Electrophilic Aromatic Substitution Formal Lab

Topics: Electrophilic aromatic substitution, Benzene, Sulfuric acid Pages: 6 (1646 words) Published: December 11, 2011
Electrophilic Aromatic Substitution
The objective of this experiment was to illustrate electrophilic aromatic substitution by synthesizing p-nitroanilide (as well as ortho) from acetanilide by nitration. The para form was separated from the ortho form based on solubility properties using recrystallization techniques. Synthetic equations:

Physical Properties & Hazards of Reagents/Products: (all taken from Sigma-Aldrich website)

MM = 135.16 g/mol
Melting point = 113-115°C
Hazards: acute toxicity

Sulfuric acid
MM = 98.08 g/mol
Boiling point = 290°C
Density = 1.840 g/mL
Hazards: corrosive to metals and skin, serious eye damage

Nitric acid
MM = 63.01 g/mol
Boiling point = 120.5°C
Density = 1.480 g/mL
Hazards: oxidizing liquid, corrosive to metals and skin, serious eye damage

MM = 46.07 g/mol
Boiling point = 78°C
Density = 0.789 g/mL
Hazards: flammable

MM = 180.16 g/mol
Melting point = 215-217°C
Hazards: acute toxicity

MM = 180.16 g/mol
Melting point = 92-94°C
Hazards: acute toxicity

MM = 18.02 g/mol
Boiling point = 100°C
Density = 1.00 g/mL

The nitrating agent was prepared by slowly adding cold concentrated sulfuric acid (1.7 mL, 0.0319 mol) to cold concentrated nitric acid (0.6 mL, 0.0141 mol) in a 50 mL Erlenmeyer flask. The mixture was carefully swirled in an ice bath to ensure that the two concentrated acids were thoroughly mixed together. In a second 50 mL Erlenmeyer flask, acetanilide (1.0 g, 0.0074 mol) was dissolved in concentrated sulfuric acid (1.5 mL, 0.0281 mol) by having the acid slowly added to the solid while the mixture was swirled. Heating with a hot plate was also required to dissolve the acetanilide. When all of the solid had dissolved, the flask was cooled in an ice bath. The cold nitrating agent was added drop-wise to the cold acetanilide mixture. The flask was swirled after each addition of the nitrating agent. The flask was kept immersed in the ice bath so that the temperature of the reaction would not rise. The drop-wise addition of the nitrating agent took approximately 5-10 minutes. Including the time of adding the nitrating agent, the reaction was kept in the ice bath for a total of 20 minutes with intermittent swirling. Ice water (10 mL, 0.555 mol) was carefully added to the flask. The mixture was thoroughly swirled to dilute the acids and was allowed to stand for about 5 minutes with occasional swirling. After the 5 minutes, solid nitroacetanilde formed. The solid was collected by vacuum filtration and rinsed with cold water. The solid was allowed to dry over the Buchner funnel for several minutes. A small amount of this solid was saved in a small test tube. The filtrate was disposed of in the waste jar in the hood. The filter flask was rinsed out with a small amount of water. The remainder of the solid was recrystallized from hot ethanol. The solid was collected by vacuum filtration. A TLC was ran on the crude solid, the recrystallized solid, and the filtrate from the recrystallization. The solid was allowed to dry until the following lab when it would be weighed and have a melting point taken. Calculations

Theoretical Yield:
1.0 g acetanilide x 1 mol/135.16 g = 0.0074 mol acetanilide 0.0074 mol acetanilide x 1 mol p-nitroacetanilide/1 mol acetanilide = 0.0074 mol p-nitroacetanilide 0.0074 mol p-nitroacetanilide x 180.16 g/1 mol = 1.33 g p-nitroacetanilide Percent Yield:

(Actual/Theoretical) x 100 = (0.17 g/1.33 g)x100 = 12.8% yield Rf calculations:
First spot: (center of first spot/ solvent front) = 3.7 cm/ 5.2 cm = 0.71 Second spot: (center of second spot/ solvent front) = 4.6 cm/ 5.2 cm = 0.88 Data & Results
The actual yield of p-nitroacetanilide was 0.17 grams corresponding to a 12.8% yield. The melting point was found to be 210-212°C, confirming that the product’s identity was indeed the p-nitroacetanilide. A TLC was performed on the crude...

References: 1) Sigma-Aldrich website
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