Hydrogen peroxide, H2O2 - an inorganic chemical compound from the group of peroxides, one of the reactive oxygen species. It was obtained for the first time by Louis Thénard in 1818 by reacting barium peroxide with nitric acid.
The structure of the molecule
The system of O − O − H bonds around the oxygen atoms in the H2O2 molecule is nonlinear (similar to the H − O − H system in water), moreover, the H − O − O − H atoms form a dihedral angle (about 90 ° in the solid phase).
Structure of the hydrogen peroxide molecule
The first and now only historical method of obtaining hydrogen peroxide on an industrial scale was the Thénard process:
BaO2 + H2SO4 → BaSO4 + H2O2 Currently, it is most often the so-called by anthraquinone method by oxidation of 2-ethyl-9,10-anthracenediol with oxygen gas passed through a solution of this compound in a mixture of appropriately selected solvents. The peroxide is separated by extraction with water, and the remaining 2-ethylanthraquinone in the solution is regenerated by reduction with hydrogen gas to 2-ethyl-9,10-anthracenediol, catalyzed with palladium on a suitable support or with nickel compounds. In industrial production methods, the cycle of both reactions (oxidation and reduction) is carried out alternately.
The dilute peroxide aqueous solution obtained by this process is concentrated by careful evaporation of water under reduced pressure, thereby obtaining a solution with a maximum concentration of 70%. Further concentration leads to an explosion. More concentrated solutions and completely pure peroxide are probably obtained by freezing it from an aqueous concentrated solution.
Another, less frequently used method is the oxidation of isopropanol:
(CH3) 2CHOH + O2 → (CH3) 2C O + H2O2 The reaction is free radical and does not require additional catalysts as it is catalyzed by H2O2 (a small amount of it is added to the substrate to accelerate the initial phase). Its second industrial product is acetone. This method was used in the second half of the 20th century; in the first decade of the 21st century, only two installations were operational in the former USSR. Other alcohols undergo the same reaction, but in the case of primary alcohols, the formed aldehydes are oxidized by H2O2 to carboxylic acids, which excludes their use in this process.
Hydrogen peroxide can also be obtained by the electrolytic method from H2SO4 or NH4HSO4:
2H2SO4 → H2S2O8 + H2 ↑
2NH4HSO4 → (NH4) 2S2O8 + H2 ↑ In both cases, H2O2 is then obtained by hydrolysis:
S2O2−8 + 2H2O → 2HSO − 4 + H2O2
Hydrogen peroxide at room temperature is a syrupy, colorless (when concentrated becomes pale blue) liquid with a melting point of −0.44 ° C and a boiling point of approximately 150 ° C. It has strong oxidizing properties, resulting from the formation of atomic oxygen during its decomposition (the so-called nascendi oxygen):
H2O2 → H2O + P Pure hydrogen peroxide is unstable - it decomposes exothermically (often explosive) into water and oxygen under the influence of heat, ultraviolet light and contact with certain metals (e.g. manganese) and metal oxides.
2H2O2 (aq) → 2H2O (l) + O2 (g) This decomposition is catalyzed by many particulate substances, for example silver, platinum and manganese (IV) oxide.
Its decomposition is also catalyzed by iodides, with H2O2 oxidizing I− to I2, and the reaction of H2O2 with iodine (or iodates) is an oscillatory reaction:
5H2O2 + I2 → 2HIO3 + 4H2O
5H2O2 + 2HIO3 → I2 + 6H2O + 5O2 ↑ Catalase is an efficient enzyme for decomposing hydrogen peroxide.
Due to the fact that it reacts easily with many metals and also decomposes on contact with glass, it should be stored in pressure bottles made of thick-walled polyethylene or aluminum and not exposed to daylight or heat sources. Its complex with sodium carbonate of the hydra type