Microscale Hydration of Norbornene

Microscale Hydration of Norbornene

Introduction:

        The purpose of this lab was to perform an acid catalyzed hydration of norbornene to determine which of two stereoisomeric products was obtained. Knowing the hydration mechanism, the end product should be an alcohol. During this experiment the regiochemistry of addition was the same for both products but the stereoselectivity of addition could have resulted in either product: exo-norborneol or endo-norborneol. [1] Multiple liquid-liquid extractions were performed during the lab experiment in order to isolate the end product by removing impurities. Water is immiscible with methylene chloride, therefore extraction could be performed with the two liquid compounds. Water was used to wash the organic liquid, which was later removed by taking away the aqueous layer or removed by the introduction of anhydrous sodium sulfate. Methylene chloride was used to extract, then later removed by heat. [1] This resulted in a purified product that was able to be tested.

Infrared spectroscopy is used to determine what functional groups and covalent bonds are present in a specific substance. By exposing an organic molecule to infrared radiation, the radiant energy has the opportunity to match that of a specific molecular vibration energy. When the match occurs, absorption takes place and a graph can be made to correspond to these absorptions. [2] Since exo-norborneol and endo-norborneol are stereoisomers (diastereomers), the covalent bonds are identical. The analysis process must be taken a step further to the specific wavenumber length of the C-O stretch in each product. [4] This will ultimately determine what stereoisomer is present in the end product.

Experimental:

        To the 5-mL vial was added water 0.25 mL and a spin vane. The vial was placed in an ice bath and concentrated H2SO40.5 mL was added dropwise. The ice bath was removed and norbornene 150 mg was added to the vial and stirred until dissolved. The solution was transferred to a test tube and the vial was washed with water 1 mL. The solution in the vial was added to the test tube and then placed in an ice bath. To the test tube was pipetted dropwise 6 M NaOH3.5 mL. The mixture was swirled and the pH was checked using moist blue litmus paper. The paper did not turn red so no additional base was added. The test tube was removed from the ice bath and allowed to return to room temperature.

        To the 5-mL vial was added methylene chloride 1.5 mL. The vial was capped then swirled gently and vented two times. The cap was removed and the bottom organic layer was transferred to a separate 5-mL vial. Methylene chloride 1.5 mL was added to the aqueous solution and the first extraction was repeated. The second methylene chloride extract was combined with the first. The organic solution was washed by water 1 mL by capping the vial and shaking gently. The bottom organic layer was filtered through a pipet, containing anhydrous sodium sulfate on top a cotton stopper, into a separate, clean 5-mL vial with a boiling chip. The solvent was evaporated by heating the vial in a sand bath. The vial was allowed to cool to room temperature before it was weighed to determine the yield of product. [1]

Results and Discussion:

A final product was obtained and an IR spectrum was collected. The hydration reaction can produce two separate stereoisomeric products as is shown in Figure 1.

[pic 1]

Figure 1: Acid catalyzed hydration mechanism of norbornene. [1]

Both products are almost identical, except for the difference in spatial arrangement of the the hydroxyl group on the first carbon. This C-O bond is the bond that was observed in order to determine which product was formed at the end of the reaction. Both products have a small difference in their wavenumbers, at the C-O bond as shown in Figure 2.

[pic 2]

Figure 2: Table of differences between exo and endo norborneol. [4]

In the spectra it was expected to see the presence of an O-H bond, signifying the reaction was a complete transition from norbornene to exo or endo norborneol. [1] A C-O bond should also be present at either 1000 cm-1 or 1030 cm-1 in reference to Figure 2. [4] The IR was taken and Figure 3 shows the results.

[pic 3]

Figure 3: IR spectrum of the end product, taken in the lab.

        At approximately 3300 cm-1, is a peak that corresponds to the O-H bond of the alcohol that makes norbornene, norborneol; the reaction was complete. The peak at about 2900 cm-1 corresponds to the Csp-3 - H bonds, which further confirms the complete production of norborneol. The last peak occurs at exactly 1000 cm-1. This peak represents the C-O bond of norborneol and ultimately shows the production of exo-norborneol according to Figure 2. [3] Other sections of the graph were also taken into consideration. Between 2400 cm-1 and 1650 cm-1, the spectrum shows some impurities. However, overall the IR spectrum is consistent with that of pure exo-norborneol.

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