Lab 9 Preparation of Alcohols Reduction of Fluorenone and Lucas Test for Alcohols PDF

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Lab 9: Preparation of Alcohols: Reduction of Fluorenone and Lucas Test for Alcohols Katja Gonzalez Lab Partner: Kyle Leonida 2018/04/16

Methods and Background

Figure 1: 9-Fluorenone to 9-Fluorenol Mechanism

The main goal of this experiment was to prepare 9-fluorenol by reducing the given weight (by the instructor) of 9-fluorenone by use of sodium borohydride as represented in Figure 1. The sodium borohydride was used because it is specific when targeting the double bond between carbon and oxygen. The method of recrystallization allows for the assurance that all the impurities of the 9-fluorenol have been removed so it is able to purify. To know and distinguish that you have created 9-fluorenol IR spectroscopy and melting point method were completed. To affirm presence of the alcohol formation Lucas tests were completed. With this testing there was also a final examination between which was primary, secondary (your compound) and tertiary alcohols. This reaction of the organic compound is a reduction which means that there is an increased electron density located at the carbon atom. This is because of the carbon bond that is replaced with a more electronegative atom. An example can include a new hydrogen carbon bond formation by adding one or more halogens to the functional group. This can also be considered a reduction reaction, another way this can occur is with the decrease of the carbon atoms oxidation number, some gain in electrons, hydrogen gains bond and the oxygen have a loss of bonds. On the opposite hand, oxidation reactions occur when the electron density around the carbon

decreases. This happens when a carbon atom has gone from bonding to a less electronegative atom to a more electronegative atom. Other factors that can conclude oxidation include the increase in the oxidation number on the carbon atom, loss of electrons, oxygen gaining bonds and hydrogen losing bonds. Carbonyl compounds are usually reduced down by alcohols using catalytic hydrogenation or metal hydrides. During reduction aldehydes become primary alcohols while ketones turn into secondary alcohols. When utilizing reaction agents to reduce a molecule is could end in the reducing agents becoming oxidized. There are three main reducing agents that are used in reductions reactions of organic chemistry. They include molecular hydrogen, lithium aluminum hydride and sodium hydride. To reduce the pi bonds in the presence of metal catalysts hydrogenation is used. This can cause the addition of H2 across the carbon-carbon double bond. When looking at metal hydrides they reduce the polar pi bonds but do not cut down/reduce the carbon-carob multi-bonds. This is because of how differently they work by adding the nucleophilic hydride onto the electrophilic site. LAH is the of the stronger reagents and is used to reduce imines, ketones, carboxylic acids, ester, aldehydes and amines. NaBH4 is known as being not as strong as LAH so it can be used to reduce only imines, ketones and aldehydes. Knowing whether you have completed an oxidation or reduction reaction can be tricky which is why oxidation number of the carbon atom needs to be calculated throughout the reaction. This is the number of electron in the molecule that can be used to determine if either the increase or decrease of the central atom end in bonds all as ionic. When there is an increase of the carbon throughout the reaction this is an oxidation whereas if there is a decrease of oxidation number on the carbon is considered a reduction. When calculating the oxidation things to keep in mind include: for everyone atom attached to carbon that is more electronegative add one, subtract one for every less electronegative atom that is bound to carbon and zero is added or subtracted for any carbon carbon bonds. To view the progress of the reaction thin layer chromatography is used for comparing a pure sample of 9-fluorenone to the mixture created in lab(9-fluorenol). A co spot of half pure fluorenone and half mixture created in lab was used to view the two liquids side by side. The TLC plate is only considered complete when 9-fluorenone is no longer visible in the reaction mixture after the reaction has completed.

To finalize our product recrystallization is completed. This occurs when the solid is dissolved in a solvent at very high temperatures which allows for the formations of crystals to reform. This relies mostly on the fact that solids are most soluble in very hot solvents in comparison to cold ones. In order for the solid to precipitate it is dependent upon the solubility of the solvent that utilized when the viewing the extremes in temperatures. The upper extreme that is used is the boiling point of the solvent when the lower limit is less than 0 due to the use of ice water present in this lab. To verify that 9-fluorenol was achieved melting point and IR spectroscopy were obtained. When view the IR graph two large peaks should be seen one for the carbon carbon double bond between 1620-1680 cm-1 and the other for the OH alcohol stretch between 3200-3600 cm-1. As for the melting point we should see between 155 to 157 degrees Celsius. If impurities are present when completing melting point it can cause a depression in the temperature as well as if the solid is heated too quickly. The final test in this lab was Lucas testing which tests for the formation of alcohols. This can also classify between which are primary, secondary and tertiary alcohols. The rate determination step is when there is a formation of carbocation which will then cause an increase in the rate as well as an interaction in the stability of the carbocation. When looking at the rate it should be seen that tertiary happens the quickest then secondary and finally primary will be unreactive to the mixtures with the Lucas test. A positive test is seen when the clear liquid becomes cloudy due to the formation of the alkyl chloride which is not soluble in water.

