Oxygen traps

The endoperoxy hydroperoxide (36) results from the hydroperoxide (35) by sequential peroxy radical generation, (>-exo trig cyclisation and oxygen trapping <96SL349>. 

The decomposition, either thermal or under N2, of [0(AuPR3)3]0Tf (R = Ph, Me) in organic solvents has been studied the phosphine acts as an efficient oxygen trap and gold nanoparticles are produced.2727... 

Although no other examples have been reported, oxygen trapping of azo-derived triplet diradicals provides a potentially versatile strategy for the synthesis of bicyclic peroxides under neutral conditions. 

Use of mild conditions was crucial and the development of diimide reduction of singlet oxygenates, silver-salt-assisted displacement of halide by peroxide nucleophiles, peroxymercuration and demercuration, peroxide transfer from organotin to alkyl triflates, and oxygen trapping of azoalkane-derived diradicals have all played a part in providing the rich harvest of new bicyclic peroxides described herein. 

The carboxylic acid derivatives li-lm can only be matrix-isolated if the corresponding quinone diazides 2i-2m are irradiated with monochromatic blue light (k = 436 nm).81 91 92 UV or broad-band visible irradiation rapidly results in the decarboxylation of the carbenes. As expected, the IR and UV/vis spectra of the carbenes are very similar to that of la. Oxygen trapping results in the formation of the photolabile carbonyl oxides 7. Thus, the carbenes li-lm were identified both spectroscopically and by their characteristic reaction with molecular oxygen. 

The matrix photochemistry of 2n24 and 2o92 is completely analogous to that of 2a. The primary irreversible loss of nitrogen from 2 produces carbenes 1 in photostationary equilibria with cyclopropenes 3 (Scheme 15). The relative amounts of 1 and 3 formed in the matrix depends very much on the wavelength used for the irradiation. Both carbenes In and lo were chemically identified by oxygen trapping. UV irradiation (248 nm) of In produces a mixture of indeneketene 21, CO, and indenylidene 22 (Scheme 14). 

To evolve H2 for measurement of D/H burn 5 mg dry sawdust in 1 atm. 02 in a cupric oxide furnace at 750 °C. Use oxygen purified over silica gel and cupric oxide to ensure that the 02 is hydrogen free. Freeze out H20 and C02 in a liquid oxygen trap. Release C02 at dry ice temperature. React H20 vapor on clean uranium shavings at 950 °C, thus producing H2 quantitatively. 

Carotenoids are of physiological interest because some of them are precursors of vitamin A. They have been in the news recently because many exhibit radical or single oxygen trapping ability and as such have potential antioxidant activity in vivo. They may reduce the risk of cardiovascular disease, lung cancer, cervical... 

At low temperature, propene behaves like another alkene and undergoes a simple addition of a halogen across the double bond to form 1,2-dichlo-ropropane. These conditions minimize the possibility of forming chlorine atoms (chlorine free radicals), and the presence of oxygen traps the few that do form. However, when the conditions promote the formation of chlorine atoms, a substitution occurs to produce 3-chloropropene. 

Singlet oxygen reactions measured at [dye] = 3.0 x 10 4 using 2,5-dimethylfuran as the singlet oxygen trap solvent MeOH at 20°. 

Rose Bengal singlets are quenched by other electron acceptors, including several which are singlet oxygen traps. Davidson and Trethewey [261] have... 

These data suggest that oxygen is necessary for the solid-state photochemical reaction to occur. It was proposed that oxygen traps the metal radicals produced in the photolysis of the metal-metal bonds, thereby preventing radical recombination (eq. 25). If oxygen diffusion is rate limiting then... 

The direct conversion of alkenes 337 to secondary alcohols 341 was also achieved using an excess of sacrificial secondary alcohol, such as isopropanol, as the hydrogen source (entry 14) [392-394]. Although the mechanistic details are not completely understood, it is likely that the reaction follows a similar course involving hydrocobaltation/oxygen trapping and reduction (see below). In addition to products 341 and the corresponding ketones, which were formed in similar ratios as before, 2 equiv. of water were also detected. 

Air will oxidize the dithionite ion (which allows it to be used as an oxygen trap), and many metals are reduced to the zero oxidation state by the ion. 

Oxygen-free nitrogen (prepared by flushing commercial gas over hot, reduced copper mesh or by passage through an oxygen trap). 

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