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Maha Haroon Xuan Duong Chem 233 CRN:18713 04/15/2021 Lab Report: Organic Chemistry 1, Lab 8:Preparation of Alcohols:Reduction Fluorenone & Lucas Test for Alcohols

● Introduction The goal of the lab was to prepare 9-Fluorenol by reducing 9-Fluorenone with the use of Sodium Borohydride, NaBH4-.The reduction is singled out for the carbon-oxygen double bond. The product is then purified by recrystallization and characterized by Infrared (IR) Spectroscopy and melting point analysis. To verify the formation of alcohol, a Lucas Test is performed. The test will note the different structures of alcohol: primary (1◦), secondary (2◦), and tertiary (3◦ ). The secondary structure in the lab is the product, 9-Fluorenol. Reduction is a basic type of chemical reaction, and is the opposite of oxidation. In organic chemistry, reduction is the process of carbons forming covalent double bonds, rather than the gaining of electrons. However, reduction of organic compounds experience an increase in electron density due to the replacing of a bond with carbon with a more electronegative atom. Examples of more electronegative atoms are nitrogen, oxygen, or with a carbon-hydrogen bond. Reductions are also characterized by a reaction where new carbon-hydrogen bonds are formed by adding hydrogen to a functional group. In border terms, reduction is a gain of electron density and a replacement from a more electronegative to a less electronegative atom. Oxidation, on the other hand, is a loss of electron density with a replacement of a less electronegative to a more electronegative atom. Oxidation number is the number assigned to an element that represents the number of electrons lost or gained, and if the number is negative, by an atom of that element in the compound. If the oxidation number of the carbon atom increases, it is considered an oxidation. If the carbon’s oxidation number decreases, the result would indicate a reduction. The oxidation number refers to an increase in carbon that produces an oxidation, and a decrease in carbon results in a reduction. There are three simple rules that determine the actual number: 1. For every atom bound to a carbon that is more electronegative than the carbon, add 1. 2. For every atom bound to a carbon that is less electronegative than the carbon, subtract 1. 3. For every time a carbon is bound to another carbon, add 0. Reducing agents, however, are species that reaction and cause another molecule to become reduced. In other words, reducing agents become oxidized over the course of the reaction. Carbonyl compounds tend to be reduced to alcohols. This reduction is commonly done by catalytic hydrogenation or with metal hydrides. Sodium Borohydride may also be used for alcohols or aqueous solutions because it reacts more rapidly with the carbonyl group than with the solvent. Lithium Aluminum Hydride, LiAlH4 or LAH, will react rapidly with protic solvents. In this experiment, a reduction of imines, with the use of Sodium Borohydride, along with the transfer of hydride ion from BH4- to the electrophilic carbonyl carbon.Pure compounds are homologous samples consisting only of molecules with the same structure. However, possible contamination may still be evident in pure compounds.The process of recrystallization involves dissolving the solid in an appropriate solvent at an elevated temperature and allowing the crystals to reform on cooling, so that any impurities remain in solution. Another alternate method is melting the solid allowing the crystals to reform so that the impurities are left. Another test will be used, called the Lucas test, which will be used to distinguish between primary, secondary, and tertiary alcohols. The reagent is a mixture of concentrated hydrochloric acid and zinc chloride, which will convert the alcohols to the corresponding alkyl chlorides. For primary alcohols, the reagent will have no apparent reaction.

In the secondary alcohols, it will react more rapidly, and in the tertiary alcohol, it will have an instantaneous reaction. A positive test will be shown by a cloudy solution. We will also be using TLC, since it helps separate mixtures into their individual components. This method will be used with sample sizes and TLC plates. A couple of the experimental extracts, a mixture of the extraction and an authentic sample, and a pure authentic sample will be placed on the plate and into a mixture of mobile phase composition. The experiment will utilize a mixture of Ethyl Acetate/Hexanes. The solvent would rise up if in the mobile phase, and stay still if it is in the stationary phase. Polarities are important in determining how well a pure substance separates from a mixture. We know that the Silica gel contains an alcohol (OH) functional group, making it a polar molecule. As a result, any polar molecule that comes across the silica gel will get attached to it and become immobile. If a nonpolar solvent is used, then nonpolar molecules will interact with the nonpolar solvent and travel through the stationary phase. The more polar the sample is, the slower it will move up the plate, and the less polar, the faster the compound exits the plate. With this, we will be able to prepare 9-Fluorenol by reducing 9-Fluorenone with the use of Sodium Borohydride, NaBH4-, then the product is purified by recrystallization and characterized by Infrared (IR) Spectroscopy and melting point analysis. To verify the formation of alcohol, we performed a Lucas Test, which will note the different structures of alcohol: primary (1◦), secondary (2◦), and tertiary (3◦ ).

