Eperiment 4: Etraction Part A: Separation of Acidic, Basic and Neutral Substances Part B: Isolation & Analysis Reading: Mohrig, ammond & Schatz Ch. 11 pgs 113-132 Ch. 12 pgs 132-141 Ch. 20 pgs 277-310 Carey Ch. 13 pgs 574-581 watch the technique video on the course website Etraction Pulling a compound (or compounds) out of one phase into another solid/liquid making a cup of tea liquid/liquid most common in lab liquids must be immiscible Used for the isolation, purification, and/or separation of compounds - isolation of potential therapeutics from natural sources - remove water soluble impurities from an organic reaction miture typically inorganic salts means of preliminary purification (wash) - separate two organic compounds bearing different functional groups Terminology - etract: pulling out what you want - wash: removing what you don't want both are effectively the same process This technique is based on solubility differences Etraction: ow Does it Work Organic vs. Aqueous Layer: Top or Bottom? Organic compound in a separatory funnel with two immiscible liquids - two layers - typically an organic solvent & water - relative solvent densities will determine which layer is which (e.g. top or bottom) Layers are mied by inverting funnel gently; will separate on standing Compound () will distribute (partition) itself between the layers (phases) - equilibrium based on rel. solubility of in each layer - organic layer will contain neutral organic compounds - aqueous layer will contain organic & inorganic salts less dense layer more dense layer Consider the solvent density vs. water less dense (top layer) more dense (bottom layer) Densities of Some Common Etraction Solvents solvent density heanes 0.672 diethyl ether 0.713 benzene 0.879 water 1.000 saturated NaCl (aq) 1.198 dichloromethane 1.335 chloroform 1.498 " Drain lower layer out the bottom; Pour upper layer out the top separatory funnel If don't know densities add a few drops of water to the separatory funnel - water will join the aqueous layer
Distribution Coefficient (K) Ratio of concentrations of a compound [X] in the layers is known the distribution coefficient (K) K = [X] in organic solvent [X] in water If know solubility's, can calculate K solubility of X in organic solvent solubility of X in water If for compound X: solubility in water is 5g/100 ml "solubility in an organic solvent is 35 g/100 ml 35g/100mL K = B 0.35 = = 7 5g/100mL A 0.05 Etraction Etraction Efficiency: - For an efficient etraction (water organic solvent), K 4 - If K < 1, will be difficult to etract the compound from water What if etraction efficiency is poor?? - increase number of etraction steps more efficient to carry out multiple small etractions than 1 large one even if K 4 so 3 5mL etraction better than 1 15mL etraction - saturate the aqueous layer with NaCl ("salting out") shift the equilibrium (change K) ow can we use etraction to separate two (or more) organic compounds? - modify solubility? K gives us information about etraction efficiency General Principles # start with a miture of compounds dissolved in an organic solvent # Separation of a Miture by Etraction Etract With Removes Why? water 2 O polar, low MW compounds inorganic acids & bases polar organics with <5 carbons solubility acid Cl basic compounds inorganic bases R-N 2 Cl R N 2 R N 2 Cl weak base NaCO 3 strong base NaO Na 2 CO 3 strongly acidic compounds inorganic acids R-CO 2 (pka 5) acidic compounds O (pka 10) O NaCO O 3 R O R O Na O NaO O Na
Drying Agents Used to remove final traces of water from organic solutions Typically anhydrous, inorganic salts readily hydrate Typical drying agents include: Drying Agent calcium chloride CaCl 2 calcium sulfate CaSO 4 magnesium sulfate MgSO 4 potassium carbonate K 2 CO 3 sodium sulfate Na 2 SO 4 Capacity high low high medium high Speed medium fast fast medium slow Applications hydrocarbons generally useful not for very acid sensitive cmpds not for acidic cmpds generally useful Procedure - add a small amount of solid drying agent to the organic solution - swirl; drying agent should be free flowing (not clumped); avoid ecess - let stand (swirl occasionally) for 5-15 minutes - filter or decant solution away from drying agent Net Week (October 3-7) Eperiment 4: Etraction A. Separation of a 3-Component Miture by Etraction strong organic acid - benzoic acid (carboylic acid) organic base - 4-chloroanaline (amine) neutral substance - 1,4-dimethoybenzene (ether) B. Isolation & Analysis recover compounds by neutralization/filtration or evaporation evaluate success of separation by TLC & melting