Some of those effects include sea level rise, ocean warming, acidification, and deoxygenation.
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According to our model, we will witness widespread deoxygenation by 2030 or 2040.
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By the 2040s, Long's models predict that evidence for ocean deoxygenation will be widespread.
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They hope to eventually understand the effects of ocean warming and deoxygenation on these deep-sea communities.
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Unfortunately for them, the seas are now gradually losing oxygen, a problematic marine event known as deoxygenation.
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The decline, called deoxygenation, is largely attributed to climate change, although other human activities are contributing to the problem.
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There have been naturally occurring hypoxic events along the Oregon coast, for example; this area is very susceptible to deoxygenation.
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But for many organisms including humans, a little deoxygenation is the difference between enjoying life and being dizzy, lethargic, or dead.
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Since ocean deoxygenation is intrinsically linked to climate warming, substantial action to mitigate climate change will be required to reverse the trend of oxygen loss.
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Map showing when the signal for deoxygenation due to global warming becomes visible in the ocean, with blues indicating areas where a signal is already being seen.
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"The fact that ocean deoxygenation is occurring and will continue to occur, likely at an accelerated rate, is a near-certainty if human-driven warming continues," Long said.
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Carbon accumulation, ocean acidification and deoxygenation, pollution, reef decline, melting ice caps, sea level rise, and violent storms are all related and feeding off each other, and whatever actual change arises from this conference will owe to its intersectionality.
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"We are an ocean world, run and regulated by a single ocean, and we are pushing that life support system to its very limits through heating, deoxygenation and acidification," said Dan Laffoley of the International Union for Conservation of Nature, a leading environmental group that tracks the status of plant and animal species, in response to the report.
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Phosphoric acids ((RO)2PO2H) catalyze the deoxygenation of phosphine oxides by hydrosilanes.
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The Barton–McCombie deoxygenation is an organic reaction in which a hydroxy functional group in an organic compound is replaced by a hydrogen to give an alkyl group. It is named after British chemists Sir Derek Harold Richard Barton (1918–1998) and Stuart W. McCombie. The Barton-McCombie deoxygenation This deoxygenation reaction is a radical substitution. In the related Barton decarboxylation the reactant is a carboxylic acid.
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The deoxygenation of phosphine oxides has been extensively developed because many useful stoichiometric reactions convert tertiary phosphines to the corresponding oxides. Regeneration of the tertiary phosphine requires cheap oxophilic reagents, which are usually silicon-based. These deoxygenation reactions can be subdivided into stoichiometric and catalytic processes.
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Deoxyribose is generated from ribose 5-phosphate by enzymes called ribonucleotide reductases. These enzymes catalyse the deoxygenation process.
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Ocean deoxygenation is an additional stressor on marine life. Ocean deoxygenation is the expansion of oxygen minimum zones in the oceans as a consequence of burning fossil fuels. The change has been fairly rapid and poses a threat to fish and other types of marine life, as well as to people who depend on marine life for nutrition or livelihood.Oceans suffocating as huge dead zones quadruple since 1950, scientists warn The Guardian, 2018Ocean's Oxygen Starts Running LowFinding forced trends in oceanic oxygenHow global warming is causing ocean oxygen levels to fall Ocean deoxygenation poses implications for ocean productivity, nutrient cycling, carbon cycling, and marine habitats.Laffoley, D. and Baxter, J. M. (eds.) (2019) Ocean deoxygenation : everyone’s problem, IUCN Report.
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Ocean warming exacerbates ocean deoxygenation and further stresses marine organisms, limiting nutrient availability by increasing ocean stratification through density and solubility effects while at the same time increasing metabolic demand.Bednaršek, N., Harvey, C.J., Kaplan, I.C., Feely, R.A. and Možina, J. (2016) "Pteropods on the edge: Cumulative effects of ocean acidification, warming, and deoxygenation". Progress in Oceanography, 145: 1–24.
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Taxusin is a taxane isolate derived from Taxus wallichiana. Taxusin can be used to synthesize taxadiene -diol and -triol derivatives via deoxygenation.
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The reagent is ideal for reductive aminations ("Borch Reaction"). In conjunction with tosylhydrazine, sodium cyanoborohydride is used in the reductive deoxygenation of ketones.
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Threats to the species include sedimentation, pollution, and deoxygenation of its native lakes caused by slash-and-burn agriculture and nearby oil plantations.
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2,3-BPG, the most concentrated organophosphate in the erythrocyte, forms 3-PG by the action of bisphosphoglycerate phosphatase. The concentration of 2,3-BPG varies proportionately to the [H+]. There is a delicate balance between the need to generate ATP to support energy requirements for cell metabolism and the need to maintain appropriate oxygenation/deoxygenation status of hemoglobin. This balance is maintained by isomerisation of 1,3-BPG to 2,3-BPG, which enhances the deoxygenation of hemoglobin.
