Acidic vs. Basic Conditions in the Nucleophilic Ring-openings of 1,2 Epoxyhexane PDF

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Acidic vs. Basic Conditions in the Nucleophilic Ring-openings of 1,2 Epoxyhexane Introduction: An epoxide forms a cyclic ether with very high ring strain, making it highly susceptible to ring-opening reactions. Epoxides undergo different reactions in acidic conditions versus when they are reacted in basic conditions. The purpose of today’s lab is to react the epoxide in both basic and acidic conditions to achieve different products of the ring-opening reaction. The percentage of each major product will then be calculated at the end of the experiment. 1,2 epoxyhexane will be used as the electrophile in both the acidic and basic reactions. Sodium methoxide is the nucleophile in the basic reaction, and the methanol acts as the nucleophile in the acidic reaction as well as the reagent in which the 1,2-epoxyhexane, in the case of the acidic reaction, or sodium methoxide, in the basic reaction, dissolves. Diethyl ether is used to extract the products in both reactions. Sulfuric acid is used to create an acidic environment for the reaction to occur. Sodium bicarbonate is used to wash the acidic reaction mixture, and ammonium chloride is used to wash the basic reaction mixture. Magnesium sulfate is used to dry the organic layers in both the acidic and basic reactions. Liquid-liquid extraction, reflux, and gas chromatography will be used in today’s experiments to aid in achieving and identifying the desired final products. IR is used to verify the product identity, and gas chromatography is used to analyze whether or not the achieved products line up with the predicted products of each reaction. Balanced Chemical Equation:

Mechanism:

Table of Reagents: Compound Name

Structure

MW (g/mol)

BP (℃)

MP (℃)

Density (g/mL)

1,2-epoxyhexane

100.08 34

118120

--

0.8310

Sulfuric acid

150.20

237239

--

0.976

methanol

32.04

64.7

--

0.7910

Diethyl ether

74.12

34.6

--

0.7134

Sodium bicarbonate

84.01

--

270

2.2

Magnesium sulfate

120.37

--

1,124

2.65

Sodium methoxide

54.03

--

1-5

0.97

Ammonium chloride

53.49

--

328

1.53

Safety Information: 1,2-epoxyhexane causes skin, eye, respiratory, and digestive tract burns and can be harmful if

swallowed. Proper ventilation should be ensured, and the snorkel should remain on at all times in order to prevent inhalation. Contact with the skin and eyes should be avoided by wearing glasses, proper clothing, and gloves. Inhalation of this chemical may be fatal due to spasm, inflammation, edema of the larynx and bronchi, and chemical pneumonitis. Sulfuric acid causes skin, eye, respiratory, and digestive tract burns and can be harmful if swallowed. Proper ventilation should be ensured, and the snorkel should remain on at all times in order to prevent inhalation. Contact with the skin and eyes should be avoided by wearing glasses, proper clothing, and gloves. This product may be fatal if the mist is inhaled. Concentrated sulfuric acid reacts violently with water as well as many other chemicals. Use clean glassware and ensure proper disposal to avoid cross-contamination. Methanol is toxic and can be fatal or cause blindness. This substance causes skin, eye, respiratory, and digestive tract burns and can be harmful if swallowed. Proper ventilation should be ensured, and the snorkel should remain on at all times in order to prevent inhalation. Contact with the skin and eyes should be avoided by wearing glasses, proper clothing, and gloves. This chemical can cause CNS depression. Methanol is flammable and should be kept from open flames and heated surfaces. Diethyl ether is a flammable chemical and should not be in close proximity to open flames or heated surfaces. This chemical should not be inhaled or come into contact with skin as it can cause irritation of the respiratory system, skin, and eyes. When in use, diethyl ether should be kept in a ventilated area to prevent inhalation. Goggles, gloves, and proper attire should be worn to ensure protection from direct exposure. Sodium bicarbonate is considered a relatively harmless chemical as it is not highly flammable nor toxic, but caution should still be exercised. Inhalation of large amounts of powder should be avoided as this can cause respiratory irritation, and ingestion can induce gastrointestinal irritation. Proper eyewear and gloves should be worn to ensure protection from direct contact. Magnesium sulfate causes skin, eye, and respiratory inflammation and can be harmful if swallowed. Proper ventilation should be ensured, and the snorkel should remain on at all times in order to prevent inhalation. Contact with the skin and eyes should be avoided by wearing glasses, proper clothing, and gloves. Sodium methoxide is flammable as a liquid and vapor. This substance should be kept from heated surfaces and open flames. It is corrosive to metals and is toxic if contacted to the skin, swallowed, or inhaled. Severe skin burns and eye damage can result. Proper ventilation should be ensured, and the snorkel should remain on at all times in order to prevent inhalation. Contact with the skin and eyes should be avoided by wearing glasses, proper clothing, and gloves. Ammonium chloride is harmful if ingested or inhaled. Proper ventilation should be ensured, and the snorkel should remain on at all times in order to prevent inhalation. Contact with the skin and eyes should be avoided by wearing glasses, proper clothing, and gloves as ammonium

chloride can cause skin and eye irritation.

