Give the reagents required for the nitration of toluene (methylbenzene) to 2,4,6-trinitrotoluene and provide a mechanism.

The reagents needed are sulphuric acid and nitric acid. It may be useful to notice that nitric acid here acts as a stoichiometric reagent, in that it is used up in the reaction to nitrate the toluene, but sulphuric acid acts as a catalyst, and is regenerated in the final step. The mechanism begins with a reaction between the sulphuric and nitric acids, to produce NO₂⁺ (the electrophilic species), water and HSO₄^-. The mechanism for this is the stronger acid, nitric acid, removing a proton from the sulphuric acid, then decomposing to produce the products. Then the benzene ring in toluene, being electron rich, attacks the electrophile produced to disrupt the aromaticity and leave a positively charged intermediate species (a wheland intermediate,) which quickly loses a proton to become the more stable product. (4-nitrotoluene) this process then occurs a further two times to give the product in the question.