Figure 2: Sn1 Reaction with the Lucas Reagents

Experimental Procedure Part I: Synthesis of 9-Fluorenol The assigned weight of 1.10g of 9-fluorenone was given by our TA. From this, multiple calculations needed to be completed in order to know the amounts of sodium borohydride,

sulfuric acid and methanol that we need for the reaction to work properly. The 1.10g of 9fluorenone is first added into a 50 mL Erlenmeyer flask that contains the calculated amount of 11.11 mL of methanol. This was heated gently with occasional swirling to ensure proper dissolving of the 9-fluorenone. Once fully dissolved the flask was removed from heat and set aside to cool to room temperature for about 3-5 minutes. At room temperature, the sodium borohydride was measured to 0.115g and placed directly into the reaction mixture which was swirled with vigor to dissolve the sodium borohydride. This unstopped mixture was to be set aside for 20 minutes at room temperature until the mixture became colorless. At this point in time a TLC plate is completed before moving on. A silica plate with a 1:9 ethyl acetate: hexane mixture was used as an eluent to complete this method that tests for the confirmation that the reaction has completed. The first lane was a pure sample of 9-fluorenone, the second lane was a mix between the pure 9-fluorenone and the mixture you have created, and the last and final lane was just the mixture created in this lab. These plates were then examined under a UV light with the spots circled by the TA present in lab. From this Rf values of the 9fluorenone and hopefully our mixture 9-fluorenol are calculated. Moving back to the mixture, 1.197 mL of 3M sulfuric acid was added into the mixture and was placed on the heating mantle to heat gently. Swirling was used to dissolve the solid formed. This should be completed with watch glass in place so no important components of the mixture dissolve out. Once the solid is dissolved, it is removed from heat, cooled to room temperature, then placed into an ice bath still having the watch glass in place. A noticeable form of a precipitate should form between 5-10 minutes. This solid is then filtered through a Buchner funnel and filtration flask to wash the solid with an ample amount of water (at least 200 mL). To assure that the water is coming out neutral after filtration pH paper was used. The solid was then completely dried before being ready to be placed onto the heating mantle. Methanol is heated to a hot temperature and a small amount is placed with the obtained dried solid. The flask should be kept at a constant high heat on the mantle until all of the solid has dissolved. A watch glass should be used to trap any vapors trying to escape while being heated. Once everything has dissolved it is removed off of the heating mantle for the last time. It let to sit at room temperature and then placed into an ice bath. Once recrystallization has occurred the crystals are then run through a Buchner funnel to filter and dry anything that should not be present in a pure sample. The final product is weighed, and percent yield can then be calculated.

Melting point and IR spectroscopy is then completed with these crystals. For IR spectroscopy there needs to be preparation of dissolving 0.10g of crystals and 0.50 mL of CDCl2 in an NMR tube needs to be completed Part II: Confirmation of Alcohol Formation by Lucas Classification Test To start 1.0 mL of the Lucas reagent was added to each of the three tubes. In the first tube 5 drops of the known tertiary alcohol was placed inside. A noticeable color change from clear to cloudy should be seen almost instantaneously. If there is no change the tube can be shaken for up to five minutes. The test is repeated in the remain two tubes using the created secondary alcohol and given primary alcohol. As for the solid it needs to be dissolved before placing into the tube and this is done with a small amount of ethanol.

Data Acquisition i.

Reaction Table Molecular Compound Weight (g/mol) 9-Fluorenone 180.19 Sodium 37.83 borohydride Methanol 32.04 Sulfuric acid

ii.

