8/13/2019 Electrophilic Aromativ Substitution

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Julio InterianoOrganic Chemistry II2/11/13

Electrophilic Aromatic Substitution – Preparation of methyl m-nitrobenzene

Purpose: To perform an electrophilic aromatic substitution of methyl benzoate with nitric acid

MSDS

CompoundName

MolecularForm

bp C mp CDensityg/mol

MWg/mol

Hazards

MethylBenzoate

C8H8O2  199.6 -12.5 1.0837 136.15 Generally stable

Sulfuric Acid H2SO4  337 10 1.84 98.079 Pollutant, corrosive, toxic

Nitric Acid HNO3  83 -42 1.5129 63.01 Corrosive, flammable

Methanol CH4O 65 -98 791.80 32.04 Flammable, toxic

Procedure:

  Add 15 mL of Concentrated sulfuric acid to 50-mL flask with stir bar, set in ice bath

and stir.   When cooled, add 7.0 mL methyl benzoate 

  Combine 5 mL of sulfuric acid and 5 mL of nitric acid. Cool solution in ice bath

  Add slowly to methyl benzoate solution and stir until reaction is complete. Set aside

for 20 min in room temp

Isolation and Purification of Product

  Transfer solution onto a pile of ice andwash with more ice cold water

  Collect solid in Buchner funnel using suction

  Wash with 10 mL ice cold methanol. Allow to dry  Recrystallize impure compound with 20 mL methanol by heating and stirring.

  Solid precipitates out. Use suction filtration to separate

  After drying for 1 week record melting point and mass

  Preform IR spectrum on both reactant and product (No access to IR machine)

I

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Results and Observations:

  After adding the acid solution to the methyl benzoate solution the product produced and

orange/rusty color. As the reaction proceeded forward it dulled to a mustard-yellow color. The

flask then steamed for ~3 minutes.

  Before drying, the product weighed 14.67 grams.

  Mass of dried product: 5.55 grams

  Melting point of product: 65 – 70 O Celsius

Questions:

1)  Mechanism:

2)  COOMe is an Electron Withdrawing Group and is therefore a Meta-Directing group. The formation

of the ortho product is slower than the meta product formation due to the resonance structures

present in the molecule. The meta position is the most electron dense part of the ring and is

therefore when the electrophile bonds.

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Julio InterianoOrganic Chemistry II2/11/13

3)  Most of the products stopped at a single nitration opposed to double nitration despite excess nitric

acid being used because both NO2 and COOMe are EWG’s. EWG’s pull creates electron dipoles

towards the groups and away from the benzene rings. This lack of electron density may add to the

inability for the benzene ring to react with and accept more EWG’s (a second NO2 group).