Essay Preparation of 4-Bromoaniline

1861 Words Feb 28th, 2013 8 Pages
Preparation of 4-bromoaniline
Introduction
Aromatic compounds tend to undergo electrophilic aromatic substitutions rather than addition reactions. Substitution of a new group for a hydrogen atom takes place via a resonance-stabilized carbocation. As the benzene ring is quite electron-rich, it almost always behaves as a nucleophile in a reaction which means the substitution on benzene occurs by the addition of an electrophile. Substituted benzenes tend to react at predictable positions. Alkyl groups and other electron-donating substituents enhance substitution and direct it toward the ortho and para positions. Electron-withdrawing substituents slow the substitution and direct it toward the meta positions.
Aromatic compounds also undergo
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Aniline 93.1 10 0.107 Yes
Ethanoic anhydride 102.1 12 0.118 No
Glacial ethanoic acid 60.1 25 0.416 No

No. moles produced by aniline = 0.107 moles
Theoretical mass of N-phenylethanamide = n*MR = 0.107 × 135 = 14.44g
Percentage yield = actual yield (g)/theoretical yield (g) × 100 = (11.9/14.44) × 100 = 82%
For preparation of N-(4-bromophenyl) ethanamide:
Product RMM Volume used/ g Volume used/ mL Moles used Limiting reagent?
N-phenylethanamide 135.2 5 0.0370 No
Bromine 159.8 2.1 0.0131 Yes

No. moles produced by bromine = 0.0131 moles
Theoretical mass of N-(4-bromophenyl) ethanamide = n*MR = 0.0131 × 159.8 = 2.10 g
Percentage yield = actual yield (g)/theoretical yield (g) × 100 = (5.00/2.10) × 100 = 238%
For preparation of 4-bromoaniline:
Product RMM Volume used/ g Volume used/ mL Moles used Limiting reagent?
N-(4-bromophenyl) ethanamide 214.1 5 0.0234 Yes
Hydrochloric acid 36 50 5.00 No

No. moles produced by N-(4-bromophenyl) ethanamide = 0.0234 moles
Theoretical mass of 4-bromoaniline= n*MR = 0.0234 × 214.1 = 5.01 g
Percentage yield = actual yield (g)/theoretical yield (g) × 100 = (1.60/5.01) × 100 = 32%

Discussion
The preparation of N-phenylethanamide from aniline was the first step of the experiment.

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