Exp2 Oxof Indanol - hi r\\]sadfghjkuilo;p\'[ ] PDF

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Dry Lab Worksheet

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EXPERIMENT #2 HYPOCHLORITE OXIDATION OF 1-INDANOL Reference Material: MAHSH Chapter 3: Laboratory Notebooks and Prelaboratory Information MAHSH Chapter 10: Extraction (sections 10.1, 10.2) MAHSH Chapter 11: Drying Organic Liquids and Recovering Reaction Products MAHSH Chapter 18: Thin-Layer Chromatography (sections 18.1-18.6, 18.8, 18.9) MAHSH Chapter 21: Infrared Spectroscopy (sections 21.5-21.10) MAHSH Chapter 22: Nuclear Magnetic Resonance Spectroscopy MAHSH Chapter 23: 13C NMR Spectroscopy (sections 23.1-23.3) Klein Chapter 12: Alcohols and phenols (section 12.4)

This dry lab will cover the oxidation 1-indanol (Scheme 1) to the corresponding ketone, 1indanone. This reaction makes use of common household bleach as the oxidizing agent and a phase transfer catalyst (PTC) which will be described a little later. Ethyl acetate (EtOAc) is the solvent for this reaction. First, for oxidations of this type, there are two general mechanistic themes: 1) the hydrogen of the hydroxyl group is first converted into a good leaving group (-L) followed by 2) an E2 process that eliminates the carbinol hydrogen1 and the leaving group (Scheme 2). Scheme 1

Scheme 2

A possible mechanism for the oxidation with bleach is shown in Scheme 3. Initially the alcohol is protonated such that water becomes the leaving group in a subsequent substitution reaction

1 In organic chemistry, “carbinol” is an old-school term for the carbon bound to the hydroxyl oxygen in an alcohol (e. g. C-OH). Therefore, carbinol hydrogens are those hydrogens bound to this carbon.

giving what is called a hypochlorite ester (R-O-Cl). An E2 reaction then gives the carbonoxygen double bond. Scheme 3

Question 1: The proposed mechanism for the oxidation of 1-indanol with bleach will follow the similar mechanism shown in Scheme 3. Assuming the second step in the mechanism undergoes an SN2 type mechanism, finish the proposed mechanism for the reaction below by including the two intermediates that appear and drawing in the curved arrows to show the flow of electrons for each step.

Click here to see the video on phase tranfer catalysts that accompanies the next paragraph. There is a problem when choosing a solvent performing a reaction like this in a pure organic solvent like ethyl acetate. The alcohol, 1-indanol, is very organic soluble. Bleach, which is available as an aqueous solution, is organic insoluble. If bleach remains organic insoluble and is unable to come into contact with the alcohol in the organic solvent, no reaction will take place. So, how would one make an insoluble material soluble? One way to achieve this is to “trick” the insoluble material by encapsulating it within a substance that is soluble. For this reaction, we

will start with a biphasic mixture of ethyl acetate and aqueous sodium hypochlorite. We will then treat this mixture with tetrabutylammonium hydrogen sulfate, a common phase transfer catalyst (PTC). The ammonium portion of this compound has four butyl branches making it quite soluble in many organic solvents. However, as an ammonium salt, it is also very water soluble. Tetrabutylammonium ions may therefore pass freely between the aqueous and organic phases of biphasic solutions. Tetrabutylammonium cations can also encapsulate hypochorite ions, pass into the organic phase of the reaction, and release them making them available to react with the organic soluble alcohol (Scheme 4). Scheme 4

Question 2: Which of the two ammonium ions (A or B) would you expect to be a more effective phase transfer catalyst for the oxidation of 1-indanol? Explain why. (Note: this question is rather tricky. Do your best to answer)

Experimental: Hypochlorite Oxidation of 1-Indanol To a 100 mL round bottom flask equipped with a small magnetic stir bar, 30 mL of fresh bleach, 30 mL of ethyl acetate, 2.00 g of 1-indanol, and 0.30 g of tetrabutylammonium hydrogensulfate was added (Figure 1a). The mixture was stirred vigorously at room temperature (Figure 1b). Figure 1. a) The reaction after all of the reagents were added to the flask, and b) the reaction when stirred vigorously a) b)

Question 4: Calculate the theoretical yield.

