Islam lab 9 - Lecture notes 21.2 PDF

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Chem 233

Yangbasai Dong

Preparation of Alcohols: Reduction of Fluorenone and Lucas test for Alcohols Background and Methods: Reduction reaction to prepare alcohol is widely using in our daily life. For example, Automobiles are powered by internal combustion engines, and various parts of the engines can become very hot. To prevent damage caused by overheating, a liquid coolant is used to transfer some of the heat away from the sensitive engine parts. In most climates, pure water is unsuitable as a coolant because it can freeze if outdoor temperatures drop below 0ºC. To prevent freezing, a coolant called antifreeze is used. Antifreeze is a solution of water and other compounds that significantly lower the freezing point of the mixture. Ethylene glycol and propylene glycol are the two most commonly used compounds for this purpose. The purpose of the lab was to prepare 9-Flurenol by reducing 9-fluorenone using sodium borohydride. The reaction is specific for the carbon-oxygen double bond. The product is purified by recrystallization and characterized by melting point analysis and IR spectroscopy. Alcohol formation is verified by performing the Lucas test. The test for 9-fluorenol (secondary alcohol) will be compared to known alcohols to note the differences between primary, secondary, and tertiary. Sodium borohydride functions as a source of hydride (H:-) and the solvent functions as the source of a proton (H+). The solvent can be ethanol, methanol, or water. The precise mechanism of action has been heavily investigated and is somewhat complex. Nevertheless, Mechanism 13.1 presents a simplified version that will be sufficient for our purposes. The first step involves the transfer of hydride to the carbonyl group (the CRO bond), and the second step is a proton transfer. Mechanism. Thin Layer Chromatography is typically used to analyze the progress of organic reactions and will also be used to check the progress of the reaction in this lab In TLC the stationary phase is bound to a solid support plate, Aluminum with a Silicon coating in this experiment. The plate is placed in a developing chamber with the mobile phase lining the bottom with a small amount of the sample above the mobile phase. A pencil is used to mark the starting point of the sample then again to mark the ending point of the mobile phase and the spots of the separated sample.

(Lab Manuel- Main mechanism) Table 1: Compound 9-flurenone Sodium Borohydride Methanol Sulfuric acid

Molecular Weight 180.19g/mol 39.04 g/mol 32.04 g/mol 98.08 g/mol

Density (g/mL) or M (mmol/mL) N/A N/A

0.792 g/mL 1.00 g/ml 3.00 mol/l Chemical Theory and Analytical Techniques:

Reaction Weight or Volume 1.20 0.126

mmol

Equivalent

6.66 3.33

1.0 0.5

12.12ml 4.44ml

299.7 13.32

45 2.0

Reductions and Oxidation are common organic chemistry reactions. Usually it is assumed it is assumed that Oxidation is the loss of electrons or an increase in oxidation state by a molecule, atom, or ion. Reduction is the gain of electrons or a decrease in oxidation state by a molecule, atom, or ion. But in organic chemistry what happened is simple a change in the electron density around carbons as a result of covalent Bonding if the electron density increases this is reduction if it decreases this is oxidation. To determine the oxidation state of simple inorganic compounds, you assume that the oxidation state of all but one of the elements in the compound is known and determine the remaining element by difference, since the sum of all oxidation number must be zero. For example, in KMnO4, potassium is always +1, each oxygen is -2 (for a total oxidation number of -8) and thus the manganese must be +7.

A similar approach is taken in organic compounds, but a carbon is nearly always the unknown. Carbon atoms can have any oxidation state from -4 (e.g. CH4) to +4 (e.g. CCl4). If there is more than one carbon in the molecule, each needs to be calculated. The simplified mechanism of sodium borohydride can be seen below, sodium borohydride is a good reducing reagent but it is not the strongest it only can reduce Ketones and aldehydes to Alcohols and unlike LAH which will also react with Ketones and aldehydes it will not react with carboxylic acids. This selectivity is a result of the high electronegativity of boron which forces the electrons to be closer to the boron which makes them lees free to attack where in LAH the Al is less electronegative. Another thing to look at is the target of the attack, the carboxylic acid is more difficult to react with as a result of the extra resonance which it has that masks the positive charge on the carbon. The last thing to look at is the counter ion, for example if we compare sodium borohydride with LAH we would see that LAH counter ion is Li which is a better counter ion than Na, This allows the structure being attacked to be more staple thus more likely to be reduced. The combination of these three factors result in the selectivity we see in sodium borohydride. In this lab excess sodium borohydride will be used so it is not the limiting reagent.

