You are watching: 9-fluorenone to 9-fluorenol mechanism
Preview textHanna ThomsonLab 9Tuesday 8am EricaLab 9 Preparation of Alcohols: Reduction of Fluorenone and Lucas Testfor AlcoholsMethods and BackgroundThe 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 usingrecrystallization and verify our results by preforming a Lucas test to test for the presence of analcohol group, melting point analysis, IR and NMR spectroscopy, and lastly comparing theresults of our Lucas test to those of primary and tertiary alcohols.Reduction reactions are classified by the gain in electron density around the carbonatom in which the reduction is happening, by the addition of a more electronegative atom suchas nitrogen, oxygen, halogens, or a carbon-hydrogen bond in place of a carbon-carbon multiplebond. Another way to look at this type of reaction is the process of “saturating” a molecule bythe addition of hydrogens across a double of triple bond. Before the addition of hydrogen, themolecule has some degree of unsaturation because of the multiple bond but after thereduction reaction occurs, the molecule is said to be saturated. Reduction reactions result in adecrease in the oxidation number of a carbon atom, at the beginning of our reaction 9fluorenone has an oxidation state of +2, and after the reduction happens we are left with 9fluorenol which has an oxidation state of 0. Oxidation states are classified by adding 1 for everybond carbon makes to a more electronegative bond, and subtracting one for every bond carbonFigure 1.makesto a less electronegative bond. Therefore, since our starting material has a carbon tooxygen double bond (more electronegative than carbon) we would add two, resulting in anoxidation state of +2. At the end of the reaction, we are left with 9-fluorenol with a carbon toalcohol bond, where we would add one for the carbon to oxygen bond, but then we wouldsubtract one because of the remaining carbon to hydrogen bond since hydrogen is lesselectronegative than carbon, resulting in an oxidation state of 0. A visual representation ofassigning an oxidation state to our starting materials and products is shown below in figure 1.Hanna ThomsonLab 9Tuesday 8am EricaThere are several different reagents used in reduction reactions, some of the mostcommon being molecular hydrogen with a metal catalyst, lithium aluminum hydride, andsodium 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 likeother 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 acarbon-hydrogen bond and breaking the carbon-oxygen bond resulting in a lone pair aroundoxygen in which a proton from the sulfuric acid protonates the oxygen with the lone pair on itcreating 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 atomsattached to boron in sodium borohydride may transfer to form a borate salt. The mechanismFigure 2.Hanna ThomsonLab 9Tuesday 8am Ericaprimary 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 alcoholprovided and faster than the primary alcohol provided which shouldn’t react at all in the Lucastest. 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 spectroscopiesalong with analyzing the melting point. While running IR spectroscopy, we would expect to seea broad O-H stretch around 3200-3500 1/cm if our reaction went to completion. For NMR, wewould expect to see a triplet around 7.65ppm and a multiplet around 7.45ppm both integratedto 4H, corresponding to the two benzene groups present in 9-fluorenol. We would see adoublet around 5.60ppm integrated to 1H corresponding to the hydrogen attached to theoxygen in the alcohol group, and another doublet around 2.06ppm integrated to 1Hcorresponding to the hydrogen attached to the same carbon our alcohol group is bonded to.The melting point of 9-fluorenol is 152-155 degrees C, so we would expect to observe a meltingpoint range around there.Our results for the reduction reaction of 9-fluorenone to 9-fluorenol using sodiumborohydride as a reducing reagent and 3M sulfuric acid in the acidic workup concluded thereduction of the ketone in to an alcohol group, by a positive Lucas test, observing expected IRpeaks, and analyzing the boiling point. Upon running TLC after reacting 9-fluorenone withsodium borohydride in a 9:1 ratio of ethyl acetates and hexanes, we found that our reactionwas complete by the lower Rf value of our reaction spot vs. the co-spot and the spot of thepure sample of 9-fluorenone, because of the more polar identity of our reaction sample. Our Rfvalue of our reaction sample was 0.31 whereas the Rf value for the co-spot was 0.66 and the Rfvalue for the pure sample of 9-fluorenone was 0.70. Following the acidic workup andrecrystallization, we ran IR where we observed an O-H stretch at 3307.40(1/cm) in which wewould expect to see if our reaction went to completion. We did not run NMR because oftechnical complications, however we observed the boiling point to be around 153 to 156degrees 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 additionof our 9-fluorenol product. When running the Lucas test with the tertiary alcohol (tertiarybutanol) provided, we observed a precipitate very quickly after about 5 seconds, and noprecipitate at all for the primary alcohol (1-butanol) provided.ProcedureHanna ThomsonLab 9Tuesday 8am EricaSynthesis of 9-fluorenolWe began by adding the assigned 1.1g of 