Experiment 10_ Green Chemistry

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Feb 20, 2024

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1 11/20//21 Experiment 10: Green Chemistry Goals : Design a more environmentally friendly synthesis of a target product by changing the type of solvent, amount of solvent, or the amount of starting material/reagent. Analyze TLC data to determine whether the synthesize was successful. Write an abstract about results and discuss how you would modify the conditions or add more analysis in the future. Reaction Schemes: Control Reaction: “Greener” Reaction: Replacing t-butanol with acetone Acetone (C H O) (expect cis- diol) (expect cis diol)
2 Reagent Table: Compound Molecula r Weight (g/mol) Density (g/mL) Used Equiv. Safety Potassium permanganate (KMnO 4 ) 158.03 2.70 100 mg 0.00188 mols Oxidizer, irritant, health hazard, environmental hazard Cyclohexene (C H ) ₁₀ 82.15 0.81 50 μL 0.000482 mols Flammable, acute toxic, irritant, health hazard, environmental hazard T-butanol ( C₄H₁₀O) 74.12 0.78 2 mL 0.0210 mols Flammable, irritant Acetone (C H O) 58.08 0.79 2 mL 0.0287 mols Flammable, irritant Sodium Hydroxide (NaOH) 39.997 1.5 1 mL 0.213 mols Corrosive, causes severe skin burns and eye damage
3 Water (H O) N/A N/A 9 mL (to create 0.1 M NaOH from 1 M NaOH) N/A Hexane (C H ) ₁₄ 86.18 0.659 1 mL 0.192 mols Irritant, flammable Ethyl Acetate ( C 4 H 8 O 2 ) 88.11 0.902 3 mL 0.0767 mols Irritant, flammable Cis-cyclohexane-1,2-diol (C H O ) ₁₂ Trans- cyclohexane-1,2-diol 116.15 1.2 TLC spotting Irritant P-anisaldehyde (C H O ) 136.15 1.12 TLC stain Irritant
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4 Procedure : The control reaction: Cyclohexene and Potassium Permanganate 1. Dissolve 100 mg of KMnO4 in 4 mL of 0.1 M NaOH solution in a 25 mL Erlenmeyer flask with a stir bar. 2. Cool the KMnO4 solution in an ice bath. Wipe any excess KMnO4 off the outside of the flask before placing it in the ice bath. 3. Using a micropipette, add 50 μL of cyclohexene to 2 mL of t-butanol in a 4 mL vial. 4. Quickly add the cyclohexene solution into the potassium permanganate. 5. Stir the reaction mixture in the ice bath for 5 min. 6. Remove from the ice bath and stir for 10 min. 7. Spot a sample of the reaction on a TLC plate. On the same TLC plate, spot samples of commercially purchased cis-cyclohexane-1,2-diol and trans-cyclohexane-1,2-diol. 8. Run the TLC plate in 75/25 EtOAc/hexane. 9. Visualize the TLC plate by dipping it in p-anisaldehyde stain, dabbing on a paper towel to remove excess stain, and then heating on a hot plate provided in the fume hood. 10. Circle all spots in pencil on the TLC plate. Store all developed TLC plates in the hood. “Greener” Reaction Procedure: Replacing t-butanol with acetone 11. Dissolve 100 mg of KMnO4 in 4 mL of 0.1 M NaOH in a 25 mL Erlenmeyer flask with a stir bar. 12. Cool the KMnO4 solution in an ice bath. Wipe any excess KMnO4 off the outside of the flask before placing it in the ice bath. 13. Using a micropipette, add 50 μL of cyclohexene to 2 mL of acetone in a 4 mL vial. 14. Quickly add the cyclohexene solution into the potassium permanganate. 15. Stir the reaction mixture in the ice bath for 5 min. 16. Remove from the ice bath and stir for 10 min. 17. Spot a sample of the reaction on a TLC plate. On the same TLC plate, spot samples of commercially purchased cis-cyclohexane-1,2-diol and trans-cyclohexane-1,2-diol. 18. Run the TLC plate in 75/25 EtOAc/hexane. 19. Visualize the TLC plate by dipping it in p-anisaldehyde stain, dabbing on a paper towel to remove excess stain, and then heating on a hot plate provided in the fume hood. 20. Circle all spots in pencil on the TLC plate. Store all developed TLC plates in the hood.