(Mechanism Nabh4 -Lab Manual) In the use of infrared spectroscopy (IR), vibrations caused by the stretching, bending and twisting of the molecule’s bonds is measured. The infrared spectrum is measured in wavenumber in cm-1 where a span from 600 cm-1 to 4000 cm-1 is used for functional groups. Depending on the amount of infrared absorbed in the stretch, bend, or twist, a peak for percent transmittance is obtained. This wavenumber should fall within a certain range of a particular functional group which can be used to identify the presence of that functional group.

(SparkNotes-IR data) Recrystallation is useful for purifying solids where the solid is dissolved in an appropriate solvent at an elevated temperature allowing the crystals to re-form on cooling, so that any impurities remain in the solution. The choice of solvents should allow for reasonable solubility when the solvent is at a high temperature and insoluble when the temperature is decreased. The method to testing the melting point was to pack a few grains of the unknown solid into a testing glass then insert it into the melting point machine. The sample is observed through a magnifier on the machine. The melting point machine would slowly apply more heat to the sample until the sample begins to melt, at which point you would observe the thermometer reading.

TLC will be used to analyze the progresse of the reaction. In TLC the stationary phase is bound to a solid support plate, Aluminum with a Silicon coating in this experiment. The plate is placed in a developing chamber with the mobile phase lining the bottom with a small amount of the sample above the mobile phase. A pencil is used to mark the starting point of the sample then again to mark the ending point of the mobile phase and the spots of the separated sample. The TLC uses capillary action to pull both the solvent and the compounds up the plate. Lucas test is used to distinguish between primary, secondary, and tertiary alcohols. A mixture of ZnCl2 and HCl increases the reactivity of alcohols toward acids. ZnCl2 is a strong acid that reacts with the lone pair electrons on the oxygen of alcohols forming a ZnCl-OH complex which is shown in the mechanism below.

(Lab Manuel- mechanism of Lucas test) This complex dissociates to yield carbocation which reacts with chloride ion to form alkyl chloride product. The rate determining step is the formation of carbocation so the rate will increase the more staple the carbocation. This would mean that tertiary alcohols will react faster than secondary and secondary will be faster than primary. A positive result will be seen if the solution turns from clear to cloudy and the speed of the reaction will judge if it is tertiary or secondary. Experimental Procedure:

To begin the lab, the glassware and instruments were thoroughly cleaned to ensure no contaminants were present. We were assigned a mass of 1 g of 9-Fluorenone and then we did the calculations to decide on mass and volumes we will need to do the reactions. 1. We transferred 1.2 g of 9-Fluorenone into a 50 ml Erlenmeyer flask while being heated and then 12.12 ml methanol was added and the solution turned yellow after the 1.2 g dissolved the solution was taken off the heating and cooled to room temperature. 2. 0.126 g of borohydride was weighted and then added to the flask excess sodium borohydride will be used so it is not the limiting reagent all that is needed is 0.25 equivalence but we are using 0.5. 3. The flask was swirled for few minutes until it dissolved. The solution turned colorless in 10 minutes. 4. Thin layer chromatography was then used to test if the reaction went to completion. 5. First one TLC plates was labeled, the far left spot being pure 9-flurenone, the middle spot being a co-spot sample of pure 9-flurenone and reaction mixture, and the far right spot being only the reaction mixture. 6. The TLC chamber was then assembled by putting a 1:9 ethyl acetate: hexane mixture lining the bottom of a beaker with an observation plate covering the top to avoid loss of the volatile liquids. 7. The samples were then applied to the corresponding spots of the TLC plate and placed in the TLC chamber with forceps. 8. Once the mobile phase nearly reached the top of the TLC plates, the plates were removed. UV lamps were used to analyze the TLC plates.

