Williamson Ether Synthesis: Exploring 4-Bromophenol Lab
School
University Of Georgia**We aren't endorsed by this school
Course
CHEM 2212
Subject
Chemistry
Date
Dec 10, 2024
Pages
11
Uploaded by MateMask5849
Williamson Ether Synthesis of 4- BromophenolCHEM 2212LJeremy SandersIntroduction:This lab is focused on the process of synthesis. The specific form of synthesis conducted duringthe experiment is called Williamson Ether Synthesis. This reaction involves the combination of analkoxide ion with a primary alkyl halide to yield an ether. In this experiment, a phenoxide ion will beformed after the deprotonation of 4-bromophenol. The phenoxide ion will then serve as the nucleophile inthe SN2 attack on a primary alkyl halide. The identity of the alkyl halide will be determined using the IRand H NMR spectra of the final purified product. Gaining an understanding of synthesis is importantbecause it is a fundamental laboratory technique that scientists use to generate a variety of compounds.The main laboratory techniques used during this experiment are reflux, liquid/liquid extraction, thin layerchromatography, FTIR, and H NMR. Reflux is a technique in which a solute (which has a lower boilingpoint) is boiled off into a gas and then condensed back into a liquid as it returns back to its originalstarting position. This results in a separation between the solute and solvent due to a difference in boilingpoint. Liquid/liquid extraction is an isolating technique that utilizes the difference in solubility betweenimmiscible liquids to isolate one of the products. Thin layer chromatography is a technique that separatesmixtures through a solid stationary phase and a mobile liquid phase. The technique utilizes the differencein solubilities and polarities of the substances within the mixtures to separate the mixtures. IRspectroscopy and H NMR are used in this lab to find the identity of a chemical compound through variouscharacteristics such as functional groups, bond stretches, and coupling constants. One notable limitationof this experiment is that throughout the experiment, a portion of the product may be lost as the product istransferred from one apparatus to another. This could skew the results of the experiment by decreasing thepercent yield that is performed at the end of the experiment.
Balanced Equation:Reaction Mechanism:Table of Reagents:NameStructureMW (g/mol)MP (℃)BP (℃)Density(g/cm3)4-bromophenol173.0166.4N/A1.84Potassiumhydroxide56.11360N/A2.041-bromopentane151.04-95N/A1.20
1-bromo-3-methylbutane151.04-112N/A1.2611-bromobutane137.02-112N/A1.27TetrabutylammoniumBromide322.37102-106N/A1.039Diethyl ether74.12N/A34.60.7134MethyleneChloride84.97N/A36.91.33Water18.02N/A100.01.00SodiumSulfate142.04N/AN/AN/ASafety Information:a)General Safety Information-Be aware to not seal the reflux apparatus air tight-Safety glasses and gloves must be worn at all times throughout the experiment-Avoid hot surfaces, sparks, and open flames
-All liquid waste should be disposed of in the correctly labeled bottles in the fume hood atthe end of lab-Make sure that the snorkel is turned on and absorbing all potentially toxic fumes andvapors-Silica gel is a respiratory irritant so it should not be inhaled in large amountsb)Specific Lab Information-4 – bromophenol is an eye and skin irritant and can cause damage to the respiratory tractif inhaled. This chemical should be kept away from exposed skin and should not beinhaled in large amounts.-Potassium hydroxide is an eye and skin irritant and can cause damage to the respiratorytract if inhaled. It is also corrosive. This chemical should be kept away from exposed skinand should not be inhaled in large amounts.-1-bromopentane is an eye and skin irritant, flammable, and can cause damage to therespiratory tract if inhaled. This chemical should be kept away from exposed skin andshould not be inhaled in large amounts. It should also be kept away from open flames.-1-bromo-3-methylbutane is an eye and skin irritant, flammable, and can cause damage tothe respiratory tract if inhaled. This chemical should be kept away from exposed skin andshould not be inhaled in large amounts. It should also be kept away from open flames.-1-bromobutane is an eye and skin irritant, flammable, and can cause damage to therespiratory tract if inhaled. This chemical should be kept away from exposed skin andshould not be inhaled in large amounts. It should also be kept away from open flames.-Tetrabutylammonium Bromide is an eye and skin irritant and can cause damage to therespiratory tract if inhaled. This chemical should be kept away from exposed skin andshould not be inhaled in large amounts.
