LAB 1 Oxidation of an Unknown Alcohol PDF

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Lab 1

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Identification of an Unkown Alcohol and its Oxidized Ketone using FTIR and 1H NMR Introduction In the introductory experiment for CHEM 2212L is aimed at the identification of a secondary alcohol reagent. In order to determine the structure of the secondary alcohol, it will be oxidized using bleach (NaOCl 5% w/v in water). Oxidation, in this specific circumstance, will consist of the reduction of the number of C-H bonds in the secondary alcohol. Considering the possible identities of the starting alcohol, 2-pentanol, 3-pentanol, and 3-methyl-butan-2-ol, we will create a ketone product using the techniques of quenching, and liquid/liquid extraction. Quenching will deactivate any unreacted agents in the solution and liquid/ liquid extraction is used to separate the product from the other components of the mixture. Lastly, the identity of the ketone product and ultimately the starting secondary alcohol will be found using FTIR spectroscopy, and 1H NMR spectroscopy.

Balanced Equation

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Reaction Mechanisms

Table of Reagents Name

Structure

2-pentanol

Molecular weight (g/mol) 88.148

Melting point

Boiling point

Density (g/cm3)

Solubility in water

n/a

n/a

3-pentanol

88.148

-63.68

116

n/a

n/a

3methylbutan2ol Glacial acetic acid

88.148

-117.2

131

n/a

n/a

60.052

16.6

118

n/a

n/a

Sodium hypochlorite Sodium bisulfite

74.44

n/a

n/a

n/a

n/a

104.061

n/a

n/a

n/a

n/a

Sodium hydroxide

39.997

n/a

n/a

n/a

n/a

Magnesium sulfate anhydrous Methylene chloride

120.366

n/a

n/a

n/a

n/a

84.93

-96.7

39.6

1.33

15.8 g/L @ 30℃

water

18.015

0

100

9997 kg/m3

n/a

58.44

-10

>100

1200 kg/m3

n/a

Brine

NaCl (aq)

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Safety Information •

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• • • • • •

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2-pentanol vapors may cause eye irritation, contact may cause eye irritation, and tearing. May cause skin irritation. May cause nausea, vomiting, or diarrhea if ingested. Inhalation of large concentrations can affect the central nervous system. It is flammable so keep away from open flames or sparks. Wear gloves and goggles when handling. 3-pentanol is acutely toxic for oral ingestion and inhalation. It can cause skin irritation, and eye irritation. It is flammable, so keep away from any open sparks or flames. Wear gloves and goggles when handling. 3-methylbutan-2-ol is flammable in liquid and vapor form. It is acutely toxic if inhaled and may cause respiratory information. Wear gloves and goggles when handling. Glacial acetic acid is flammable and can cause serious eye damage. It is acutely toxic to skin, oral ingestion, and inhalation. Wear gloves and goggles when handling. Sodium hypochlorite is corrosive to metals and can cause serious eye damage. It is a skin irritant. Wear gloves and goggles when handling. Sodium bisulfite has acute oral, dermal, and inhalation toxicity. Wear gloves and goggles when handling. Sodium hydroxide is corrosive to skin and metals. It can cause serious eye damage, including burning. Wear gloves and goggles when handling. Magnesium sulfate anhydrous can cause skin, eye, respiratory and gastrointestinal irritation. Some lab experiments have shown chronic mutagenic effects from exposure so make sure to take all necessary precautions, including wearing gloves and goggles while handling. Methylene chloride can cause skin corrosion and irritation, serious eye damage and has some central nervous system toxicity with single exposure. Repeated exposure can damage liver, kidneys and even blood. Has been identified as a carcinogen so minimize exposure and wear proper safety equipment. Water is nontoxic and nonflammable. Brine can cause eye irritation but is mostly nontoxic and nonflammable.