Experimental Procedure: Acidic Conditions: 1. 0.5g of 1,2-epoxyhexane is measured out and placed in a microscale round bottom flask (14/10) followed by 5mL of methanol and a spin vane. The solution is stirred. 2. 1 drop of concentrated sulfuric acid is added to the solution, and the solution is allowed 30 minutes to stir. 3. The reaction is washed in a 125mL separatory funnel with 5mL of saturated sodium bicarbonate solution. Layers are not formed during this washing. 4. The product is extracted twice, each time with 10mL od diethyl ether. 5. The ether layers are combined and dried with magnesium sulfate. 6. Into a 50mL round bottom flask, the liquid is decanted. 7. The organic layer in the flask is immersed in room temperature water to undergo Rotovap until there is no change in the mass of the product. The final mass is recorded. Basic Conditions: 1. 0.4g of sodium methoxide powder is measured and placed in a microscale round bottom flask (14/10) along with 5mL of methanol and a spin vane. The solution is stirred. 2. 0.5g of 1,2-epoxyhexane is added to the flask. The solution is refluxed for 30 minutes. 3. The solution is washed in a 125mL separatory funnel with 5mL of saturated ammonium chloride solution. No layers form. 4. The product is extracted twice, each time with 10mL of diethyl ether. 5. The organic layers are combined and dried with magnesium sulfate. 6. Into a 50mL round bottom flask, the solution is decanted. 7. The organic layer in the flask is immersed in room temperature water to undergo Rotovap until there is no change in the mass of the product. The final mass is recorded. Gas Chromatography Analysis: 1. 2mL of methanol and one drop of the product are added to a small vial. 2. The retention times, as well as peak placement, is recorded as the GC of the product is conducted. The GC spectrum of the product is compared to the GC spectrum of the starting material to ensure that the reaction has occurred fully. 3. Each product is matched to each retention time. 4. Product ratios of each reaction are calculated by evaluating the area in which each signal occurred.

Autumn Sturhahn CHEM 2211L TA: Tung Dinh 27 February 2020 Acidic vs. Basic Conditions in the Nucleophilic Ring-openings of 1,2 Epoxyhexane: Post Lab Results: -Limiting Reagent Calculations: Acid Catalyzed Ring Opening:

1mol 1,2−epoxyhexane 1 mol 2−methoxy−1−hexanol x x 100.16 g 1−2 epoxyhexane 1 mol 1−2−epoxyhexane 133.2 g 2−methoxy−1−hexanol = 0.702g 2-methoxy-1-hexanol 1mol 2 −methoxy−1 −hexanol

0.528g 1,2-epoxyhexane x

0.7914 g methanol 1 mol methanol x x 1 mL methanol 32.04 g methanol 1 mol 2−methoxy−1−hexanol 133.2 g 2−methoxy−1−hexanol x =16.3g 2-methoxy-11mol 2 −methoxy−1 −hexanol 1 mol methanol

5.0 mL methanol x

hexanol 1,2-epoxyhexane is the limiting reagent. Base Catalyzed Ring Opening:

1mol 1,2−epoxyhexane 1 mol 1−methoxy−2−hexanol x x 100.16 g 1−2 epoxyhexane 1 mol 1−2−epoxyhexane 133.2 g 1−methoxy− 2−hexanol = 0.672g 1-methoxy-2-hexanol 1mol 1 −methoxy−2 −hexanol

0.505g 1,2-epoxyhexane x

0.7914 g methanol 1 mol methanol x x 1 mL methanol 32.04 g methanol 1 mol 1−methoxy−2−hexanol 133.2 g 1−methoxy− 2−hexanol x =16.1g 1-methoxy-21mol 1 −methoxy−2 −hexanol 1 mol methanol

