Oxygen, atmosphere, aqueous phase

Gooch (1997, 2002) emulsified fatty acids and oils and autoxidized them under greater than atmospheric pressure of oxygen or air to produce a network polymer or gel that did not flow after applying the emulsion to a surface and allowing the aqueous phase to evaporate. By this method, the viscosity and crosslink density was adjusted to control rheological properties, including viscosity and flow-out. 

The following route is described in US Patent 4,145,552 At ambient temperature, over a period of thirty minutes, a solution of 33.8g (O.lmol) of (-)-vincadiformine in a mixture of 140 ml of anhydrous dimethylformamide and 140 ml of anhydrous toluene is added to a suspension of 2.64 g (0.11 mol) of sodium hydride in a mixture of 200 ml of anhydrous tetrahydrofuran, 20 ml of anhydrous hexamethylphosphotriamide (EMPT) and 18.7 ml (0.14 mol) of trimethyl phosphite. When the release of hydrogen has finished (about two hours later), the solution is cooled to -10°C and then stirred under an oxygen atmosphere until absorption ceases (duration 3 hours). Still at -10°C, 136 ml of glacial acetic acid are added, and the mixture is then left at ambient temperature for two hours. After the addition of 500 ml of 1 N sulfuric acid, the aqueous phase is isolated, reextracted with 150 ml of isopropyl ether, made alkaline with 350 ml of 11 N ammonia, then extracted 3 times with 300 ml aliquots of methylene chloride. After drying over calcium... 

The causes of the anomalies of sulfate and other oxygen-bearing materials in the atmosphere and in extraterrestrial materials are the topic of active research. Aqueous-phase oxidation of S(IV) causes an MIF in sulfate only if the oxidant has an MIF oxygen isotopic composition (Lee et al., 2001). Hence, the anomalous values of... 

The discovery of the anomalous oxygen isotopic compositions of atmospheric sulfate provides a new means for identifying sulfate of atmospheric origin. Rainwater and aerosols from southern California were found to have A O values in the range of 0%o to -K.5%o (Lee et al., 2001). The average A O of snow sulfate in the Rocky Mountains (Colorado, USA) was - -1.3%o. Sulfate in ice cores, massive sulfate deposits, and Dry Valley soils from various locations also have MIF (Bao et al., 2000 Lee et al., 2001). There appears to be seasonality in the A O of sulfate in precipitation, with higher values in the winter and lower values in the summer, probably due to seasonal changes in climatic elfects that favor aqueous phase S(IV) oxidation in winter relative to summer (Lee and Thiemens, 2001). 

Other evidence for low Archean atmospheric oxygen concentrations come from studies of mass-independent sulfur isotope fractionation. Photochemical oxidation of volcanic sulfur species, in contrast with aqueous-phase oxidation and dissolution that characterizes the modem sulfur cycle, may have been the major source of sulfate to seawater in the Archean (Farquhar et al., 2002 Farquhar et al., 2000). Distinct shifts in and in sulfide and sulfate from... 

Removes soluble impurities from substrates, washing Dissolves oxygen and other atmospheric gases (Henry s Law) Serves as media for homogeneous aqueous phase reactions Serves as liquid media for heterogeneous reactions and equilibria Serves as continuous phase for dispersions and emulsions Hydrates dyestuffs in solution, as well as dye sites in fibers... 

Because of the ready access of atmospheric oxygen to a metal surface exposed to a thin liquid layer, the most common cathode reaction (see Chapter 1, Volume 4) for metals exposed to a thin aqueous phase is the oxygen-reduction process (see Chapter 1, Volume 4) ... 

In all, the question of which process is rate limiting in atmospheric corrosion depends on many factors, including metal ion and cation transport properties through the corrosion products, and the access of oxygen through the aqueous phase. 

In a cyclic voltammogram recorded with a glassy carbon disk electrode modified by the crosslinked Co-PEI complex film, the uncatalyzed reduction of oxygen was observed at potentials lower than -0.3 V. As such, a significant increase in the current magnitude was noted for the electrode surface modified with the thin Co-PEI membrane under an air atmosphere due to the oxygen enrichment from the aqueous phase. 

For natural waters and hydrometeors, reaction (5.81) is the key formation process of hydrated electrons. However, little is known about the rate of formation of superoxides in natural aqueous solution. It is clear that different photosensitizers (and mixtures of them) provide a large variety of photocatalytic oxygen activation. The formation of hydrated electrons can explain many processes such as autoxidation and corrosion. This looks at first confusing because Q q works as a reducing species but the key oxidizing species in solution is the OH radical (a strong electron acceptor similar to the atmospheric gas phase), which is produced in a chain of electron transfer processes ... 

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