Organic Chemistry - Lab 9 - Lecture Notes 99: Preparation And Reduction Of Alcohols PDF

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Lab 9: Preparation of Alcohols: Reduction of Fluorenone and Lucas Test for Alcohols Milan Patel April 6, 2016 Methods and Background The main purpose of this experiment was to reduce 9-Fluorenone to 9-Fluorenol by using sodium borohydride (NaBH4). The structures of reagent and product are shown in the Figure 1. We were also supposed to calculate the amount of reagents required in order to perform the reaction. Ultimately, characterize the product by melting point analysis, IR spectroscopy and Lucas classification test. In addition, Thin-layer chromatography (TLC) analysis was performed in order to check the progress of the reaction. Recrystallization of crude product was also used to obtain the pure product and get rid of as much impurities as possible. In this experiment, the percent yield and the retention factors were also calculated.

Figure 1: 9-Fluoerenone (Left) and 9-Fluorenol (Right) The reaction theories used in this experiment is the oxidation/reduction reactions. Oxidation is a process which involves loss of electrons, gain of bonds to oxygen and also loss of bonds to hydrogen. This means that there is a loss of electron density at a carbon atom in a molecule, usually by forming a new bond with an electronegative atom, or by breaking a bond with hydrogen. Whereas, reduction reactions involve the gain of electrons, loss of bond to oxygen atom and also gain bonds to hydrogen. This means that there is an increase in electron density at a carbon atom, which can be a result of replacing a bond between the carbon and an electronegative atom by a carbon-hydrogen bond. Oxidation and reduction reactions are very common in both organic chemistry and inorganic chemistry. Thus, the surest way to determine reaction type such as if the reaction is an oxidation or a reduction is to calculate the oxidation number of the carbon atom which is changing during the reaction. Furthermore, for any carbon atom, its oxidation number can be assigned by adding 1 for every bond that carbon makes to a more electronegative atom, subtracting 1 for every bond that carbon makes to a less electronegative atom, and by adding 0 for every bond to another carbon atom. If the oxidation number of a carbon atom increases from the reactant to the product, it is said to be an oxidation reaction. Similarly, if the oxidation number decreases from the reactant to the product, it is said to be a reduction reaction. As it can be seen in Figure 1, that the oxidation for our reactant is +2 and for our product is 0, this means that there was a decrease in the oxidation number, hence this reaction is said to be a reduction reaction.

Carbonyl carbon in a compound is usually reduced to alcohols by catalytic hydrogenation. For example, ketones can be reduced to secondary alcohols, and aldehydes are reduced to either primary alcohols or carboxylic acids depending on the reducing agent used. In a research laboratory, the most common reducing agents are lithium aluminum hydride (LAH or LiAlH4) and sodium borohydride (NaBH4). Molecular hydrogen with a metal catalyst is also another example of reducing agent, and can be used to reduce alkenes, alkynes, aldehydes, ketones, imine, and nitro groups. In this experiment, 9-Fluorenone is reduced to 9-Fluorenol using sodium borohydride. Lithium aluminum hydride is more reactive than molecular hydrogen and can be used to reduce aldehydes to carboxylic acids, or esters to primary alcohols. Sodium borohydride is more selective, and can be used to reduce aldehydes to primary alcohols, but does not react with esters. Since sodium borohydride is the most selective, and it also reduces ketones to alcohols, it is the reagent for our reduction reaction. Figure 2 represents the mechanism for this reaction. This is an oversimplified version of the mechanism; in reality all of the four hydrogens attack the ketone.

Figure 2: Overall Simplified Mechanism for conversion of 9-fluorenone to 9-fluorenol In order to confirm the process of the reaction, the TLC analysis could be performed. TLC could be used in this experiment due to different functional groups and their varying polarity. As shown in figure 3, we could prepare three spot, one with pure 9-fluorenone, second with 9-fluorenone + reaction mixture and third with only reaction mixture. The alcohol is more polar than ketone due

