Reduction of Camphor- Editor PDF

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Reduction of Camphor

Lead Author: Lois Metuge Reviewer: Elliott Burnet Editor: Amber Sanders

Introduction Reduction and oxidation reactions, also known as redox reactions, occur frequently in nature and drive many biological systems. Redox reactions involve the transfer of electrons by either grain or loss of electrons. Reduction is the gain of electrons while oxidation is the loss electrons, so therefore if one molecule is being oxidized another is being reduced. In this experiment, the focus is on the reduction of camphor.2 Camphor is a natural occurring ketone and can be drawn in a bridged bicyclic molecule as shown in Figure 1; it also contains a planar carbonyl group which can be reduced using a complex hydride like sodium borohydride.2 Since the carbonyl group of camphor is planar, the complex hydride can attack it at two faces, making two stereospecific alcohols: isoboreneol and boreneol.2 Sodium borohydride can attack at the top face and bottom face.2 The top face attack produces the boreneol alcohol which a bicyclic bridge in the exo position, and the bottom face attack produces the isoboreneol alcohol, a bicyclic bridge that is in the endo position.2 The intermediates for the two face attacks are protonated by methanol.2 Figure 1 shows the step wise mechanism for the reduction of camphor using sodium borohydride. Determining which product was formed in this lab involved using methods like melting point analysis, IR spectroscopy and an NMR graph.2 The melting point of isoboreneol and boreneol differ slightly at 208 °C and 212 °C respectively as shown in Table 1.2

Figure 1: Detailed mechanism of the reduction of camphor by sodium borohydride.2

Table 1: Table of Reagents1,2 Reagents Camphor Sodium borohydride Boreneol Isoboreneol Methanol Diethyl ether Magnesium

Density (g/cm3)

Molecular weight (g/mol) 152.23 31.83

Boiling point (°C) 209 500

Melting point (°C) 175 400

0.992 1.07

154.25 154.25 34.04 74.12 120.366

213 213 64.7 34.6 NA

208 212 -97.6 -116.3 1124

1.01 1.01 0.792 0.7134 2.66

Sulfate (MgSO4) Experimental 0.104 grams of weighed out camphor and 10 mL of methanol were added into a 10 mL Erlenmeyer flask.2 This solution was swirled until the camphor fully dissolved.2 Next, 0.10 grams of sodium borohydride (NaBH4) was added into the 10 mL flask in four portions while continuing to stir the solution.3 The NaBH4 was added in small four portions to prevent it from violently reacting.3 Once the NaBH4 was added, the solution was put in a hot water bath to boil for about 2 minutes.2 After heating, it was allowed to cool to room temperature.2 After cooling, 3.5 mL of ice water was added into the reaction mixture in the flask.2 At this point a white precipitant began forming which indicated that the product was forming.3 The solid product was then vacuum filtrated using a Hirsch funnel.2 The solid was allowed to dry on the filter paper for several minutes.2 After drying, the solid was transferred into a 10 mL Erlenmeyer flask and 4.5 mL of ether was added to dissolve the product.3 To dry the organic product and absorb any excess moisture, a small of amount of MgSO4 was added.2 In the second part of the experiment, another 10 mL flask was weighed, and the organic product was transferred into this flask.2 Any excess organic product left in the previous flask was rinsed with additional 1.0 mL of ether and was decanted into the weighed-out flask.2 In the hood, the contents of the 10 mL weighed flask were placed back into the warm water bath so the solvent could evaporate out.2 Once evaporated, a precipitant formed at the bottom of the flask which was indicative of the product.3 The flask was then weighed again to get the final product mass.2 The product was also used to find its melting point using a melting point apparatus, its IR data, and the NMR data.2 Results The starting product mass of 0.104 grams of camphor was weighed out.3 This value was used to calculate the theoretical yield as shown in Eq. 1. The theoretical yield was calculated to be 0.105 grams. The final product mass, which is mass of the final product obtained after evaporation, was calculated to be 0.0862 grams.3 The starting product and final product were Actual yield ∗100 as shown in Eq. 2. used to calculate percent yield using the formula Theoritical yied Eq. 1.

0.104 g Camphor ∗1 mol Camphor 1 ∗1 mol borneol 152.25 g Camphor ∗154.25 g borneol 1 mol Camphor =0.105 grams 1 mol borneol

Eq. 2.

0.0862 grams ∗100=82.10 % 0.105 grams The melting point analysis done on the final product gave a result of 198-204°C.3 Next, the IR and NMR graphs obtained are shown below. Figure 2 shows the IR graph of the starting

product and Table 2 describes all the important peaks and functional groups. Figure 3 shows the IR graphs of the final product and Table 3 describes all important peaks and functional groups. Figure 4 shows the NMR graph of the final product and which peaks represent which product isomer.

