Bromination of Acetanilide

The objective of this experiment was to use melting point and NMR to determine which of two isomers, ortho or para, would most likely form after brominating Acetanilide through electrophilic aromatic substitution. Procedure/Observations: 1. Weigh out ~280 mg of acetanilide in a 10 mL r. b. flask with a stir bar. 2. Then, add 2. 0 mL of glacial acetic acid using a calibrated Pasteur pipet. 3. Stir the mixture until all of the acetanilide has dissolved. It may be necessary to add more acetic acid dropwise until full dissolution has occured. In the fume hood, add 0. 6 mL of 4. 1 M bromine solution in acetic acid. 5. Cap the round bottom flask before returning to the bench. 6. For 15-20 minutes, stir the reaction mixture at room temperature so that the reddish-orange coloration will fade and a solid precipitate will form. 7. Return to the hood and add a few more drops of the bromine solution in the hood if all the coloration fades. 8. Once the reaction is complete, return to the hood. 9. Transfer the mixture to a 25 mL Erlenmeyer flask with 10 mL of water. 10. Rinse the reaction flask out using another 5. 0 mL of water. 11. Using a Pasteur pipet, add 30% sodium thiosulfate dropwise while swirling until the bromine coloration is no longer visible. 12. Return to the bench to complete the final work-up. 13. Cool the reacting mixture in an ice bath. 14. Collect the solid precipitate using a Hirsch funnel through vacuum filtration. 15. Wash with ice cold water to complete the transfer. If the crude product is yellow, disconnect the vacuum, add a few drops of the sodium thiosulfate solution, then reconnect the vacuum. Follow with 1 or 2 washings of ice cold water. 17. Dry the crude product 5-10 minutes using the vacuum. 18. Recrystallize the crude product using an ethanol/water mixed solvent combination. Be sure to dissolve the crude product in the minimal volume of hot ethanol with swirling. 19. Add water dropwise until a cloud point is reached. 20. Rewarm the solution until it is clear again. 21. Allow the solution to cool until crystals form before icing. 22. On a Hirsch funnel under vacuum using cold water washings collect the crystals. Continue the vacuum for 5-10 minutes to dry. 8. Find the final weight and calculate the yield. 9. Find the melting point of the product, then obtain the 1H NMR of the product in CDCl3. Overall Reaction: Mechanisms: Stoichiometric Table: CompoundMolar Mass (g/mol)Density (g/mL)mg or mLMmolMolar equiv. Acetanilide (Limiting Reagent)135. 171. 22333. 0 mg2. 46 1. 00 Bromine soln. 159. 803. 1190. 6 mL24. 610. 0 Glacial Acetic acid60. 051. 0492 mL34. 914. 2 Calculations 1) Moles of Acetanilide Used = 0. 333g/135. 17g/mol *1000 = 2.46mmol. Moles of Bromine Solution Used = 4. 1M * 0. 0006L = 24. 6mmol 3) Moles of Glacial Acetic Acid Used = 1. 049g/ml * 2. 00ml * 1mol/60. 05g/mol = 34. 9mmol 4) Molar equivalent of Bromine soln. = 24. 6 mmol / 2. 46mmol = 10. 0 5) Molar equivalent of Glacial Acetic Acid = 34. 9mmol / 2. 46mmol = 14. 2 6) Theoretical Yield of Product = 214. 07g/mol * 0. 00246mol = 0. 527g 7) Crude yield of product = 0. 1471g 8) Actual Yield of Product = 0. 0912g 9) Percent recovery from recrystallization = 0. 0912g/0. 1471g * 100 = 61. Percent yield = 0. 0912g/0. 527g * 100 = 17. 3% Results: Theoretical Yield of Product: 0. 527g Actual Yield of product: 0. 0912g Percent yield from recrystallization: 61. 9% Percent Yield of Product: 17. 3% Literature Melting Point Range: 166-170Â °C Experimental Melting Point Range: 165. 5-166. 5Â °C NMR Data: Shift (ppm)SignalIntegrationAssignment 7. 382-7. 434Multiplet 4 (2 for each aromatic proton-overlapping)Aromatic protons ortho and meta to the acetamido group 7. 260SingletProteolated SolventCDCl? impurities 2. 168Singlet3Methyl group