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Ocean deoxygenation is projected to increase hypoxia by 10%, and triple suboxic waters (oxygen concentrations 98% less than the mean surface concentrations), for each 1 °C of upper ocean warming.
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The reaction is even effective for the synthesis of sensitive amines such as aziridines: :Removal of a tosyl group from an N-tosylamide using SmI2 In the Markó-Lam deoxygenation, an alcohol could be almost instantaneously deoxygenated by reducing their toluate ester in presence of SmI2. : Markó-Lam deoxygenation using SmI2 The applications of SmI2 have been reviewed. The book Organic Synthesis Using Samarium Diiodide, published in 2009, gives a detailed overview of reactions mediated by SmI2.
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Its biosynthesis from mannose-1-phosphate follows a pathway similar to that of colitose, but is different in that it is aminated and does not undergo 3-OH deoxygenation or C-5 epimerization.
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For example, an ethyl group is an alkyl group; when this is attached to a hydroxy group, it gives ethanol, which is not an alkane. To do so, the best-known methods are hydrogenation of alkenes: :RCH=CH2 \+ H2 → RCH2CH3(R = alkyl) Alkanes or alkyl groups can also be prepared directly from alkyl halides in the Corey–House–Posner–Whitesides reaction. The Barton–McCombie deoxygenation removes hydroxyl groups from alcohols e.g. :Barton–McCombie deoxygenation scheme and the Clemmensen reductionMartin, E. L. Org. React.
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An even more convenient hydrogen donor is provided by trialkylborane-water complexes Deoxygenation of Alcohols Employing Water as the Hydrogen Atom Source David A. Spiegel, Kenneth B. Wiberg, Laura N. Schacherer, Matthew R. Medeiros, and John L. Wood J. Am. Chem. Soc. 2005, 127, 12513-12515. () such as trimethylborane contaminated with small amounts of water. Barton-McCombie deoxygenation with trialkane borane and water In this catalytic cycle the reaction is initiated by air oxidation of the trialkylborane 3 by air to the methyl radical 4.
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Denise Breitburg is an American marine ecologist specializing in the effects of deoxygenation on marine systems and organisms such as oysters and jellyfish. She is Principal Investigator, and Senior Scientist, at the Smithsonian Environmental Research Center (SERC).
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Warming water temperatures mean low solubility of oxygen and increasing deoxygenation, while also increasing the oxygen demands of ectothermic organisms by driving their metabolic rates higher. This positive feedback loop compounds the effects of reduced oxygen concentrations.
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Although the land is releasing millions of tons of as a result of deforestation, thawing of permafrost, and other global warming-related phenomena, plants are growing faster and taking up more in response. This trend is not enough to counter rising levels in the atmosphere, but it is slowing their increase. Keeling is active in studying ocean warming, stratification of the upper ocean, and ocean deoxygenation. Ocean models predict declines in oxygen, and significant deoxygenation has been observed over the last fifty years in both North Pacific and tropical oceans.
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Since then, a number of researchers have also started working on the deoxygenation of lipid-based feeds to fuel-like hydrocarbons via decarboxylation/decarbonylation as an alternative to hydrodeoxygenation, the reaction most commonly employed to convert lipids to hydrocarbons.
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Deoxygenation increases the relative population of anaerobic organisms such as plants and some bacteria, resulting in fish kills and other adverse events. The net effect is to alter the balance of nature by increasing the concentration of anaerobic over aerobic species.
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A patient cannot breathe while under the influence of this drug. In small children, cardiac arrest is the ultimate result of deoxygenation due to lack of respiration. Jones claimed she was trying to stimulate the creation of a pediatric intensive care unit in Kerrville.
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Dicarbonylbis(cyclopentadienyl)titanium is the chemical compound with the formula (η5-C5H5)2Ti(CO)2, abbreviated Cp2Ti(CO)2. This maroon-coloured, air- sensitive species is soluble in aliphatic and aromatic solvents. It has been used for the deoxygenation of sulfoxides, reductive coupling of aromatic aldehydes and reduction of aldehydes.
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These feeds have the additional advantage of tending towards being highly saturated, which requires lower pressures of hydrogen for deoxygenation reactions. Both unsaturated and saturated feeds can processed by deCOx, however unsaturated feeds often present more problems. Indeed, unsaturated feeds tend to exacerbate catalyst deactivation and result in lower hydrocarbon yields.
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Catalytic recombination or deoxygenation is used to remove oxygen (O2) impurities. The process is also known as a 'deoxo' process. The oxygen reacts with the hydrogen to form water vapor, which can then be removed by a dryer if necessary. The catalysts that are used are based on platinum group metals (PGM).
