Lab 9 Preparation of Alcohols: Reduction of Fluorenone PDF

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9 Preparation of Alcohols: Reduction of Fluorenone and Lucas Test for Alcohols lab report by Hanna Thomson...

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Hanna Thomson Lab 9 Tuesday 8am Erica

Lab 9 Preparation of Alcohols: Reduction of Fluorenone and Lucas Test for Alcohols Methods and Background The purpose of this lab was prepare 9-fuorenol by reducing the ketone present in 9fluorenone using sodium borohydride as a reducing agent. We then purify our product using recrystallization and verify our results by preforming a Lucas test to test for the presence of an alcohol group, melting point analysis, IR and NMR spectroscopy, and lastly comparing the results of our Lucas test to those of primary and tertiary alcohols. Reduction reactions are classified by the gain in electron density around the carbon atom in which the reduction is happening, by the addition of a more electronegative atom such as nitrogen, oxygen, halogens, or a carbon-hydrogen bond in place of a carbon-carbon multiple bond. Another way to look at this type of reaction is the process of “saturating” a molecule by the addition of hydrogens across a double of triple bond. Before the addition of hydrogen, the molecule has some degree of unsaturation because of the multiple bond but after the reduction reaction occurs, the molecule is said to be saturated. Reduction reactions result in a decrease in the oxidation number of a carbon atom, at the beginning of our reaction 9-fluorenone has an oxidation state of +2, and after the reduction happens we are left with 9-fluorenol which has an oxidation state of 0. Oxidation states are classified by adding 1 for every bond carbon makes to a more electronegative bond, and subtracting one for every bond carbon makes to a less Figure 1. electronegative bond. Therefore, since our starting material has a carbon to oxygen double bond (more electronegative than carbon) we would add two, resulting in an oxidation state of +2. At the end of the reaction, we are left with 9-fluorenol with a carbon to alcohol bond, where we would add one for the carbon to oxygen bond, but then we would subtract one because of the remaining carbon to hydrogen bond since hydrogen is less electronegative than carbon, resulting in an oxidation state of 0. A visual representation of assigning an oxidation state to our starting materials and products is shown below in figure 1.

Hanna Thomson Lab 9 Tuesday 8am Erica

There are several different reagents used in reduction reactions, some of the most common being molecular hydrogen with a metal catalyst, lithium aluminum hydride, and sodium borohydride. Sodium borohydride is what we used as a reducing agent in this lab, because of it’s ability to reduce aldehydes, ketones, and imines without being too harsh like other reagents such as lithium aluminum hydride. The mechanism for this reaction is as follows; a hydrogen from the borohydride attaches itself to the carbonyl on the 9-fluorenone, creating a carbon-hydrogen bond and breaking the carbon-oxygen bond resulting in a lone pair around oxygen in which a proton from the sulfuric acid protonates the oxygen with the lone pair on it creating a new carbon-oxygen-hydrogen bond resulting in an alcohol group, or 9-fluorenol. However the mechanism is a bit more complex than that in which four hydrogen atoms attached to boron in sodium borohydride may transfer to form a borate salt. The mechanism for

Figure 2.

Hanna Thomson Lab 9 Tuesday 8am Erica

this reaction is shown below in figure 2.

After running the reaction of 9-fluorenone with sodium borohydride, we ran a TLC test to monitor our reaction progress. There were three spots, one spot with a pure sample of 9fluorenone, a co-spot with a sample of our reaction and a pure sample, and the last spot was just our reaction. During this test we are looking for differences in polarities between our starting materials (pure sample of 9-fluorenone) and our reaction mixture. We would expect our reaction sample to be more polar than our starting material because of the presence of an alcohol group vs. our reactant with a ketone group, so therefore we would expect our reaction sample spot to have a lower Rf value than the co-spot and the pure sample of 9-fluorenone because of it’s higher polarity being drawn to the polar silica gel on the TLC plate and the spot not traveling as far up the plate. After completing our reaction via acidic workup, we were to perform a Lucas test to test for the presence of an alcohol group amongst testing given tertiary and primary alcohols. The Lucas test utilizes an Sn1 mechanism where zinc chloride is a strong lewis acid and reacts with the oxygen in the alcohol group, which then forms a carbocation after the dissociation of ZnClOH and reacts with the chloride ion from hydrochloric acid to form an alkyl chloride product which is the precipitate we observe. Since this test utilizes an Sn1 reaction, we would expect tertiary alcohols to react fastest and form precipitate faster than the reactions of secondary and

