Solutions, transition metal peroxide

Solid state O NMR spectroscopy, 185 Solutions, transition metal peroxide characterization, 1068-72 Solvated electron addition, thymine hydroperoxide formation, 926-7 Solvents... 

Deprotonation of H2O2 yields OOH , and hydroperoxides of the alkali metals are known in solution. Liquid ammonia can also effect deprotonation and NH4OOH is a white solid, mp 25° infrared spectroscopy shows the presence of NH4+ and OOH ions in the solid phase but the melt appears to contain only the H-bonded species NH3 and H202. " Double deprotonation yields the peroxide ion 02 , and this is a standard route to transition metal peroxides. 

The second part of the chapter will be dedicated to the reactivity of transition metal peroxides, either isolated or formed in solution in catalytic processes, toward several classes of substrates. Hopefully this survey, where particular emphasis is placed on the selectivity aspects of these reactions, will present to the readers the potential of metal catalyzed oxidations with peroxides and highlight the perspective for researchers in the field. 

Ketone Peroxides. These materials are mixtures of compounds with hydroperoxy groups and are composed primarily of the two stmctures shown in Table 2. Ketone peroxides are marketed as solutions in inert solvents such as dimethyl phthalate. They are primarily employed in room-temperature-initiated curing of unsaturated polyester resin compositions (usually containing styrene monomer) using transition-metal promoters such as cobalt naphthenate. Ketone peroxides contain the hydroperoxy (—OOH) group and thus are susceptible to the same ha2ards as hydroperoxides. 

Peroxohydrates are usually made by simple crystallization from solutions of salts or other compounds in aqueous hydrogen peroxide. They are fairly stable under ambient conditions, but traces of transition metals catalyze the Hberation of oxygen from the hydrogen peroxide. Early work on peroxohydrates has been reviewed (92). 

Alkyl hydroperoxides are among the most thermally stable organic peroxides. However, hydroperoxides are sensitive to chain decomposition reactions initiated by radicals and/or transition-metal ions. Such decompositions, if not controlled, can be auto accelerating and sometimes can lead to violent decompositions when neat hydroperoxides or concentrated solutions of hydroperoxides are involved. 

Zirconium carbide is inert to most reagents but is dissolved by hydrofluoric acid solutions which also contain nitrate or peroxide ions, and by hot concentrated sulfuric acid. Zirconium carbide reacts exothermically with halogens above 250°C to form zirconium tetrahaHdes, and with oxidizers to zirconium dioxide in ak above 700°C. Zirconium carbide forms soHd solutions with other transition-metal carbides and most of the transition-metal... 

However, under anhydrous conditions and in the absence of catalytic impurities such as transition metal ions, solutions can be stored for several days with only a few per cent decomposition. Some reductions occur without bond cleavage as in the formation of alkali metal superoxides and peroxide (p. 84). 

The thermodynamic functions (AH, AS, AG(298 K)) of hydrogen peroxide reactions with transition metal ions in aqueous solutions are presented in Table 10.1. We see that AG(298K) has negative values for reactions of hydroxyl radical generation with Cu1+, Cr2+, and Fe2+ ions and for reactions of hydroperoxyl radical generation with Ce4+, Co3+, and Mn3+. 

Enthalpies, Entropies, and Gibb s Energies of Transition Metal Ion Oxidation-Reduction Reactions with Hydrogen Peroxide in Aqueous Solution (T = 298 K) [23]... 

The values of the rate constants for the reactions of transition metal ions with hydrogen peroxide in an aqueous solution are presented in Table 10.2. 

Rate Constants of Transition Metal Ion Reactions with Hydrogen Peroxide in Aqueous Solutions... 

The first is an alkaline solution of hydrogen peroxide, which oxidizes organic matter. The second is an acid fluoride solution which removes silica. The third is an acid solution of hydrogen peroxide which removes transition metals. The process was developed by RCA Corporation in 1970 and widely used thereafter by the electronics industry. 

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