Lab report 9 - Dehydration of 2-Methylcyclohexanol PDF

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Dehydration of 2-Methylcyclohexanol...

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Natalie Loveridge CHEM 2221L 11/22/2020 Dehydration of 2-Methylcyclohexanol Introduction: The purpose of this experiment is to dehydrate 2-methylcyclohexanol in the presence of phosphoric acid, distill the alkene products as they are formed, and then analyze the product composition via gas chromatography. Dehydration of alcohols can often synthesize alkenes (and water), and this process is often performed by heating the alcohol in the process of a strong acid. Many alkene products can be formed via this dehydration reaction because 2methylcyclohexanol is an unsymmetric alcohol and because of the carbocation formation in the E1 mechanism. In this experiment, the 2-methylcyclohexanol was dehydrated with phosphoric acid and the alkene products were fractionally distilled. At the end, the distillate was washed and dried and analyzed via gas chromatography. The calculated theoretical yield of the product was 4.73 grams, and the reaction of this dehydration is mapped out in figure 1 below. Figure 1: Dehydration of 2-Methylcyclohexanol

Procedure: This experiment was carried out as described in the given manual procedure. No changes or adjustments were made. Results: In this experiment, 2-methylcyclohexanol was dehydrated to form a series of alkene products. The calculated theoretical yield was 4.73 grams. The calculations for the theoretical yield are shown below. Theoretical Yield: 6mL * 0.9360 g/mL * mol/114.19g = 0.04918 mols 2-methylcyclohexanol Molar Mass of Product = 96.17 g/mol

96.17 g/mol * 0.04918 mols = 4.73g

The actual yield of this experiment, after fractional and simple distillation, was 4.1mL or 3.33g. The calculations are shown below. Actual Yield: 4.1 mL * 0.8112 g/mL = 3.33g

The percent yield was 70.4%, and was calculated below. (3.33g/4.73g)*100 = 70.4% The gas chromatography trace was also taken for the final product and is shown below in figure 2. Figure 2: Gas Chromatography Trace

The two products that were formed (1-methylcyclohexene and 3-methylcyclohexene) can be seen at peaks 4 and 5. The major product, 1-methylcyclohexene, can be seen at peak 5 and the minor product, 3-methylcyclohexene, can be seen at peak 4. According to the GC analysis report, the area of peak 4 (3-methylcyclohexene) was 115609 and the area of peak 5 (1-methylcyclohexene) was 558446. These areas were compared to analyze the ratio of products (1-methylcyclohexene to 3-methylcyclohexene) formed in the calculations below. Ratio of 1-methylcylohexene to 3-methylcyclohexene: 558446:115609 = 4.83:1 Finally, the IR spectra of the initial starting material and the IR spectra of the final product were taken and analyzed.

Figure 3: FTIR spectra of 1-methylcyclohexanol

Figure 4: FTIR spectra of final product

Conclusion: The dehydration of 2-methylcyclohexanol was successful in forming two alkene products, 1-methylcyclohexene and 3-methylcyclohexene. One can conclude this because of the high percent yield, the GC analysis showing two solid product peaks, and the final IR spectra. In regard to the GC analysis, the major product, as seen in the 5th peak of the GC analysis, is 1methylcyclohexene. One can see this because the reported area is greater for the 5th peak than the 4th peak. The predominance of this product is because the methyl group and the double bond together create a more substituted carbon. The final IR spectra also indicated that the hydroxyl group had been successfully removed since there was a lack of the peak seen at around 3500 cm-1 in the original IR spectra of 1-methylcyclohexanol. If 3-methylcyclohexanol were dehydrated, the products would be 3-methylcyclohexene and 4-methylcyclohexene. Neither cyclohexane would predominate. This is because, according to Zaitsev’s rule, the more substituted alkene will be the major product. In this reaction, the alkenes are equally substituted, so neither products would predominate....