5 TLC plates: Developing Solvent: 75/25 EtOAc/hexane Visualization: p-anisaldehyde 5: control reaction for 5 minutes 10: control reaction for 10 minutes 5A: “greener” reaction for 5 minutes 10A: “greener” reaction for 10 minutes C: cis-cyclohexene-1,2-diol T: trans-cyclohexene-1,2-diol Rfs: Plate 1: Rf (5) = 1.4/5.3 = 0.264 Rf (C) = 1.4/5.3 = 0.264 Rf (T) = 1.1/5.3 = 0.208 cyclohexe ne Another product is produced This plate did not develop well - additional product is still shown The “greener” reaction produces another product - side effect of being more green 1 2 3 4 Plate number
6 Plate 2: Rf (10) = 1.3/5.2 = 0.25 Rf (C) = 1.4/5.2 = 0.269 Rf (T) = 1.2/5.2 = 0.231 Plate 3: Rf (5A1) = 1.3/5.0 = 0.26 Rf (5A2) = 2.9/5.0 = 0.58 Rf (C) = 1.4/5.0 = 0.28 Rf (T) = 1.2/5.0 = 0.24 Plate 4 (inaccurate rfs): Rf (10A1) = 0/5.6 = 0 Rf (10A2) = 0.2/5.6 = 0.0357 Rf (C) = 0.3/5.6 = 0.0536 Rd (T) = 0.3/5.6 = 0.0536 TLC analysis : For all of the TLC plates, cyclohexene was present at the top of the plate. But as time went on, less of the cyclohexene product was present. This makes sense people more of the cis-diol (and another product from the “greener” reaction) is formed. In the first control reaction plate (5 minutes), the reaction spot Rf matched up with the Rf of the cis-diol (both 0.264). This demonstrates that the product produced from the reaction resembles the cis-diol the most. This pattern appears in the second control reaction plate (10 minutes), further proving that the cis-diol is evident after the control reaction. On the first “greener” reaction plate (5 minutes), two spots were evident. These spots both appeared very light on the plate meaning that the concentration of the products were not very high. With these two products, it is hard to determine if the cis or trans product has resulted from this reaction, but most likely the cis diol was produced because it was present in the control reactions. The second “greener” reaction plate (10 minutes) did not develop as well as it should have, but two products in the reaction spot were also present. This means that when using the “greener” reaction option, the additional product is the side effect in being more green.
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7 Calculations:
8 E factor: Observing the Success of a “Greener” KMnO4 Dihydroxylation Reaction Deena Aboul-Hassan Abstract:
9 Solvents do not directly contribute to the structure of the reaction products but are necessary for the chemical reaction to occur. While reducing the amount of solvent is important to keep track of, the choice of solvent is significant and can guide chemists in choosing safer solvents. The goal of this experiment is to determine if “greener” reactions can be just as successful in producing the same product as the control reaction. In this lab, we tested the dihydroxylation reaction with KMnO4 and cyclohexene. The control organic solvents included 0.1 M NaOH (water) and t-butanol. For the “greener” reaction the organic solvents included 0.1 M NaOH and acetone. The reaction was cooled in an ice bath for 5 minutes (with stirring) and then proceeded out of the ice bath for an additional 10 minutes. TLC analysis was taken after 5 minutes and then after an additional 10 minutes to determine the success of the products. The findings on the TLC plates indicated that the “greener” reaction produced less of the expected cis-cyclohexane-1,2-diol along with a trace of an additional product compared to the control reaction that produced a higher concentration of the cis diol. This means that when examining an NMR of the control product, it would more closely match up to the theoretical NMR structure and peaks than the “greener” reaction. Overall, the “greener” reaction produces more “side effects” and is less effective than the control reaction. Keywords : Dihydroxylation, organic solvents, green chemistry, atom economy, thin-layer chromatography (TLC)
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