Hydrogen Peroxide : Autoxidation

The formation of hydrogen peroxide during the slow oxidation of phosphorus, oil of turpentine, and metals by gaseous oxygen in the presence of water, was studied by Schonbein in 1858. He found that the oxygen is equally divided in oxidising the substance (e.g., lead) and in forming hydrogen peroxide;

Pb + O₂ + H₂O = PbO + H₂O₂.

Clausius (1858) considered that the oxygen molecule contained a positively and a negatively charged atom of oxygen, called antozone and ozone, respectively. The antozone formed hydrogen peroxide with water or, if indigo solution or another oxidisable substance was present, it oxidised the latter,

Traube (1882) suggested that in oxidation processes in the presence of gaseous oxygen the oxygen molecule unites as a whole with the oxidisable substance to form a holoxide, or moloxide. For example, in the combustion of hydrogen the latter unites with O₂ to form hydrogen peroxide as a primary product: H₂ + O₂ = H₂O₂. The reaction between zinc, water and oxygen he represented as:

Zn + O H₂ + O₂ = ZnO + H₂O₂,

and the primary oxidation of carbon monoxide as: CO + OH₂ + O₂ = CO₂ + H₂O₂.

Bach (1897) concluded that the substance undergoing oxidation (autoxidiser, A) itself unites with a molecule of oxygen to form an unstable higher oxide, which may then react with water or some other acceptor, B, to give the lower oxide of A, and H₂O₂ or BO:

A + O₂ = AO₂.

AO₂ + H₂O = AO + H₂O₂,

AO₂ + B = AO + BO.

With metals, the unstable higher oxides PbO₂, ZnO₂, are not the ordinary known ones, which do not give hydrogen peroxide with water.

According to Engler and Wild, the oxygen molecule is first opened up to form -O-O-, which combines with the activator (e.g., turpentine) to form the unstable peroxide. In some cases these unstable peroxides have been isolated. The bleaching and disinfecting properties of turpentine are due to its ability to activate oxygen in this way. Turpentine forms a peroxide on standing in a loosely stoppered bottle.

Expt. 7. - Add a little turpentine to dilute potassium iodide and starch solution in an open flask, shake, and allow to stand. A blue colour is produced.

Protein crystallography
Chemistry guide
Hydrogen Peroxide
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