Figure 3: Normal TLC analysis to identify the process of the reaction

to the hydroxyl group on the alcohols. Thus, on the normal TLC plate the ketones will move further compared to the alcohols because it will be more attracted to the mobile phase than the polar stationary phase. Thus, the retention factor of our product is expected to be smaller for product than the reactant. Due to this property difference we can compare each compound’s movement and see if the reaction has occurred to the completion. Furthermore, the Lucas test can be used to distinguish among tertiary, secondary and primary alcohols. In this test the mixture of HCl and ZnCl2 is used as a reagent. The benefit of using this mixture is that it increases the reactivity of the alcohol toward the acid due to the fact that ZnCl2 is a strong Lewis acid that reacts with the lone pair electrons of the oxygen of the alcohol as shown in figure 4. The ZnCl-OH complex forms and then dissociates to yield a carbocation. This carbocation then reacts with the chloride ion to form an alkyl chloride product. Since the ratedetermining step of the reaction is carbocation formation, the reaction rate increases with increasing carbocation stability. Therefore, tertiary alcohols react fastest than secondary alcohols, and primary alcohols do not react at all. In this test, the alkyl chloride is not soluble in aqueous solution, whereas the starting alcohol is soluble. Thus, a change from a clear to cloudy solution after adding the alcohol to the Lucas reagent constitutes positive test. Additionally, the rate of change in color will distinguish between tertiary and secondary alcohols. However, one disadvantage of this test is that the starting alcohol needs to be soluble in the Lucas reagent, and smaller alcohols tend to be the most successful with the Lucas test. Thus, with the large alcohols this test might not be promising to get the positive results.

Figure 4: Reaction Mechanism for the Lucas Classification Test for Alcohols In this experiment, IR spectroscopy can also be used to finalize that the reaction went to completion and we converted 9-fluorenone to 9-fluorenol. IR could we helpful because the both starting compound and the ending compound have different functional groups. The starting compound, 9-fluorenone, has carbonyl group. Whereas, our product 9-fluorenol has hydroxyl group. Thus, we should expect a broad peak between 3200-3600 cm-1 for our final product and not any sharp peak at ~1715 cm-1. In addition, the melting point analysis will also be performed to find the purity of the product. In this lab experiment, a weight of 9-fluorenone will be assigned to each group. Based upon this amount, we were supposed to calculate the amount of sodium borohydride, methanol, and sulfuric acid required for the reaction. Overall, our results showed that the percent yield for our product was 25.27% and the melting point range was 152 oC – 154 oC. The percent yield was

very low. However, the melting point range was very close to actual melting point range of the product. The IR graph also had a broad peak at 3310.50 cm-1, a sharp peak at 1450.33 cm-1 and no peak for carbonyl carbon group (~1715 cm-1). This suggested the presence of an alcohol group, aromatic carbons and no carbonyl group, respectively. Overall, we were able to prepare 9fluorenol form the reduction reaction of 9-fluorenone. Experimental Procedure Part I: Reduction Reaction Procedure First of all, we were assigned the weight of 9-fluorenone by our TA, and we took 0.9 g of 9fluorenone. Then, the required calculations were performed to figure out the initial weight of the additional reagents as shown in the data table 1. 0.9 g of 9-fluorenone was mixed with 9.1 mL of methanol and poured into a 50 mL Erlenmeyer flask. The flask was swirled and gently heated until all of the 9-fluorenone dissolved. The solution was then cooled to room temperature and 0.09 g of sodium borohydride was added and was swirled vigorously to dissolve the reagent. The reaction was allowed to stand for 10 minutes at room temperature with occasional swirling. The reaction was slowly changing its color from yellow to clear. Then, A TLC plate was marked with 3 spots. The first spot represented pure 9-flourenone which was obtained from the hood, the second spot was a co-spot which contained the reaction mixture and the pure 9-flourenone, and the third spot was the reaction mixture. The TLC plate was placed in a beaker with 1:9 ethyl acetate: hexanes solution which acted as the solvent. The Rf values were calculated and the TLC plate was observed under UV light and observations were recorded. About 0.98 mL of 3 M Sulfuric acid was added to the reaction mixture. The flask was gently heated until the entire solid was dissolved. The flask was then removed from the heating mantle and cooled to room temperature and then was placed in an ice bath. After the solid had precipitated again, vacuum filtration was used to dry the product. The product was washed with 200 mL of water and made sure the filtrate was neutral. The filtrate was tested with pH paper. The final product was recrystallized using ~20 mL of hot methanol and was placed on a heating mantle. Once the entire solid had been dissolved it was removed from the heating mantle and allowed to be cooled at room temperature and then was immersed on an ice bath. The product was filtered and dried using a vacuum filter as shown in figure 5. The additional cold ~40 mL of methanol was used to wash the final product. Then, the final product was weighed and melting point, IR spectrum and Lucas tests results were collected.

