Hydrogen peroxide decomposition in 1-5 mol dm-3 KOH and 1-2 mol dm-3 NaOH solutions is a first-order reaction with respect to undissociated hydrogen peroxide. The decomposition is catalysed by compounds of heavy metals (Fe, Cu) present as trace impurities in these solutions and is first order with respect to them. The hydroxyl ion concentration exerts a significant effect on the decomposition rate, which has been explained by its influence on the activity of catalysing species having colloidal character, which are probably the active sites for the decomposition.The kinetics of hydrogen peroxide decomposition in dilute solutions of alkali hydroxides have been studied by many authors, especially with regard to using these solutions for bleaching cellulose and textile materials. However, the results of these studies are difficult to compare, as the spontaneous decomposition of peroxide is apparently a catalysed reaction whose rate is also affected by the nature and concentration of trace impurities present. It has long been known that bases accelerate the decomposition of peroxide and that the content of trace heavy-metal impurities has the principal influence on the reaction rate.l According to Biirki and Schaaf,2 peroxide decomposition in dilute alkali hydroxide solutions is a first-order reaction with respect to the peroxide, the decomposition rate increasing with increasing hydroxide concentration (from 5 x lo-* to 0.2 mol dm-3 NaOH). It was later found that peroxide decomposition is fastest at a ratio of peroxide concentration to that of hydroxide of t~0~-~ or three.6 From the former value, at which about one half of the peroxide is present as perhydroxyl ions, it was derived by AbeP that peroxide decomposition proceeds through the reaction of perhydroxyl ions with undissociated (A) peroxide molecules :HOT + H 2 0 2 -+ H 2 0 + 0, + OH-.The decomposition of peroxide in pure hydroxide solutions was considered to be an uncatalysed reaction, resulting from the oxidising properties of the peroxide molecules and the reducing properties of the perhydroxyl i o m 3 Similar dependences of the decomposition rate on the total alkalinity were found in pure solutions of potassium and sodium hydroxide in the presence and in the absence of colloidal catalysts (Pt, Au, Pd).3In agreement with the results of Abe13, Duke and Haas' found that the experimental dependence of the peroxide decomposition rate on the total alkalinity at a constant total peroxide content is analogous to the dependence of the product c(H202) c(H0;) on the total alkalinity. They concluded that peroxide decomposition obeys the equation where a is the total peroxide content in the solution and c(H20,) and c(H0,) are the concentrations of undissociated peroxide and perhydroxyl ions, respectively. Peroxide da/dt = k c ( H 2 0 2 ) c(H0,) 2349

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The generation of gaseous singlet oxygen by gas‐liquid reaction of chlorine with alkaline solution of hydrogen peroxide in spray form was studied experimentally on the originally designed device with a fast separation of reacted liquid from gas. The singlet oxygen yield, residual chlorine, and water vapor content in gas were measured under different experimental conditions of the centrifugal spray singlet oxygen generator (CSSOG) using nitrogen as a dilution gas. A characteristic feature of the CSSOG is a high utilization of the chemicals and production of singlet oxygen at a very high total pressure even near the atmospheric pressure. This generator developed originally for driving a chemical oxygen‐iodine laser (COIL) could be employed also as an efficient singlet oxygen source in material science, chemical synthesis, and others.

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This paper is a contribution to the current discussion on the Einstein coefficient for spontaneous emission (A-coefficient) of singlet delta oxygen, O2(g), that is often used for an evaluation of O2(g) concentration in a chemical oxygen-iodine laser (COIL). The published values of the A-coefficient vary in a wide range, corresponding to a radiative lifetime of O2(g), , from ~53 to ~151 min. This could make an evaluation of COIL operation questionable. In this paper, the Einstein A-coefficient is estimated, based on the comparison of O2(g) concentrations determined by two independent methods: electron paramagnetic resonance and emission spectroscopy. Within the accuracy of the experimental techniques used, the value of the A-coefficient resulting from our investigation is (2.24±0.40) × 10-4 s-1, corresponding to of ~74 min. This result is more consistent with the value of 2.58 × 10-4 s-1 of Badger et al [1] than with the value of 1.47 × 10-4 s-1 reported recently by Mlynczak and Nesbitt [2], who raised doubt about the Badger et al value.

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The rate of formation of hydrogen peroxide by cathodic reduction of oxygen in porous electrodes made of natural graphite, electrographite, carbon black and active carbon has been studied, as well as the catalytic effect of these materials on spontaneous decomposition of alkaline solutions of hydrogen peroxide. The measured data revealed that the greatest current yields of hydrogen peroxide were attained with electrodes made of low-surface kinds of carbon black which simultaneously had the lowest catalytic effect on the spontaneous decomposition of hydrogen peroxide.Cathodic reduction of oxygen can proceed, according to the character of electrode material and the reaction conditions, either in two consecutive two-electron steps which can be, e.g. for alkaline medium, expressed by equations 02 + H 2 0 + 2 e --;.. HO l + OH-; Ef98 = -0,076 V,HO l + H 2 0 + 2 e --;.. 3 OH -; Ef98 = + 0'878 V, (B) or as a direct four-electron reaction, described by the overall equation 02 + 2 H 2 0 + 4 e --;.. 40H-; Ef98 = + 0'401 V. (C)Two-electron reduction of oxygen according to reaction (A) proceeding under the formation of hydrogen peroxide as a relatively stable intermediate, takes place e.g. on mercury and on some carbonaceous materials 1 , 2. Direct four-electron reduction according to overall Eq. (C) is known to proceed, at least in part, on electrodes made of noble metals (Pt, Au, Rh)3 -6. The primarily . formed hydrogen peroxide, or the perhydroxyl anion, however, is not a thermodynamically stable product and therefore it can spontaneously decompose to form again gaseous oxygen and water or hydroxyl ions according to the overall equation (again written for alkaline medium) 2 HOi' --;.. 20H-+ °2 ; Ll.Cf98 = -184'09 kJ . (D) This, from the point of view of hydrogen peroxide preparation, unwanted decomposition reaction is considerably catalyzed by various both homogeneous and heterogeneous catalysts, present in the reaction system.