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- isolate and purify caffeine from tea leaves - characterize the caffeine extracted from tea leaves - calculate the percent yield of caffeine



Highlighted Concepts Genus: Camellia
Species: C. sinensis
Binomial name: Camellia sinensis
- a small shrub about 3 to 6 feet tall - flowers with small white blossoms that have a delightful scent during fall - likes well-drained, sandy soil that is on the acidic side





Highlighted Concepts Types of Tea to be tested Highlighted Concepts Components of Tea Leaves ► Cellulose – the major structural material of all plants ► Caffeine – one of the major water-soluble substances present in tea leaves ► Tannins – high molecular weight, water-soluble compounds that are responsible for the color of tea ► Flavonoid pigments – a naturally occurring water-soluble phenolic compound belonging to a large group that includes many plant ► Chlorophyll – the green pigment in plants that captures the light energy required for photosynthesis Highlighted Concepts Systematic name: 1,3,7-trimethyl-1H- purine-
2,6(3H,7H)-dione Other name: 1,3,7-trimethylxanthine
1,3,7-trimethyl-2,6-dioxopurine Molecular formula: C H N O
Molecular mass: 194.19 g/mol
Melting point: 238°C
Solubility in water: slightly soluble
Highlighted Concepts - increases the blood pressure - stimulates the central nervous system - promotes urine formation - stimulates the action of the heart and lungs Uses: - treats migraine - increases the potency of analgesics - relieves asthma attacks Highlighted Concepts - is an alkaloid belonging to methylxanthine family Structures of common alkaloids Highlighted Concepts - is an alkaloid belonging to methylxanthine family Xanthine and its Derivatives Highlighted Concepts - no solvent used - if imputirties have similar P as sample, separation will be - removes occluded materials - often faster than recrystallization Materials and Apparatus for Isolation of Caffeine • Separatory funnel • Erlenmeyer flask • Suction flask • anhydrous Na SO • Sublimation apparatus Solid- Liquid Extraction Filtrate
For liquid-liquid
extraction

Liquid-Liquid Extraction Lower layer
Lower layer
Lower layer
Upper layer
Upper layer
Upper layer
Upper layer
Upper layer
Hydrated
iPrOAc layer
Evaporate to dryness Crude Caffeine
Caffeine
make sure that the apparatus is properly installed and sealed avoid opening the sublimation tube so as to maintain the pressure inside cold finger should always be "cold" stop when the sample become brown or black be careful in removing the cold finger (crystals formed on the test tube can be easily knocked off) Recrystalization Single solvent recrystallization. • The mixture dissolved in the smallest amount of hot solvent to fully dissolve the • Solution is then allowed to cool. • As the solution cools the solubility of compounds in solution drops. This results in the desired compound dropping (recrystallizing) from solution. • The crystallization process requires an initiation step, such as the addition of a "seed" crystal. Data and Results Caffeine Extraction Worksheet
Tea extract #
Description
Volume of Extract (mL)
Amount of caffeine in Extract (mg/mL) HPLC Sample 1
Total Caffeine in 100 mL sample
Tare weight of rb flask
Final weight of flask + dried caffeine
Crude caffeine isolated (mg)
Yield of Crude Caffeine (%)
(5)/(2)*100
Purity of crude caffeine (%)
HPLC Sample 2
Corrected Yield (%)
Purity of purified caffeine (%)
HPLC Sample 3
Melting point of Crude Sample
Melting point of Purified Sample
Data and Results Caffeine Extraction: Final Report - the method of separating a substance from a mixture by dissolving one or more of the components in a solvent Solvents for extraction: Easily removed Desired constituent is soluble Non-reactive Flow chart of separation of caffeine from tea leaves cellulose
caffeine
chlorophyll
tannins
flavonoids
Extraction with H O (100°C) Extracted leaves Aqueous tea solution caffeine
chlorophyll
tannins
flavonoids
Flow chart of extraction of caffeine from tea leaves caffeine
chlorophyll
tannins
flavonoids
Extraction with ETOAc Aqueous solution caffeine
impurities of tannins caffeine
impurities of tannins Liquid-Liquid Extraction – is used for separation of complex mixtures by selective partitioning between two phases, between two immiscible liquids. AQUEOUS EXTRACT
ETOAc EXTRACT
Hydolyzable tannins Non-hydrolyzable tannins Impurities of chlorophylls Distribution Coefficient - ratio of the concentrations of the solute in each solvent at a particular temperature - it is independent of the total concentration and the actual amounts of the two solvents mixed where C is the concentration of solute in the extracted solvent (organic) C is the concentration of solute in the original solvent (aqueous) Distribution Coefficient x is the amount of solute extracted by the extracting solvent V is the volume of the organic solvent G is the original amount of solute V is the volume of water - used as method for purification if the vapor pressure of the impurities in a solid are significantly lower than that of a solid sample - compounds with high vapor pressure can be sublime at normal atmospheric pressure - compounds that have P ≈ 1 mm Hg at room temperature sublime slowly - can be achieved when pressure is reduced - compounds with nonpolar symmetrical structures that have high m.p. but also high P sublime readily

Source: https://www.students2science.org/files/Caffeine_extraction_Intro_slides.pdf

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