Acid-Base Extraction Lab Procedure PDF

Acid-Base Extraction CHEM 215 Organic Chemistry Laboratory I Fall 2024-2025 Chemistry Department  What will you learn? Theory of extraction Choosing the extraction solvent Acid-Base extraction Separatory funnel Drying agents Procedure flow-c...

Acid-Base Extraction CHEM 215 Organic Chemistry Laboratory I Fall 2024-2025 Chemistry Department  What will you learn? Theory of extraction Choosing the extraction solvent Acid-Base extraction Separatory funnel Drying agents Procedure flow-chart in acid-base extraction  Extraction Method of separation To extract: To get what you want out of a mixture Types: Liquid-Liquid extraction Solid-Liquid extraction  Organic and Aqueous phases Two phases must be insoluble in each other – Organic phase (organic compounds are dissolved) – Aqueous phase (water soluble compounds are dissolved) Phases are positioned wrt their densities! Denser liquid is always the bottom phase Phases in the separatory funnel How to choose the extraction solvent? Must be immiscible with the first solvent in which you have the solute Must dissolve the solute better The solute will distribute itself according to the partition coefficient K for these two solvents Must not react with the solute Should be easy to evaporate  Acid-Base extraction Today you will learn a particular case to separate organic acidic or basic compounds from a mixture. Your mixture will contain one of these: 1. Organic acid and a neutral compound (RCOOH and RH) OR 2. Organic base and a neutral compound (RNH2 and RH) All components are soluble in ether. How can one separate this mixture? Reactions to make organic compounds water soluble RCOOH + NaOH RCOO- Na+ + H2O Water Water soluble insoluble, dissolved in ether RNH2 + HCl RNH3+Cl- Water Water soluble insoluble, dissolved in ether No rxn with NaOH or RH HCl, thus never becomes Water water soluble, remains insoluble, in organic phase dissolved in ether Dissolve the solid mixture (RCOOH or RNH2) +RH in ether NaOH aq. Aqueous phase Organic phase RCOO- Na + RNH2, RH HCl aq. HCl aq. Aqueous phase Organic phase RCOOH RNH3+ Cl- RH ppt Drying agent filter Evaporate NaOH aq. solvent RNH2 ppt filter How to use the separatory funnel? The valve (stopcock) should be lubricated and closed Always put a beaker under the funnel Never more than ¾ full! Use an iron ring to hang the funnel Shake gently, invert and depressurize Remove the stopper Collect the bottom layer Let the remaining layer out from top into another flask Never throw away layers until the experiment is completely finished Careful with pressure building-up! Pressure build-up in the funnel is due to high vapor pressure of some solvents or due to a gas like CO2 evolved from a reaction during the mixing. How to use the separatory funnel? Types of separatory funnel  Drying agents Each time you do extractions with water there will be residual water in your organic phase You must dry your product with a drying agent Drying agents are anhydrous salts that combine with water When all water is tied up you decant or filter the mixture leaving the drying agent behind  Examples to drying agents anhydrous CaCl2; anhyd. MgSO4; anhyd. Na2SO4...and others How to employ?  Procedure Take an unknown mixture (1.5 g) from your assistant – Acidic (0.5 g) and neutral (1 g) – Basic (0.5 g) and neutral (1 g) – Give your unknown number on the lab report! Dissolve in ether (ROR) (diethyl ether or tert-butyl methyl ether) Follow the below given flow chart (and your lab manual) to separate compounds Collect components separately Identify them with the help of melting points Dissolve the solid mixture (RCOOH or RNH2) +RH in ether NaOH aq. Aqueous phase Organic phase RCOO- Na + RNH2, RH HCl aq. HCl aq. Aqueous phase Organic phase RCOOH RNH3+ Cl- RH ppt Drying agent filter Evaporate NaOH aq. solvent RNH2 ppt filter  Identification of the unknown Components of the unknown can be determined by measuring their mp’s and matching with the below given values: Possible unknowns Melting range(oC) Benzoic acid 121-122 Salicylic acid 159-160 3-nitroaniline 114-115 4-nitroaniline 146-149 1-chloro-3-nitrobenzene 41-45 1-chloro-4-nitrobenzene 81-84 Isolation of caffeine from tea and Sublimation CHEM215 Organic Chemistry laboratory I Fall 2024-2025 Chemistry Department  Parts of the experiment Take caffeine from tea leaves into hot water (solid-liquid extraction) (water solubility of caffeine is 670mg/mL at 100 oC; 2.2 mg/mL at 25 oC) To