Experiemnt #10- CHEM 2212

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University Of Georgia *

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Chemistry

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Feb 20, 2024

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I. Introduction Electrophilic aromatic substitution reactions involve an a hydrogen attached to an aromatic ring being replaced by an electrophile. In this experiment, Friedel-Crafts alkylation will occur between an unknown tertiary alcohol and 1,4-dimethoxybenzene. This is an activated electron- rich aromatic system. The electrophilic part of this reaction is a carbocation, therefore; carbocation rearrangements can occur. This can result in a mixture of products. The benzene ring acts as the nucleophile. Because the resulting product is more activated than the original material, dialkylation can occur. II. Balanced Equation III. Reaction Mechanism + 2 mol R OH H OSO 3 H R OH 2 O O R O O R H OSO3H O O R R O O R R H O O OSO3H R R IV. Table of Reagents Reagent Structure Molecular weight Melting Point or Boiling Point Density

1,4- dimethoxybenzen e O O 1,4-dimethoxybenzene 138.167 g/mol MP: 54-56 1.053 g/mL Glacial acetic acid O OH glacial acetic acid 60.052 g/mol 1.05 g/mL Sulfuric acid S O O HO OH sulfuric acid 98. 079 g/mol 1.83 g/mL Methanol OH methanol 32.04 g/mol BP: 64.7 water H O H water 18.06 g/mol BP: 100 V. Safety Information a. General safety information i. Always wear safety goggles, gloves, and lab coat. ii. Ensure snorkel is in place and working properly. iii. Working with flammable liquids. b. Specific safety information i. 1,4-dimethoxybenzene- causes skin and eye irritation and respiratory irritation ii. Glacial acetic acid- flammable, burns skin, serious eye damage, keep away from flame iii. Sulfuric acid- skin and metal corrosive, serious skin and eye damage can occur iv. Methanol- flammable, do not breathe in VI. Experimental Procedure 1. 0.690 grams of 1,4-dimethoxybenzene and 1.5 mL of unknown alcohol combine into Erlenmeyer flask with 1.5 mL of glacial acetic acid. 2. Place flask in ice bath and then add 1.5 mL of sulfuric acid dropwise. a. Possibly turn pink 3. Add stir bar and let reaction stir for 10 min. 4. Place reaction vessel in ice bath and slowly add 15 mL of ice-cold water. 5. Swirl vessel and let sit in ice bath for a couple min. 6. Filter using Büchner funnel. 7. Wash flask with 5.0 ml DI water. 8. Use 5.0 ml of ethyl alcohol to wash reaction flask again. 9. Scrape crystals into beaker and add 10.0 mL hot methanol to recrystallize.

10. Let sit on hot place to let crystals dissolve. 11. Put in ice bath for a few min. 12. Filter again using suction filtration. 13. Rinse flask with DI water 14. Dry product in oven 15. Obtain weight of final product and determine melting point range. In-Lab: VII. Data and Observations a. Unknown alcohol code: 264P12Q6 b. Initial weight of 1,4-dimethoxybenzene: 0.697 g c. Initial weight or volume of unknown alcohol: 1.5 mL d. Final weight of product: 0.775 g e. While the reaction mixture was stirring it turned a light pink and white chunks formed. The final product was a powdery white solid. VIII. Results a. Limiting reagent calculations i. Unknown alcohol 1.5 mL x (0.81g/ 1mL) x (1 mol/ 88.15 g) x (1 mol/2 mol) = 0.00689 mol ii. 1,4-dimethoxybenzene (limiting reagent) 0.697 g x (1 mol/ 138.16g) x (1 mol/ 1 mol) = 0.00504 mol b. Percent yield calculations i. Theoretical yield 0.00504 mol x (278.44g / 1mol) = 1.403 g ii. Percent yield (0.775g/1.403 g) x 100 = 55.2 % c. IR spectrum 1,4-dimethoxybenzene

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The signals at 3071 and 1610 cm-1 indicate the presence of a benzene ring. The signal at about 1260 cm-1 indicates a C-O stretch. d. IR spectra Unknown

The signals at 3000, 1600, and 1500 cm-1 as w3ell as overtone indicate a benzene ring. The signal at 1300 cm-1 indicates a methyl group. e. HNMR Spectra Unknown Because the product is known to be dialkylated, the presence of a signal at 6.7 with 2 hydrogens suggest a tetra substituted benzene ring. The singlet with 6 protons belongs to the protons on the methoxy group. The singlet with 12 protons belongs to the two methyl groups on the tertiary alcohol. The multiplet with 4 hydrogens are the hydrogens attached to the inner carbon of the tertiary alcohol. The multiplet with 6 hydrogens indicates the methyl groups on the end of the tertiary alcohol. f. Unknown alcohol HO 2-methylbutan-2-ol g. Dialkylated product

O O 1,4-dimethoxy-2,5-di-tert-pentylbenzene Post-Lab: IX. Discussion and Conclusion The unknown tertiary alcohol was found to be 2-methylbutan-2-ol. Once this was discovered the final product was determined to be 1,4dimethoxy-2,5-di-tert-pentylbenzene. This was concluded by using the unique signals on the unknown alcohol’s HNMR spectrum. The HNMR showed a tetra substituted benzene ring which indicated the product was dialkylated. The limiting reagent for this experiment was the 1,4-diemthoxybenzene. This led to a percent yield of 55.2%. This is slightly low which could be attributed to the reaction not being given ample time to react. Also, product was left behind between transfers of reaction flask to filtration apparatus. X. Post- Lab Questions 1. Provide structures for the major, disubstitution Friedel-Crafts product(s) of the following reactions : Br + Br O O

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2. Provide a detailed mechanism for the Friedel-Crafts alkylation reaction provided below. You must clearly show how the electrophilic species is generated as well as all possible resonance forms of any conjugated intermediates formed during the course of the reaction: 3. Provide structures for two compounds that could be used in place of tert-butyl alcohol to form 1,4-di-tert-butyl-2,5-dimethoxybenzene from 1,4-dimethoxybenzene via a Friedel-Crafts reaction: O O 1,4-di-tert-butyl-2,5-dimethoxybenzene O O Cl Cl AlCl3 AlCl3 H H H B