Lab 8 Preparation of alcohols Reduction of 9-Fluorenone PDF

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Tanvi Kulkarni 11/09/2020 Lab 8: Preparation of alcohols: Reduction of 9-Fluorenone Methods and background: The purpose of this lab was to prepare 9-fluorenol by taking 9-fluorenone and using sodium borohydride as a reducing agent to get rid of the ketone that is in 9-fluorenone. After the 9-fluorenol is isolated, we will purify it through the process of recrystallization and then verify the results by performing a Lucas test. The lucas test allows us to determine if there is a presence of an alcohol group. We will also do melting point analysis, IR and NMR spectroscopy to test the primary and tertiary alcohols. To turn 9-fluorenone into 9-fluorenol, the process of a reduction reaction will have to take place. A reduction reaction means the product gains an electron around the carbon atom. It will turn into a more electronegative atom like nitrogen, oxygen, or a carbon-hydrogen bond instead of having a carbon-carbon bond. The overall effect on the carbon atom in a reduction reaction is a decrease in the oxidation number. The 9-fluorenone that we begin with has an oxidation number of +2, but after the reduction reaction occurs the final product of 9-fluorenol has an oxidation number of 0. The oxidation state changes by adding 1 for every carbon bond that makes it a more electronegative bond, we also subtract 1 for every bond that carbon makes to make a less electronegative bond. So we see that our starting 9-fluorenone has a double bonded carbon to oxygen which means we would add 2 because of the double bond, thus it has an oxidation state of +2. The 9-fluorenol that is our final product has a carbon alcohol bond and it would be +1 for the carbon oxygen bond but then it would also be -1 because there is a carbon hydrogen bond. Because hydrogen is less electronegative than carbon, that's why we would subtract 1 so then the oxidation state of 9-fluorenol would be 0.

In this lab specifically,

we use sodium

borohydride as the

reducing reagent. The

Tanvi Kulkarni 11/09/2020 reason we use this specific reagent is because it can reduce aldehydes, ketones, and imines without being too harsh on the product. The way sodium borohydride reacts with 9-fluorenone is that a hydrogen from borohydride attaches to the carbonyl in the 9-fluorenone which will then create a carbon-hydrogen bond. It then breaks the carbon-oxygen bond which leaves a lone pair on the oxygen . A proton from the sulfuric acid protonated the oxygen and creates a new carbon-oxygen-hydrogen bond which results in 9-fluorenol. The mechanism is slightly altered because there are 4 hydrogen atoms attached to the boron in sodium borohydride and this may cause a borate salt to form. When we have reacted 9-fluorenone with our reagent, we did a thin-layer chromatography test to test the reaction. We placed three spots on the TLC plate, the first was a pure sample of 9-fluorenone, the middle spot was a co-spot which was the reaction and the pure sample, the third spot was only the reaction. By doing this test, we look for the difference in the polarities of the reaction mixture and the pure sample. Looking at the structures of our reaction mixture, it would be more polar because of the alcohol group so the sample spot would have a lower Rf value. The 9-fluorenone pure sample with a high polarity would get drawn to the silica gel on the TLC plate so the spot would not travel as far. We then performed the Lucas test to check for the presence of an alcohol group. The Lucas test uses an Sn1 mechanism which leads to the formation of carbocation after ZnCl-OH dissociates and reacts with the chloride ion from hydrochloric acid. This then forms the alkyl chloride product which is what we test and observe. Because it uses Sn1 reaction, the tertiary alcohol would react the fastest and form precipitate faster than secondary and primary alcohols. Procedure: Before beginning the experiment, make sure safety attire like goggles and gloves are worn at all times. A sample of 9-fluorenone was added to a flask and dissolved in methanol. Then sodium borohydride was added and the reaction was swirled for about 15 minutes. Over time, the reaction should turn colorless. During the time, a TLC was taken to monitor the progress of the reaction. In a small beaker, a small amount of 1:9 ethyl acetate:hexane was added, enough to coat the bottom of the beaker.

Tanvi Kulkarni 11/09/2020 The TLC plate was then spotted, three spots were made. The first spot was a pure sample of 9-fluorenone, the second was a co-spot, and the third was the reaction material. The TLC plate is then added to the TLC chamber and the solvent is allowed to elute up the TLC. About a cm from the top, the TLC plate is taken out and the solvent line is marked. The TLC plate must be seen under UV light. The spots are then circled so the Rf values can be calculated. To quench the reaction, 3M sulfuric acid is added in parts. Adding in parts, will alleviate the fizzing of the reaction. The product is then heated to redissolve the precipitate, if necessary more methanol was added. The flask is then cooled to room temperature and added on ice. The product is then filtered and washed with water. The fluorenol is continued to be washed until the ph of the water coming out of the funnel is neutral. This ensures that all the acid is removed from the product. Once all the acid is washed, the crude fluorenol is then recrystallized. The recrystallization solvent is methanol. The crude fluorenol is added to a beaker and dissolved in the minimum amount of hot methanol. Once dissolved, its placed on the bench to cool to room temperature. Then it is placed on ice and crystals should be forming at this point. If no crystals are forming then some solvent should be boiled off. The crystals are then filtered through vacuum. The suction is continued to be applied to remove any solvent. Once the crystals are suction dried, they are massed so percent yield can be calculated. Lucas test procedure: The analysis of 9-fluorenol will be done using Lucas test. We will be comparing our product which is a secondary alcohol, to two other alcohols, primary (ethanol) and tertiary (t-amyl). About 1 mL of each was added into three test tubes with about a mL of Lucas reagent. The test tube contents were then mixed and observations were made based on the reactivity of each alcohol with the reagent. The fluorenol was then analyzed by IR. A background scan was taken first. After, a small amount of the sample was added onto the ATR optical sampler and the hammer was dropped to minimize air gaps. The spectrum was then taken and any relevant peaks were recorded.

