Question

1. CoCl2*6H2O reacting with ammonium chloride, ammonia, and hydrogen peroxide to form hexaamminecobalt(III) chloride and water

2. cobalt (II) nitrate hexahydrate reacting with ammonium carbonate, concentrated ammonia, and hydrogen peroxide and water to form [Co(NH3)4CO3]NO3

Both synthesis above include hydrogen peroxide. What is the purpose of this hydrogen peroxide? Could we use a different cobalt starting material and skip the addition of hydrogen peroxide?

Answer 1

In the above mentioned inorganic complex synthesis reactions, hydrogen peroxide is used as an oxidizing agent that oxidizes the cobalt (II) reactant to the cobalt (III) product. This reaction is best done by using concentrated H₂O₂ in basic ammonia solution. It generates only OH^– as reduced product and the presence of ammonia helps in immediate stabilization of Co(III) by formation of amine complexes.

If we skip this adding H₂O₂ and use different cobalt(III) starting material, Co(III) ion will not be stable in aqueous media, rather it would form the strongly oxidizing hexaaqua complex. Hence, we would not get the desired product.