Electrophilic Bromination - Mandatory Assignment - Organic Chemistry PDF

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2/14/18 Experiment #3: Electrophilic Bromination The purpose of this lab experiment is to understand and perform an electrophilic aromatic substitution of bromine using acetanilide. Mechanism

Ethanol Acetanilide Potassium

Boiling point °C

Melting Point °C

Amount used

46.0 135.16 167.0

0.79 1.22 3.27

78.3 304 NA

-114 114.3 350

2 mL 200 mg 0.085 g

bromate N-(4bromophenyl) acetamide Hydrobromic acid

214.06

1.54

353.4

165-169

NA

80.9

1.49

122

-11

0.3 mL

Acetic acid

60.0

1.05

118.1

16.6

2 mL

Structures 1.

2.

3.

Ethanol

N-(4-bromophenyl) acetamide

Acetanilide

MSDS 1. Acetanilide: irritation of eyes and skin. Combustible at high temperatures.

2. Acetic acid: irritation of eyes and skin. Flammable. 3. Potassium bromate: irritant of skin and eyes. Causes eyes redness, skin burns, itching if overexposed. 4. Ethanol: irritant of eyes and skin. Flammable. 5. N-(4-bromophenyl) acetamide: irritant of eyes and skin. 6. Hydrobromic acid: corrosive. Avoid contact with skin and eyes. Procedure 1. Place 200 mg of acetanilide into a 25 mL Erlenmeyer flask. 2. Add 0.085 g of potassium bromate and 2 mL of acetic acid. 3. Begin stirring, KBrO3 will not completely dissolve and the reaction will remain heterogenous. 4. Add 0.3 mL of 48% hydrobromic acid to this mixture and stir for 30 minutes. •

While stirring chill 25 mL of water.

5. After the mixture has stirred for 30 min pipette the reaction mixture slowly into the chilled water. 6. Allow to stand for 15 min. 7. Filter the precipitate using either a Hirsch or Büchner Funnel 8. Recrystallize with 2 mL of ethanol 9. Collect MP, percent yield, and NMR.

Calculations Mass of acetanilide: 0.2078g Mass of final product: 0.0991g

0.2078 g ×

1 mol acetanilide 1mol ∏ . 214.06 g =0.329 g × 1mol A . × 1 mol ∏ . 135.16 g acetanilide

Percent Yield 0.0991 g × 100=30.1 % 0.329 g Conclusion/Discussion An electrophilic aromatic substitution of bromine to acetanilide was performed during this lab experiment to form N- (4-bromophenyl) acetamide. The reaction was set to reflux for 30 min and after it was heated crystals were formed. The crystals were collected and recrystallized; after recrystallization a melting point was taken ranging from 160-167°C. These values were lower than the accepted values of 165-169°C which indicates that the product may have some impurities or some starting material. An NMR was taken for this product; HA appeared around 10 ppm since this proton is attached to a nitrogen is going to be more downfield. HB are the aromatic protons around 7.5 ppm showing two peaks since these hydrogens are in different environments. HC are the methyl protons, showing a singlet around 2.2 ppm. In addition, the NMR showed some toluene; two peaks around 7 ppm were shown. Like mentioned before, the melting point was lower than the accepted value indicating impurities or starting material which were shown in the NMR. The expected values on the IR would be N-H around 3300 cm-1, acetyl group at ~ 2900 cm-1, the C-C aromatic double bonds at ~1500-1600 cm-1, C-Br bond at ~515-650 cm-1 and the CO double bond at ~1600 cm-1. The calculated percent yield for this product was 30.1%....