Hydroxyl ions, decomposition

In solution, chlorine dioxide decomposes very slowly at ambient temperatures in the dark. The primary decomposition process is hydrolysis of chlorine dioxide into chlorite and chlorate ions. The hydrolysis rate is a function of the concentration of hydroxyl ions and temperature, proceeding rapidly at solution pH values above 10 ... 

Other methods exist for the precipitation of tantalum and niobium hydroxides for subsequent use as oxide precursors. Application of ammonium carbonate, (NH4)2C03, instead of ammonia solution, also seems to have potential for the precipitation of tantalum and niobium hydroxides. Ammonium carbonate is relatively stable in aqueous media at room temperature and does not initiate the precipitation of hydroxides. Increasing the temperature of the solution causes hydrolysis and decomposition of ammonium carbonate yielding hydroxyl ions and an increase in pH, as follows ... 

The active alkoxyl radicals formed by this reaction start new chains. Apparently, the hydroperoxide group penetrates in the polar layer of the micelle and reacts with the bromide anion. The formed hydroxyl ion remains in the aqueous phase, and the MePhCHO radical diffuses into the hydrocarbon phase and reacts with ethylbenzene. The inverse emulsion of CTAB accelerates the decay of hydroperoxide MePhCHOOH. The decomposition of hydroperoxide occurs with the rate constant k = 7.2 x 1011 exp(-91.0/R7) L mol-1 s-1 (T = 323-353 K, CTAB, ethylbenzene [28]). The decay of hydroperoxide occurs more rapidly in an 02 atmosphere, than in an N2 atmosphere. 

Ozone bleaching technology, 21 46 for recycled pulps, 21 51-52 Ozone contactors/dispersion devices, 17 801-802 Ozone decomposition in acidic solution, 17 773 hydroxyl ion initiated, 17 771—772 Ozone deficit problem, 17 785 Ozone delignification technology, 21 46 Ozone-depleting substances, in release agents, 21 598... 

There are certain reactions, e.g. inversions of sucrose and methane etc. in which the rate of reactions were found to be proportional to the concentration of H+ ions. Similarly, there are reactions which are catalyzed by OH ions, e.g. conversion of acetone into diacetone alcohol or decomposition of nitroso-triacetoneamine. These are known as specific hydrogen ion catalyzed or specific hydroxyl-ion catalyzed reactions. Also there are some reactions in which both H+ and OFF ions act as catalysts probably along with water. The undissociated acid or base have negligible effect on the rate of reaction. The hydrolysis of ester is an example in which both H+ and OH ions act as catalyst... 

Abstract In this chapter, the depression mechanism of five kinds of depressants is introduced respectively. The principle of depression by hydroxyl ion and hydrosulphide is explained which regulates the pH to make the given mineral float or not. And so the critical pH for certain minerals is determined. Thereafter, the depression by cyanide and hydrogen peroxide is narrated respectively which are that for cyanide the formation of metal cyanide complex results in depression of minerals while for hydrogen peroxide the decomposition of xanthate salts gives rise to the inhibitation of flotation. Lastly, the depression by the thio-organic such as polyhydroxyl and poly carboxylic xanthate is accounted for in detail including die flotation behavior, effect of pulp potential, adsorption mechanism and structure-property relation. 

Figure 3. Scheme of ozone decomposition mechanism in water. P = promoter (e.g. ozone, methanol), S = scavenger or inhibitor (e.g. /-butanol, carbonate ion), I = initiator (e.g. hydroxyl ion, perhydroxyl ion) (adapted by Beltran [35]). 

Astatohalobenzenes have also been prepared from the corresponding haloaniline isomers by decomposition of their diazoniiun salts under conditions similarly described for astatotoluenes vide supra). Here again, relatively low radiochemical yields (10-26%) were obtained. Again, this has been attributed to the competing reaction of hydroxyl ions present in the aqueous solution in a much higher concentration than At , leading to the by-product formation of phenols 99,100,105). 

Thus, antioxidant effects of nitrite in cured meats appear to be due to the formation of NO. Kanner et al. (1991) also demonstrated antioxidant effects of NO in systems where reactive hydroxyl radicals ( OH) are produced by the iron-catalyzed decomposition of hydrogen peroxide (Fenton reaction). Hydroxyl radical formation was measured as the rate of benzoate hydtoxylation to salicylic acid. Benzoate hydtoxylation catalyzed by cysteine-Fe +, ascorbate - EDTA-Fe, or Fe was significantly decreased by flushing of the reaction mixture with NO. They proposed that NO liganded to ferrous complexes reacted with H2O2 to form nitrous acid, hydroxyl ion, and ferric iron complexes, preventing generation of hydroxyl radicals. 

When pH increased from 2 to 7, the removal rate of fluorene increased however, a subsequent increase in pH from 7 to 12 reduced the removal efficiency back to about the rate at the pH of 2. The increase of pH leads to an increase in the hydroxyl-ion-catalyzed decomposition of ozone into hydroxyl radicals however, the amount of ozone available to undergo direct photolysis and produce hydrogen peroxide will decrease with increasing pH. Eventually more hydroxyl radicals will be produced, which is particularly important at pH 12 (Beltran et al., 1995). The rate of oxidation of fluorene is given by ... 

The reaction may be taken a step further using a mixture of acetylene and carbon monoxide. The products are particularly sensitive to reactant concentration, solvent, and available moisture, and can be visualized as the growth of an organic chain, bonded to a nickel atom, by the successive insertion of CO or acetylene molecules, which is interrupted at various points by the uptake of a proton or hydroxyl ion or by decomposition of the intermediate. This may be followed by rearrangement, or further reaction with molecules of solvent. 

On the other hand, the indirect type of ozonation is due to the reactions of free radical species, especially the hydroxyl radical, with the organic matter present in water. These free radicals come from reaction mechanisms of ozone decomposition in water that can be initiated by the hydroxyl ion or, to be more precise, by the hydroperoxide ion as shown in reactions (4) and (5). Ozone reacts very selectively through direct reactions with compounds with specific functional groups in their molecules. Examples are unsaturated and aromatic hydrocarbons with substituents such as hydroxyl, methyl, amine groups, etc. [45,46],... 

Pure barium peroxide hydrate Ba02-8H20 is precipitated when barium hydroxide is added to a hydrogen peroxide solution. Hydrogen peroxide is not a stable substance its solution decomposes slowly in any event into oxygen and water. This decomposition is greatly hastened by suspended solid matter and by hydroxyl ions in the following preparation one should work to minimize the amount of this decomposition. 

The McLafferty rearrangement in certain carboxylic acids initially forms the ion (CH2 = C(OH)2)t, which then undergoes metastable ion decomposition to lose a hydroxyl radical. With the labelled ions [CD2 = C(OH)(OD)]t and [CH2=C(OH)(OD)]t, the isotope effect 7oh/ od has been measured as 0.38 [526, 753], 0.56 [342] and 0.42 [407], i.e. OD- loss was more probable than OH - loss. This observation has been interpreted [407, 526] in terms of the rate-determining step... 

Decomposition voltage is usually calculated under the assumption of a catho-lyte with unit activity of hydroxyl ions (a0lI- — 1) and anolyte with unit activity of chloride ions (ra,-- = 1). Under these conditions the reversible decomposition voltage of an alkali chloride can be determined by the following equation ... 

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