Figure 5: Vacuum Filtration Apparatus

Part II: Confirmation of Alcohol Formation by Lucas Classification Test After obtaining the final product, the Lucas Classification test was performed. Three clean test tubes were obtained and 1 mL of the Lucas reagent was added to each. To one test tube 0.3 mL of t-butanol (tertiary alcohol) was added. To the second test tube, 0.3 mL of the reaction mixture (secondary alcohol) was added. In order to prepare the secondary alcohol for this test, solid crystals of obtained product were dissolved in ~0.3 mL of ethanol. And finally, to the third test tube, 0.3 mL of 1-butanol (primary alcohol) was added. And the observations were recorded in the data tables.

Data Acquisition/Presentation Table 1: Reaction Reagent Table Compound 9-Flourenone

Molecular Weight 180.19 g/mol

Density or Molarity N/A

Reaction Weight 0.9 g

mmol

Equivalents

4.99

1.0

37.83 g/mol

N/A

0.093 g

2.49

0.5

32.04 g/mol

0.792 g/mL

9.1 mL

224.7

45

98.08 g/mol

1.00 g/mL 3.00 mol/L

.98 mL

9.99

2.0

Sodium Borohydride (NaBH4) Methanol Sulfuric Acid (H2SO4)

0.9 g 9 Flourenone ×

(1 mol Flourenone ) 0.5 mol NaBH 4 37.83 g NaBH 4 × × 1 mol NaBH 4 ( 180.19 g Flourenone ) 1 mol Flourenone

= 0.093 g

NaBH4 0.9 g 9 Flourenone ×

(1 mol Flourenone ) 1 mL methanol 45 mol Methanol 32.04 g methanol × × × 1 mol Methanol 0.792 gMethoanol ( 180.19 g Flourenone ) 1 mol Flourenone

=9.1 mL Methanol 0.9 g 9 Flourenone ×

(1 mol Flourenone ) 2.0 mol H 2 SO 4 98.08 g H 2 SO 4 × × = 0.98 mL 1 mol H 2 SO 4 ( 180.19 g Flourenone ) 1 mol Flourenone

0.9 g 9 Flourenone ×

(1 mol Flourenone ) ×1000=4.99 mmol ( 180.19 g Flourenone )

0.093 g NaBH4 ×

( 1mol NaBh 4 ) × 1000=2.49 mmol ( 37.83 g NaBH 4)

9.1 mL Methanol ×

( 0.792 g Methanol ) ( 1mol Methanol ) × ×1000=224.7 mmol 1 mL Methanol 32.04 g Methanol

0.98 mL Sulfuric Acid ×

( 1 mL Sulfuric Acid ) ( 1 mol Sulfuric Acid ) ×1000=9.99 mmol × 98.08 g Sulfuric Acid 1 g Sulfuric Acid

Calculating Percent Yield Actual Yield = 0.23 g 9-Flourenol Theoretical Yield: 0.9 g 9 Flourenone ×

(1 mol Flourenone ) 1 mol 9 Flourenol 182.22 g Flourenol × × = 0.91 g 9180.19 g Flourenone 1 mol Flourenol 1 mol Flourenone ) (

Flourenol

Percent Yield: Actual Yield ×100 Theoretical Yield

=

0.23 g ×100 = 25.27 % 0.9 g

Figure 6: TLC Plate Observed under UV light. This image is not scaled.

Calculating Retention Factor Retention Factor (Rf) =

Distance Traveled by the Solute Distance Traveled by the Solvent

Rf for Pure 9-Flourenone =

2.1 cm 3.49 cm

= 0.60 cm 2.1 cm 3.49 cm

Rf for Pure 9-Flourenone (Co-Spot) =

Rf for Reaction Mixture (Co-Spot) =

Rf for Reaction Mixture =

0.8 cm 3.49 cm

0.8 cm 3.49 cm

= 0.60 cm

= 0.23 cm

= 0.23 cm

Table 2: Amount of liquid used during the reaction Data Amount Amount of Water used to neutralize filtrate

400 mL

Amount of methanol used to dissolve the solid

20 mL

Amount of methanol used to filter recrystallized product

40 mL

Table 3: TLC Analysis and Retention Factors Spot Rf Value Pure 9-Flourenone

0.60 cm

Pure 9-Flourenone (Co-Spot)

0.60 cm

Reaction Mixture (Co-Spot)

0.23 cm

Reaction Mixture

0.23 cm

Table 4: Melting Point Analysis Actual Melting Point Range oC Observed Melting Point Range oC

Product 9-Flourenol

155-157

152-154

Table 5: IR Spectroscopy -1

Wavenumber (cm ) 3310.50

Functional Group Hydroxyl group

1450.33

Aromatic Carbons

The IR spectroscopy graph is attached to this report.

