Nitration of Toluene and determination of product distribution.
Purpose
a) Study electrophilic aromatic substitution reaction (EAS)
b) Study regioselectivity for EAS reactions
Chemicals Materials
150 – mL beaker
Toluene 400-mL beaker
Sulfuric acid (conc.) 125-mL flask
Nitric acid (conc.) Separatory funnel
Ice
Dichloromethane
2M NaOH
Introduction
Benzene rings are components of many important natural products and other useful organic
compounds. Therefore, the ability to put substituents on a benzene ring, at specific positions relative to
each other, is a very important factor in synthesizing many organic compounds. The two main reaction
types used for this are both substitutions: Electrophilic Aromatic Substitution (EAS) and Nucleophilic
Aromatic Substitution (NAS). The benzene ring itself is electron-rich, which makes NAS difficult,
unless there are a number of strongly electron-withdrawing substituents on the ring. EAS, on the other
hand, is a very useful method for putting many different substituents on a benzene ring, even if there
are other substituents already present. Electrophilic Aromatic Substitution chapter describes the factors
involved in the regioselectivity for EAS reactions using benzene rings, which already have substituents
on them.
In this experiment you will put a nitro (—NO2) group on a benzene ring, which already has a methyl
group, attached to it (methyl benzene - Toluene). The actual electrophile in the reaction is the nitronium
ion (NO2+), which is generated in situ ("in the reaction mixture" HNO3/H2SO4) using concentrated nitric
acid and concentrated sulfuric acid.
Here is the general mechanism for the the nitration of just a benzene ring. Remember, you will be
nitrating toluene which can produce three different isomers as well as potentially di-nitration.
