Question

What is the active electrophile in the nitration of the Toluene Experiment?

Answer 1

Nitration

1. Nitration is the process of treating or combining Nitric acid or Nitrate.
2. The substitution of the Nitro group $\left(-{\mathrm{NO}}_2\right)$ takes place in organic compounds.

The active electrophile in the Nitration of Toluene Experiment

1. The nitration of Arenes such as Benzene or Toluene is an electrophilic substitution reaction in which Nitronium ions $\left({\mathrm{NO}}_2^{+}\right)$ is an electrophile.
2. The different steps of the reaction are:

Step 1: Formation of electrophile:

• When concentrated Nitric acid ${\mathrm{HNO}}_3$ and Sulphuric acid ${\mathrm{H}}_2{\mathrm{SO}}_4$ are mixed with each other then the Nitronium ion is formed.
• Nitronium ion is the active species and is the primary electrophile.
• After the protonation of Nitric acid, a weak base is left such as water and ${\mathrm{HSO}}_4^{-}$ ion.
• This weak base helps in removing the proton by splitting the Carbon-Hydrogen bond and reforms it into a Carbon-Carbon bond from the Carbon atom that bears the Nitro group.
• The reaction is highly exothermic in nature.
• Nitration can be used in producing explosives like converting Toluene to Trinitrotoluene, and Guanidine to Nitroguanidine.
• The chemical reaction occurs as follows:
• $$\begin{gathered} {\mathrm{H}}_2{\mathrm{SO}}_4\left(\mathrm{aq}\right)+{\mathrm{HNO}}_3\left(\mathrm{aq}\right)\to {\mathrm{NO}}_2^{+}\left(\mathrm{aq}\right)+{\mathrm{HSO}}_4^{-}\left(\mathrm{aq}\right)+{\mathrm{H}}_2\mathrm{O}\left(\mathrm{l}\right) \\ \mathrm{Nitronium}\mathrm{ion} \end{gathered}$$
• Step 2: Formation of sigma complex:
• The double bond of toluene attacks the nitronium ion forming a complex.
• Step 3: Formation of mononitrotoluene:
• The lone pair of oxygen in the water molecule takes the hydrogen atom and form a mononitrotoluene.

Complete reaction:

1. In Toluene the Methyl group present in it is more reactive in comparison to Benzene in an electrophilic aromatic substitution reaction.
2. Nitration takes place at the ortho and para position in Toluene to form Nitrotoluene isomers.
3. When the formed isomer is heated it will give Dinitrotoluene and finally converted into Trinitrotoluene which is very explosive.