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● Procedure Part 1: Synthesis of 9-fluorenol 1: Add weight of 9-fluorenol to a 50 mL erlenmeyer flask. Swirl and heat until all of the 9-fluorenol is dissolved. 2: Cool the solution to room temperature. Weigh and calculate the amount of sodium borohydride and add it immediately to the flask in one portion. Swirl the flask to dissolve the reagent 3: Allow the reaction to stand at room temperature for 20 min, with occasional stirring. The reaction should be colorless. If not, add more sodium borohydride and stir until colorless 4: Before working up the reaction, take a TLC plate, and using 1:9 ethyl acetate:hexanes, confirm that the reaction is complete. The TLC plate should contain three lanes: 1) pure 9-fluorenone; 2) pure 9-fluorenone + reaction mixture (known as a co-spot); 3) reaction mixture. Examine the TLC plate under UV light and circle the spots you observe. Calculate the Rf values of 9-fluorenone and 9-fluorenol 5: Work up the reaction by adding 3M sulfuric acid to the reaction mixture. Heat the flask and swirl for 5-7 minutes so the solid formed will dissolve. 6: Remove the flask from the heat and cool to room temperature. Prepare an ice bath until the solid precipitates for 5-10 min 7: Filter the solid and wash thoroughly with water, at least 200 mL. Test the water coming out of the Büchner funnel after washing using pH paper to ensure it is neutral. Dry the product attached to the vacuum. 8: Recrystallize the final product using the minimum amount of hot methanol possible. Heat 10–20 mL of methanol and add the hot solvent to the product until it just dissolves.Once all the 9-fluorenol is dissolved, remove the solution from heat and let it cool first to room temperature and then in an ice bath. Filter the final product and dry it attached to the vacuum.

9: Weigh the final product and calculate percent yield. Make sure to do this before performing any tests or characterization 10: Characterize your product by melting point analysis and IR and NMR spectroscopies. For NMR, dissolve ~100 mg in ~0.5 mL CDCl3 and place in NMR tube

Part II: Confirmation of Alcohol Formation by Lucas Classification Tes tLucas Test Procedure 1.Prepare three test tubes by adding 1 mL of the Lucas reagent to each. 2. To one test tube add 5 drops of the tertiary alcohol. A positive test is indicated by the solution becoming cloudy. If the solution does not become cloudy immediately, shake the test tube for up to 5 min. If the solution does not become cloudy in that time the result is “no reaction” (i.e., a negative test) 3. Repeat the procedure for the secondary ( product) and primary alcohol. Note that the product is a solid, so prepare a solution of 9-fluorenol in 0.3 mL of ethanol before performing the test. 4: Compare the results of the test for primary, secondary, and tertiary alcohols.

● Equations/Calculations for reactions

Compound

MW (g/mol)

D (g/mL) or M (mmol/mL)

Rxn weight (g or mL)

mmol

equivalents

9-fluorenone 180.19

n/a

6.77g

37.6 mmol

1.0

Sodium Borohydride

37.83

n/a

0.711 g

18.8 mmol

0.5

Methanol

32.04

0.792 g/mL

54.2 g

1692 mmol

45

1.00 g/mL 3.00 mol/L

7.38 g

75. 2 mmol

2.0

Sulfuric Acid 98.08

% yield

86%

g yield

5.82 g

Rf value

0.38 ( 9-fluorenone) 0.19 (9-fluorenol)

( 9-fluorenone & 9-fluorenol)

Lucas test 1

Negative

Lucas test 2 ( Product, 9-fluorenol)

Positive

Lucas test 3

Positive

5: The melting point of the product is lower than the reported literature value because the product may contain some impurities. Impurities in a solid crystal can cause a decrease in the melting point, since it disturbs the crystals energy. So while the product was going through a process of recrystallization, it may have some impurities left, which caused the product to have a lower melting point than reported.

