Lab Report 9 - Lecture notes 9.0 PDF

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Lab 9: Preparation of Alcohols: Reduction of Fluorenone and Lucas Test for Alcohols Zeba N. Siddiqui (Partner: Keti Berberi) November 5, 2014

Methods and Background: The goal of the lab was to prepare 9-Fluorenol by reducing 9-Fluorenone with the use of Sodium Borohydride, NaBH4; this preparation can be found in Figure 1. 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◦). These structures are found in Figure 2. It should also be noted that the secondary structure in the lab is the product, 9-Fluorenol.

Figure 1 Reaction of 9-Fluorenone with Sodium Borohydride to Produce 9-Fluorenol

Figure 2 Primary, Secondary and Tertiary Structures of Alcohol

Reduction is a basic type of chemical reaction. It is often symbolized by [H] 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. Example of more electronegative atoms are nitrogen, oxygen, or a halogen 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. To simplify, reduction is a gain of electron density and a replacement from a more electronegative to a less electronegative atom. Oxidation, oppositely, 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, 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. Consequently, if the carbon’s oxidation number decreases, the result would indicate a reduction. Organic functional groups comprising of double and triple bonds undertake reduction by the net addition of the elements of one or two molecules of hydrogen across the pi, π, bond or bonds. The starting compound is unsaturated, while the final product is saturated with respect to hydrogen. The saturated product contains only single bonds and can absorb no more hydrogens. Calculations of the oxidation number basically refers to an increase in carbon produces an oxidation, consequently, a decrease in carbon results in a reduction. Three simple rules, however, 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 are species that reaction and cause another molecule to become reduced. Simply, 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, Figure 3, 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, Figure 4, reacts rapidly with protic solvents thus, it must be used in anhydrous ethereal solvents.

Figure 3 Sodium Borohydride

Figure 4 Lithium Aluminum Hydride

In the experiment, a reduction of imines by the use of Sodium Borohydride along with the transfer of hydride ion from BH4- to the electrophilic carbonyl carbon with concomitant transfer of the electron-deficient boron atom to the carbonyl oxygen. All four of the hydrogen atoms attached to boron is transferred to produce boron salt. Boron salt, however, decomposes upon the presence of water and acid to yield 9-Fluorenol. Pure compounds are homologous samples comprising only of molecules with the same structure. However, possible contamination may still be evident in pure compounds. With these additional impurities, incorrect structural characterizations and would produce false conclusions. 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. An alternate method involves melting the solid in the absence of the solvent then allowing the crystals to reform so that the impurities are left in the melt.

Almost all solids are more soluble in hot than in cold solvent, something solution crystals take advantage of. For illustrate, if you were to dissolve the solid in hot solvent, an amount insufficient to dissolve the solid in cold solvent, then crystals should form when the hot solution is allowed to cool. The extent of the solid precipitates is dependent upon the solubility difference in the particular solvent at temperatures between the extremes used. The upper extreme is relied upon the boiling points while the lower limit depends on experimental convenience. Impurities observed in the original solid mixture that has dissolved and has remained dissolved after the solution has cooled, isolation and separation of the crystals that have formed should ideally provide pure material. Opposing the above, impurities may not dissolve in the hot solution and would need to be removed by filtration before the solution is cooled. Hypothetically, crystal formation is more pure than the original solid mixture. Often, the solid is not pure after crystallization. Melting point is the method used to identify the purity. To reiterate, the steps to recrystallization is as the following: selection, dissolution, decoloration, formation, isolation, and drying. Melting point is the point where a solid would melt. It is psychical property defined as the temperature at which the phases of a liquid and solid occur in equilibrium without an alteration of temperature. With saying that, the sample would not liquefy at a single temperature point, however, over a temperature range in which the solid begins to melt and then is transformed into a liquid. If the crystalline sample is pure, then it should liquefy over a narrow or sharp range. The start of a solid melting is characterized as a softening, which describes the shrinking of the solid sample. However, it is not always possible to observe this softening, so the use of a range is appropriate. For example, an experimental compound recorded a melt at 115◦C. That would be an improper number, a range is needed at, for example, 114-116◦C. A common method to

determine melting point is the use of a capillary tube, found in Figure 5. In this method, an organic solid is placed in the capillary tube. A comparison between the acquired temperature values with the standard values can be found in an index or catalog which will identify an unknown compound.

