Question

In the benzoin oxidation, the initial blue color changes to green as the reaction proceeds. why?

Answer 1

Benzoin is oxidized to benzil due to coupled oxidation using copper (II) as a catalytic transfer oxidant. The cupric acetate is reoxidized from cuprous state by ammonium nitrate, which itself gets reduced to ammonium nitrite, further decomposing to water and nitrogen.

2Cu⁺ + 2H⁺ + NH₄NO₃ → 2Cu²⁺ +H2O + NH₄NO₂

The reaction of decomposition of ammonium nitrite into nitrogen and water is as follows:

2Cu²⁺ + H₂O + NH₄NO₂  →  2Cu²⁺ + N2 + 3H₂O

During the reaction, copper is reduced from Cu (II) blue to Cu (I) green, because of this, at the time of benzoin oxidation, the initial blue color changes to green as the reaction moves further.

Answer 2

Initial blue color changes to green during the benzoin oxidation it is because during the reaction, the copper in the in the mixture is being reduced, making it as a blue color. After that, there will a mixture of two solutions where it will turn into a green solution. Specifically, Cu2+ and Cu+.