● Conclusion In this lab, we were able to produce 9-Fluorenol by reducing 9-fluorenone using sodium borohydride. We also performed the Lucas test to classify the different types of alcohols, according to primary, tertiary, and or secondary. To distinguish the different types of functional groups, we did an IR spectroscopy and an NMR graph. Based on the results, the lab was successful. The yield of the final product was given to us at 86%. This percent yield is close to 100%, showing that the 9-fluorenol was successfully reduced to 9-fluorene. Our starting grams was 6.77 grams, and our calculated percent yield was given at 86. We were able to find how much of the 9-fluorenone was isolated, which was 5.82 grams, which is acceptable. The reason why it wasn’t 100% could be due to the mass of product likely going down after recrystallization because, while the chilled solvent is saturated and should release some crystals, some of the desired material will remain dissolved in the cold solvent and will be lost when the crystals and solvents are separated. Other possible errors could be the excessive washing by solvent, etc.Based off of the testing of our reaction, we were also able to run a TLC to see if our reaction was progressing. We prepared a TLC plate and marked three spots on it, a product, reactant, and a co-spot. We then ran the TLC under the solvent of 1:9 ethyl acetate: hexane, and observed these Rf values seen in the calculation section. We can see that the pure 9-fluorene had an Rf value of 0.38 cm, and the reaction product had a Rf value of 0.19 cm. This shows that the reaction was in progress. The Rf values were accurate based on the molecules because the pure solvent has an OH group which makes it more polar, hence having a larger Rf value than our reaction product. Some errors in the TLC calculations can be due to which screen we measure in, since different screens can detect different calculations. Although there can be a slight error because of this, it is shown and proven that the pure fluorene is more polar and has a larger Rf value than the product. The completion of the IR spectroscopy helped distinguish the many different functional groups in the expected product. We were able to identify an alcohol stretch at about 3334-1 cm and found an aromatic ring stretch at about 700 -1 cm. We were also able to see the H NMR corresponding to the IR graph, which can verify the functional groups found. These graphs can also prove that the experiment was successful. Lastly, we were able to perform The Lucas test to see and classify the alcohols in the product. Since this test runs under a SN2 environment, the rate determining step is the formation and stability of the carbocation. In hindsight, the tertiary carbocation is the most preferred and stable for a formation of an alcohol and the stability will decrease if it were a secondary or and be even less stable if it is a primary alcohol. Based on the observations, when we mixed the Lucas reagent and the reaction mixture, we were able to see a cloudy, smoky color upon adding the reagent; which was on the tertiary alcohol. Hence, proving to be a positive test of the Lucas test. On the secondary alcohol, we were able to see a cloud like color,

but it wasn’t as quick as the tertiary, but it still reacted with the lucas reagent, therefore a positive outcome. On the primary, we saw no reaction with the lucas reagent, therefore a negative outcome. Since the lucas goes by the SN2 reaction, the order in which the alcohols reacted was proven to be true. Based on this lab’s result, the experiment was successful.

●Post-Lab Questions: 1. For each of the reactions shown below, indicate whether it is a net reduction, an oxidation, or neither and calculate the change in oxidation number for any carbon being reduced or oxidized.

2. Explain the purpose of adding dilute (3 M) and not concentrated sulfuric acid to the reaction during work up. Sulfuric acid during the work up was to generate H+ ions. Concentrated sulfuric acid can't be used because it is mainly an oxidising agent and doesn't have the required acidic strength to release H+ ions. If diluted acid is used, then the oxidising property is reduced and H+ is evolved.

3. 9-fluorenone is colored (bright yellow color) but 9-fluorenol is not (white). What accounts for this difference? 9-fluorenone has a C=O group. This functional group shows absorption in the UV-visible region, which as a result , the color is yellow. However, 9-fluorenol contains a functional group OH which cannot absorb in the UV region. So there is no absorption in the visible region and it appears white

4. Balance the following sodium borohydride reduction equation below.

5.Calculate oxidation states of carbon atoms with *

6. Calculate the theoretical amount of NaBH4 needed to convert 720 mg of A to B. Show your work. Draw the structure of possible by-products of this transformation....