Copper peroxide, CuO₂,H₂O

At 0° C. neutral hydrogen peroxide converts an aqueous suspension of cupric hydroxide into the brown, crystalline peroxide. It is also produced by the interaction of solutions of cupric chloride and hydrogen peroxide with alcoholic potash at -40° or -50° C., and by the action of an ether-solution of hydrogen peroxide. on very finely powdered cupric hydroxide at 0° C. The product is always more or less impure. When moist, it decomposes rapidly with evolution of oxygen and formation of cupric oxide, but the decomposition of the dry substance is slow. In its reactions it behaves as a peroxide. Moser assigns to it the formula . The name peroxites has been suggested for the true salts of hydrogen peroxide.

The compounds obtained by the action of hydrogen peroxide on cupric hydroxide are regarded by Aldridge and Applebey as probably consisting of a mixture in varying proportions of cupric oxide and hydroxide with a yellow, gelatinous peroxide of the formula CuO₂. A solution of sodium copper carbonate, Na₂Cu(CO₃)₂, reacts with hydrogen peroxide to precipitate a very unstable, yellowish-brown peroxide, containing more oxygen than would correspond with the formula Cu₂O₃, but less than that required by CuO₂.

In 1844 Kruger obtained pink solutions by the chlorination of alkaline suspensions of cupric hydroxide, and attributed the colour to the presence of salts (" cuprates ") of an acidic peroxide of copper. Aldridge and Applebey regard these so-called cuprates as having no real existence, the pink colour observed by Kruger being considered to be due to the formation of permanganate from traces of manganese dioxide.

This copper peroxide, Cu₂O₃, is stated to be formed as an orange-yellow substance by electrolytic oxidation with a high current-density at a copper anode immersed in concentrated caustic alkali, and also by the action of alkaline hypochlorite and hypobromite on cupric hydroxide and copper. Various investigators have described a compound with the same formula. An example is the interaction of potassium persulphate with a mixture of cupric hydroxide and barium hydroxide cooled with ice and salt, colour changes taking place in the solution, and a tenuous, amaranth-red precipitate being deposited. The substance formed yields oxygen with sulphuric acid, liberates chlorine from hydrochloric acid, oxidizes ammonia in the cold to nitrogen and nitrous acid and traces of nitric acid, decolorizes permanganate, and liberates iodine from potassium iodide. It is not a peroxide, since with dilute acids it does not yield hydrogen peroxide, and therefore differs from the orange-yellow peroxide obtained by means of hydrogen peroxide. The ratio between the percentages of copper and active oxygen present corresponds with the formula Cu₂O₃.