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GATE 2026 CY – Question 26

Inorganic Chemistry · Organometallics: 18-Electron rule; metal-alkyl, metal-carbonyl, metal-olefin and metal-carbene complexes and metallocenes. Fluxionality in organometallic complexes. Types of organometallic reactions. Homogeneous catalysis – Hydrogenation, hydroformylation, methanol to acetic acid process, olefin metathesis and Wacker oxidation. Heterogeneous catalysis – Fischer-Tropsch reaction, Ziegler-Natta polymerization. · 1 mark · Multiple select

The interconversion of oxidation states of metal(s) observed in Wacker process is(are)

  1. Pd(II) / Pd(0)
  2. Cu(II) / Cu(I)
  3. Pd(IV) / Pd(II)
  4. Cu(II) / Cu(0)

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Correct answer: (A) Pd(II) / Pd(0); (B) Cu(II) / Cu(I)

Explanation

The **Wacker process** oxidises ethylene to acetaldehyde with $\text{PdCl}_2$ as the catalyst, $\text{CuCl}_2$ as the co-catalyst and $O_2$ as the final oxidant.

1. $\text{Pd(II)}$ binds the alkene, and water attacks it, forming acetaldehyde. In this step $\text{Pd(II)}$ is reduced to $\text{Pd(0)}$. **Pd(II)/Pd(0)** ✓
2. $\text{Cu(II)}$ reoxidises $\text{Pd(0)}$ back to $\text{Pd(II)}$ and is itself reduced to $\text{Cu(I)}$. **Cu(II)/Cu(I)** ✓
3. $O_2$ (with HCl) reoxidises $\text{Cu(I)}$ back to $\text{Cu(II)}$.

$\text{Pd(IV)}$ and $\text{Cu(0)}$ do not appear. Answer **A and B**.