take caffeine from water into an organic solvent (dichloromethane (DCM) is our extraction solvent) (liquid-liquid extraction) Remove the solvent to obtain impure caffeine Purify caffeine by sublimation Characterize caffeine (melting point, IR, NMR)  What will we learn? Structure and properties of caffeine Liquid-liquid extraction? – Properties of an extraction solvent: must be immiscible with the first solvent, must dissolve the solute better, must not react with the solute, should be easy to evaporate Partition coefficient ( K ) What else is present in tea? Separation flow-chart Sublimation as a purification method Characterization by: – Melting point (compare to literature value) – Spectroscopic methods (IR, NMR) Chemical properties -alkaloid (-ine) ex. nicotine, cocaine, morphine, quinine... -basic -bitter taste -analgesic -stimulant Liquid-liquid extraction How to choose the extraction solvent? Must be immiscible with the first solvent in which you have the solute Easily dissolve the solute The solute will distribute itself according to the partition coefficient K for these two solvents Should not react with the solute Should be easy to evaporate  Partition Coefficient A solute, A, in a liquid-liquid extraction, is partitioned between to solvents depending on its relative solubilities in these two solvents. K= (C1/C2)eq Concentration of A in the organic phase (C1) Concentration of A in the aqueous phase (C2) Kow serves as a measure of the relationship between lipophilicity (fat solubility) and hydrophilicity (water solubility) of a substance. The value is greater than one if a substance is more soluble in fat-like solvents such as octanol, and less than one if it is more soluble in water.  What else is present in tea? Tannic acids (polyphenols) Saponins (form emulsions easily!) Chlorophyll Other minor quantities of organics (cellulose, glucose, proteins...) + CAFFEINE!  Separation flow-chart Tea leaves Caffeine, tannic acids, saponins, chlorophyll, other organics hot water+Na2CO3 Caffeine, SALTS of tannic acids, organics, chlorophyll CH2Cl2 (extraction solvent) AQUEOUS ORGANIC (CH2Cl2) SALTS of tannic acids (ionic) Caffeine Na2CO3 Chlorophyll Organics remove solvent Saponins Caffeine + Chlorophyll  Procedure Dissolve 10 g Na2CO3 in 100 mL water and heat to boiling. Add 3 tea bags and infuse for 7 minutes. Prepare another 50 mL boiling water. Take the tea bags out of Na2CO3 solution, squeeze and infuse them in this 50 mL of hot water for 5 minutes. Combine the two aqueous solutions and cool. Extract with 20 mL portions of CH2Cl2 three times. Be careful not to shake vigoreously to avoid emulsions!  Procedure continued Combine CH2Cl2 solutions and dry over anhydrous CaCl2 (or Na2SO4 ) Evaporate the solvent on the steam bath (Crude caffeine will crystallize out of the solution) Record the weight of your crude caffeine Sublime crude caffeine for purification (Demo) Record the melting point of purified caffeine  Solutions are combined and cooled in ice bath, because Na2CO3 solution is too hot to do the extraction with DCM. Na2CO3 solution Water Sodium Sulfate Extracted caffeine: 64 mg Phase diagram Sublimation of caffeine Solid Gas (sublimation) Gas Solid (deposition) Sublimed caffeine Water outlet Water inlet Connected to Vacuum Cold Finger Caffeine Cold Finger Deposited Caffeine Deposited Caffeine  Synthesis of Soap CHEM215 Organic Chemistry Laboratory I Fall 2024-2025 Chemistry Department  Esterification reaction Carboxylic acids and alcohols react to produce esters and water This is known as esterification and is reversible The reaction can be forced in either direction by appropriate choice of conditions  Esterification and Hydrolysis Forward reaction is esterification Reverse reaction is hydrolysis  Ester + water---Carboxy. acid + Alcohol In alkaline medium base promoted hydrolysis gives the salt of the carboxylic acid When the ester used is a triglyceride (ester of glycerol and fatty acids) the forming salt will be SOAP and the reaction is called SAPONIFICATION 3NaOH(aq) Triglyceride -------------------------------Soap + Glycerol , Hydrolysis Saponification (Soap making) Reaction  Structure of a triglyceride Found in fats and oils, R groups are long chain hydrocarbons (18-22) Carbons Glycerol (1,2,3-propanetriol) FATS OILS  Mixture of  Mixture of triglycerides triglycerides  Solid at room  Liquid at room temperature temperature  Saturated  Unsaturated hydrocarbon tail hydrocarbon  Animal origin tail  Vegetable