Experimental Procedure Students will start by obtaining a beaker filled with a water and ice mixture. This ice bath will be used to cool the reaction and keep it under thermodynamic control. Next, 2.1 g of one of the unknown secondary alcohol reagents will be placed into a 100mL round bottom flask, and the unknown code will be recorded. A stir bar and 1.75 mL of glacial acetic acid will need to be added to the round bottom flask. At this point it is imperative that the round bottom flask containing the reagents be in an ice bath as the next reaction is exothermic and can be dangerous. After the solution has cooled in the ice bath, over the course of 10 minutes 36 mL of sodium hypochlorite will need to be added to the flask in a dropwise manner. Great caution should be exercised to not add too much of the reagent too fast as the reaction releases heat. Once all of the sodium hypochlorite has been added, the solution should be left to cool in the ice bath for an extra 20 minutes. Now the main mechanism of the experiment has occurred. The next steps will be to test the contents of the solution, neutralize any of the unused reagents and isolate the

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desired product. It is still important to leave the flask containing the solution in the ice bath until the extraction step because any unreacted reagents can still cause a release of heat. In this series of steps, a student will test for an excess of sodium hypochlorite in the reaction. An excess of sodium hypochlorite means that one can assume of the secondary alcohol has reacted and sodium hypochlorite is no longer functioning as a limiting reagent. To test for this excess, a student will need to extract a small amount of the reaction solution using a glass pipette and drop it onto a strip of KI-starch paper. A change in color from white to blue means the solution contains excess oxidant. No change means the student should add more (5mL at a time) sodium hypochlorite in a dropwise manner until the test results in a change in color. After concluding that there is excess sodium hypochlorite in the solution, we can now neutralize or deactivate any unreacted reagents in the solution. This process is called quenching. The student will quench the solution by obtaining 10 mL of saturated sodium bisulfite and adding 4 mL of the sodium bisulfite to the round bottom flask containing the reaction. The reaction solution will then need to be tested by dropping a small amount of the solution onto a potassium iodide test strip to ensure that there are no remaining unreacted reagents. If the paper remains white then the quenching was successful, if the paper turns blue then small amounts of the sodium bisulfite should be added to the reaction solution until a positive test is achieved. In order to extract the ketone product from the reaction, the solution must first be washed with a basic reagent. The reagent used in this reaction 6 M sodium hydroxide. A student is to collect 4.5 mL of the 6 M sodium hydroxide and add it to the reaction solution. He or she then needs to test the pH of the solution to ensure a basic pH. If the solution is not basic after the initial addition of sodium hydroxide, then 1.5 mL aliquots will need to be added until the solution is basic. The reaction solution should be left to stir for 10 minutes after this step. Testing the structure of the ketone product is the ultimate goal of this experiment, however, the ketone product still lies in a solution with other chemicals. To isolate the product the solution will undergo a liquid/liquid extraction procedure. 5 mL of dichloromethane should be added to the round bottom flask and stirred to incorporate. The solution will then need to be placed into a separatory funnel to separate the layers and extract the organic layer. These steps will need to be repeated twice for assurance of extraction of the product. After the organic component has been removed, the student is to combine both extractions and wash the liquid with 10 mL of deionized water first and then 10 mL of brine. Anhydrous magnesium sulfate is used to dry the organic component and suction filtration will remove the solid drying agent. The mass of the isolated product is to be recorded and analyzed using FTIR spectroscopy and 1H NMR spectroscopy.

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Oxidation of an Unknown Alcohol Post-Lab Questions:

1. (4pts) Provide the appropriate product(s) formed as a result of the following

reactions:

2.

(4pts)

What was the role of the sodium hypochlorite

(NaOCl 5% w/v in water) in this experiment? What does it form in situ when combined with acetic acid? Be specific in your answer. ✓ Sodium hypochlorite combines with acetic acid in situ to produce hypochlorous acid. Hypochlorous acid is the oxidizing agent that will interact with the secondary alcohol.

3. (4pts) What was the role of the saturated sodium bisulfite solution (NaHSO3) in this experiment? Why was it added to the reaction mixture? Be specific in your answer.

