(5r)-Menthone Synthesis Lab Report

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(1R,2S,5R)-(-)-Menthol crystals were used to prepared (2S,5R)-(-)-menthone in a one-step reaction. Then, the (-)-menthone was used to synthesize a mixture of two of its derivatives in another one-step reaction. The (-)- menthone was first synthesized in a modified Jones reaction using pyridinium cholorochromate (PCC) as seen in Scheme 1.1 The (-)-methone was then used to produce a mixture of (2S,5R)-(-)- methone and (2S,5R)-(+)-methone via an acid-catalyzed epimerization reaction (Scheme 2) as well as to reduce to (1R,2S,5R)-(-)-menthol in Scheme 3 using sodium borohydride. The optical rotation, IR spectrum, 1H NMR spectrum, Mass spectrometry, and Gas Chromatography (GC) were used in the experiment to determine the optical rotation and stereochemistry…show more content…
Compound 2 was reduced by sodium borohydride to form 4 and its stereoisomer 5. The hydride in sodium borohydride acted as a nucleophile and attacked the carbonyl group in 2. Depending on the top of bottom position where the hydride attacked, 4 or 5 would be formed.3 From the study, the IR spectrum (Figure 8) showed frequencies at 3392 cm-1, 2868 cm-1, and 1455 cm-1, which specified the functional groups: -OH, sp3 CH3, and the –CH2 bend of the cyclohexane ring. In addition, the proton NMR spectrum (Figure 9) indicated that the peak at 4.1 ppm was the hydrogen from the –OH functional group. In addition, the peaks at 0.9 ppm were said to be the hydrogens from the –CH3 functional group, and the peaks at 1.1 ppm, 2.0 ppm, and 3.2 ppm were from the hydrogens of the cyclohexane ring. When compared the proton NMR spectrum of the mixture of 4 and 5 (Figure 9) with the starting compound 1 (Figure 2), Figure 2 seemed to have a more distinct peaks than Figure 9 ; thus, it could be said that the dominant compound in the mixture was 5 instead of 4. From the GC data (Figure 10), 99.5% compound 5 was said to be synthesized, and the other 0.466% was determined to be compound 4. The literature ratio values for the products of the reduction of (-)-menthone were 65 % neomenthol and 35 % menthol when the reduction reaction used sodium borohydride as a reducing agent. 2 However, the ratios from the study was way higher than the ones in the literature; this could be due to qualitative errors or different in the environmental factors where the GC of the sample was determined. In addition, the specific rotation of the mixture was determined to be [α]obs: -0.203 and [α]: -176⁰. Because neomenthol was more stable than the menthol compound, assuming the conformation of menthol functional groups were all axial, and neomenthol compound had the –CH3 and the isopropyl functional groups in the equatorial

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