-Diethyl ether is an eye and skin irritant, flammable, and can cause damage to therespiratory tract if inhaled. This chemical should be kept away from exposed skin andshould not be inhaled in large amounts. It should also be kept away from open flames.-Methylene chloride is an eye and skin irritant, flammable, and can cause damage to therespiratory tract if inhaled. This chemical should be kept away from exposed skin andshould not be inhaled in large amounts. It should also be kept away from open flames.-Sodium sulfate is an eye and skin irritant and can cause damage to the respiratory tract ifinhaled. This chemical should be kept away from exposed skin and should not be inhaledin large amounts.Experimental Procedure:1.Observe the TA as they prepare the conjugate base of 4-bromophenol Microwave-PromotedWilliamson Ether Synthesis2.Collect 8 mL of the solution prepared by the TA and place it into the white Teflon microwavevessel3.Add 2.90 g of tetrabutylammonium bromide followed by 3.02 g of the unknown alkyl halide(assigned by TA) to the microwave vessel4.Add a stir bar to the vessel and then return the vessel to the TA.5.The TA will finish the assembly by sliding the vessel into its outer sleeve6.A microwave procedure will be used to reflux the solution for ~30 minutes, followed by a coolingperiod.7.The TA will remove the assembled vessels from the microwave and open them inside the fumehood once the vessel has sufficiently cooled after the reflux process. The TA will then return thewhite Teflon vessel.Extraction:
8.Remove the stir bar from the vesssel and then pour the solution from the microwave vessel into aseparatory funnel9.Next, add 10 mL of DI water and 10 mL of diethyl ether to the separatory funnel. Mix theresulting mixture well.10. Separate the resulting layers into 2 clean, labeled beakers11. Return the aqueous layer to the separatory funnel and extract with another 10 mL portion ofdiethyl ether. Separate the resulting layers into 2 clean, labeled beakers.12. Combine the 2 organic layers and then wash the layer 3 times with 15 mL of 5% KOH. Makesure to set aside the aqueous layer after each wash.13. Use sodium sulfate to dry the ether layerColumn Chromatography:14. A column will be prepared by the TA which will be used to purify the product15. Secure the column with a clamp and pack the column by adding a steady amount of methylenechloride through the top of the column using a pipette16. Add the product mixture into the column using a clean pipette17. Add 5-10 mL of methylene chloride to the column after all of the product mixture has been added18. Return the column to the TA and transfer the product mixture to a clean, pre-weighed beakerSolvent Removal and Thin Layer Chromatography:19. Position the snorkel over the beaker containing the purified product20. Boil off the solvent at ~40 degrees Celsius and assign one partner to monitor the removal of thesolvent closely21. The other partner should spot 4-bromophenol dissolved in methylene chloride and the alkylbromide onto a TLC plate. There should be enough room left on the plate for a third spot of thepurified product22. Spot the dilute purified product on the TLC plate and run the plate in methylene chloride aftermost of the solvent has been removed from the product
23. Continue the solvent removal process until the ether and methylene chloride has been removedand then collect the mass of the final product24. Collect a HNMR and FTIR spectrum with the assistance of the TA.Data and Observations:-Starting weight of 4-bromophenol: 3.46 g-Starting weight of alkyl bromide: 3.01 g-Unknown Code: WE812932-Starting weight of 25% potassium hydroxide: 7.12 g-Starting weight of TBAB: 2.932 g-Reflux time: 30 mins-Volume of water added before wash: 10 mL-Volume of diethyl ether used to rinse spin vane: 10 mL-Volume of diethyl ether extractions: 10 mL-Volume of 5% KOH washes: 45 mL-Weight of the recovered product : 3.03 g
Results:Limiting Reagent:(3.46 g bromophenol) * (1 mol bromophenol / 173.01 g) * ( 1 mol 1-bromopentane / 1 mol bromophenol)* ( 151.06 g / 1 mol 1-bromopentane) = 3.02 g 1-bromopentane needed 3.02 g of the alkyl halide wouldbe needed to fully consume the bromophenol used. 3.019g were used, meaning that by a very smallmargin, the alkyl halide was the limiting reagent.Percent Yield:(3.019 g 1-bromopentane) * (1 mol 1-bromopentane / 151.06 g) * ( 1 mol 1-bromo-4-(pentyloxy)benzene / 1 mol 1-bromopentane) * (243.06 g / 1 mol) = 4.86 g (theoretical yield)%Yield = (3.03g / 4.86g) * 100% = 62.35%Product HNMR:
Product IR:Discussion/ Conclusion:After completion of the experiment, it was determined that our reaction had a percent yield of62.35%. The loss in expected product is likely due to the loss of product in each transfer between thevarious apparatuses utilized in the lab. Some of the organic layer could have also been lost during theliquid-liquid extraction process.Once the final product was obtained and weighed, it was determined to be 1-bromo-4-(pentyloxy)benzene, based on its IR and HNMR spectra, indicating that the alkyl bromide used in thereaction was 1-bromopentane. The FTIR spectrum was analyzed to determine whether any startingmaterials remained in the final product. The spectrum did not include any peaks indicating the presence ofan OH group, meaning that there was no remaining reactant in the final product. The HNMR spectrumwas used to determine the exact identity of the final product. The spectrum contains 6 unique peaks, 4 ofwhich have integration values of 2, and the other 2 having values of 3 and 4. The only alkyl halide of the3 options that would exemplify these peaks is 1-bromopentane.
Post-Lab Questions:1)2) A phase transfer catalyst is a catalyst that promotes the transition of a reactant from one phase toanother within a reaction. The phase-transfer catalyst in this week’s experiment was Diethyl ether. Theaddition of diethyl ether helped to accomplish the reaction this week by moving the product from theaqueous phase to the organic phase. This phase change was a necessary step needed to occur for thereaction to be complete.3)
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