✓ Sodium bisulfite is introduced in to the reaction mixture to neutralize any remaining hypochlorous acid. 4. (4pts) What where the potassium iodide strips used to test for during your reaction? Why were the strips used to test the initial reaction mixture? Why were they used to test the neutralized reaction mixture? Be specific in your answer.

✓ KI starch paper tests for oxidizing agents. In this experiment the KI starch paper tested for hypochlorous acid. The initial test was to determine if there was enough hypochlorous

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acid in the reaction mixture to oxidate all of the available secondary alcohol to ketone. Essentially to verify that hypochlorous acid was no longer the limiting reagent. KI starch paper was used to test the neutralized mixture to test for any remaining unreacted hypochlorous acid in the solution.

5. (2pts) What was the purpose of the base (hydroxide) wash? Be specific in your

answer.

✓ The base sodium hydroxide wash in this experiment was used to remove any impurities. In this case the impurities were any salts created by the previous neutralization reaction.

6. (6pts) What is the difference between a wash and an extraction? Clearly define both of these terms/techniques. Can these terms be used interchangeably? What solvent(s) did you use for extraction during this experiment? What solvent(s) did you use for washing during this experiment?

✓ Washing is the process of selectively removing unwanted compounds from a mixture using a solvent. Extraction is the process of selectively removing a compound of interest from a mixture using a solvent. These terms cannot be used interchangeably. The solvent used in extraction in this experiment is dichloromethane. The solvent in washing in this experiment is sodium hydroxide.

Results and Discussion and Conclusion

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The strong IR peak just to the right of 3000 suggests the presence of sp3 hybridized hydrogens and the extension of this peak into a region suggesting a presence of a hydrogen bonded to a carbonyl group. The presence of a strong peak around 1700 is evidence of a carbon oxygen double bond. All peaks are consistent with those that would be produced by the expected ketone product. No real evidence of left-over starting alcohol as a peak suggesting an oxygen hydrogen stretch is not present.

According to the HNMR, the triplet in the 1.0 ppm region suggests the existence of protons that have 2 neighbors. The quadruplet in the 2.5 ppm region suggests the existence of protons with 3

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neighbors. The only molecule with this proton configuration and display of symmetry in product bank is pentan-3-one. Pentan-3-one (structure found below) is the ketone product of the oxidation of the secondary alcohol 3-pentanol, which is, based on the spectroscopy data, the identity of the unknown alcohol chosen at the beginning of the experiment. The unidentified peak on the far right of the spectroscopy graph (0.0 ppm) could be indicative of an oxygen bound proton from residual starting material, but no evidence of starting material was found in the FTIR spectroscopy. Lastly, the peak on the far left of the graph (5.5 ppm) was labeled as a residual solvent peak by the laboratory staff before it was posted on ELC.

Calculations

Limiting Reagent 2.121𝑔

1𝑚𝑜𝑙

3− 𝑝𝑒𝑛𝑡𝑎𝑛𝑜𝑙 1

𝑚𝑜𝑙𝑠

1.836𝑔

1𝑚𝑜𝑙 𝑔𝑙𝑎𝑐𝑖𝑎𝑙 𝑎𝑐𝑒𝑡𝑖𝑐 𝑎𝑐𝑖𝑑 ∗

1

= .0306 𝑚𝑜𝑙𝑠 60.052𝑔/𝑚𝑜𝑙

39.96𝑔

1𝑚𝑜𝑙 𝑁𝑎𝑂𝐶𝑙

𝑚𝑜𝑙𝑠

1 𝑚𝑜𝑙 3-pentanol is the limiting reagent.

Percent Yield 2.121𝑔 3 − 𝑝𝑒𝑛𝑡𝑎𝑛𝑜𝑙 1

1𝑚𝑜𝑙

1𝑚𝑜𝑙

1𝑚𝑜𝑙 𝑔 𝑜𝑓 𝑝𝑒𝑛𝑡𝑎𝑛 − 3 − 𝑜𝑛𝑒

. 953 𝑔 − 2.067𝑔 ∗ 100 = 53.9%

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2.067𝑔

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