point confirm identity of separated components by IR Ep 4 Notebook: Research Plan MUST be a flowchart use the entire page for the flowchart; eperimental section will follow on a new page DUE: Distillation Lab Report (ep 3) Lab Reports are due at the beginning of your regular lab session Etraction Overview Etraction Technique: The Basic Setup 1. Your miture contains the following components (dissolve in ether) 2. Separation of the 4-chloroaniline (an amine) is achieved by etracting the miture with acid Ar-N 2 + Cl Ar-N 3 + Cl - 3. The benzoic acid (a carboylic acid) is separated upon etraction with base Ar-CO 2 + NaO Ar-CO 2 - Na + 4. The 1,4-dimethoybenzene will remain in the organic layer separatory funnel set in a ring (be sure it is the right size) stopper & stopcock should fit avoid leaks stopcock should be closed collection flask below "just in case" add solution slowly avoid spills - use a funnel solution must be cool avoid large pressure build up ring stand stopper funnel (optional) metal ring stopcock should be closed note that the tip of the funnel is below the rim of the flask empty flask or beaker
Etraction Technique: Separation add appropriate aqueous reagent to the solution stopper the funnel and invert hold on to the stopper vent carefully release pressure; vent gases point funnel away from yourself & others repeat several times DON'T SAKE avoid emulsions set funnel back into ring allow layers to separate be sure you know which layer is which remove stopper so funnel will drain drain lower layer through stopcock keep tip of funnel below rim of container pour upper layer out through top avoid contamination CAUTION escaping gases hold stopper securely Eperimental Details Separation 1. Obtain approimately 1.5g compound miture (1:1:1 ratio by weight) - record accurate weight (does not need to be 1.50g) 2. Dissolve in ether transfer resulting solution to the separatory funnel - use a little etra solvent to complete transfer 3. Add Cl to the separatory funnel; stopper and invert separatory funnel to mi - be sure you know which layer is which - vent frequently to prevent pressure build-up 4. Separate layers - wait for separation to occur, then drain lower layer aqueous layer - will contain amine salt (flask #1) - organic layer remains - will contain benzoic acid & 1,4-dimethoybenzene 5. Repeat steps 3-4 - to ensure complete etraction of the amine from the organic layer - REMEMBER: multiple etractions using smaller amounts of reagent are more efficient than a single etraction with the same reagent volume Eperimental Details Eperimental Details 6. Add NaO to separatory funnel; stopper and invert sep funnel to mi - mi thoroughly -- deprotonation of benzoic acid is a bit slow 7. Separate layers as before - wait for separation to occur, then drain lower layer aqueous layer - will contain carboylic acid salt (flask #2) - organic layer remains - will contain 1,4-dimethoybenzene 8. Repeat steps 6 & 7 - to ensure complete etraction of the carboylic acid from the organic layer 9. Wash organic layer with saturated NaCl (aq) - preliminary drying - drain lower layer out through bottom (set aside to discard later) - pour top layer out through top of sep funnel (flask #3) will contain 1,4-dimethoybenzene Isolation of Components Flask 3: organics; dry over anhydrous Na 2 SO 4 swirl to mi; should be some free-flowing solid - more is not better - let sit for 5-10 min (keep busy while you wait) decant liquid into tared roundbottom flask concentrate using the rotary evaporator - no sand baths Fire azard - INT: place flask with organics in back of hood and do something else while you wait for the rotavap Flask 1: acidic etracts; make basic with concentrated NaO (check p) Ar-N 3 + Cl - + NaO Ar-N 2 ($) cool & collect crystals Flask 2: basic etracts; make acidic with concentrated Cl (check p) Ar-CO 2 - Na + + Cl Ar-CO 2 ($) cool & collect crystals
Eperimental Details Finishing Up 1. dry samples - samples #1 & 2 will be very wet; first press between two pieces of filter paper, then dry under vacuum (be sure side arm test tube is clean) 2. weigh samples (& calculate % recovery) - how much of each compound can you epect to recover? 3. determine melting point of each compound 4. evaluate success of separation by TLC - spot initial 1:1:1 miture, plus 3 isolated components - developing solvent is chloroform (use in the hood) - how can you tell if separation was successful? 