Oxygen with hydrocarbons

It is estimated that photosynthesis is a sink for around 60 billion tons of carbon every year, by far the strongest mechanism for carbon dioxide removal from the atmosphere. (This removal is almost exactly balanced by the respiration of animals, which combines oxygen with hydrocarbons to produce carbon dioxide and water vapor.)... 

Chemical radicals—such as hydroxyl, peroxyhydroxyl, and various alkyl and aryl species—have either been observed in laboratory studies or have been postulated as photochemical reaction intermediates. Atmospheric photochemical reactions also result in the formation of finely divided suspended particles (secondary aerosols), which create atmospheric haze. Their chemical content is enriched with sulfates (from sulfur dioxide), nitrates (from nitrogen dioxide, nitric oxide, and peroxyacylnitrates), ammonium (from ammonia), chloride (from sea salt), water, and oxygenated, sulfiirated, and nitrated organic compounds (from chemical combination of ozone and oxygen with hydrocarbon, sulfur oxide, and nitrogen oxide fragments). ... 

The formation of such multiply coordinated surface intermediates would be expected to be enhanced by adsorption of multi-functional reagents, e.g., oxygenates with hydrocarbon chains more reactive than saturated alkyl ligands. To test this hypothesis, we have also examined the adsorption and reaction of allyl alcohol (CH2=CH-CH20H) and acrolein (CH2=CH-CHO) on the Rh(lll) surface. While these molecules do exhibit evidence for interaction with the surface via both their oxygen and vinyl functions, and while they appear to preserve the divergence of decarbonylation pathways observed for their aliphatic counterparts, their reactivity patterns add yet another layer of complexity to the puzzle of oxygenate decarbonylation. 

Thus, mechanistic studies of autoxidations in heterogeneous systems suffer from ambiguities similar to their homogeneous counterparts. There is no unequivocal evidence for the direct reaction of chemisorbed oxygen with hydrocarbon substrates under mild conditions. Catalysis of autoxidations proceeding by reaction with intermediate hydroperoxides is a more likely explanation. 

Hydrocarbon polymers are particularly susceptible to attack by atomic oxygen in LEO. The reactions of atomic oxygen with hydrocarbon molecules in the gas phase serve as models for the relatively unstudied reactions of atomic oxygen with a hydrocarbon surface. A wealth of knowledge of gas-phase reactions is available, largely because these reactions are important in combustion and in atmospheric chemistry. Studies of both reaction kinetics and dynamics have revealed many of the mechanisms by which atomic oxygen reacts with gaseous alkanes and alkenes. A summary of probable reaction pathways is presented in Fig. 4. 

Nowhere is cooperativity between sites on a catalyst more necessary than in catalytic oxidation. No diatomic molecule is as diverse in its reactions or as difficult to control as dioxygen — yet as productive of important products. Molecular design of multifunctional surfaces provides an opportunity to create an environment for control of the reactions of molecular oxygen with hydrocarbons. 

Fire refining, the final smelting operation, removes further impurities and adjusts the oxygen level ia the copper by air oxidation followed by reduction with hydrocarbons, ammonia, or reformed gas (CO + H2). 

In contrast to other cryogenic fluids, liquid oxygen is slightly magnetic. It is also chemically reactive, particularly with hydrocarbon materials. Oxygen thus presents a safety problem and requires extra precautions in handling. 

The need for highly cost-efficient oxygen transfer in fermentations such as those with hydrocarbon feedstocks has led to air-hft fermenters as shown in Fig. 24-4. The worlds largest industrial fermenter was... 

Because of the importance of hydroperoxy radicals in autoxidation processes, their reactions with hydrocarbons arc well known. However, reactions with monomers have not been widely studied. Absolute rate constants for addition to common monomers are in the range 0.09-3 M"1 s"1 at 40 °C. These are substantially lower than kL for other oxygen-centered radicals (Table 3.7). 454... 

New dimensions were found in silicon chemistry with the possibility of replacing some or all oxygen atoms with other atoms or groups. Partial replacement with hydrocarbon groups in the middle of this century led to the important silicones. 

It is well known that strong electrophiles such as carbocations are reduced by organosilicon hydrides (Eq. 1).3,70,71 On the other hand, simple mixtures of organosilicon hydrides and compounds with weakly electrophilic carbon centers such as ketones and aldehydes are normally unreactive unless the electrophilicity of the carbon center is enhanced by complexation of the carbonyl oxygen with Brpnsted acids3,70 73 or certain Lewis acids (Eq. 2).1,70,71,74,75 Using these acids, hydride transfer from the silicon center to carbon may then occur to give either alcohol-related or hydrocarbon products. 

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