Figure 5 Capillary Tube

A Lucas Test is a test used to distinguish between primary, secondary, and tertiary alcohols. The reagent used is a mixture of concentrated hydrochloric acid and zinc chloride, this converts alcohols to the corresponding alkyl chlorides. For primary alcohols, the reagent give no apparent reaction. For secondary alcohols, the reagent reacts more rapidly, an observational change can occur round five to twenty minutes. And finally, the reagent reacts instantaneous with tertiary alcohols. A positive test is dependent upon the fact that the alcohol is soluble on the reagent, whereas the alkyl chloride is not, thus the formation of a second layer or cloudy solution is a positive test. Limitations, however, exist. This setback is that the starting alcohol, needs to be soluble in the Lucas reagent, thus a specific type of alcohol is required. The most successful alcohol types are ones with six or less carbons. TLC also helps separate mixtures into their individual components. This method is used with smaller sample sizes and utilizes TLC plates. These plates are thin sheets, one side coated with silica gel and the other side layered with aluminum, and example can be found in Figure 6. Drops of the experimental extract, a mixture of the extraction and an authentic sample, and a

pure authentic sample are to be placed on the plate and into a mixture of mobile phase composition; the experiment utilizes a 9:1 mixture of Ethyl Acetate/Hexanes. The solvent would rise up if in mobile phase, and stay still if in stationary phase. Polarities are important in determining how well a pure substance separates from a mixture. 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 attach to it and become immobile. On the other hand, if a nonpolar solvent is used, then nonpolar molecules will interact with the nonpolar solvent and travel through the stationary phase, the silica gel. Thus, the more polar the sample is, the slower it will move up the plate; consequently, the less polar, the faster the compound exits the plate.

Figure 6 An example of a Thin Layer Chromatography (TLC)

Name

Formula

MW

9Fluorenone

C13H8O

180.21 g/mol

9-Flourene

C13H10O

182.22 g/mol

Solid

Sodium Borohydrid e

NaBH4

37.84 g/mol

Solid

Methanol

CH3OH

32.04 g/mol

Liquid

Ethanol

CH3CH2OH 46.07 g/mol

Liquid

Sulfuric

H2SO4

Thick

96.08

Physical State Solid

BP/MP/Densit y BP: 32°C MP:83.5°C D: n/a BP: n/a MP:153-154°C D: n/a BP: n/a MP: decomposes 1.074 BP:64.5°C MP:-97.8°C D:0.7915 BP:78.5°C MP:-114.1°C D:1.84 BP: 270°C

Safety Hazards proper proper disposal proper disposal caustic -> gloves

proper disposal proper disposal corrosive-

Acid Lucas Reagent

ZnCl2 or HCl

Water

H 2O

g/mol

liquid

MP: -35

135.32 or 36.46 g/mol 18.02 g/mol

Liquid

BP: 371°C MP: -18°C D: 0.89 BP: 100°C MP: n/a D:1:

Liquid

> gloves proper disposal n/a

Table 1 Reaction Table

Experimental Procedures: Part I: Synthesis of 9-Fluorenol: Reduction Reaction Procedure. What is first needed is the calculated 9-Fluorenone weight. This must be transferred into a 50mL Erlenmeyer flask with the calculated volume of methanol. The flask is then heated and is swirled. Cool the solution in room temperature. Immediately after, add the calculated amount of Sodium Borohydride. Swirl vigorously and do not use a stopper. A stopper would build up pressure in the flask, causing a possible explosion. For twenty minutes, allow the solution to sit at room temperature, however, occasionally swirl. The reaction should be colorless by the, or before the time. A TLC test is needed. A silica gel plate dipped within a 9:1 Ethyl Acetate: Hexanes. Three spots should be performed. One containing pure 9-Fluorenone, another containing pure 9-Fluorenol, and the middle is the co-spot containing an overlap of both pure compounds. Next is to add the calculated 3M Sulfuric Acid to the mixture. Swirl and heat the flask for 5-7 minutes. A watch glass to prevent complete evaporation is necessary. Solids should dissolve. Cool the mixture to room temperature and then place in an ice bath until the solid precipitates, this should take 5-10 minutes. Table 3 has all the necessary calculations to proceed the lab. Filer the solid and wash with at least 200mL of water. Test the water directly escaping out of the funnel for it pH level. The water must be neutral to proceed to the next step. Recrystallize the final product using minimum amount if hot methanol possible. Heat about 10-20mL of methanol

and then add it to the solvent until it just dissolves. During dissolution, keep a watch glass on at all times. Once it is all dissolved, cool the mixture then o=place it in an ice bath. After, filter the final product and dry attached to vacuum. Weight the final product and calculate the percent yield, then characterize by melting point analysis and IR Spec. Part II: Confirmation of Alcohol Formation by Lucas Classification Test: Lucas Test Procedure. Prepare three test tubes with 1mL of the Lucas reagent. In Test Tube #1 add about five drops of the tertiary alcohol. In Test Tube #2, add about five drops of the product, which is the secondary alcohol. In Test Tube #3, add about five drops of primary alcohol. A positive test will indicate an instantaneous change from clear to cloudy, this is a positive test for tertiary alcohols. If not immediately, but after some time, the clear mixture become cloudy, this observation indicates a positive result for secondary alcohols. The change should occur for a primary alcohol, any change would indicate a false result due to contamination or something else. However, because the product is a solid, mix a spatula full of the product with about 0.3mL of ethanol and then add it to the test tube after it has dissolved.