Observations

Table 6: Lucas Test Observations Primary Alcohol Secondary Alcohol 1-Butanol 9-Fluorenol

Tertiary Alcohol T-Butanol

Test

Positive No Emulsion

Positive Emulsion formed

Positive Emulsion formed

Rate of Reaction

N/A

Slower

Very quick

Conclusion The main purpose of this experiment was to reduce 9-Fluorenone to 9-Fluorenol by using sodium borohydride, and calculate the amount of reagents used, then finally characterize the product by various analysis and test such as melting point, IR spectroscopy and Lucas test. TLC analysis was also performed to track the process of the reaction, and recrystallization was used to produce the pure product from crude product sample. After obtaining the 9-fluorenol, the percent yield for this experiment was over 25.27% which suggests that we were not careful and lost lots of product while performing the reaction. Errors that could explain the very low percent yield might be that we had to transfer the product several times from one container to other in order to perform filtration. While transferring the product mixture we had some white powder stick to the surface of the flasks and Buchner funnel. In addition, while washing the product with water we had lost lots of white product material along with water. This was also confirmed after using the pH paper. It indicated that we had little acidic drainage instead of being neutral. In order to avoid this error, the experiment needs to be carried out in a very precise manner. All the equipment

should be washed and dried before starting the reaction, care needs to be taken so that there is less contamination and we need to make sure to transfer all the material possible from one container to other. After performing the melting point analysis, we were able to conform that out product did not have much of impurities after recrystallization. The observed range of our product was 152-154 oC which is almost the same as actual range (155-157 oC). The reason behind a point low melting point range could be that we might had melted the product at high temperature and quickly. However, being a short range proved that the product had almost impurities in it. Before adding sulfuric acid, while performing the reaction, TLC analysis was performed in order to figure out if the reaction had reached the completion, and it was observed that the reaction had gone to completion. As seen above data table that the Rf values for the co-spot of pure 9fluorenone and the spot for 9-flourenone were same (Rf = 0.60). Also for the third spot, which was the reaction mixture had same Rf value (Rf = 0.23) as co-spot’s reaction mixture. Additionally, the Rf value for mixture reaction was smaller than the first spot (0.23 < 0.60) and there were no extra spots seen on the TLC plate. This indicates that the reaction went to completion since the product had higher polarity than the reactant; the product had a higher affinity for the polar stationary phase which has a lower retention factor. So the TLC analysis indicated that the reaction was complete and successful which indicated that we did not have to wait for entire 20 minutes. IR spectrum graph were also in favor of the product. As shown in the data table 5 and graph attached, we observed a broad peak at 3310.50 cm-1. This peak suggested the presence of hydroxyl group in our collected product because 9-fluorenol contains an O-H group in it. In addition, we were also able to observe peaks for aromatic carbons of the 9-fluorenol at 1450.33 cm-1. The main observation from the graph was the absence of a peak at ~1715 cm-1 which represents the peak for carbonyl carbon in the 9-fluorenone. Finally, all of these analysis suggested that we had successfully reduced the 9-fluorenone into 9-fluorenol. The final test that was performed was the Lucas Test. In that, 1-Butanol was used as the primary alcohol, 9-Flourenol (Our Product) was used as the secondary alcohol, and t-Butanol was used as the tertiary alcohol. As seen from the data that the results from this test were positive. The primary alcohol didn’t form an emulsion and the tertiary alcohol was the fastest to react, while the secondary alcohol was slower but it did react. However, some of the class groups observed that the secondary alcohol formed emulsion faster than the tertiary, and the reason explained was that the 9-fluorenol has two aromatic rings which stabilizes the product by resonance stabilization. However, for our product it was slower than the tertiary. The reason could be that while dissolving the product into ethanol, we had obtained lots of ethanol instead of 0.3 mL thus the reaction was so fast that we couldn’t observed anything. This is because the ethanol is very reactive itself. Additionally, Lucas test is very successful with small alcohol with six carbons. However, 9-fluorenol is relatively very large alcohol structure which could be a reason that we had different results than most of the class. Despite of not reacting fast with Lucas test, the overall results suggested that our experiment was successful. Ultimately, this experiment was successful at performing the reduction reaction and preparing 9Flourenol. Although the reaction was successful, the product obtained was very less due to not

being careful while performing the experiment. However, the melting point analysis, IR spectroscopy graph and Lucas test finalized that, indeed, our product was successfully formed from 9-flurenone by reduction reaction. After all, we were able to applied learned techniques such as recrystallization, vacuum filtration to obtain the final product being 9-fluorenol. References Gilbert, J.C. and Martin, S.F., Experimental Organic Chemistry, Cengage Learning, New York, 2011, 4th Ed....