9-fluorenone to a 50mL Erlenmeyer flaskcontaining our calculated volume of 11.1mL of methanol from our reaction table (displayed inthe 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 ofsodium borohydride and immediately added it to our reaction flask, and swirled the flask untilall the reagent dissolved. This reaction caused a lot of hydrogen gas to form which caused someof our product to spill out of the top of the flask, which turned in to a solid in which we laterjust added back in to our reaction mixture and swirled until it dissolved again. We allowed thisreaction mixture to cool to room temperature for 20minutes with occasional swirling, and untilthe reaction went from a yellow color to completely colorless.After 20 minutes of cooling to room temperature, we ran a TLC plate with our reactionmixture, a pure sample of 9-fluorenone, and a co-spot containing both in a solvent of a 1:9mLratio of ethyl acetate and hexanes. We calculated the Rf values of all the spots to ensure ourreaction was complete in this stage.For the acidic workup portion of this reaction, we added the calculated 1.2mL of 3Msulfuric acid (4.07mmol/mL) to the reaction mixture and heated the mixture and swirled inorder to dissolve the precipitate formed by the addition of the sulfuric acid. We ended uphaving 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 roomtemperature and then to an ice bath until we observed a precipitate form. We filtered the solidusing vacuum filtration and washed with water until the water filtering through was neutral orgreen according to the pH test strips.After the water filtering through our product was observed to be neutral, we dissolvedour solid in 20mL of hot methanol, while heating to help the solid dissolve. We allowed oursolution to cool to room temperature once everything was dissolved, and then transferred toan ice bath. Once the precipitate formed, we filtered it using vacuum filtration and allowed theproduct 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 IRspectroscopies as well as analyzed the boiling point using the boiling point apparatus. Howeverthe NMR’s were not turning out well so we skipped that portion of the procedure completelyand just ran IR and analyzed the boiling point before moving on to the Lucas test.Lucas Test ProcedureWe began by preparing three test tubes with 1mL of the ZnCl2 in HCl (Lucas testreagent) to eachHanna ThomsonLab 9Tuesday 8am Ericaour solvent line reached to 3.2cmFor the pure sample of 9-fluorenone: (2.5cm)/(3.2cm)=0.70For the co-spot: (2.1cm)/(3.2cm)=0.66For our reaction mixture: (1.0cm)/(3.2cm)=0.31Percent YieldPercent 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 thereaction 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 groupO-H stretchC-HC-OWavelength (1/cm)Peak at 3307.40Peak at 3037.30Peak at 1022.42Data and observations table% yieldRf valueMelting point (C)9-fluorenol0.31153-156Tertiary butanol-1-butanol-Hanna ThomsonLab 9Tuesday 8am EricaIR (1/cm)NMRLucas TestOH (3307.04), C-H(3037.30), C-O(1022.42)Precipitate afterabout 10 seconds--Precipitate afterabout 5 secondsNo precipitateformedConclusionOur objective in this lab was to reduce 9-fluorenone to 9-fluorenol usingsodium borohydride as a reducing reagent and sulfuric acid as the acidic workup. We thenverified our results using the Lucas test for rate of substitution on our secondary alcohol vs. aprimary and tertiary alcohol. We verified our reaction went to completion by the formation ofan 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 reactionwas complete before running the acidic workup and recrystallizing. Our TLC showed that ourreaction 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 wasmore attracted to the polar silica gel resulting in a lower Rf value.After the acidic workup and recrystallizing with hot methanol, we calculated apercent yield of 90.9% with a theoretical yield of 1.1g and an actual product yield of 1.0g. Weobserved the melting point of our product to be around 153-156 degrees Celsius, where theactual melting point of 9-fluorenol is 152-155 degrees Celsius. Upon running IR spectroscopy weobserved an O-H stretch at 3307.40(1/cm) which we expected to observe if our reaction wentto completion and we successfully reduced the ketone to an alcohol in 9-fluorenone. we alsoobserved peaks at 3037.30(1/cm) which corresponded to the C-H bond formed on the carbonwhere the new alcohol group is bonded to, as well as a peak at 1022.42(1/cm) corresponding tothe C-O single bond formed by the reduction of the ketone as well.
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We did not run NMR due totechnical difficulties of the NMR machine, however after running the Lucas test we observedthe pattern we would expect to see upon the formation of a secondary alcohol after thereduction of 9-fluorenone to 9-fluorenol. We observed precipitate immediately after theaddition of 5 drops of tertiary alcohol provided to us in lab to the Lucas test reagent, and withthe addition of our product (the secondary alcohol) we observed precipitate after about 10seconds, a little bit slower than we observed for the tertiary alcohol, and no reaction with theprimary 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 wesuccessfully reduced the ketone in 9-fluorenone to an alcohol in 9-fluorenol using sodium