Organic Chemistry Lab II
Organic Chemistry Lab II CHM 333
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This 5 page Class Notes was uploaded by Emmy Vandervort on Sunday October 25, 2015. The Class Notes belongs to CHM 333 at University of Michigan - Flint taught by Staff in Fall. Since its upload, it has received 38 views. For similar materials see /class/228618/chm-333-university-of-michigan-flint in Chemistry at University of Michigan - Flint.
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Date Created: 10/25/15
Extractions Background The key to performing any reaction is puri cation This o en requires multiple extractions to separate your product from side products or starting materials In this experiment you will separate a mixture of acidic basic and neutral substances by successive extractions from ether The basic material is 4chloroaniline while the neutral substance is naphthalene You will determine the identity of the acid by choosing from benzoic acid 4chlorobenzoic acid salicylic acid or mtoluic acid 3methylbenzoic acid Procedure Week 1 Obtain your unknown acid and weigh the contents into a tared small beaker Add to this 05 g of 4chloroaniline and 05 g of napthalene Dissolve this mixture in about 50 mL of diethyl ether If small quantities do not dissolve heat gently on a steam bath Bring volume back up to 50 mL ifneeded Transfer your solution to a 125 mL separatory funnel Add 25 mL of 5 HCl and stopper the lnnel Invert the lnnel and shake vigorously for a few seconds at a time remember to vent o en Do this until no pressure is released upon venting the lnnel Since diethyl ether has a boiling point of only 35 C anal heat is released as the layers mix you must frequently vent the funnel to prevent the pressure build up from blowing the stopper out The aqueous layer now contains the protonated amine while the ether layer holds the neutral and acid substances Place the separatory lnnel in a ring supported on a ring stand remove the stopper and drain the aqueous layer into an Erlenmeyer ask that is labeled HCl extract Repeat the step above with another 25 mL portion of 5 HC combining the aqueous layers Cover with parafilm and set in your drawer until next week To the original ether layer still in the separatory lnnel add 25 mL of 5 NaHC03 cautiously Stopper the lnnel and proceed as you did above Be care ll C02 is also being evolved vent even more Remove the stopper draw off the aqueous layer and place it in a ask marked base extract Repeat the process however this time you should test the water layer with litmus paper to see if it is basic If the layer was not basic you must repeat the process a third time Cover with para lm and set the base extract in your drawer until next week The neutral compound is still in the ether layer To remove most of the water that has dissolved in this layer during the extraction steps add 50 mL of saturated NaCl vent the lnnel and shake a few times then draw off the lower aqueous layer into a beaker marked waste Extractions Remember Murphy 3 law third corollary states that if you throw away a layer before isolating your product the product is in the layer you threw away Transfer the ether to an erlenmeyer ask Dry the organic layer by adding enough anhydrous sodium sulfate to the liquid until it stops clumping and some remains as a loose powder in the solution The drying agent should be added slowly a small amount at a time in order to prevent the formation of large chunks of drying agent that are wet on the outside but still powdery on the inside and to avoid excessive heating due to hydration of the drying agent Separate the organic solution from the sodium sulfate by gravity ltration into a tared small beaker add a boiling stick Remove the solvent by evaporation on a steam bath being care ll to not get steam in your beaker in the hood Discontinue the evaporation when only a small amount of material remains even if no crystals are present Allow the beaker to cool and then draw air over the top to remove the last traces of ether When the material is dry weigh the material and take a melting point Calculate the percent recovery of naphthalene Week 2 Add a clean stir bar to the ask marked base extract and place it on a stir plate stir at a medium speed Acidify the combined basic aqueous layers by slowly adding 6 M HCl until the foaming ceases and there is no further precipitation or the solution is at pH 3 Transfer your solution to your cleaned 125 mL separatory funnel Using 20 mL of diethyl ether rinse any remaining material in your ask to the seperatory lnnel Do this until all 20 mL has been transferred to the separatory lnnel Stopper the lnnel and proceed as you did before to extract the unknown acid back into ether Remove the stopper draw olT the aqueous layer into your original ask and transfer your ether layer to a clean ask marked acid compound Transfer your aqueous layer back to the seperatory funnel and extract with another 20 mL of ether Combine the ether layers in the separatory lnnel and extract once with 50 mL of saturated NaCl solution Discard the aqueous layer and dry the ether layer with sodium sulfate as before Separate the organic solution from the sodium sulfate by gravity ltration into a tared small beaker add a boiling stick Remove the solvent by evaporation on a steam bath in the hood Discontinue the evaporation when only a small amount of material remains even if no crystals are present Allow the beaker to cool and then draw air over the top to remove the last traces of ether When the solids are dry weigh the material and take a melting point Calculate Simple and Fractional Distillation Modified from Williamson K L Macroscale and Microscale Organic Experiments 1989 DC Heath and Co p 83 85 Set Up You will be doing two distillations Using simple distillation you will be determining the boiling point and percent composition of the azeotrope formed by toluene and water Using fractional distillation you will be determining the volume and identity of two unknown liquids in a mixture Assemble the apparatus for simple distillations as shown in Fig 141 of your textbook Assemble the apparatus for fractional distillation as shown in Fig 152 of your textbook One or two boiling stones should be put in the ask to promote even boiling Each ground joint is lightly greased by putting a small amount of grease lengthwise around the inner joint and followed by wiping it around the joint with a paper towel Piece the joints together with a twisting motion When a