Lab Report 9 - Alkenes from alcohols: Analysis of a Mixture by Gas Chromatography PDF

Preview

Summary

Alkenes from alcohols: Analysis of a Mixture by Gas Chromatography...

Description

Lab Report 9 Alkenes from Alcohols: Analysis of a mixture by Gas Chromatography Henry Hoang, Angel Diaz, Sharup Majumdar CHM 2210L March 30th, 2020

Introduction: Reactions that can be used to form products that have double bonds, or alkenes, are know as elimination reactions because a small molecule is lost in the process. Alcohols can be protonated easily to form protonated alcohols that have good leaving groups such as H2O. This experiment will focus on creating alkenes from alcohols using elimination reactions, which usually implies that a molecule is lost during the reaction. An elimination reaction proceeds through three steps: the removal of a proton, formation of a carbon-carbon pi bond, and the breaking of the bond to the leaving group that can result in two different mechanisms of E1 and E2 (Hunt). An E2 mechanism is a concerted elimination reaction because the steps involving a loss of a leaving group and proton transfer occurs as one step involving no intermediates. An E1 mechanism is a unimolecular elimination reaction because there is only one molecule involved in the transition state of the rate determining step. In this unimolecular reaction, the loss of a leaving group and the proton transfer step occurs separately instead of happening in the same step. The rate of an E2 reaction is dependent on the concentration of the base and the substrate with one occurring if there is a high concentration of a strong base and if there is a good leaving group such as HI. The rate of an E1 reaction is dependent on only the concentration of the substrate and occurs most rapidly with the presence of weak bases, stable carbocations, and good leaving groups.

Experimental Section:

Table of Chemicals: olar Mass(g/mol) .15 g/mol .13 g/mol .13 g/mol

Physical Properties clear, colorless liquid colorless volatile liquid clear, colorless liquid

Put 1.5 coni while m sulfur and th

Obtai stock chro avoid 5m

Results: Mass of Product (g) 0.8g

Percent yield (%) 63.3%

Calculations: Percent yield = (actual yield/theoretical yield) * 100% Actual yield = 0.8g/70.13(g/mol) = 0.0114 mol Theoretical yield = 1.6g/88.15(g/mol) = 0.018 mol Percent yield = (0.0114 mol/0.018 mol) * 100% = 63.3%

Discussion: In this experiment, the percent yield was calculated to being 63% after acquiring a mass of 0.8g of the product. The 2-methyl-2-butanol that was originally added to the solution had a mass of 1.6g. Using these two masses, the percent yield was calculated after finding the moles of each mass using the molar mass. The actual yield was calculated to being 0.0114 moles, while the theoretical yield was determined to be 0.018 moles. After dividing the actual yield by the theoretical yield and multiplying by 100%, the percent yield was determined to be 63% which is higher than 50%. In analyzing both the gas chromatogram and the data table underneath, the first peak was observed to have a retention time of 1.785 minutes, whereas the second peak had a retention time of 2.243 minutes. The retention time for the first peak was shorter than the second one, so this meant that the first peak was more volatile and reacted slightly quicker than the compound in the second peak. The second peak can be assumed to be the major product which is 2-methyl-2-butene because of its large area, whereas the first peak can be assumed to be the minor product, 2-methyl-1-butene because of its drastically smaller area. The percentage of the first peak was only 9.1% which indicates that it is the minor product, while the second peak was 90.9% which shows that it is the major product. Conclusion: The aim of this experiment was to prepare a mixture of 2-methyl-1-butane and 2-methyl-2butene from 2-methyl-2-butanol by employing sulfuric acid as a catalyst and to analyze the products formed by gas chromatography. The experiment was a success in meeting its objectives because two peaks appeared on the gas chromatogram, showing that both products were formed.

This showed that an acid catalyzed base reaction took place as the 2-methy-2-butanol and sulfuric acid were being distilled. As this was taking place, the alcohol was protonated into water which allowed for a leaving group and a carbocation to form. The use of chromatography allowed for an analysis of the reaction mixture with factors such as, area, height, concentration, and time retention being used to determine the major and minor product. The techniques learned in this experiment can be applied to real world situations, for example: gas chromatography is a techniques used throughout forensic science in investigate criminal cases in the form of blood or cloth samples, arson verification, or blood testing after death to determine levels of alcohol, drugs, or poisons in the body (5 Uses of Chromatography in Everyday Life). This experiment accomplished what it set out to do because new techniques and skills were learned in this lab, from gas chromatography to simple distillations to produce alkenes from alcohols. References: Hunt, I. Ch 5 : Elimination. Ch 5 : Elimination. University of Calgary. (Accessed March 30, 2020) 5 Uses of Chromatography in Everyday Life. Chromatography Today. (Accessed March 31, 2020) National Center for Biotechnology Information. PubChem Database. 2-Methyl-2-butanol, CID=6405, https://pubchem.ncbi.nlm.nih.gov/compound/2-Methyl-2-butanol (accessed on Mar. 30, 2020)

National Center for Biotechnology Information. PubChem Database. 2-Methyl-1-butene, CID=11240, https://pubchem.ncbi.nlm.nih.gov/compound/2-Methyl-1-butene (accessed on Mar. 31, 2020) National Center for Biotechnology Information. PubChem Database. 2-Methyl-2-butene, CID=10553, https://pubchem.ncbi.nlm.nih.gov/compound/2-Methyl-2-butene (accessed on Mar. 31, 2020) Weldegirma, S. Experimental Organic Chemistry Laboratory Manual, 8th Edition 2020. University of South Florida. ProCopy Inc....