• Using platinum nanocatalyst, a two-member team at the Indian Institute of Technology (IIT) Madras has successfully converted petroleum waste-product toluene into benzoic acid.
  • Benzoic acid is used as a food preservative (E210) and medicine for fungal/bacterial infection.
  • Toluene is converted into benzoic acid through selective and controlled oxidation in the presence of a catalyst — binaphthyl-stabilised platinum nanoparticles (Pt-BNP).

Tell us about the Green oxidant

  • Generally, organic reactions are carried out using organic solvents, which makes it expensive and also generates toxic waste.
  • So in a departure from current practice, the team led by G. Sekar from the institute’s Department of Chemistry has used water as solvent to make it environment-friendly.
  • Also, a green oxidant (70% aqueous tert-butyl hydroperoxide or TBHP) is used for converting toluene into benzoic acid.
  • When toluene is oxidised, it gives four products. But when we use the catalyst that we developed, only benzoic acid is produced. No alcohol, aldehyde or ester is produced.
  • The yield of benzoic acid varied from 68-96% depending on whether the toluene used is electron-deficient or electron-rich.
  • Generally, platinum nanoparticles are not stable in nature as they tend to agglomerate and become macroparticles.
  • The catalytic activity is reduced once it becomes macroparticles.
  • The binaphthyl that is bound to platinum nanoparticles acts as a stabiliser and prevents nanoparticle agglomeration.
  • Binaphthyl bound to platinum nanoparticles makes the catalyst easy to handle and stable.
  • It is the stability of the catalyst to remain as nanoparticles that allows us to recover it and reuse the catalyst up to five times.
  • There was no change in the size of the catalyst even after being reused five times.
  • Toluene when oxidised gets converted into benzoic acid.
  • Molecular oxygen when used alone does not oxidise toluene and so no benzoic acid is generated. So the researchers used TBHP as an oxidiser.
  • The catalyst reacts with TBHP to initiate the oxidisation reaction where toluene gets converted into benzoic acid through a series of reaction steps.
  • When used alone, a large quantity (four parts of TBHP to 1 part of toluene) of TBHP would be required for the conversion, which will not be economically favourable.
  • In order to reduce the amount of TBHP used, the researchers also used molecular oxygen.
  • In the presence of molecular oxygen, only two parts of TBHP are needed for the conversion.
  • So molecular oxygen behaves as a co-oxidiser.
  • Molecular oxygen is cheap, so using it along with TBHP helps in reducing the cost.”
  • The use of TBHP along with molecular oxygen also increased the yield of benzoic acid.