Hanna Thomson Lab 9 Tuesday 8am Erica

primary alcohols. Considering we have a secondary alcohol as our product from our reaction, we would expect to observe precipitate slower than the given sample of tertiary alcohol provided and faster than the primary alcohol provided which shouldn’t react at all in the Lucas test. The Sn1 mechanism for the Lucas test reaction is shown below in figure 9.3.

To further conclude our reaction went to completion we ran IR and NMR spectroscopies along with analyzing the melting point. While running IR spectroscopy, we would expect to see a broad O-H stretch around 3200-3500 1/cm if our reaction went to completion. For NMR, we would expect to see a triplet around 7.65ppm and a multiplet around 7.45ppm both integrated to 4H, corresponding to the two benzene groups present in 9-fluorenol. We would see a doublet around 5.60ppm integrated to 1H corresponding to the hydrogen attached to the oxygen in the alcohol group, and another doublet around 2.06ppm integrated to 1H corresponding to the hydrogen attached to the same carbon our alcohol group is bonded to. The melting point of 9fluorenol is 152-155 degrees C, so we would expect to observe a melting point range around there. Our results for the reduction reaction of 9-fluorenone to 9-fluorenol using sodium borohydride as a reducing reagent and 3M sulfuric acid in the acidic workup concluded the reduction of the ketone in to an alcohol group, by a positive Lucas test, observing expected IR peaks, and analyzing the boiling point. Upon running TLC after reacting 9-fluorenone with sodium borohydride in a 9:1 ratio of ethyl acetates and hexanes, we found that our reaction was complete by the lower Rf value of our reaction spot vs. the co-spot and the spot of the pure sample of 9-fluorenone, because of the more polar identity of our reaction sample. Our Rf value of our reaction sample was 0.31 whereas the Rf value for the co-spot was 0.66 and the Rf value for the pure sample of 9-fluorenone was 0.70. Following the acidic workup and recrystallization, we ran IR where we observed an O-H stretch at 3307.40(1/cm) in which we would expect to see if our reaction went to completion. We did not run NMR because of technical complications, however we observed the boiling point to be around 153 to 156 degrees Celsius, where the actual boiling point of 9-fluorenol is 152 to 155 degrees Celsius. After running the Lucas test, we observed precipitate after about 10 seconds after the addition of our 9-fluorenol product. When running the Lucas test with the tertiary alcohol (tertiary-butanol) provided, we observed a precipitate very quickly after about 5 seconds, and no precipitate at all for the primary alcohol (1-butanol) provided. Procedure