98.08

Density (g/mL) or M (g/mol) n/a

Rxn Weight or Volume (g or mL)

mmol Equivalents

1.1 g

6.1

1.0

n/a

0.115 g

3.05

0.5

0.792 g/mL

11.11 mL

274.7

45

1.197 mL

12.2

2.0

1.00 g/mL 3.00 mol/L

Relevant Equations Rf =

distance of component distance of eluent

Percent yield =

actual value ×100 % theoretical value

iii.

Calculations Reaction Table calculations: - 9-Fluorenone 1 mol 1000 mmol 1.1 g × =6.1 mmol × 1 mol 180.19 g -

Sodium borohydride 6.1 mmol× 0.5=3.05 mmol = 0.00305 mol

0.00305 mol BNa×

37.83 g BNa =0.115 g 1 mol BNa

-

Methanol 6.1 mmol× 45=274.7 mmol=0.2747 mol 1 mL 32.04 g methanol × 0.2747 mol methanol × =11.11mL 1 mol methanol 0.792 g

-

Sulfuric acid 6.10 mmol x 2.0=12.2 mmol=0.0122 mol 98.08 g sulfuric acid 1.00 mL =1.197 mL × 0.0122 mol sulfuric acid × 1g 1 mol sulfuric acid

Rf values Rf 9-fluorenone = Rf 9-fluorenol =

1.7 cm = 0.57 3.0 cm 0.8 cm = 0.27 3.0 cm

Percent Yield Percent yield = iv.

1.83 g × 100 1.1 g

Data Table Compound Starting mass (g) Product mass (g) Rf value Melting points (°C)

= 166% yield

9-Fluorenone 1.1 ----------------------------0.57 83.5 Melting point of product (°C) 137.9-139.7 Percent yield 166%

9-Fluorenol ----------------------------1.86 0.27 152-155

v.

vi.

vii.

Lucas Test Primary alcohol Negative No reaction

Secondary alcohol Positive Immediate

IR spectrometry Wavenumber (cm-1) 3307.32 1644.39, 1475.69 1450.09 – 946.70

Functional Group OH group, alcohol C=C, aromatic C-C, C-H

NMR spectrometry Ppm 7.96 6.71 5.63

Functional Group Aromatic Alcohol group C-H next to the alcohol group

Tertiary alcohol Positive Immediate

Conclusion The purpose of this lab was to prepare 9-fluorenol from 9-fluorenone through reduction reactions. Confirmation of the formation of an alcohol was determined through the Lucas Classification test, and the various functional groups were found through IR and NMR spectroscopy. Looking at the TLC plates Rf values of 0.57 for 9-fluorenone and 0.27 for fluorenol were found. This shows the greater polarity of 9fluorenol over 9-fluorenone which is because the retention rate will be the lowest of the two. Once the procedure was completed a weighed sample of 1.86 g was found giving a 166% yield from the 1:1 g of 9fluorenone that we started with. This is either due to our product not being dried to the fullest or there were still presences of impurities in our solid. When looking for impurities a further confirmation of this would be the melting point which was relatively low in comparison the point it needed to be. After looking at the IR spectroscopy it is notable that an alcohol has formed as there is an observed curve at

3307.32 cm-1. To further affirm that what structures are present in the compound it was noticed that there was a curve at 1644.39 cm-1 which means this could have a carbon carbon bond. Although these are good signs when we examined NMR is was a different story. On or near 6.43 ppm there was no clear presence of what should have been an alcohol instead they closest spot that formed was a 6.71 ppm. A presence if an aromatic ring was found where there was an entire peak from 7.96 pp, to 6.71 ppm. The one bond on bond that is worth looking into is the peak located at the 5.63 ppm. This is an indication that is a carbon hydrogen bond that is bonded to an alcohol group. There were a few peaks that should not have been present in the graph which shows that there were clearly impurities present in our compound. The final testing done for Lucas classification turned out just as the manual described them as. The primary stayed clear and negative while the secondary and tertiary turned cloudy for a positive test. Something to note for these tests was how immediate our test turned positive for the secondary alcohol which should have taken a little bit more time to process. This can indicate either the solution to dissolve the solid was to highly concentrated for the tube or further justifies the presence of impurities in the compound.

References Gilbert, J.C., and Martin, S.M., Experimental Organic Chemistry, 5th Edition, Cengage Learning, Boston, MA, 2011.

Landrie, C.L., and McQuade, L.E., Organic Chemistry: Lab Manual and Course Materials, 3rd Edition, Hayden-McNeil, LLC, Plymouth, MI, 2013....