Competing Nucleophiles Lab

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  • Topic: SN2 reaction, Nucleophilic substitution, NMR spectroscopy
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  • Published : February 8, 2011
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Title: Competing Nucleophiles (Exp 24, pp 211-221, pp 808-823, pp 836-842)

The purpose of this experiment is to determine the nucleophilic strength of chloride and bromide ions as it reacts with 1-butanol (n-butyl) and 2-methyl-2-propanol (t-butyl alcohol) under SN1 and SN2 conditions. Method:

40 g of ice and approximately 30 ml of sulfuric acid is cautiously added to a 100 mL beaker respectively. Weigh 7.6 g of ammonium chloride and 14.0 g of ammonium bromide and place it in another beaker, crushing the lumps until a powdery mixture remains. The powdery mixture is then transferred to a 125 mL Erlenmeyer flask. Add the ammonium salts into the sulfuric acid mixture. Heat is applied to dissolve the salt. Once the solution has fully dissolved, allow it to cool until the warm substance is touchable. A prolonged waiting period can cause the solution to recrystallize and this process would have to be repeated again. Place 6.0 mL of water in a 15 mL centrifuge tube marking the tube at the 6.0 mL level and replace the water with the solvent-nucleophile mixture. The tube is set aside for the t-butyl experiment. The remaining mixture is placed in a 25 mL round bottom flask. Competitive Nucleophiles with 1- Butanol (n-butyl alcohol)

Assemble a reflux apparatus including the 25 mL round bottom flask and a heating mantle as a heat source. 5 mL of n-butyl alcohol is added to the flask by detaching the flask and adding the alcohol via a Pasteur pipet. Allow the mixture to boil at a temperature sustainable for a gentle boil for approximately 75 minutes. After this process has been completed, turn the heat off and allow the mixture to cool for approximately 10 minutes. Once ten minutes has elapsed, carefully place the flask into a cool water bath (without ice) until the mixture cools to room temperature. At this point, an organic layer should be visible. Transfer this solution into a separatory funnel. Drain most of the bottom aqueous layer into a beaker. Using a Pasteur pipet transfer the organic layer along with remaining aqueous layer into a centrifuge tube. 1.5 mL of water is added to the tube and shaken gently. Allowing the layers to separate, remove the bottom aqueous layer. 2 mL of saturated sodium bicarbonate is added to the solution and the bottom aqueous layer is removed. Add approximately 0.4 g of anhydrous sodium sulfate to a 10 x 75 mm test tube. The organic layer is then relocated to the test tube. With a spatula or glass rod, stir the solutions and place a stopper on the opening of the tube. Allow the solution to settle for approximately 10 minutes or until it appears clear. This solution only is conveyed to a microfuge tube using a Pasteur pipet, covering the cap with parafilm. Competitive Nucleophiles using 2-methyl-2-propanol (t-butyl alcohol)

1.5 mL of t-butyl alcohol is added to the 15 mL centrifuge tube that was set aside. The tube is then shaken vigorously for approximately 5 minutes, occasionally releasing the pressure of the tube. Allow the fully dissolved solution to settle for approximately 10 minutes. Distinct layers should be visible at this point. Using a Pasteur pipet, carefully remove the bottom aqueous layer. After waiting an additional 10-15 seconds, remove the remaining lower layer including some of the organic layer in order to ensure the complete removal of water. Add 0.05 g of sodium bicarbonate to a 10 x 75 mm test tube. The organic layer is added to the test tube and bubbling should be observed. Once the bubbles have ceased and a clear liquid is observed, decant the liquid into a microfuge tube covering the cap with parafilm. Refrigerate the tubes overnight. The solutions for both the n-butyl and t-butyl alcohols are tested in the NMR spectrometry, Gas Spectrometry, and the refractive index is determined. Equations: See notebook.

Mechanism: See notebook.
The whole premise of this experiment is to test the nucleophilic strength of chloride and bromide in an...
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