Hanna Thomson Lab 9 Tuesday 8am Erica

Synthesis of 9-fluorenol We began by adding the assigned 1.1g of 9-fluorenone to a 50mL Erlenmeyer flask containing our calculated volume of 11.1mL of methanol from our reaction table (displayed in the reaction table of the data portion), and heated and swirled the mixture until all the 9fluorenone dissolved in the methanol. We cooled the solution to room temperature and weighed out our calculated 0.12g of sodium borohydride and immediately added it to our reaction flask, and swirled the flask until all the reagent dissolved. This reaction caused a lot of hydrogen gas to form which caused some of our product to spill out of the top of the flask, which turned in to a solid in which we later just added back in to our reaction mixture and swirled until it dissolved again. We allowed this reaction mixture to cool to room temperature for 20minutes with occasional swirling, and until the reaction went from a yellow color to completely colorless. After 20 minutes of cooling to room temperature, we ran a TLC plate with our reaction mixture, a pure sample of 9-fluorenone, and a co-spot containing both in a solvent of a 1:9mL ratio of ethyl acetate and hexanes. We calculated the Rf values of all the spots to ensure our reaction was complete in this stage. For the acidic workup portion of this reaction, we added the calculated 1.2mL of 3M sulfuric acid (4.07mmol/mL) to the reaction mixture and heated the mixture and swirled in order to dissolve the precipitate formed by the addition of the sulfuric acid. We ended up having to add about 2mL more methanol to get mostly all of the solid to dissolve. After everything was dissolved we removed the reaction from heat and let cool to room temperature and then to an ice bath until we observed a precipitate form. We filtered the solid using vacuum filtration and washed with water until the water filtering through was neutral or green according to the pH test strips. After the water filtering through our product was observed to be neutral, we dissolved our solid in 20mL of hot methanol, while heating to help the solid dissolve. We allowed our solution to cool to room temperature once everything was dissolved, and then transferred to an ice bath. Once the precipitate formed, we filtered it using vacuum filtration and allowed the product to dry fully by just leaving the vacuum on for about 15 minutes. We then weighed our final product and calculated percent yield, and ran NMR and IR spectroscopies as well as analyzed the boiling point using the boiling point apparatus. However the NMR’s were not turning out well so we skipped that portion of the procedure completely and just ran IR and analyzed the boiling point before moving on to the Lucas test. Lucas Test Procedure We began by preparing three test tubes with 1mL of the ZnCl2 in HCl (Lucas test reagent) to each

Hanna Thomson Lab 9 Tuesday 8am Erica

To one test tube, we added 5 drops of the tertiary alcohol provided (tertiary butanol) and observed how fast a precipitate formed (if any). To another test tube, we added 5 drops of our reaction mixture (9-fluorenol, a secondary alcohol) and observed how fast we observed a precipitate form. To the last test tube we added 5 drops of the primary alcohol provided (1butanol) and observed if any precipitate formed and how quickly. We then compared the results of these tests to further conclude our reaction went to completion and we did in fact produce a secondary alcohol by a reduction reaction. Data and Observations Reaction Table (Table 1) Compound

9-fluorenone Sodium borohydride (NaBH4) Methanol (MeOH) Sulfuric acid (H2SO4)

Molecular Weight (g/mol) 180.19 37.83

Density (g/mL) or (mmol/mL) -

Reaction weight (g) or (mL)

Mmol

Equivalence

1.1g 0.115469g

6.10467 3.05233

1.0 0.5

32.04

0.792

11.11327mL

274.71015

45

98.08

1.0g/mL 3.0mol/L

1.19749mL 4.0697mmol/m L

12.20934

2.0

Sample calculation for reaction table: To find amount of NaBH4 needed from assigned 1.1g of 9-fluorenone. (1.1g 9-fluorenone)/MW (180.19g/mol)=0.00610467 mols of 9-fluorenone. Multiply by 1000 to get 6.10467mmols of 9-fluorenone which is our 1.0 equivalences. 0.5 equivalents of NaBH4 x 6.10467mmol of 9-fluorenone=3.05233mmol of NaBH4. 3.05233mmol of NaBH4/1000=0.00305233mols of NaBH4. 0.00305233mols of NaBH4 x MW (37.83g/mol)=0.115469g of NaBH4 needed for the reaction. TLC plate and Rf values The left spot corresponds to the pure sample of 9-fluorenone provided in lab, and the middle spot corresponded to our co-spot containing both the pure sample and our reaction mixture, the right spot corresponds to our reaction mixture after the addition of sodium borohydride to 9-fluorenone and methanol. Rf values= (distance spot traveled)/(distance solvent traveled)

Hanna Thomson Lab 9 Tuesday 8am Erica

our solvent line reached to 3.2cm For the pure sample of 9-fluorenone: (2.5cm)/(3.2cm)=0.70 For the co-spot: (2.1cm)/(3.2cm)=0.66 For our reaction mixture: (1.0cm)/(3.2cm)=0.31

Percent Yield Percent yield formula: (actual yield)/(theoretical yield)x100= % yield. Our theoretical yield is 1.1g of product from the 1.1g of 9-fluorenone assigned to us in the reaction table above (table 1) Our actual yield at the end of recrystallization was 1.0g. % yield: (1.0g)/(1.1g)x100= 90.9% IR spectroscopy