9. The UV light allowed the components to be observed, where a pencil marked the location of each section. This was then copied into the lab notebook. TLC (Picture taken during lab)

10. 4.44 ml of 3 Molar sulfuric acid was added to the reaction forming a solid and then it was heated and swirled for 5 minutes to dissolve that solid. 11. Once the solid was dissolved the flask was removed of the heating apparatus and cooled down in an ice bath until a solid precipitate is formed. 12. The solid was filtered and until the PH paper indicated it was neutral then it was dried. Next heated Methanol was added to the product while being heated until the solid was dissolved. Finally the solution was filtered and dried. Characterization procedure 1. The first tested procedure to characterize the 9-fluorenol sample involved using IR spectroscopy. 2. The method to the infrared spectrometer was to first thoroughly clean the machine surface with acetone and clean cotton swabs, where any contact is encountered with chemicals.

3. Once clean, the solid sample was placed on the testing surface, held by the solid clamp. 4. The computer generated a spectrum of data that is analyzed to find peaks that pertain to different Carbon bonds and functional groups associated with bond vibrations and stretching. Characterization Two 1. Lucas test was used to distinguish between primary, secondary, and tertiary alcohols. 2. We began by cleaning 3 tubes and adding 1 ml of Lucas reagent (mixture of ZnCl2 and HCl) and then around 0.3 ml tertiary alcohol which was provided was added to tube one and around 0.3 ml primary alcohol which was provided was added to tube two and finally 0.3 ml secondary alcohol which we prepared was added to tube two. The observations were recorded in our lab notebooks. Data Acquisition: Mass 9-flurenone: 1.000 g Mmol 9-flurenone= 1.000g * [1 mol/(180.19g/mol)]*1000 mmol/1 mol = 5.55 mmol 9-flurenone Compound

Molecular

Density (g/mL)

Reaction Weight

mmol

Equivalent

9-flurenone Sodium

Weight 180.19g/mol 39.04 g/mol

or M (mmol/mL) N/A N/A

or Volume 1.20 g 0.126 g

6.66 3.33

1.0 0.5

Borohydride Methanol Sulfuric acid

32.04 g/mol 98.08 g/mol

0.792 g/mL 1.00 g/ml

12.12 ml 4.44 ml

299.7 13.32

45 2.0

3.00 mol/l Mass of empty flask = 125g Mass of flask with solid = 126.1 g Mass of solid = 1.1g

Molecular weight of solid = 182.22 g/mol Actual Value: 1.1g * (1 mol/ 182.22 g) = 0.00604moles

Original mass = 1.2 g Molecular weight of solid = 182.22 g/mol Theoretical Value: 1.20 g * (1 mol/182.22 g) = 0.00666 moles Percent Yield = (actual)/ (theoretical) *100% Percent Yield = (0.00604 moles)/ (0.00666 moles) *100% =90.7 %

TLC data: 9-fluorenol: Rf =

TLC sketch

1 = 0.17 5.8

9-fluorenone: Rf =

1.9 =0.32 5.8

IR spectrum data: Substance

Wavenumber (cm-1)

Functional Group

9-fluorenol

3200-3550 1433.68-1618

O-H stretch C=C (Benzene ring)

Melting Point: 9-fluorenol actual melting point: 152 -155 ºC 9-fluorenol observed melting point: 145-148 ºC Lucas test: 1 ml lucas solution +0.3 ml tertiray alchahol(provided). Clear turned to cloudy- very fast- positive for tertiray Lucas test: 1 ml lucas solution +0.3 ml secoundary alchahol (our sample). Clear turned to cloudy- medium speed- positive for secoundary Lucas test: 1 ml lucas solution +0.3 ml primary alchahol (provided). Clear didnt change- Negative Data Analysis:

