Conversion of Alcohol to Alkyl Halides

Topics: Distillation, Alcohol, Ethanol Pages: 8 (2553 words) Published: August 3, 2013
Conversion of Alcohols to Alkyl Halides
Ankita Patel
August 6, 2013

This lab consisted of the conversion of alcohols into alkyl halides through common substitution methods. These methods include SN1 and SN2 mechanism, both of which can occur for this type of reaction. For both reactions, the first step of protonation will be to add hydrogen to the –OH group and then the rest of the reaction will proceed according to the type of mechanism. SN1 reactions form a cation intermediate once the H2O group leaves, then allowing a halide (such as Br) to attack the positively charged reagent1. On the other hand, SN2 reactions are one-step mechanism in which no intermediate is formed and the halide attaches as the leaving group detaches1. Rearrangements of the product are possible during the SN1 mechanisms, but not for SN2 mechanisms. This lab will examine the reaction of 1-propanol and 2-pentanol with NaBr in H2SO4, in which the H2O acts as the leaving group and Br as the attaching nucleophile (1). After the reaction has taken place through reflux and distillation, the product is able to be examined through NMR and IR spectroscopy analysis. Finally, these graphs will help in determining the products of each reaction and the type of mechanism used.



Mechanism of 1-propanol:

Mechanism of 2-pentanol:

Table of Reagents
Compound| Molecular Weight| Boiling Point| Melting Point| Density| 1-propanol| 60.10 g/mol| 97 °C| -127 °C| 0.804 g/mL| 2-pentanol| 88.15 g/mol| 119 °C| -50 °C| 0.812 g/mL| NaBr| 102.89 g/mol| 1396 °C| 747 °C| 0.733 g/mL|

H2SO4| 98.08 g/mol| 337 °C| 10 °C| 1.84 g/mL|
1-bromopropane| 122.99 g/mol| 71 °C| -110 °C| 1.354 g/mL| 2-bromopropane| 122.99 g/mol| 59 °C| -90 °C| 1.31 g/mL| 2-bromopentane| 151.04 g/mol| 117 °C| -95 °C| 1.223g/mL| 3-bromopentane| 151.04 g/mol| 119 °C| -97 °C| 1.216 g/mL| NaHCO3| 84.01 g/mol| decomposes| 60 °C| 2.2 g/mL|

The purpose of the IR Spectroscopy experiment was to measure the bonds in certain organic compounds. Each sample was analyzed on NaCl plates. NaCl does not absorb the radiation in the ranges that are examined. Because the NaCl plates are water sensitive, they were handled on the edges to avoid mistakes in the measurements. Any smudges were wiped off with the solvent. The data was then shared with other groups to obtain the information for the other reagents. The following week‘s experiment dealt with the conversion of alcohols to alkyl halides. 3.5 grams of NaBr and 6 mL of 9 M H2SO4 were added to a 25 mL round bottom flask. 2.5 mL of 2-pentanol and boiling chips were added next. This mixture was then heated under reflux for 20 minutes by the use of a sand bath. Next, the round bottom flask was cooled with an ice bath before the condenser was removed in order to prevent the loss of volatile organic product. A few more boiling chips were added and the flask went through a simple distillation. Do not stop distilling until the drip rate of the distillate slows significantly. The distillate was then transferred to a separatory funnel and 10 mL of water was added. After mixing, the layers were separated and the organic layer was washed with 10 mL of 5% aqueous NaHCO3. The dry product was weighed and a yield was calculated. Finally, samples were prepared for NMR analysis and also ran through an IR spectrum as well. Results:

Figure 1: IR Spectrum for 1-propanol

The results for the Infrared Spectroscopy of 1-propanol showed the complete adsorption of the O-H broad peak that was at 3804 cm-1, thus an indication that there was not a mixture of the products and reactants. It also indicated that the reaction went to completion (completely converting the alcohol to the alkyl halide). The IR of the product did indeed show C-H sp3 hybridized carbons at about 2948 cm-1. There was a C-H wag around 1260cm-1 that indicated it was a terminal alkyl halide. Even...

References: Brown, William Henry, Christopher S. Foote, Brent L. Iverson, and Eric Anslyn. Organic Chemistry. Belmont, CA: Brooks/Cole Cengage Learning, 2009. Print.
Hill, Richard K. and John Barbaro, Experiments in Organic Chemistry, 3rd Edition; Contempory Publishing Company of Raleigh Inc., 2005; T1-4, E2.
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