(table 2 IR peaks) Functional group O-H stretch C-H C-O

Wavelength (1/cm) Peak at 3307.40 Peak at 3037.30 Peak at 1022.42

Data and observations table % yield Rf value Melting point (C)

9-fluorenol 0.31 153-156

Tertiary butanol -

1-butanol -

Hanna Thomson Lab 9 Tuesday 8am Erica

IR (1/cm)

NMR Lucas Test

OH (3307.04), C-H (3037.30), C-O (1022.42) Precipitate after about 10 seconds

-

-

Precipitate after about 5 seconds

No precipitate formed

Conclusion Our objective in this lab was to reduce 9-fluorenone to 9-fluorenol using sodium borohydride as a reducing reagent and sulfuric acid as the acidic workup. We then verified our results using the Lucas test for rate of substitution on our secondary alcohol vs. a primary and tertiary alcohol. We verified our reaction went to completion by the formation of an alcohol group by running IR spectroscopy and analyzing the boiling point of our product. We ran TLC after the addition of sodium borohydride to ensure our reaction was complete before running the acidic workup and recrystallizing. Our TLC showed that our reaction mixture had a lower Rf value than the co-spot as well as the pure sample of 9fluorenone, meaning our product was more polar than our starting materials considering it was more attracted to the polar silica gel resulting in a lower Rf value. After the acidic workup and recrystallizing with hot methanol, we calculated a percent yield of 90.9% with a theoretical yield of 1.1g and an actual product yield of 1.0g. We observed the melting point of our product to be around 153-156 degrees Celsius, where the actual melting point of 9-fluorenol is 152-155 degrees Celsius. Upon running IR spectroscopy we observed an O-H stretch at 3307.40(1/cm) which we expected to observe if our reaction went to completion and we successfully reduced the ketone to an alcohol in 9-fluorenone. we also observed peaks at 3037.30(1/cm) which corresponded to the C-H bond formed on the carbon where the new alcohol group is bonded to, as well as a peak at 1022.42(1/cm) corresponding to the C-O single bond formed by the reduction of the ketone as well. We did not run NMR due to technical difficulties of the NMR machine, however after running the Lucas test we observed the pattern we would expect to see upon the formation of a secondary alcohol after the reduction of 9-fluorenone to 9-fluorenol. We observed precipitate immediately after the addition of 5 drops of tertiary alcohol provided to us in lab to the Lucas test reagent, and with the addition of our product (the secondary alcohol) we observed precipitate after about 10 seconds, a little bit slower than we observed for the tertiary alcohol, and no reaction with the primary alcohol in the Lucas reagent. After running all the tests to test for the reduction of a ketone in our reaction, we observed what we had hypothesized in the beginning of our experiment meaning we successfully reduced the ketone in 9-fluorenone to an alcohol in 9-fluorenol using sodium

Hanna Thomson Lab 9 Tuesday 8am Erica

borohydride as the reducing reagent along with the acidic workup and recrystallization with methanol. References Gilbert, J.C., and Martin, S.M., Experimental Organic Chemistry, 6th edition, Cengage Learning, Boston, MA, 2015 Landrie, C.L., McQuade, L.E., Yermolina, M.V., Organic Chemistry: Lab Manual and Course Materials, 8th edition, Hayden McNeil, LLC, Plymouth, MI, 2018 J. (n.d.). Reagent Friday: Sodium Borohydride (NaBH4). Retrieved from https://www.masterorganicchemistry.com/2011/08/12/reagent-friday-sodium-borohydridenabh4/ Langenegger, Tobias, and Xiaoqiang, Guo. Synthesis of 9-Fluorenol. Zurich, 12/11/2007. Swiss Federal Institute of Technology Zurich. http://n.ethz.ch/~nielssi/download/5.%20Semester/Praktikum%20Organische%20Chemie%20I %20f%FCr%20Biol.%20Pharm.Wiss./Reports/Old%20Reports/Praktikum-OCI-Teil-11/Praktikum %20OCI%20(Teil%201)/9-fluorenol.pdf...