Ex1

• Tea Leaf Composition

  • Cellulose
  • Organic Acids
  • Tannins
  • Alkalois
• Cellulose

  • major component of plant cell wall
  • water insoluble
  • most abundant organic polymer on Earth
• Organic Acids

  • water soluble compounds containing acidic functional groups
• Caffeine is an alkaloid
• Tannins

  • water soluble, high molecular weight polyphenols that are pale yellow to light brown color
  • yield glucose and gallic upon hydrolysis
  • acidic in nature
• Like dissolves like
• Alkaloids

  • group of highly diverse natural products that contain one or more basic nitrogen atoms in a heterocyclic ring or in an aliphatic side chain
  • derived from amino acids
  • biological properties have led to their use as pharmaceuticals, narcotics, stimulants, and poisons
• Properties of Alkaloids

  • slightly soluble in water — salts formed on the reaction with acids are freely soluble
  • most are crystalline solids, some are amorphous (free form)
  • free alkaloids are soluble in ether, chloroform, or other nonpolar organic solvents
  • some are non polar due to lack of oxygen in structure
  • Have high melting points
• Alkaloids' degree of basicity varies greatly, depending on the structure, and presence and location of other functional groups.
• Caffeine

  • major component of tea extract
  • diuretic and cardiac respiratory psychic stimulant
  • the world's most popular psychoactive substance
• Steps in Isolation of Alkaloids from Tea Leaves

  1. Preliminary extraction with water
  2. Addition of sodium carbonate
  3. Extract with dichloromethane
  4. Removal of dichloromethane by evaporation
• Extraction

  • extraction solute from one solvent to another
• Factors affecting Extraction

  • particle size of the sample (smaller the particle size, higher the yield)
  • sample to solvent ratio
  • type of solvent
  • length of extraction period
  • temperature (solubility increases in high temperature)
  • pH
• Solid-Liquid Extraction

  • separation process based on the preferential dissolution of 1 or more of the components solid mixture
  • extract solute (as much as possible), using limited quantity of solvent = concentrated extract
  • Solvent must be able to dissolve solute of interest
• Solid-Liquid Extraction

  Extracting Solvent: Water

  • allows separation of water soluble in water insoluble components of tea
  • involves determining the polarity / solubility of target compound
• Solid-Liquid Extraction

  Involves: Boiling of Mixture

  • Since caffeine is sparingly soluble in hot water from tea leaves
  • Not all caffeine can be extracted
  • increase in temperature, increases solubility of alkaloids in water ensuring maximum yield
• protonated caffeine = caffeine has charge = soluble in aqueous layer
• Solid-Liquid Extraction

  Addition of sodium carbonate Na2CO3

  • keeps caffeine in molecular form
  • keeps solution basic — prevents protonation of caffeine
  • if ever caffeine is protonated due to acidity of tea solution after boiling, the carbonate deprotonates it
  • molecular form is more soluble in organic solvent
• Solid-Liquid Extraction

  Addition of sodium carbonate Na2CO3

  • Deprotonates tannins (or convert tannins into soluble salts) = making it polar = increases solubility of tannins in water = remain in aqueous layer during liquid-liquid extraction
• Liquid-Liquid Extraction

  Extracting solvent: chloroform or dichloromethane

  • alkaloids are preferentially transfers from aqueous layer to organic layer
• Liquid-Liquid Extraction

  • also known as partitioning
  • widely-used classic and simple technique for extraction of liquid samples
  • comprises a step of mixing (contracting), followed by a step of phase separation
  • consists of preferential transfer from one solvent to another; 2 immiscible liquids
  • one of the solvents is water or an aqueous mixture, other is a nonpolar organic solvent
• Liquid-Liquid Extraction

  Transfer of mixture to be extracted in a separatory funnel in addition of extracting solvent

  • results to the formation of layers, wherein the denser the solvent will be at the bottom layer
• Separatory Funnel

  • laboratory glassware used in liquid to liquid extractions
  • to separate the components of a mixture into 2 immiscible solvent phases of different densities
• Liquid-Liquid Extraction

  Shaking of separatory funnel

  • alkaloids are preferentially transferred from aqueous to organic layer
  • vigorous mixing is favorable to the transfer of the extractable solute from one solvent to other
  • may also impair the ease of phase separation = forming emulsions
• Emulsion

  • dispersion of slightly miscible liquids
  • due to rapid / vigorous shaking or extracting the mixture is hot
  • has intermediate solubility = difficult to collect
  • can be prevented by gentle swirling
  • can be disrupted by:
  • breaking using stirring rod
  • addition of salt of brine solution = increases ionic strength of the aqueous layer and facilitates separation of 2 phases (salting out) = lowering solubility of organic compound in water
• Liquid-Liquid Extraction

  Pressure buildup

  • occurs due to a portion of the solvent evaporates when separatory funnel is shaken
  • heat of hand contributes to pressure buildup
  • opening the stopcock from time to time would prevent pressure buildup
• Liquid-Liquid Extraction

  Testing Organic and Aqueous Layer

  • Water test
  • immiscible: organic layer
  • miscible: aqueous layer
• Liquid-Liquid Extraction

  Drying of Organic Extract

  • removes excess water through addition of drying agent (ex. sodium sulfate Na2SO4)
• Drying Agent

  • also known as dessicant
  • hygroscopic substance that induces or sustains a state of dryness in its vicinity by removing traces of water from organic solution
• Factors Governing Choice of Drying Agents

  1. possibility of reaction with substance being extracted
  2. speed of drying agent removes water from the solvent
  3. efficiency of the process
  4. ease of recovery from drying agent
• Sodium sulfate

  • widely used drying agent
  • removes water from most solvents
  • cannot be used with hot solutions
• Magnesium Sulfate

  • dries solution more completely than Na2SO4
  • sometimes causes rearrangement of epoxides
• Calcium chloride

  • incompatible with oxygen and nitrogen containing compounds
  • useful in removing traces of methanol and ethanol
• Separatory funnel minimizes contamination of 2 layers, lower layer should always be drained from the bottom and upper layer is poured out from the top of the funnel.
• Summary of Exercise 1 Experiment

  
• Distribution coefficient

  • specific at given temperature
  • always greater than 1
  • stepwise extraction increases efficiency

  
• Extraction Efficiency - The percentage of the original amount of a substance that is actually extracted from the solvent
• The higher the amount of solute extracted, the more efficient (or higher extraction efficiency) is the extraction.
• A multi-step extraction method is always more efficient than a single-step extraction method.
• When a large batch of solvent is used to extract a solute, only around 30 % of the product will be extracted and 70 % of the extract will remain in the original sample.