SC CHEM 333 - Williamson Ether Synthesis Pre-Lab (5 pages)

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Williamson Ether Synthesis Pre-Lab



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Experiment 9 Williamson Ether Synthesis Pre Lab By Cameron Kahn 14 November 2013 TA James Collie Objectives In this lab one will learn Williamson Ether Synthesis He she will start with guaiacol and 3chloro 1 2 propanediol and using Williamson Ether Synthesis will end up with 3 2methoxyphenyloxy 1 2 propanediol as the product Simultaneously one will extract the natural product from Mucinex and then compare both product s melting point and IR analysis Intro In a Williamson Ether Synthesis the alkoxide functions as the nucleophile and attacks the electrophilic C of the alkyl halide displacing the bromide and creating the new C O bond Synthesis of Ethers The mechanism by which a Williamson Ether Synthesis works is by a bimolecular nucleophilic substitution otherwise known as a Sn2 reaction Primary alkyl halides are preferred in this reaction due to steric hindrance First discovered in nature Guiafensin has been used for many years including the use by Native Americans as a remedy The use of Guiafensin today is used in cough medicines and due to the demand synthesis is needed to create volume for the masses In this experiment one will compare the tablet natural form versus the synthesized form in order to identify which one is more pure In this experiment the use of acetonitrile as the solvent is needed for the reaction to undergo Sn2 Unlike phenoxide Acetonitrile is polar aprotic therefore eliminating any acid base chemistry that could occur Acetonitrile will not degrade any of the reagents before their used and has a boiling point of 82oC Handy The properties of Acetonitrile works well for a Sn2 reaction to occur In a Williamson Ether Synthesis a phase transfer catalyst is used however for our experiment the use of a catalyst will not be used In a typical Williamson Ether Synthesis the reaction is catalyzed with tetramethylammonium bromide This is important to note because a phase change causes an inorganic ion to move from aqueous solution to organic solution Without the phase transfer catalyst the starting reagents would not come in contact with each other therefore the reaction would not take place Mechanism 2 Page Procedures First step one will set up the reflux apparatus Next add 3 55mL of Guaiacol solution into a 25mL round bottom flask along with 1mL of 6 25M NaOH and a boiling stone Connect the flask to the apparatus and begin to heat using a variac setting of 65 for about 10minutes He she is looking for the solution to boil but not reflux higher than halfway up the column Obtain 0 5mL of 3 chloro 1 2 propanediol and mix with 0 5mL of Acetonitrile Using a pipette add the alkyl halide mixture drop wise to the reflux column once the solution in the flask begins to boil more slowly Add the drops over a 5 7 minute interval Then allow the mixture to continue to heat for 45 minutes While this process is occurring obtain a Mucinex tablet and perform the following extraction of guaiafensin record amount of active ingredient in the tablet crush tablet to a fine powder and add 5mL ethyl acetate and stir at room temperature for 10minutes Handy If needed to dissolve heat slightly Using hot gravity filtration remove any impurities and keep filtrate Using the filtrate add 10mL hexane White cloudy precipitant should form after mixture is let stand for 2 3minutes Using an ice bath allow mixture to cool and crystallize Collect the product by vacuum filtration and wash with 5mL cold hexane Handy Calculate percent recovery of tablet versus reported amount Then record melting point and IR of the sample Back to the reflux apparatus After about an hour of the original solution refluxing transfer the flask to a Roto Vap to remove solvent After solvent has been removed add 3mL of deionized water to dissolve the salt that has formed Using a separatory funnel transfer the contents of the flask for separation Add 10mL of ethyl acetate and swirl Remove the aqueous layer and using this layer wash with another 10mL of ethyl acetate Separate the organic layer and combine both organic layers into a 50mL Erlenmyer Flask Using a microscoop of magnesium sulfate allow to dry the excess water out of the sample Then with the use of the Roto Vap evaporate the remaining solvent until a yellow hue liquid remains Handy Add the product to a 20mL scintillation vial along with a magnetic stir bar and place into an ice bath Two things could happen at this point if crystals form perform suction filtration and if no crystals form keep the sample in the vial and allow the sample to refrigerate until next lab Obtain a melting point and crude mass of the product and recrystallize using ethyl acetate and hexane Then obtain a pure melting point and pure mass to calculate the percent yield and percent difference He she should consult with the TA if any of the steps are unclear 3 Page Apparatus Figure 1 Reflux Apparatus Synthesis of Ethers Reagent Table Name Structure MW g mol Melting oC 27 Boiling oC 205 Density g mL 1 129 Guaia Properties Colorless aromatic compound component of wood smoke Light and air sensitive col 124 14 3chloro 1 2propanediol 110 Sodium Hydroxide NaOH 39 99 Ethy l Acetate 88 10 213 1 322 318 1390 2 13 83 6 77 1 0 8945 Light and air sensitive Acrid smell Emits toxic fumes of HCL when burning Corrosive material Colorless odorless solid Hygroscopic Colorless flammable liquid with a pleasant fruity odor 4 Page H 95 69 0 659 Colorless flammable liquid with a mild gasoline like odor exane 86 1766 Hygroscopic drying agent white powder 1124 2 66 Mag nesium Sulfate 120 36 White solid with a clay like consistency 78 80 Guaifenesin 198 22 Disposal Immediately alert TA if any spills occur during the experiment Dispose of liquid organic waste in properly labeled container under fume hood Dispose of any organic solid waste in the container labeled organic solid waste under fume hood Any soiled gloves need to be placed in the proper glove container Unneeded trash or paper towels need to be placed in the general waste basket Any broken glass needs to be cleaned up by the TA to avoid injury and should be placed in the proper broken glass container Finally wash excess aqueous liquids down the drain with plenty of water References 1 Handy G 2012 Chemistry 334l essential of organic chemistry laboratory Montgomery Alabama QDE Press 2 Synthesis of Ethers Synthesis of Ethers McGraw Hill Company n d Web 09 Nov 2013 5 Page


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