9.3 Hydrogen peroxide

Hydrogen peroxide (H ₂ O ₂ ) is a very pale blue liquid but appears colorless in dilute solution. It is prepared by the oxidation of anthraquinol, e.g., [link] . The hydrogen peroxide is extracted with water from the anthraquinone solution and the 20 - 40% solution is purified by solvent extraction. An alternative process involves the oxidation of isopropanol in either the vapor or liquid phase at 100 °C and ca . 15 atm, [link] . The products are separated by fractional distillation.

In the gas phase H ₂ O ₂ adopts a gauche conformation ( [link] ), but there is only a low barrier to rotation about the O-O bond.

Hydrogen peroxide is a liquid at standard temperature and pressure (25 °C, 1 atm) due to the presence of strong hydrogen bonding similar to found in water. In fact, the liquid range for H ₂ O ₂ (Mp = -0.43 °C, Bp = 150.2 °C) is actually broader than water, and it is slightly more viscous than water. Hydrogen peroxide has a density of 1.44 g/cm ³ , and is 10 ⁶ times less basic that water.

As with water, H ₂ O ₂ is a good solvent because of its polar nature and broad liquid temperature range, however, it is dangerous in its pure state due to its facile (ΔH = -99 kJ/mol) auto decomposition, [link] , as well as its strong oxidizing nature.

Hydrogen peroxide is usually sold as 3 - 12% solution for home use; however, laboratory and certain industrial applications require 30% solutions.

Aqueous solution are weakly acidic (K = 1.5 x 10 ^-12 ), [link] . However, there is no exchange of oxygen atoms between H ₂ O ₂ and H ₂ O in the liquid phase.

As expected hydrogen peroxide is a strong oxidizing agent, [link] , however, it can also act as a reducing agent, [link] .