good seal is obtained the joint will appear almost transparent Do not use excess grease as it will contaminate the product Make sure the hoses are securely connected to the condenser and water enters from the bottom opening Because of the large heat capacity of water only a very small stream 3 mm diameter is needed too much water pressure will cause the tubing to pop off Connect designated glass joints with blue Keck clamps Make sure that the bulb of the thermometer is below the opening into the side arm of the distillation head to ensure the proper temperature reading In any distillation the ask should not be more than twothirds full at the start Great care should be taken not to distill to dryness because in some cases highboiling explosive peroxides can become concentrated Week 1 Simple Distillation of a Toluene Water Mixture to Determine the Temperature and Percent Composition of its azeotrope Place a mixture of 20 mL of water and 20 mL of toluene and a boiling chip in a dry 100 mL roundbottomed ask and assemble the apparatus for simple distillation using your 100 mL graduated cylinder as your receiving ask Place a small amount lt50 mg of NaCl in your graduated cylinder to promote the separation of layers You may insulate the distillation head by wrapping it with foil Be care ll not to wrap the Keck clamps as they may melt if overheated A er making sure all connections are tight heat the ask strongly until boiling starts Then adjust the heat until the distillate drops at a regular rate of about one drop per second Record the temperature at which the distillate is being collected When the temperature starts to rise again What does this indicate discontinue the distillation Allow the two layers to separate in the graduated cylinder and record the respective volumes of water and toluene that were collected TLC Analysis of Analgesic Drugs Procedure modified from Pavia Kriz Lampman Engel Introduction to Organic Laboratory Techniques a small scale approach 1998 Harcourt p 8184 Initial Preparations You will need a capillary micropipette to spot the plates The preparation of these pipettes is described and illustrated in Technique 20 Section 204 A common error is to pull the center section out too far when making these pipettes with the result that too little sample is applied to the plate If this happens you won t see any spots Follow the directions care ally A er preparing a micropipette obtain six TLC plates These plates have a exible backing but they should not be bent excessively Handle them care ally or the adsorbent will ake off Also you should handle them only by the edges the surface should not be touched Using a lead pencil not a pen and a strait edge lightly draw a line across the short side of the plates about 1 cm from the bottom On three of the plates make one mark on the line you just made remembering that you do not want to scrape off the silica see gure These are the points at which the samples will be spotted On one plate make ve marks equally spaced and make three on the remaining two Finding the optimal solvent Developing Chamber You will use plates 13 spotted with the reference mixture to nd the optimal solvent You will be given a choice of three running solvents 99505 ethyl acetate EtOAc acetic acid HOAc 257455 hexaneEtOAcHOAc and 1584505 hexaneEtOAcHOAc Obtain 10 mL of each solvent mix and place it in separate labeled small Erlenmeyer asks Take a large round lter paper and cut off on side to create a strait edge Place this paper in your 400mL or 600mL beaker so that the straight edge is down and the solvent will wick up the paper Pour your rst solvent mix in the beaker and place your watch glass on top to prevent evaporation Your developing chamber will be ready when solvent has saturated the lter paper When you are ready to try the next solvent pour the used solvent back into the labeled ask Keep your large beaker open for a couple of minutes for evaporation and then pour in the next solvent There is no need to wash the beaker or change the paper between solvent changes Spotting the Plate In six clean labeled test tubes obtain No5 mL of each of the knowns the mixture of knowns standard reference mix Ref 1 and a small amount of acetone The standard reference mixture Ref 1 is spotted on plates 13 Develop each plate in one of the solvent mixtures above The correct method of spotting a TLC plate is described in Technique 20 Section 204 It is important that the spots be made as small as possible but not too small With too much sample the spots will tail streak across the plate and will overlap one another a er development With too little sample no spots will be observed a er development The optimum applied spot should be about 12 TLC page 2 mm 116 in in diameter Between different samples clean your micropipette by dipping it into acetone followed by blotting the tip on a paper towel Repeat the acetone wash at least two more times Plates 13 Plate 4 Plates 5 and 6 Developing the Plate Carefully place the spotted plate in the chamber and allow the spots to develop You want to be sure that the solvent level in the beaker is below your spots otherwise your material will be washed into the solvent and not up the plate Also be sure the plates are placed in the developing chamber so that their bottom edge is parallel to the bottom of the beaker straight not tilted if not the solvent front will not advance evenly increasing the difficulty of making good comparisons If you have more than one plate developing at a time the plates should face each other and lean back in opposite directions When the solvent front has significantly slowed its progress up the plate or it is within 1 cm of the top remove each plate from the chamber and using a lead pencil mark the position ofthe solvent front Set the plate on a piece ofpaper towel to dry Visualization of the Plate When the plates are dry observe them under a shortwavelength light will appear green UV lamp located in the IR room Lightly outline all of the observed spots with a pencil Before proceeding make a sketch of the plate in your notebook and note any differences in the appearance of the spots that you observed Using a ruler marked in millimeters measure the distance that each spot measure from the topmost edge of the spot has traveled relative to the solvent front Calculate Rf values for each spot Technique 20 Section 209 The optimal solvent miX will be the one that separates the spots by the most distance
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