Lab 8 Write up-William Ether Synthesis PDF

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Williamson Ether Synthesis Introduction: The Williamson ether synthesis is a phenomenal experiment that helped put 2 compounds together. This synthesis is a SN2 reaction (Kunz,Waldmann, 1991) that we see below of a nucleophile that misplaced a halide ion from the alkyl halide to give the compound an ether from the alkoxide ion which gives us an ether. This reaction shows the inversion of the chemical structure. The chiral centers are flipped and that the elimination reaction to create the reduction in the chemical structure (Ouellette, Rawn, 2015). Today, we will be using p-Cresol and n-Propyl iodide to create p-Cresol-n-Propyl tolyl ether. Reaction Mechanism:

Table 1: Chemicals Used in Experiment Compound

Physical Properties

Molecular Weight

p-Cresol C7 H8 O

colorless liquid bp 202 °C

n-Propyl iodide C3 H7 colorless liquid bp 202 °C

Density

Amount

Hazards

108.15 g/mol 1.02 g/mL

160 μL, x mmol

Ingestion irritation

169.99 g/mol 1.75 g/mL

140 μL, x mmol

Ingestion irritation

260 μL

Respiratory

25% NaOH solution

Colorless liquid

Tetrabutylammoniu m bromide (C4 H7 ) 4 N+Br

white solid mp 103–104 °C

322.38 g/mol

18mg 0.03 mmol

Irritation

n-Propyl p-tolyl ether

colorless liquid

150.22 g/mol 0.95

product

Do not

bp 210 °C

g/mL

swallow

Procedure: Assemble the reaction apparatus as shown in Figure 13.2a, consisting of a 3.0 mL conical vial charged with p-cresol (80 μL from Eppendorf pipette/0.08g), 25% aqueous NaOH (130 μL dispensed from Eppendorf pipette) and a spin vane. After the solution is thoroughly mixed, add tetrabutylammonium bromide (9 mg) [quickly recap the reagent bottle, since this salt will quickly absorb moisture] and n-propyl iodide (75 μL from Eppendorf pipette/0.075g) and equip the flask with a water reflux condenser. Caution: n-propyl iodide is a suspected carcinogenic agent. Dispense it in the hood. Used 0.0091 g (9.1mg) of tetrabutylammonium bromide. Heat the solution (95–100 °C) with vigorous stirring to insure good mixing of the biphasic solution. After 60 minutes, allow the solution to cool to room temperature. Note: due to the density of propyl iodide (greater than water) and the density of the product (less than water) the organic phase starts below the aqueous phase, but at the end of the reaction the organic phase is above the water. Liquid has turned a yellow-orange. Was pretty dried out at the end of 60 minutes. Add 1 mL of ether to the reaction vial. Mix the two layers and then remove the organic portion to a 1 dram vial. Repeat once. To the combined organic portion, add 5% aqueous sodium hydroxide (200 μL). Shake the solution and remove the aqueous portion. Remove any residual water from the organic portion by adding anhydrous sodium sulfate (about 100 mg). If after several minutes of agitating the mixture with a small spatula, the solution is still cloudy, add more sodium sulfate (100 mg) to get a clear solution (0.214g added). Transfer the anhydrous organic solution to a dry tared 1 dram vial. 1 dram vial is 5.911g. 6.888g after removal of aqueous layer. Rinse the sodium sulfate with ether (about 0.5 mL) and transfer this washing to the vial. Evaporate the solvent using the rotary evaporator. Concentrate crude product to a constant weight. Dispose of the aqueous portions in the liquid waste container in the hood. Weight of rotovap dram vial part 1 after was 6.02g. Prepare a small chromatography column by adding cotton, sand and silica gel (500 mg) (509 mg) to a Pasteur pipette; suspend it over a tared 1-dram vial. Add methylene chloride (0.5 mL) to the crude product and add this solution by Pasteur pipette to this dry silica gel column. Elute the column with methylene chloride (2 mL). Dispose of the column in the solid waste container. Evaporate the solvent using the rotary evaporator. Dry final product to a constant weight. Turn in the entire sample to the TA for IR analysis. Weight of dram after rotovap part 2 is 6.1g Results: The final weight of the product tested and collected was 0.189g. Percent yield of n-Propyl iodide = 6.6% Percent yield of p-Cresol = 11.1%

Figure 1:IR of p-Cresol

Figure 2: IR of n-Propyl tolyl ether

Figure 3: H-NMR of n-Propyl-p-tolyl ether

Discussion: Besides taking the time to heat the solution for 60 minutes, the experiments did seem to go well. We mixed the compounds and rotovap the solution to give us the product that we were searching for. Rotovap for part one of the experiment took longer than finishing the experiment and rotovapping again to collect the product. We did collect 0.189g of n-Propyl-p-tolyl ether. Due to our percent yield from the final product, we know that we are missing some from the number of compounds we have used to get from start to finish. This was a 15% yield of the product that we do not have. This can be due to human error in either making precise measurements or to not collected all of the product from the pipette. H-NMR The bonds at D come from the C-H bonds that are from the aromatic structure from pCresol. The aromatic CH bonds are split depending on the side they are on. The right side that the CH bonds are connected on the side of the OH bond to the aromatic structure is at 6.8 whereas the CH bonds that are connected on the side of the CH3 bond to the aromatic

structure are 7.1. The bonds at 2.3 represent the CH3 bond that starts at the beginning of pCresol. The CH2 bonds at A come from the n-Propyl iodide. The CH3 bond at B come from nPropyl iodide. The CH2 bonds at C come from the CH2 bond found in n-Propyl iodide. The bond farthest to the right is the Oxygen bond from p-Cresol. Works Cited: Halterman, R. Morvant, M. 2017. Organic Chemistry Laboratory Manual. University of Oklahoma, 2017, p. 94-98 Kunz, Horst, and Herbert Waldmann. Comprehensive Organic Synthesis. Elsevier Science Ltd, 1991. “16 - Ethers and Epoxides.” Organic Chemistry Study Guide: Key Concepts, Problems, and Solutions, by Robert J. Ouellette and J. David Rawn, Elsevier, 2015, pp. 277–297....