Dissociation, of hydrogen peroxide

The perhydroxyl ion, OOH , derived from the dissociation of hydrogen peroxide in alkaline solution, is generally considered the active agent in the bleaching of wood pulp using hydrogen peroxide. This ionization may be expressed by the following reversible reaction ... 

Luo, X. and Rizzo, T.R. (1991). Unimolecular dissociation of hydrogen peroxide from single rovibrational states near threshold, J. Chem. Phys. 94, 889-898. 

At the end of the eighteenth and the beginning of the nineteenth century the influence of metals and oxides on the decomposition of several substances was studied by many scientists. It was noticed that contact with different substances gives very different products. An example is the decomposition of alcohol in the presence of copper or iron, carbon and an inflammable gas is produced. In the presence of pumice stone decomposition into ethene and water was observed. In other words, selectivity was demonstrated. Many other important milestones can be mentioned we limit ourselves to a few. Thenard investigated the dissociation of ammonia in contact with metals. In 1813 he found that the dissociation occurs over various metals, provided they are hot. Later he systematically studied the dissociation of hydrogen peroxide. He concluded that some of the solids studied... 

Figure 2.4 Dissociation of hydrogen peroxide under alkaline pH.

Edse 134 deduces a lower limit of 102 7 0 9 kcal to i)(OH) from the work of Urey et a/.530 on the photochemical dissociation of hydrogen peroxide. 

From measurements of the influence of temperature on the reaction rates and analysis by the method described above, Cullis and Hinshelwood [38] give mean values of the activation energy of the initiation step, Eq = 110 kcal. mole for KCl vessels and Eq = 92 kcal. mole for CsCl coated vessels. This would be consistent with initiation by H2 + M = H + H + M, which requires 104 kcal. mole . Ashmore and Dainton [39] reached similar conclusions. However, Lewis and von Elbe [52] point out that, since the activation energy of the hydrogen dissociation is at least equal to its heat of dissociation (104 kcal. mole ), the maximum possible rate of dissociation is only about 10 of the observed initiation rate. This rules out hydrogen dissociation as the initiating step. Lewis and von Elbe cite this as support for the initiation step which they themselves had proposed earlier [23], namely the dissociation of hydrogen peroxide... 

Employing the latter value as the energy of the O—H bond we obtain for the dissociation of hydrogen peroxide into two peroxide groups H2O2 = 20H d// = 56 6 kcals... 

The central O—O bond in hydrogen peroxide has a dissociation energy of 17,350 cm-1, an amount of energy which can be more than achieved by excitation of the v = 6 overtone of an O—H bond. As a consequence, there have been a number of experimental and theoretical studies of overtone induced dissociation of hydrogen peroxide. 

Figure 4.13. Dissociation of hydrogen peroxide on nonreduced Ti02 surface.

Fig. 5.1 Reaction scheme for the photolytic dissociation of hydrogen peroxide. knA is the hydrogen abstraction rate constant...

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