Zinc Peroxide

Thenard obtained an incompletely peroxidised oxide of zinc by (a) dissolving zinc hydroxide in hydrochloric acid containing hydrogen peroxide and precipitating with an alkali hydroxide; (b) acting on gelatinous zinc hydroxide with hydrogen peroxide.

Haass precipitated zinc salts with ammonia in the presence of hydrogen peroxide and obtained white precipitates that, after drying at 110° C., varied in composition between Zn₅O₈ and Zn₃O₅.

Kouriloff, by evaporating zinc oxide or hydroxide nearly to dryness with dilute hydrogen peroxide solution, obtained a white, finely crystalline powder, to which he assigned the formula ZnO₂.Zn(OH)₂.

de Forcrand agitated zinc oxide with hydrogen peroxide solution and obtained Zn₃O₅.2H₂O, Zn₃O₅.3H₂O, and Zn₄O₇.4H₂O as gelatinous white precipitates that became white powders on drying. They were stable in air, but on heating Zn₄O₇.4H₂O to 100° C. it became Zn₃O₅.3H₂O. By continued treatment with hydrogen peroxide he obtained 2ZnO₂.5H₂O, which, however, gradually changed into Zn₃O₅.2H₂O.

He preferred to formulate these substances as -

3ZnO.2H₂O₂.3ZnO.H₂O+2H₂O₂ or
HO.Zn.O.Zn.O.Zn.OH+2H₂O₂.4ZnO.H₂O+3H₂O₂ or
HO.Zn.O.Zn.O.Zn.O.Zn.OH+3H₂O₂.ZnO.H₂O+H₂O₂ or
HO.Zn.OH+H₂O₂.

Eijkmann described the preparation of 3ZnO₂.Zn(OH)₂ by the action of 30 per cent, hydrogen peroxide on an ammoniacal solution of zinc sulphate.

Kazanecky obtained a fine crystalline precipitate of ZnO₂.H₂O by acting with 30 per cent, hydrogen peroxide on alkali zincates. It decomposed explosively at 178° C. He regarded it as

.2Zn:O:O.3H₂O.

When pure zinc oxide reacts with an ethereal solution of hydrogen peroxide, the product, after drying at 6O°-70° C., has the composition Zn₄O₇.2H₂O. It loses oxygen when heated with water at 100° C., and forms Zn₃O₅.H₂O. Both these peroxides are reddish-yellow powders that are stable under ordinary conditions and explode at 212°-216° C. Carrasco regarded them as perzincic acids -

HO.Zn.O.O.Zn.O.O.Zn.O.O.ZnOH
and
HO.Zn.O.O.Zn.O.O.ZnOH.

Ebler and Krause obtained ZnO₂.½H₂O, which they formulated as .½H₂O, by acting upon a cooled solution of zinc ethyl in dry ether with a dry ethereal solution of hydrogen peroxide. The white amorphous precipitate was decomposed by acids and slowly hydrolysed by water. A similar product was obtained by dissolving zinc nitrate in concentrated ammonia solution, cooling to -5° C., adding a concentrated solution of hydrogen peroxide, and stirring the filtered precipitate for some time with more of the hydrogen peroxide. The product was either moist ZnO₂ or ZnO₂.½H₂O.

Sjostrom obtained a white powder by carefully drying the product of the prolonged action of the calculated amount of 30 per cent, hydrogen peroxide solution on freshly ignited zinc oxide. Its composition corresponded to the formula Zn₂O(OH)(O.OH). It was stable under ordinary conditions and only slowly decomposed by 2N NaHO.

He concluded that zinc perhydrate is usually a mixture of substances derived from Zn(OH)₂ and HO.Zn.O.ZnOH, and that the hydroperoxides are of the types HO.Zn.O.OH and Zn(OH).O.Zn.O.OH.

Commercially, zinc peroxide has been prepared by allowing barium peroxide suspended in water to act on the zinc salt of an acid that forms an insoluble barium salt. The electrolytic preparation, however, is most satisfactory. A solution of zinc chloride, neutralised by adding zinc oxide, is electrolysed in a vessel containing a porous diaphragm, and hydrogen peroxide is added to the cathode cell. The precipitated hydrated peroxides are carefully dried.

The commercial product is a dense, yellowish-white powder of density 1.571, and appears to contain about 50 per cent, of ZnO₂ mixed with zinc hydroxide and free moisture. It is very stable - losing only water at 100° C. and not being decomposed by water. One part dissolves in 45,500 parts of water. It has strong antiseptic properties, and has the advantage of being odourless and non-irritant. It is soluble in acids but is indifferent to mineral hydrocarbons. This last property is important for its extensive use in ointments. It is much used in surgery and dermatology.

Preparations of zinc peroxide are known under the trade names of zinkonal, dermogen, eklogan, and zinc perhydrol.