The amount of product obtained was 1.1 g and the theoretical yield was 1.2 g. this gave us a percent yield of 90 percent. We believe some of the product was lost due to recrystallization and filtration. The IR Spectroscopy Spectrum of our product generated a broad OxygenHydrogen stretch between 3200 cm-1 and 3550 cm-1, and several Carbon-Carbon double bonds (C=C) between 1480-1600 cm-1, which signifies a benzene ring. Indicating 9-fluorenone not 9fluronone which has an IR with a Carbon-Oxygen double bond (C=O) at 1650 cm-1, and would have missed the broad Oxygen-Hydrogen stretch we see in our IR. A small sample of the compound was put into a capillary tube and placed inside the melting point machine. The melting point of the sample was determined by recording the temperature of the point where each solid sample melted. The melting point of 9-Flurenol was determined to be 150ºC, where the whole sample melted at the same time. The actual melting point range is 152 - 155 ºC. The lower melting points obtained from our sample could have occurred from the sample being heated too quickly, having an uncalibrated thermometer, measure a sample with an impurity, or measuring a wet sample. The IR spectrum rules out impurities because nothing unusual showed up. This means the sample was either heated too quickly, or an uncalibrated thermometer was used, or the sample was wet. The tertiary alcohol formed precipitate instantly. The secondary took some time to precipitate and the primary didn’t precipitate. This is a result of the stability of the carbocation being formed. Tertiary forms the most staple followed by secondary followed by primary.

Conclutsion: The Purpose of the lab was to prepare 9-Flurenol by reducing 9-fluorenone using sodium borohydride. Sodium borohydride reduces only carbon-oxygen double bond. During this lab the product is purified by recrystallization and characterized by melting point and IR spectroscopy. Percent yields were analyzed to determine the amount remaining of the product. The amount of product obtained was 1.1 g and the theoretical yield was 1.2 g. this gave us a percent yield of 90 percent. We believe some of the product was lost due to recrystallization and filtration. The IR Spectroscopy Spectrum of our product generated a broad Oxygen-Hydrogen stretch between 3200 cm-1 and 3550 cm-1, and several Carbon-Carbon double bonds (C=C) between 1480-1600 cm-1, which signifies a benzene ring. Indicating 9-fluorenone not 9fluronone which has an IR with a Carbon-Oxygen double bond (C=O) at 1650 cm-1, and would have missed the broad Oxygen-Hydrogen stretch we see in our IR.

A small sample of the compound was put into a capillary tube and placed inside the melting point machine. The melting point of the sample was determined by recording the temperature of the point where each solid sample melted. The melting point of 9-Flurenol was determined to be 155-148ºC, where the whole sample melted at the same time. The actual melting point range is 152 - 155 ºC. The lower melting points obtained from our sample could have occurred from the sample being heated too quickly, having an uncalibrated thermometer, measure a sample with an impurity, or measuring a wet sample. The IR spectrum rules out impurities because nothing unusual showed up. This means the sample was either heated too quickly, or an uncalibrated thermometer was used, or the sample was wet. TLC was used in the middle of the experiment to test if the reaction went to completion viewing the TLC under UV light showed that we had one dote from the far left spot, two dots from the co-spot and one dote from the far right spot. The far left spot being pure 9-flurenone, the middle spot being a co-spot sample of pure 9-flurenone and reaction mixture, and the far right spot being only the reaction mixture. The Rf of 9-fluorenone was 0.17 and of 9-fluorenol 0.32.The TLC indicated that the reaction went to completion. Lucas test was used to distinguish between primary, secondary, and tertiary alcohols. 1 ml of Lucas reagent (mixture of ZnCl2 and HCl) was added to each tube and then around 0.3 ml tertiary alcohol which was provided was added to tube one and around 0.3 ml primary alcohol which was provided was added to tube two and finally 0.3 ml secondary alcohol which we prepared was added to tube two. The tertiary alcohol formed precipitate instantly. The secondary took some time to precipitate and the primary didn’t precipitate. This is a result of the stability of the carbocation being formed. Tertiary forms the most staple followed by secondary followed by primary. Overall the lab was successful, The IR and the melting point showed that we got the right product and the percent yield was high.

References

Gilbert, J.C., Experimental Organic Chemistry: A Miniscale and Macroscale Approach, Gilbert & Martin, Belmont, 2015, 4th Ed., pp. 55-58, 123-125, 192-202. SparkNotes. Organic Chemistry 1 UV/Vis Spectroscopy. 2015. Retrieved from http://sparkcharts.sparknotes.com/chemistry/organicchemistry1/section13.php McQuade, Lindsey. Organic Chemistry Lab Manual and Course Materials, 2015, 4th Ed....