5. Get IR spectra from your TA - use to confirm identity of each component Some Pointers: Label your flasks - one Erlenmeyer/beaker looks pretty much like the net NEVER throw anything away until you're absolutely sure you don't need it - you can always dispose of it later - once discarded, it's tough to get it back When etracting, invert funnel gently - don't shake - keeps emulsions from forming - emulsions will take a long time before layers separate Vent frequently - avoid pressure build up - sep funnel could eplode During isolation, be sure solutions are acidic/basic (check with p paper) - do NOT dip paper into solution; use a boiling stick or glass rod - MIX TOROUGLY after each addition of Cl or NaO Come prepared - easy to get confused if you're not clear on what you're doing - must write a flow sheet for the pre-lab research plan (use the entire width of the page) Infrared Spectroscopy (IR) Infrared region of electromagnetic spectrum ": 2,500-16,000 nm #: 1.9 1013-1.2 1014 z Photon energies associated with this region are weak - not large enough to ecite electrons - can induce vibrational ecitation of covalently bonded atoms & groups Infrared Spectroscopy Absorption in specific region in IR spectrum corresponds to specific types of molecular vibrations: FREQUENCY (cm -1 ) 4000 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 Bonds to triple bonds double bonds fingerprint region Eact frequencies of vibrations determined by the strength of the bonds involved and the masses of the connected atoms O-, N- CC, CN C=O C-C, C-O, C-N, etc. Wide variety of vibrational motions; commonly talk about "stretching & bending" e.g. for C- bond C- CO, etc. C=C C=N Ar- C C C 2.5 3.0 3.5 4.0 5 6 7 8 9 10 11 12 13 14 16 (MICRON S ) symmetric stretch asymmetric stretch scissoring (in plane bending)
Infrared Spectroscopy Plot light absorbsed/transmitted as a function of frequency, can determine what types of functional groups are present in a molecule Identification of Miture Components Distinguishing features by IR spectroscopy (see Carey, pg 579) C- stretch IR spectrum of tert-butylbenzene SDBS Database National Institute of Advanced Industrial Science and Technology; 11/7/07 Carboylic acids - broad O stretch (ca. 3000 cm -1 ) - may be diffuse - C=O stretch (ca. 1710 cm -1 ) Amines - N stretch (ca. 3400 cm -1 ) - 2 bands for a N 2 group Ethers - none of the above - will likely see minor FG absorbances C- stretch (ca. 2850-3150 cm -1 ) C-O stretch (ca. 1000-1250 cm -1 ) - minor absorbances will be present in acid & amine spectra as well Infrared Spectrum of a Carboylic Acid Infrared Spectrum of an Amine (RN 2 ) R O O R-N 2 O stretch N stretch C=O stretch % NO C=O
Infrared Spectrum of an Ether Writing the Lab Report: Ep #3 Distillation OR will show minor FG absorbances only Purpose - technique eperiment: what will you learn? - what conclusions will you reach? - a general discussion of theory/epected results is not a purpose Results & Discussion - Plot data for both simple & fractional distillations (include graphs) these are essentially temp vs time plots as discussed in class raw data (# drops vs temperature) does not belong here % NO N C- stretch % NO C=O C-O stretch - Evaluate data simple distillation discuss temp vs. volume graph (equiv to temp vs. time) compare to theory (what do you epect to see)? do your results agree with your epectations? eplain what does plot tell you about composition of drops over time? e.g. what does the temperature change indicate? are the drops pure? does purity vary? report % recovery and % holdup Writing the Lab Report: Ep #3 Distillation Results & Discussion - Evaluate data fractional distillation discuss same topics as for simple distillation - Compare the two distillation techniques compare how well the two components separated in each case what data can you use? bp recorded vs known bp Temp vs. Vol plots discuss differences in % holdup and % recovery relates to the efficiency of the two processes - Decide which method is better for the separation of cycloheane & toluene clearly eplain why you made this choice (based on your results) do your findings agree with your epectations? again, first must decide what you epect to see your epectations shouldn't influence interpretation of your data Writing the Lab Report: Ep #3 Distillation Conclusion - a brief recap of your findings - make a general statement about distillation techniques you studied - should be brief (2-3 sentences) Appendi A: Calculations - Percent Recovery % recovery = amount distillate recovered (ml) amount of original solution (ml) - Percent oldup amount of material retained by the distillation apparatus % holdup = amount liquid left in flask(ml) amount of original solution (ml) 100 100