Synthesis of an Alkyl Halide: A Nucleophilic Substitution Reaction Unknown Letter: B
23 April 2013
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The purpose of the experiment was to perform a synthesis of an alkyl halide by a nucleophilic substitution reaction. The alkyl halide, along with the starting alcohol, was determined through NMR spectroscopy, gas chromatography, and IR spectroscopy.
In a 100 mL round bottom flask, containing a Teflon stir bar, 17.123 grams of sodium bromide, 17 mL of distilled water, and 8.6 mL of unknown alcohol were combined. Through the top of the condenser, 14 mL of concentrated sulfuric acid was added drop wise over a period of ten minutes. The addition of the acid created a change in color of the solution to a rustic orange color. The mixture was refluxed for 30 minutes and the solution changed to a faded yellow-orange color. Once reflux was complete, a simple distillation was set up, with the 25 mL collection graduated cylinder placed in an ice bath. The mixture was distilled and combined with the hood partners’ distilled mixture. The distillate was placed in a separatory funnel with 10 mL of distilled water. Once separated, the distillate was added to the funnel again with 9 M sulfuric acid. The organic layer was still in the funnel after separation, as distilled water was added to the solution and then 10 mL of a saturated solution of sodium bicarbonate. The organic solution was dried with anhydrous sodium sulfate for a week. The liquid product was transferred to a 25 mL round bottom flask equipped with a stir bar and a simple distillation was set up. The solution was distilled and the density of the bromide was calculated at 1.222 grams/mL with a boiling range of 87-92◦C. The theoretical yield was calculated at 12.847 grams and the percent yield was 72.3 percent. Next was the characterization and assessment of the purity of the alkyl bromide using IR spectroscopy, NMR spectroscopy, and gas chromatography. References: Mohrig, J. R.; Morrill, T. C.; Hammond, C. N.; and Neckers, D. C.; Experimental Organic Chemistry; W. H. Freeman and Company: New York, NY, 1997; pp. 76-81.
Gilbert, J. C.; and Martin S. F. Experimental Organic Chemistry, 2nd Edition; Saunders College Publishing, Harcourt Brace College Publishers, 1998; pp. 383-385.
Calculation of Theoretical Yield:
2-Butanol alcohol: 8.6 mL * 0.808 g/mL = 6.9488 grams
6.9488 g/74.12 grams of 2-Butanol = 0.0938 moles 2-Butanol
17.123 grams of NaBr / 102.9 g/mol of NaBr = 0.166 moles of NaBr
Alcohol is the limiting reagent.
1 moles of alcohol / 1 mole of 2-bromobutane = 0.0938 moles 2-bromobutane
0.0938 moles 2-bromobutane * 137.03 grams/moles = 12.847 grams of 2-bromobutane
and theoretical yield.
Calculation of Percent Yield:
9.287 grams actually obtained / 12.847 grams theoretical yield = 0.7229
0.7229 * 100 = 72.3 % yield
Density of Alkyl Halide:
Grams of distillate in graduated cylinder/ volume of distillate in mL = 9.287 grams / 7.60 mL = 1.222 g/mL of alkyl halide
The experiment performed was able to successfully identify a starting alcohol and alkyl halide using reflux, distillation, washing, and separatory funnel. Due to tests, such as gas chromatography, IR spectroscopy, boiling point, and NMR spectroscopy, being conducted, results for the experiment showed 2-bromobutane as the identified alkyl halide. IR Spectroscopy- the IR spectroscopy test was run in order to compare the functional...
References: Gilbert, J. C.; and Martin S. F. Experimental Organic Chemistry, 2nd Edition; Saunders College
Publishing, Harcourt Brace College Publishers, 1998; pp
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