Question 5: As seen in Figure 1b, proper mixing is essential for this oxidation reaction to work. Based on what can be observed in the figure, why is this so? (Hint: What is an emulsion and how does emulsification impact surface area? How would this impact the rate of reaction?)

Thin-layer chromatography (TLC) was used to monitor the organic phase after 15 and 30 minutes (1:2 EtOAc:hexane as the mobile phase). Each TLC plate contains three lanes: one for the starting material (1-indanol), one for the reaction mixture (organic phase), and a co-spot in the middle. A co-spot will contain spots of both the starting material and the reaction mixture, and it can be used as a reference for interpreting TLC results if variations are present on the TLC. Figure 2. A photo of the TLC plates obtained after a a) 15 minute and b) 30 minute reaction time. The labels on each TLC plate are as followed: SM = 1-indanol, CO = co-spot, 15 = reaction mixture at a 15 min reaction time, 30 = reaction mixture at a 30 minute reaction time. a)

b)

Question 6: Calculate the Rf value for the starting material spot and of the new spot that has formed in the reaction mixture. Click here to review TLC analysis from an Organic Chemistry I video.

Question 7: Based on the results of the TLC (Figure 2), does the evidence suggest that the reaction complete after 15 minutes? After 30 minutes? Explain your reasoning.

The organic layer was transferred to a separatory funnel. After washing the organic layer by liquid-liquid separation with two 30 mL portions of water followed by two 30 mL portions of brine (saturated NaCl solution), the the organic layer was dried over Na2SO4 and decanted into a clean, tared beaker. The organic solution that was collected in the beaker was left to dry. After a week, the organic solvent had evaporated and a white, crystalline solid was left in the beaker (Figure 3).

Figure 3. The solid left in the beaker after the organic solvent has evaporated.

Question 8: If the mass of the solid collected was 1.28 g, what is the percent yield of the product, 1-indanone?

IR spectra were obtain of the starting material (1-indanol) and of the white solid. Figure 4. IR spectrum of staring material, 1-indanol

Figure 5. IR spectrum of the collected white solid (supposed product of the reaction)

Question 9: According to the IR spectra (Figures 4 and 5), is there evidence that the desired product, 1-indanone, formed? To answer this question, look to see if signals corresponding to the functional group(s) you would expect to see with the desired product (1-indanone) are present in the IR spectrum of the white solid collected. The functional group(s) found only in the starting material (1-indanol) should have also disappeared. To know what signals you would expect to see with the fuctional groups present in a compound, refer to your IR signal chart from Organic Chemistry I Lab, useful table in the “Spectroscopy Information” content folder on Bb, or click here to see a separate chart. As a reminder, ignore any signals that appear in the fingerprint region (below 1500 cm-1).

1

H NMR spectra were obtain of the starting material (1-indanol) and of the white solid.

Figure 6. 1H NMR spectrum of staring material, 1-indanol.2

2 Please note: 1-indanol contains four diastereotopic protons. These protons add to the complexity of the spectrum in that each has a different chemical shift (ppm value) and they do not follow a simple n + 1 coupling pattern. It may be worth your while to identify the diastereotopic protons in 1-indanol.

Figure 7. 1H NMR spectrum of the collected white solid (supposed product of the reaction).

Question 10: What signal corresponds to Ha in Figure 6 (report the chemical shift)? Is this signal present in the 1H NMR spectrum of the collected white solid?

Question 11: Where would you expect the signals for Hb and Hc in the desired product to appear on the 1H NMR spectrum? What would you expect the multiplicity to be for both signals? Do you observe this in the 1H NMR spectrum of the white solid?

Question 12: How would you expect the chemical shifts of the aromatic hydrogens to be different between the starting material and the product, and why would this happen? (Hint: look for electron withdrawing or donating groups near the aromatic ring). Do you observe this difference in the 1H NMR spectra above?3

3 A document entitled “Chemical Shifts of Substituted Benzenes” found in the “Spectroscopy Information” content folder on Bb may help you with this question.

Question 13: Based on your assessment of the 1H NMR spectra (Figures 6 and 7), is there evidence that the desired product, 1-indanone, formed? Briefly explain why.

Question 13: 13C NMR spectra were not obtained for this experiment. If it were, how would you expect the signal for carbon a in the starting material to change when it becomes carbon b in the product?...