4.90mL methanol x

hexanol 1,2-epoxyhexane is the limiting reagent. -Percent yield: (Actual Yield/Theoretical Yield) x 100%= percent yield Acid Catalyzed Ring Opening:

0.770 g x 100% = 109.7% yield 0.702 g Base Catalyzed Ring Opening:

0.564 g x 100% = 83.9% yield 0.672 g

Figure 1: IR spectrum of Acid Catalyzed ring opening product

Figure 2: IR spectrum of Base catalyzed ring opening product -Gas Chromatography: Acid Catalyzed Ring Opening:

Peak 1: Retention Time (0.9767 minutes): 8.9353 counts/minute Peak 2: Retention Time (1.0942 minutes): 6.9553 counts/minute Percentage of each peak:

area of peak x 100% = percentage of each peak total area of all peaks Peak 1: Peak 2:

8.9353 x 100% = 56.23% major product (2-methoxyhexan-1-ol) 15.8906 6.9553 x 100% =43.77% minor product (1-methoxyhexan-2-ol) 15.8906

Base Catalyzed Ring Opening:

Peak 1: Retention Time (0.8558 minutes): 42.7709 counts/minute Peak 2: Retention Time (.9383minutes): 1.878 counts/minute Percentage of each peak:

area of peak x 100% = percentage of each peak total area of all peaks Peak 1: Peak 2:

42.7709 x 100% = 95.79% major product (1-methoxyhexan-2-ol) 44.6489 1.878 x 100% =4.21% minor product (2-methoxyhexan-1-ol) 44.6489

Discussion/Conclusions: The percent yield of the reaction in acid was slightly over 100%, indicating that the product was not entirely pure as there was excess material adding to the weight of the final product. This could have been due to errors in the washing and extracting process, allowing excess solvent to be drained into the organic layer. This high percent yield could have also been due to an issue with the removal of the solvent. Not allowing the solution to boil long enough may have resulted in excess solvent in the final product. To improve the methodology, greater caution could have been exercised in the washing and extracting to ensure that only the layer containing the desired product was drained into an uncontaminated beaker. The solution could

have been checked more frequently during the boiling process in order to see the progression of the weight loss of the beaker, indicating that there was still solvent remaining. The percent yield of the reaction in base was rather high, but improvements could be made. To increase the mass of the final product obtained, the solution mass should have been checked more frequently while evaporating off the solvent in order to ensure that no product was boiled off. More caution could have been taken during the washing and extracting steps to ensure that all of the layer containing the desired product was not drained out with the aqueous layer, lowering the amount of product in the solution. Looking at the Gas Chromatography results of the acid catalyzed reaction, it can be determined that the first peak is the major product, 2-methoxy-1-hexanol. It is known that in acid, 2-methoxy-1-hexanol is more likely to form due to the nucleophile attacking the more sterically hindered carbon of the epoxide ring. Because the first peak has a greater area, and therefore a greater concentration of this specific product in the solution, it can be concluded that the first peak represents 2-methoxy-1-hexanol while the second peak represents 1-methoxy-2hexanol. The results of the base catalyzed reaction indicate that the first peak is the major product as the area is much greater than that of the second peak. The first peak, and major product, of the base catalyzed reaction is assumed to be 1-methoxy-2-methanol as the nucleophile is known to attack the least sterically hindered carbon of the epoxide ring. This would leave the second peak to represent 2-methoxy-1-hexanol, the minor product of the base catalyzed reaction. The percentage of the major product is so much greater than that of the minor product as this reaction was much more regioselective while the acidic reaction yielded similar percentages for both the major and minor product, indicating a less regioselective reaction. The IR spectra taken for the product resulting from the acid catalyzed reaction contains a strong peak around 3300 c m−1❑ which correlates with the alcohol in the structure of the

c m−1❑ , and the C-O −1❑ . The IR spectra of cm

final product. C-H bonds are represented by the peaks just below 3000

bond of the methoxy group is represented by the peak around 1050 the product of the base catalyzed reaction contains the same significant peaks: a peak around 3400 c m−1❑ which correlates with the alcohol, a peak just below 3000 c m−1 representing

C-H bonds, and a strong peak around 1100 c m−1 representing the C-O bond of the methoxy. The IR spectra of the starting material would have also contained the C-H peaks below 3000 −1 and the C-O peak around 1100 c m−1 , but it would have lacked the alcohol peak cm −1

around 3300 c m

. Due to this difference, it is evident that the reaction has occurred in

solution. The absence of the peak around 3300 did not occur.

−1

cm

would be an indication that the reaction...