Data observation and calculation:

Tanvi Kulkarni 11/09/2020

Compound

MW

9-fluorenone

180.19

NaBH4

37.83

CH3OH

32.04

H2SO4

98.08

d or M

Rxn weight

mmol

equivalents

-

6.73 g

37.3

1.00

-

0.706 g

18.6

0.500

0.792 g/mol

67.8 mL

1678.5

45.0

1.00 g/mL 3 mol/L

7.31 mL

74.6

2.00

Rxn weight 9-fluorenone: 673261106/ 10^8= 6.73 g Mmol 9-fluorenone: 6.73 g x 1 mol/ 180.19 g x 1000 mmol/ 1 mol= 37.3 Mmol NaBH4: 37.3 mmol x 0.5= 18.65 mmol= 0.01865 mol 0.01865 mol x 37.83/ 1 mol=0.706 g CH3OH: 37.3 x 45=1678.5 mmol=1.68 mol 1.678 mol x 32.04 g/ 1 mol x 1mL/0.792 g= 67.8 mL H2SO4: 37.3 x 2.0= 74.6 mmol= 0.0746 mol 0.0746 mol x 98.08 g/ 1 mol= 24.8 mL Percent yield: actual yield/ theoretical yield x 100 Actual yield: % percent * theoretical yield 91%=0.91 0.91 x 6.79= 6.17 theoretical yield: (37.3 x10^-3 mol 9-fluorenone) x (4 mol 9-fluorenol/4 mol 9-fluorenone) x (182.22 g 9-fluorenol/ 1 mol fluorenol) = 6.79 g 9-fluorenol

yield

6.71 g

Lucas test

positive

Tanvi Kulkarni 11/09/2020 Rf pure spot= 2.3/ 4.7= 0.504 Rf (cospot)= 0.6/4.7= 0.128 Rf reaction= 0.6/4.7= 0.128

Compound

Lucas test

Degree of alcohol

Rate of reaction

1-propanol

negative

1

No rate

9-fluorenol

positive

2

Faster rate of reaction

Tert-butyl alcohol

positive

3

Fast rate of reaction

6. The reason the melting point of 9-fluorenol is lower than the literature value is because the product that was collected most likely contains impurities. Products that have impurities have lower melting points than the pure substances.

Tanvi Kulkarni 11/09/2020

IR spectra- 9-fluorenone 1450- aromatic ring 1590- C=C 1710- C=O 2950- Sp3 (Carbon) H NMR spectra- 9-fluorenone 7.6= aromatic ring 8.5= aromatic ring IR spectra- 9-fluorenol 1560- aromatic ring 1590- C=C 3000- Sp2 Carbon 3300- OH H NMR spectra- 9- fluorenol 6.0= aromatic ring (Sp2 carbon) 6.4= hydroxyl group 7.5=aromatic ring IR and H NMR of 9-fluorenol

IR and H NMR of 9- fluorenone

Tanvi Kulkarni 11/09/2020

Conclusion: The purpose of this lab was to reduce 9-fluorenone using sodium borohydride to create 9-fluorenol. We used the Lucas test to identify the primary, secondary, and tertiary alcohols. Using the IR spectrum and the results, we can determine that the lab was successful. The yield of the final product was 91% or 6.71 g. This is a relatively accurate yield, the mass likely went down after recrystallization due to the saturated chilled solvent that releases some crystals which decreases the mass. We then used a TLC test to see if the reaction was progressing. The TLC plate had three spots on it, the pure product, the reactant, and the co-spot. The TLC was placed in a solvent of 1:9 ethyl acetate: hexane. We determine that the co-spot and reagent moved up the TLC plate with an Rf value of 0.128 cm, the reaction was thus in progress. From looking at the four graphs of the IR and H NMR spectrums, we determined several functional groups in the product. We identified an aromatic ring at 1450 and a double carbon bond at 1590, showing that the experiment was successful. The lucas test was performed to identify the alcohols in the product. The test is run in an Sn2 environment so the rate determining step is the formation and stability of carbocation. The tertiary carbocation is the most stable for an alcohol. When the Lucas reagent was mixed with the reaction mixture the tertiary alcohol turned cloudy and smoky quickly which means it has a positive Lucas test.

Post lab questions: 1.

Tanvi Kulkarni 11/09/2020

2. Sulfuric acid is required to generate H+ ions and remove any residual amount of reagent. Concentrated sulfuric acid cannot be used because it is an oxidizing agent that does not release H+ ions. If diluted acid is used then the oxidation is reduced and H+ is created. 3. 9-fluorenone has a C=O group that is a functional group that shows the absorption around 400 nm. Because of this the color is yellow. 9-fluorenol has a functional group OH which cannot absorb in UV region so there is no absorption and it appears white.

Citations: Gilbert, J.C., and Martin, S.M., Experimental Organic Chemistry, 5th Edition, Cengage Learning, Boston, MA, 2011 Landrie, C.L., McQuade, L.E., Yermolina, M.V., Organic Chemistry: Lab Manual and Course Materials, 8th edition, Hayden McNeil, LLC, Plymouth, MI, 2018...