origin Cleansing power of soap  Procedure Dissolve NaOH in 1:1 EtOH:H2O Reflux triglyceride and aq. NaOH for 30 minutes Prepare a saturated NaCl solution Precipitate the formed soap by salting out Add colorings/perfumes Filter and rinse with cold water Shape and dry  Salting out RCOO-Na+(s) RCOO- (aq) + Na+ (aq) Saturated salt solution is prepared And the contents of the reaction flask poured into the sat. salt sol’nsoap ppts Colorings and perfumes can be added Give a shape to your soap and let dry  Chromatography CHEM215 Organic Chemistry laboratory I Fall 2024-2025 Chemistry Department  Chromatography Chroma: Color Graphy: Writing Used to separate and purify compounds Selective distribution of chemicals (solute) between a stationary and a mobile phase Depends on a physical process like: – Adsorption – Solubility – Charge – Size (GPC same as SEC) – Specific binding etc...  Introduction Principles of Chromatography Terminology Types of Chromatography – Liquid Chromatography (mobile phase is liquid) – Gas Chromatography (mobile phase is gas) Examples today: – Column Chromatography – Thin Layer Chromatography (TLC)  Adsorption Taking onto its surface (like absorbtion: taking into the bulk) The reason for adsorption is some intermolecular forces between the adsorbent and the chemical components. These forces can be: Hydrogen bonding, electrostatic attractions, van der Waals forces etc... Separation works by differences in polarity  Phases in Chromatography Stationary phase is the adsorbent Mobile phase is the solvent (eluent)  Adsorbent and Eluent The choice of the eluent and the adsorbent is of utmost importance! Adsorbent: A porous material that can hold liquids and solutions. Examples are silica gel (SiO2), alumina (Al2O3), cellulose... Eluent: The solvent that carries the components. And must be of appropriate polarity. In normal phase chromatography polarity of the adsorbent is higher than the polarity of the eluent. Our eluent in this experiment is: Isopropanol:Water (3:1 by volume)  Roles of adsorbent and eluent The adsorbent is trying to interact and hold the components whereas the mobile phase tries to move them. There is a competition between them and this leads to separation. Chemical structure of silica gel  Types of chromatography Liquid chromatography Mobile phase is liquid – Column chromatography – Thin layer chromatography – Paper chromatography Gas chromatography Mobile phase is gas Column chromatography Preparation and running of the column You need a flow of the solvent through the column. Two substances travelling down the adsorbent are held differently and leave the column at different times, which is separation. Sand is added to the top of the column so that when you pour solvent into the column it only disturbs the sand layer and leaves the silica gel layer intact avoiding bumpy points and thus, enables correct results. Eluent must be given from the top continiously during the separation. When you pour solvent into the column, it only disturbs the sand layer, and leaves the silica gel intact. For best results, you want your silica gel to be level, and not “bumpy”. Column chromatography  Thin Layer Chromatography (TLC) The adsorbent is spread as a thin layer on a solid support like aluminum, glass or plastic. The mobile phase moves through the stationary phase by capillary action and carries the components of the mixture at different speeds again depending on their relative strength of interaction with the adsorbent. Retention factor Rf value (retention factor) remains constant under an established set of conditions like adsorbent, solvent, thickness of adsorbent, amount of material spotted etc...  Uses of TLC Separate and purify compounds Determine the number of components in a mixture Determine the identity of substances Monitor progress of a reaction Check the effectiveness of a purification Monitor column chromatography Simple and Fractional Distillation CHEM 215 Organic Chemistry Laboratory I Fall 2024-2025 Chemistry Department  Uses of distillation Method of separation for miscible liquids Method of purification Method of boiling point (bp) determination  Experiment outline 1-Determine the bp of dichloromethane (DCM: CH2Cl2) by simple distillation 2-Determine the bp of isopropanol (IPA: CH3CHOHCH3) by capillary tube method 3- Separate DCM and IPA by fractional distillation Collect data for distillations (mL vs T) and plot (Lab manual page 56-57)  Boiling point The temperature at which