Oxygen sinks

Numerous ways have been proposed to explain a net loss of molecular oxygen. Oxidation of volcanic gases, ferrous iron, sulfur, sulfide, and manganese, and the accretion of hydrogen from the solar wind are among these. Such processes are sometimes referred to as oxygen sinks. Estimates by Holland (1962) indicate that the net gam and net loss over geologic time are essentially in balance. 

Since hydrogen production by currently economic methods requires concurrent generation of C02 as the oxygen sink, the dilemma in the present utilization of C02 as a starting material for more reduced organic compounds such as petrochemicals seems complete. Stated simply, an oxygen sink is required in the formation of C—H bonds from C02, but at present that sink is ultimately C02 itself. 

Diels-Alder additions in water. It also catalyzes aldehyde olefination with N2C(C02Et)2 and PPhs as oxygen sink. Its catalyzed decomposition of N2C(C02Et)2 leads to carbene transfer reactions allowing for the formation of epoxides from aldehydes and ketones, aziridines from imines and cyclopropanation. 

In this example, a ketai is mixed with an excess of acidic water. Medium Acidic water, pATa -1.7. Sources The lone pairs on the oxygens. Sinks The acidic Hs of the acid. Leaving groups No decent ones. 

I consider carbon burial in the next section. In this section, I consider the mantle cycle. Mid-oceanic ridges act as oxygen sinks. Reaction with basalt consumes dissolved oxygen and sulfate. Organic carbon in sediments subducts into the mantle. Reduced volcanic gasses vent on land and beneath the ocean. I consider the loss of H2 to space in this section as it too moves a cmstal reactant out of sight. 

A fraction of 10% of the sulfate that originally entered the hydrothermal system from the ocean continues downward and reacts with ferrous iron to form sulfide and magnetite. Some of the sulfide precipitates in the rock and the rest vents at the seafloor. The vent fluid leaches additional sulfide from the rock and carries it into the ocean. The vented sulfides then react with dissolved oxygen in the water to form sulfate. The net effect is to replace one batch of sulfate ions in the water with another that came from the rock and to transfer oxygen into oceanic cmst. The oxygen sinks from oceanic cmst being reduced... 

I am now ready to discuss the ancient Earth. At a time when the ocean was anoxic and constrained little sulfate, the oceanic crust was not a significant oxygen sink. There was little sulfate in the circulating seawater to react with the basalt and no oxygen to oxidize vented sulfides. 

EvenmaUy the deep ocean became oxic. The vented sulfide then got reduced. This process at first formed a stabilizing buffer that kept oxygen concentration in seawater down. Once the oxygen concentration reached the level that all of the sulfide was oxidized, the buffer was overwhelmed and the oxygen sink was independent of its concentration. This simation prevails today. 

Excess carbon is used as an oxygen sink to form gaseous CO and reduce the amount of oxygen on the powder surface. However, any C remaining after the reaction has to be burnt out in an oxidizing atmosphere, and this may cause some reoxidation of the Si3N4 surfaces. 

A number of steady-state methods involving oxygen absorption with an oxygen sink dissolved in the liquid have been proposed. Among the oxygen sinks, sodium sulfite was used widely in older work but is very sensitive to conditions and catalysis (usually, copper or cobalt) and renders the solution noncoalescing. Active yeast has also been used as an oxygen sink (Hickman and Nienow, 1986) for work with fermenters. 

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