-up

  Due to heat of the hand contributing to the volatility of CH2Cl2
• Releasing pressure build-up

  Venting or by opening the stopcock carefully
• Testing organic and aqueous layers

  Performing a water test - if immiscible, it is the organic layer, if miscible, it is the aqueous layer
• Factors governing choice of drying agent

  • Possible reaction with the substance, speed of water removal, efficiency, ease of recovery
• Simple distillation

  Takes advantage of the wide difference in the volatility of caffeine and dichloromethane
• Points to remember in simple distillation:
• Addition of Na2SO4

  Removes traces of water before distillation
• Recrystallization

  A purification technique that takes advantage of the effect of temperature on solubility and the tendency of crystals to form a definite lattice
• Melting point

  • The temperature at which the solid and liquid phases of a substance are in equilibrium or coexist
  • Used to establish a pure substance's identity and serve as an index of purity
• Hot gravity filtration

  Filtration by the activity of gravity alone, used for relatively quick filtration of hot samples
• Suction filtration

  Filtration with the use of a vacuum, used for fast filtration of mixtures that are not hot
• Using minimum solvent in recrystallization

  Ensures possible maximum yield of crystals, as larger solvent amounts make the solution unsaturated where recrystallization is difficult
• Advantages of hot-gravity filtration

  • Avoids premature recrystallization, aids quick filtration, use of stemless funnel and fluted filter paper
• Advantages of suction filtration

  • Useful for non-hot samples, allows optimum removal of large amounts of solvent, but can cause rapid cooling and premature recrystallization
• Important points in proper washing of crystals:
• Techniques in melting point determination:
• Causes of errors in melting point determination:
• ut is not hot and optimum removal of a large amount of solvent from the recrystallized is desired
• But if this is used instead of hot-gravity filtration, rapid cooling will occur since cold-air is allowed in as vacuum is created. This results to premature recrystallization
• Important points to remember in proper washing of crystals

  • When the crystals are not washed with cold water, adsorbed impurities will not be removed, therefore high recovery but low purity
  • When the crystals are washed with hot solvent, the desired product will redissolve, therefore low recovery but no effect on purity
• Pulverization of the sample was done on watch glass but not directly on filter paper as filter paper contains "lints" which may be incorporate as impurities with the purified sample
• Causes of Errors in MP Determination

  • Rapid heating - higher melting point than literature value
  • Presence of impurities
  • Loose, uneven packing of crystals - widens MP