the vapor pressure above the liquid equals external pressure Bp is a characteristic property of a liquid at constant pressure and varies with external pressure Vapor pressure depends on temperature (T). Increasing T increases the kinetic energy of the molecules and they escape from liquid into the vapor phase by overcoming intermolecular attractive forces  Types of distillation  Simple distillation-for liqs containing nonvolatile impurities or for 2 liqs with far apart bp’s (>25 oC)  Fractional distillation-for liquid mixtures that may have close bp’s  Vacuum distillation-for high bp liqs: as vacuum decreases ext. pressure the liq. boils at a lower T, thus possible decompositions, oxidation and degradations are avoided  Steam distillation-for high bp liqs: the vapor pressure above the liq. is increased with the help of hot water vapors and therefore the external pressure is reached earlier at a lower T. Bp determination of DCM (CH2Cl2) by simple distillation Simple distillation set-up (Lab manual page 44) Distillate (condensate): What is collected Residue: What is left behind  Data table for DCM mL distillate 0 5 10 15 20 25 T (°C) 39 39 39.5 39... Data is obtained by recording the temp. every 5 mL (Lab Manual page: 56, Question1) Use a graduated cylinder as receiving flask The 0 mL point is when the first drop comes to receiving flask  Hints for a distillation setup The bulb of the thermometer should be in the stream of vapor. The bp is difficult to measure in the liquid because of superheating of the liquid. Therefore the temperature of the vapor that is in equilibrium with the liquid is measured. Circulating air in the lab may drop the temp. Wrapping the setup will be helpful A boiling chip is added to avoid bumping of the solution Distill slowly! About 1 drop every 1-2 seconds Determination of the boiling point of IPA by capillary tube method Heat until a steady stream of bubbles come out of the capillary tube. Then remove heat, as the contents of the test tube cools, the liquid begins to flow into the capillary tube. Record the temperature as the boling point of the sample Record the temperature when the liquid begins to flow into the capillary tube Bp determination by capillary tube method Procedure Place a few milliliters of a liquid in a test tube Into the test tube, place a capillary tube closed end upward Attach a thermometer next to the test tube Insert the assembly into a water bath and begin to heat There is always vapor in equilibrium with a heated liquid As the liquid approaches its bp, a few bubbles will be observed out of the capillary tube When the temperature reaches the bp, the vapor pressure inside the capillary tube equals atm. pressure As the temperature rises just above the bp, a steady stream of bubbles are observed Allow the contents to cool (its v.p. decreases) As contents cool observe the capillary tube carefully, when the the liquid flows into the capillary tube record the temperature  Fractional distillation ptot = pA + pB Dalton’s Law pA= pA0 xA Raoult’s Law xA + x B = 1 (mole fractions sum up to 1) The mixture boils when: ptot = p ext  Boiling point-composition diagram Toluene bp 110 oC; Cyclohexane bp 82 oC Fractionating columns Fractional Distillation set-up (Lab Manual page 55) 3-Separate DCM and IPA by fractional distillation Collecting data in fractional distillation (Lab Manual page: 57, Question3) What do we expect? What if we separated the same mixture by simple distillation? Boiling point-structure correlations The bp increases as the molecular weight increases (for similar molecules only!!) Bp decreases with chain branching (more compact molecules have less surface area for contact and lower bp) Bp increases with increasing polarity (dipole- dipole interactions) Bp increases with Hydrogen bonding  Procedure outline 1) Measure the bp of DCM (30 mL) by simple distillation 2) Measure the bp of IPA by capillary tube method 3) Separate a mixture of DCM and IPA (25 mL each) by fractional distillation  How to use data in the report Show the data for the two distillations (Simple and fractional) Plot the data for simple and fractional distillations Analyze the plots Report the bp of IPA  Recrystallization CHEM 215 Organic Chemistry Laboratory I Fall 2024-2025 Chemistry Department  What will you learn? How recrystallization works? New methods: Refluxing, Vacuum filtration Melting point measurement to confirm purification  How recrystallization works? Purification method for organic material that is SOLID at room temperature (RT)  Impure sample  Dissolve (in HOT solvent)  HOT filter  Cool and crystallize  COLD filter  Choice of solvent The solvent of recrystallization MUST dissolve the sample to be purified when HOT; and must NOT dissolve when COLD. Two types of impurities could exist in the sample: SOLUBLE impurities and INSOLUBLE impurities One can take the sample into the solution and remove INSOLUBLE impurities And then cool and crystallize the sample and remove SOLUBLE impurities The solvent should not react with the sample!  