Figure 2: The IR graph of starting product camphor.3 Table 2: IR Table Breakdown for Starting Product Camphor Frequencies (cm-1) Functional group 1738.84, sharp C=O, carbonyl 2876.24-2956.74 C-H sp3 stretch

Figure 3: The reduction of camphor final product IR graph.3 Table 3: IR Graph Breakdown Final Product of the Reduction of Camphor Frequencies (cm-1) Functional group 2900-3000 C-H sp3 3200-3500 O-H

Figure 4: The NMR graph of final product boreneol (labeled).3 Utilizing the results of the NMR graph for the reduction of camphor final products, mole Single Peak Integration 4 ratio could be calculated. The mole fraction formula is of ∑ Equivalent Peak Intergraion . The integration pattern of isoborneol is 5.07 and the integration pattern of borneol is 1.00. The mole ration for both products is calculated in Eq. 3 and Eq. 4 below. Eq. 3.

Isoborneol Mole Fraction:

5.07 =0.835 moles 5.07+ 1.00 Eq. 4.

Borneol Mole Fraction:

1.00 =0.165 moles 1.00+5.07

Discussion The objective of this lab was to reduce the ketone, camphor, utilizing sodium borohydride.2 The mechanism proceeds by sodium borohydride attacking the planar carbonyl on camphor at either the “top” or the “bottom” face.2 The top face attack produces borneol as a product which is in the exo position, while the bottom face attack produces isoborneol, a product in the exo position.2 The products are stereoisomers of each other.2 The steps completed during lab proceeded successfully and produced a product that was utilized to get a percent yield,

melting point analysis, infrared graph and NMR graph.3 The percent yield as shown in Eq. 2 was calculated to be 82.10%. This is a relatively high percent yield which indicates that the product was produced effectively, though the percent yield not being higher could be a result of loss of product during decanting from one flask to the other. The evaporating process could have resulted in loss of product as well. The melting point analysis produced the results of 198204°C.3 The melting point being so low and broad indicates that the product produced is more than likely a mixture of both isoborneol and borneol (the melting point of isoborneol is 212°C, and the melting point of borneol is 208°C as seen in Table 1). The IR graph in Figure 2 shows a C=O stretch at 1738.84 cm-1, and C-H sp3 at 2876.242956.74 cm-1; these results are indicative of the functional groups present in camphor so the camphor starting product was correct. The final product IR graph shown in Figure 3 has a functional group of C-H sp3 2900-3000 cm-1 and a O-H bond at 3200-3500 cm-1. Looking at the starting material IR graph compared to the final product, it can be seen that the C=O present in the starting material is no longer in the final product, instead there is an alcohol (O-H) functional group present. This is indicative of the fact the product formed correctly, because the carbonyl group was successively reduced to an alcohol. IR graphs do not depict the specific structures of compounds formed, but

they are good for recognizing which functional groups are present. NMR graphs, on the other hand, identify specific structures. The NMR graph indicates that there is isoborneol is present at about 3.60 ppm and borneol present at about 4.00 ppm. Both stereoisomers have H beside the -OH group, but borneol -H is less shielded at 4.00 ppm than isoborneol’s -H at 3.60 ppm. Essentially the -OH group has a pull that affects borneol more than isoborneol, as a result isoborneol is the major product and is more stable than borneol. This result is also proven by the calculation of the mole ratio of isoborneol and borneol using the integration pattern of both stereoisomers. The integration pattern of isoborneol was found to be 5.07 and its mole ratio, calculated in Eq. 3, is 0.835 moles. For borneol, the integration pattern was 1.00 while its mole ratio, calculated in Eq. 4, is 0.165 moles. The mole ratio for isoborneol is higher than borneol, further proving that isoborneol is the major product. Conclusion This experiment involved the reduction of Camphor by the complex hydride sodium borohydride.2 The resulting mechanism for this reduction could proceed in two ways, with NaBH4 attacking the carbonyl on camphor at two places to produce the stereoisomers isoborneol and borneol.2 The results of this lab show that the product was produced successfully with the percent yield at 82.10% and all the functional group on IR graph moving from a C=O (carbonyl group) to a O-H (an alcohol group). The major product of the reaction was isoborneol based on the NMR graph and the mole ratio calculation. This experiment could be improved by conducting the evaporating step more carefully so as to not evaporate any product and produce a product with higher purity. The moving of solution from one flask to another also messes up the precision of product formation because some product could be lost in the process.

References 1. Burnett, E.; Metuge, L.; Sanders, A. University of Alabama at Birmingham, Birmingham, AL. Laboratory Notes for CH 238: Organic Chemistry Laboratory I, 2020. 2. Casselman, B. Reduction of Camphor Procedure. https://uab.instructure.com/courses/1532137/files/64567454?module_item_id=15830864 (Accessed October 30, 2020) 3. Casselman, B. Camphor Lab Data. https://uab.instructure.com/courses/1532137/pages/lab-data?module_item_id=15830868 (Accessed October 30, 2020) 4. Casselman, B. Alcohols to Alkyl Halides Pre-Lab Lecture. https://uab.instructure.com/courses/1519054/files/62561924?module_item_id=15422613 (Accessed October 30, 2020)...