Data Acquisition: Relevant Equations and Calculations %Yield = Actual Mass (g) x 100 Predicted Mass (g) Theoretical Mass = Starting Volume x Density x 1 x Reaction x MW Product = # grams 1 mL MW Reaction 1 mol %Error = [Theoretical Value – Experimental Value] x 100 [Theoretical Value] Retention Factor (Rf): Distance Traveled by the Substance (mm) Distance Traveled by the Solvent (mm) Theoretical Mass = 1.00g9-Fluorenone x

1 x 1 x 182.22g/mol9-Fluorenol = 1.01 grams 180.19g/mol 1 1 mol

%Yield = 10.64g x 100 = 1,053.47 1.01g %Error = [1.01 – 10.64] x 100 = 953% [1.01] 9-Fluorenone Rf Value: 27mm = 0.5mm 54mm Co-Spot Rf Value: 6.0mm = 0.1mm 54mm

27mm = 0.5mm 54mm

9-Fluorenol Rf Value: 6.0mm = 0.1mm 54mm Product (9-Fluorenol) 1,053.46 0.1mm 46-47◦C Alcohol: 3285.63cm-1 Aromatic: 3040cm-1 Alkene: 1608cm-1 Positive

% Yield Rf Value Melting Point IR

Lucas Test Table 2 Data Collection

Test Tube Number Contents Lucas Test Results

#1 Tertiary Alcohol Positive

#2 Product Positive

#3 Primary Alcohol Negative

Table 3 Lucas Test

mmol

Equivalents

n/a

Rxn Weight (g) or Volume (mL) 1.00g

5.55

1.0

37.83

n/a

0.11g

2.78

0.5

32.04

0.792g/mL

249.75

4.5

98.08

3.00mol/L

8.00g = 10.10mL 1.09g = 3.70 mL

11.10

2.0

Compound

MW (g/mol)

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

9Fluorenone Sodium Borohydride Methanol

180.19

Sulfuric Acid

Table 4 Reaction Table for Lab Calculations

Figure 7 TLC Results

Conclusion: The purpose of the lab was to prepare 9-Fluorenol by reducing 9-Fluorenone using reducing agent, sodium borohydride. The product was then purified by recrystallization and functional group were verified by melting point and IR Spec. A Lucas test was then performed to compare reactivity and stability differences between primary, secondary, and tertiary alcohols. The percent yield obtained was 1053.46%, found in Table 2. This is clearly too high, this might be due the fact that we starting off with a very high amount of 9-Fluorenone, and because of this, we accumulated too much product. The over produced product also affect other result in the experiment. While washing the product to get the water to a neutral pH, 900mL of water was used, instead of the minimum of 200mL. Also, too much methanol was used which might have contributed with the amount of products formed. Thus, the percent error was also adequately high. Going above 100%, the percent error was calculated at 953%. The large amount of product also affect the ability to dry the product in the minimum time lab was conducted. Because of this, our product had excess water contributing to a possible error in IR and melting point. However, the melting point for the product was 46-47◦C, Table 2. Not only was the excess water effecting the results, but using the apparatus after every other student affect the accuracy of the test. All apparatuses were already too hot, the product melting quiet early. The IR peaks, however, did match the functional groups required. The final product revealed and

alcohol functional group, and aromatic ring and an alkene. However, the alcohol group was not as broad as expected. This might be due to a closer attachment of the alcohol to the aromatic ring. The TLC test, however, proved accurate results. The authentic 9- Fluorenone equaled the polarity of the top distance of the co-spot. Also the authentic product, 9-Fluorenol, equaled the polarity distance of the bottom distances of the co-spot. The results indicated that the 9-Fluroenone is less polar than the product. The silica gel contains an alcohol functional group, those indicating polarity. The product is an alcohol, thus the TLC plate revealed the product to have a higher affinity to the stationary phase while the reactant, 9- Fluorenone, had a higher affinity to the mobile phase. This is found in Figure 7. As found in Table 2, the Rf value of 9-Fluorenol is 0.1mm. As found in Relative Equations and Calculations, 9- Fluorenone’s Rf value is 0.5mm. This too indicated that 9-Fluorenol is more polar that that reactant because of its lower Rf value. This, however, might be due to the product’s ability to hydrogen bond, unlike ketones ability. The co-spot, as seen in Figure 7, accurately travels the same distance as its contents. The Lucas tests also indicated accurate results. Table 3 reveals that both tertiary and secondary alcohols turn cloudy after the reagent was added to it, while the primary did not change. However, it should be noted that the secondary alcohol, the product, should take a little bit to change from clear to cloudy. This did not happen to the product. With a two second delay when compared to the tertiary alcohol, the product changed to a cloudy solution. This instantaneous change might be due to the products closer attachment of the alcohol to the aromatic ring, or because, again, the excess amount of wet product.

Reference:

Gilbert, J.C., and Martib, S.M., Experimental Organic Chemistry: A Miniscale and Microscale Approach, 4th Edition, Cengage Learning, Boston, MA, 2006. Landrie, C.L., and McQuade, L.E., Organic Chemistry: Lab Manual and Course Materials, 5th Edition, Hayden-McNeil, LLC, Plymouth, MI, 2016....