How impurities are left out? Foreign molecules cannot fit into the crystal structure of another compound (the sample being purified) Also the solution will not be saturated enough with impurities so impurities cannot come together and precipitate  Acetanilide White Crystalline mp 113-114 oC  Impure sample contains soluble and insoluble impurities  Water is chosen as the recrystallization solvent  Water solubility The solubility of acetanilide in hot water is 5.5 g/100 mL at 100 °C and its solubility in cold water is 0.53 g/100 mL at 0 °C.  Dissolve the sample under Refluxing Continious vaporization and condensation process at the boiling point of the solvent The vaporizing liquid touches the cold surface of the condenser and drops back to the reaction flask Solvent cannot evaporate away Useful for long term reactions without solvent loss at constant temperature Reflux set-up  Boiling chips A boiling chip (boiling stone) is a porous piece of tiny material added to liquids to make them boil more smoothly. Boiling chips are frequently employed when heating to avoid superheated points and bumping of the liquid. They work by providing nucleation sites so the liquid boils smoothly without bumping. In contrast to smooth glass surface boiling chips have pores filled with air, which expands upon heating to form bubbles on which homogeneous boiling can take place. A boiling chip cannot be reused,because its capillaries (pores) are filled with liquid upon cooling and the chip would be ineffective.  Greasing joints Joints should be greased with a tiny piece of grease, commonly vaseline, to seal better and to enable easy detachment of the set-up.  Decolorization Used material is: decolorizing carbon, activated charcoal, brand name: Norit  Decolorizing the sample Ultrafinely divided carbon with a large surface area to adsorb big colored molecules If high molecular weight colored impurities are present in the sample to be purified, these are primarily adsorbed onto the large surface of decolorizing carbon. Colored organic compounds are usually big molecules due to conjugation of double bonds  Steps of recrystallization Dissolve by heating Decolorize Vacuum filter (Hot filtration) Crystallize (by cooling) Cold filter (Cold filtration) Rinse (with cold solvent) Dry to measure weight and the melting point  Vacuum filtration Method of RAPID filtration because vacuum increases the filtration rate (compared to gravity filtration) Equipment needed: – Büchner funnel – Suction flask – Filter paper – Rubber hose – Vacuum source  Why rapid filtration is essential? Our sample is in solution and we want it to remain in solution. If we spend a long time for filtration, the sample will start to crystallize as the solution cools! Yield would decrease. During hot filtration insoluble impurities are removed as they never went into the solution.  Cool to crystallize and then filter Why does crystallization occur upon cooling? What is on the filter paper? What is in the filtrate? Why should one take the contents into a large opening flask (like a beaker) while cooling? Is vacuum filtration a must to collect crystals?  Procedure Dissolve acetanilide (use 3 g of acetanilide in 60 mL of water) Decolorize Hot filter Cool and crystallize Cold filter Rinse crystals with cold solvent Dry  Melting point (mp) Widely used as a tool for identification of compounds. In this experiment we will measure the mp to confirm purification. Also report the literature value in your lab report! Most organic compounds melt between 20-250 oC Intermolecular forces should be broken to melt a solid In pure samples intermolecular forces are stronger, they have higher mp’s and melt sharply (ex. 150-151 oC) In impure samples intermolecular forces are already weakened by impurities, mp decreases and impure samples melt over a wider range (ex. 141-150 oC)  Results: What to expect? Appearance? wrt weight? wrt melting point (mp)?