Lab 2 report - Reduction of Camphor to Borneol and Isoborneol PDF

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Reduction of Camphor to Borneol and Isoborneol ...

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Reduction of Camphor to Borneol and Isoborneol September 19, 2019

Abstract: The purpose of this experiment was to analyze the reduction of ketones to alcohols by using a reducing agent. The reaction was run between camphor and NaBH4 in methanol being a solvent; it has led to the formation of borneol and isoborneol isomers. The reaction mixture has undergone vacuum filtration, and following the addition of methylene chloride, the solution was dried with anhydrous Na2SO4. After isolating the product, the percent yield was calculated to be 80%. The final reaction mixture was expected to mostly have isoborneol due to NaBH4 majorly favoring endo attack of camphor at the least hindered position (Pavia, 2016); borneol should also be formed, but in fewer amounts, as it was a product of NaBH4 exo-attack in methanol solvent. The melting point obtained was determined to be 208°C, which has confirmed that isoborneol was not the only product of this reaction. Observations: 1. After undergoing vacuum filtration, the crystals did not appear powdered anymore. It indicated the evaporation of the solvent. 2. When using a drying agent, an abundant amount was used. After adding 1.25g of sodium sulfate, the solution still wasn’t completely clear. It indicated the excess of methylene chloride in the solution. 3. While obtaining the boiling point, crystals began to liquefy at 206°C and fully melted at 208°C. It indicated that there might have been more than one product of the reaction. Since the melting point range is only 2°C, it is unlikely that this difference was due to contamination.

Results: 

Product Data: Melting Point of borneol (lit.) = 208 °C* *some literature sources report it as being 202°C

Melting Point of pure isoborneol (lit.) = 214 °C Melting Point of camphor (lit.) = 175 °C Theoretical Yield = 0.0016 moles * 154.25 g = 0.25 g Melting Point of the reaction product mixture = 206-208 °C Yield = (m of flask w/product - m of empty flask) = 73.13 g – 72.93 g = 0.2 g % Yield = 0.2 g/0.25 g * 100% = 80%

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Analysis:

The % Yield of this reaction was determined to be 80%, which is a very good percent yield of the reaction. However, in methanol solvent we have expected sodium borohydride to attack camphor from the less sterically hindered side, thus, mostly forming isoborneol. While the literature value for pure isoborneol is listed to be 212°C, the melting point of the product obtained in the experiment was determined to be a range of 206-208°C. This fact is indicating that isoborneol was not the only product of this reaction; borneol isomer could have formed in small amounts and some amounts of camphor could have remained unreacted. While performing this experiment, error analysis should be done towards: -

yield of the reaction obtained due to an instrumental error; presence of solvent in product solution; possible loss of product while completing steps of the experiment; possible incomplete reduction reaction which would lead to starting material (camphor) still remaining in the final product purity of the product with the account to a literature boiling point and isomers; measuring melting point with the account to contaminations.

Conclusion: This experiment was a representation of ketones reduction to alcohols. Due to its stereochemistry, camphor was reduced by sodium borohydride into borneol and isoborneol. Two isomers were formed by NaBH4 endo- and exo-attacks of camphor in methanol solvent. The final reaction products were analyzed by obtaining the melting point and comparing it to the literature values. Borneol was predicted to be formed in much smaller amounts than isoborneol; some amount of the starting material, camphor, could still remain unreacted. Further analysis, like IR spectroscopy or mass spectrometry, might be considered to be performed in future experiments so as to determine all the reaction products and their percentage composition.

Post-Lab Questions: 1. Interpret the major absorption bands in the infrared spectra of camphor, borneol, and isoborneol. Major Absorption Bands:  Borneol: 3000 cm-1, 3380 cm-1, 1090 cm-1;  Isoborneol: 2950 cm-1, 3400 cm-1, 1070 cm-1;  Camphor: 3000 cm-1, 1780 cm-1. Functional Group Frequency Region: All three IR spectra (borneol, isoborneol and camphor) show one major absorption peak at the frequency of around 3000 cm-1, which is defined by sp3 hybridization, and indicates the presence of an alkane C-H bond in all compounds. 3380 cm-1 and 3400 cm-1 broad peaks in IR spectra of borneol and isoborneol correspond to the O-H stretch, an alcohol functional group. Fingerprint Region: A major peak at around 1780 cm-1 in camphor IR spectrum corresponds to the carbonyl group stretching, C=O functional group of a ketone. 1085 cm-1 and 1090 cm-1 frequency peaks of isoborneol and borneol correspond to secondary alcohol stretches.

2. A sample of isoborneol prepared by reduction of camphor was analyzed by IR spectroscopy and showed a band at 1750 cm-1. This result was unexpected. Why? Because a band at 1750 cm-1 corresponds to the presence of the C=O carbonyl group stretching, which is indicating that the reduction of camphor was not completed, and some amount of camphor is still remaining in the final product....