2020-organic chemistry lab2(chem225)-lab one PDF

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2020-organic chemistry lab2(chem225)-lab one...

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Lab #1: Reduction of Camphor to Borneol and Isoborneol Introduction For this experiment, we reduced camphor, a naturally occurring ketone, using sodium borohydride, into the isomers, borneol and isoborneol. When reducing camphor to a secondary alcohol, the oxidation state goes from a +2 to a +1 due to the addition of hydrogen to the electronegative oxygen. The mechanism first involves a nucleophilic attack through a hydride from NaBH4. When looking at the mechanism of this experiment, camphor can be attacked by a hydride bond through an exo or endo attack. The exo attack is more sterically hindered since there are two CH3 bonds in the way of the attack site, while the endo attack would only have one CH3 bond causing steric hindrance. For the two product possibilities, borneol is a result of the exo attack while isoborneol is a result of the endo attack. After the nucleophilic attack, the negative oxygen that attacks a proton from methanol forms an alcohol group. If we isolated these two isomers for IR spectroscopy, it would be difficult to distinguish the two, since their functional group peaks would be very similar. To accurately test and confirm which product would be produced more, we conducted NMR which gave us the ratio of the products and allows us to confirm which isomer is produced more. We also calculated our yield to see how much product we were able to recover from camphor, the starting material. Methods/Procedures (Explained in Pre-Lab) Mechanism Overall Mechanism

Detailed Mechanism

Endo attack → Isoborneol (MORE FAVORED)

Exo attack → Borneol (LESS FAVORED) Results/Observations/Analysis of Results

Observations: Some of the crystals were larger than others due to the clumping up during vacuum filtration, but a large amount of the crystals ended up being smaller. The crystals were all white/clear/opaque and powdery Percent Yield Starting Material: 250 mg of Camphor Camphor: 152 g/mol 0.25 g/152 g = 0.00164 moles of Camphor Theoretical Yield: 0.00164 moles Camphor ×

4 moles Borneol 4 moles Camphor

borneol/isoborneol Results: Pre-Weighed Flask: 27.43 grams Weight with crystals in the flask: 27.64 grams 27.64 grams - 27.43 grams = 0.21 grams recovered product

×154 g/mol Borneol = 0.2525 g

Percent Yield: 0.21 grams 0.2525 grams

× 100% = 83.17%

Melting Point of our Reactant/Product Camphor: 155.1ºC-168.4ºC Borneol/Isoborneol: 175.3ºC - 186ºC NMR RESULTS

NMR PPM/Integration Values/Percentages: Borneol: 1.000/~4.03 ppm Isoborneol: 4.5502/~3.64 ppm (1.000/5.5502) x100 = 18% → BORNEOL (4.5502/5.5502)x100 = 82% → ISOBORNEOL

Discussion/Conclusion Overall, we were able to recover a high percentage of the product, as our percent yield was 83.17%. As we were moving our product to different holding vessels, there might have been some lost material in the process, which would account for the ~0.04 gram loss. Additionally, during vacuum filtration, some of the crystal product could have been stuck to the Buchner funnel, or when we transferred it to the Erlenmeyer flask, some of the crystals could have fallen. The quality of our crystals was good as well, because the color of borneol and isoborneol is also white/clear/opaque like our pictures. Additionally, our crystals were mainly fine/smaller, as we had vacuum filtered them well to make sure they were completely dried out. Our second test to see if the reaction went to completion was IR spectroscopy, and at first, our IR graphs did not present an -OH group, but we were able to use a method where we dry loaded a single plate into the machine and the high concentration of our product on one plate allowed our expected results to show up. Our initial compound, camphor, had a carbonyl bond that occurs around 1742.29 cm^-1 and our product did not have any peaks at this value, and instead had a presence of an -OH group at around 3359.56 cm^-1 which is not found in camphor. Also, the sp3 C-H bond shows up at 2949.8 cm^-1 in borneol/isoborneol, and the normal value for sp3 C-H bonds is around 3000 cm^-1. This result also supports that our reaction went to completion. We then completed the melting points of our starting material, camphor, and our product of borneol/isoborneol, and the results were not as accurate as they should have been in comparison to the theoretical melting points. Our starting material, Camphor, that was provided

for us, is supposed to have a melting point of 175ºC but we got 155.1ºC-168.4ºC as our range. Since this material is supposed to be pure, the range should have been smaller, and the values should have been closer to 175ºC. Also for our product, we did expect a larger range and a lower value since it was a mix of borneol and isoborneol that have their -OH and -H located in different positions, making the mixture impure. The different structure of the isomers makes it easier for the compounds to break down, making it easier for them to melt as well. The expected melting point for both borneol and isoborneol was 208ºC, but our range ended up being 175.3ºC-185ºC. This range was a bit lower than we expected, but our melting point apparatus light/machine turned on and off a couple of times, so this could have disrupted the melting point process, giving us skewed results. The last test to see if our reaction went to completion and our products were pure, was NMR. According to the mechanism, the endo attack, which gives isoborneol, is from the bottom face which doesn't experience as much steric hindrance from only one CH3 group. Since the endo attack doesn’t have the two CH3 bonds that attribute to the steric hindrance of the exo attack, we expected the ratio in our NMR sample to display a greater ratio of the isoborneol than the borneol. On our graph, we had two main product peaks that are more downfield than the other signals because of the electronegative effect of the oxygen atom (Domzalski, Lab #1), and these were ~3.64 ppm and ~4.03 ppm for isoborneol and borneol, respectively. For the integration values on our NMR spectroscopy, we got 1.000 and 4.5502, making the ratio 4.5502:1. The reason for this difference is because there are chemical shifts for the CH-OH bonds that are different for borneol and isoborneol due to the different mobility, allowing the axial and equatorial hydrogens to feel the magnetic field differently (Domzalski, Lab #1). When

using the integration values on the graph, we can see the separate percentages of the isoborneol and borneol, we did (1.000/5.5502)x100 = 18% and (4.5502/5.5502)x100 = 82%. The 82% can be attributed to the percentage of isoborneol due to the explanation of why the exo attack has less steric hindrance than the endo attack which can be seen in the 18% result of the borneol. The only error in this spectroscopy is the fact that there was a presence of DCM which means that we did not successfully take out the DCM remnants when we were done dissolving any solids from our pure solution. Conclusion Our experiment showed that we were overall successful in bringing our product to completion, since we had a high yield, accurate IR peaks, and a reasonable NMR ratio. Though our melting point values were a bit lower than expected, this can be explained by the melting point apparatus’ malfunction. Also, our DCM peak was present due to our error in not taking out all of the DCM, which might have skewed the ratio slightly, but overall gave us reasonable NMR values. Post Lab Questions (None for this lab) References CS ChemDraw Pro. Computer software. Cambridge, MA: CambridgeSoft Corp., 1997. Domzalski, Allison. Lab #1 - Reduction of Camphor. January 2019. PowerPoint Presentation Hunter College. Chemistry 225 Lab Manual. Spring 2020 Pavia, Donald L. A Small-Scale Approach to Organic Laboratory Techniques . Belmont, CA: Brooks/Cole Cengage Learning, 2016. Print....