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The imidazole groups on TCDI can be easily displaced, allowing it to act as a safer alternative to thiophosgene. This behaviour has been used in the Corey–Winter olefin synthesis. It may also replace carbonothioyl species (RC(S)Cl) in the Barton–McCombie deoxygenation. Other uses include the synthesis of thioamides and thiocarbamates.
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Thus, tosylation followed by reduction allows for the deoxygenation of alcohols. In a famous and illustrative use of tosylate, 2-norbornyl cation was displaced from the 7-norbornenyl tosylate. The elimination occurs 1011 faster than the solvolysis of anti-7-norbornyl p-toluenesulfonate. Structures of the 7-norbornenyl cation with p-orbital stabilization.
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Structure of a xanthate ester Xanthate salts characteristically decompose in acid: :ROCS2K + HCl → ROH + CS2 \+ KCl This reaction is the reverse of the method for the preparation of the xanthate salts. The intermediate in the decomposition is the xanthic acid, ROC(S)SH, which can be isolated in certain cases. Xanthate anions also undergo alkylation to give xanthate esters, which are generally stable: :ROCS2K + R′X → ROC(S)SR′ + KX The C-O bond in these compounds are susceptible to cleavage by the Barton–McCombie deoxygenation, which provides a means for deoxygenation of alcohols. They can be oxidized to the so-called dixanthogens: :2 ROCS2Na + Cl2 → ROC(S)S2C(S)OR + 2 NaCl Xanthates bind to transition metal cations as bidentate ligands.
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Where possible, the water intake is placed at sufficient depth to reduce the concentration of algae; however, filtering, deoxygenation and biociding is generally required. Aquifer water from water-bearing formations other than the oil reservoir, but in the same structure, has the advantage of purity where available. River water will always require filtration and biociding before injection.
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Simons collaborated in this effort, attempting to use phase modulation of the illuminating laser to more efficiently measure hemoglobin deoxygenation in body tissue.Weng, K, Zhang, MZ, Simons K, Chance, B. Measurement of biological tissue metabolism using phase modulation spectroscopic technology. Proceedings of the SPIE, Section on Time-resolved spectroscopy and imaging of tissues, Vol. 1431, 1991, p.
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Another modification of C-3' with cyclopropane and epoxide moieties were also found to be potent. Most of the analogues without ring A were found to be much less active than paclitaxel itself. The analogues with amide side chain at C-13 are less active than their ester counterpart. Also deoxygenation at position 1 showed reduced activity.
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The direction and magnitude of the effects of ocean acidification, warming and deoxygenation on the ocean has been quantified by meta-analyses,Gruber, Nicolas. "Warming up, turning sour, losing breath: ocean biogeochemistry under global change." Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 369.1943 (2011): 1980–1996.Anthony, et al.
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The carbonyl ylide can be generated upon reaction of the dihalocarbenes with ketones or aldehydes. However, the synthesis of α-halocarbonyl ylides can also undesirably lead to the loss of carbon monoxide and the generation of the deoxygenation product. Scheme 5. α-Halocarbonyl ylide synthesis through dihalocarbene intermediates. Modified from Padwa, A.; Hornbuckle, S. F. Chem Rev 1991, 91, 263.
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The process using solid second-generation biomass sources such as switchgrass or woody biomass uses pyrolysis to produce a bio- oil, which is then catalytically stabilized and deoxygenated to produce a jet- range fuel. The process using natural oils and fats goes through a deoxygenation process, followed by hydrocracking and isomerization to produce a renewable Synthetic Paraffinic Kerosene jet fuel.
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As the oxygen is present in crude oil at rather low levels, of the order of 0.5%, deoxygenation in petroleum refining is not of much concern, and no catalysts are specifically formulated for oxygenates hydrotreating. Hence, one of the critical technical challenges to make the hydrodeoxygenation of algae oil process economically feasible is related to the research and development of effective catalysts.
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A baby with a heart condition. Note purple nailbeds. Acute arterial thrombosis of the right leg Cyanosis is defined as a bluish discoloration, especially of the skin and mucous membranes, due to excessive concentration of deoxyhemoglobin in the blood caused by deoxygenation. Cyanosis is divided into two main types: central (around the core, lips, and tongue) and peripheral (only the extremities or fingers).
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Continental weathering and redox conditions during the early Toarcian Oceanic Anoxic Event in the northwestern Tethys: Insight from the Posidonia Shale section in the Swiss Jura Mountains. Palaeogeography, Palaeoclimatology, Palaeoecology, 429, 83-99. Or even changes of the behaviour of the fauna.Caswell, B. A., and A. L. Coe (2013), Primary productivity controls on opportunistic bivalves during Early Jurassic oceanic deoxygenation, Geology, 41, 1163–1166.
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An alternative method, also used as a backup to deoxygenation towers, is to add an oxygen scavenging agent such as sodium bisulfite and ammonium bisulphite. Another option is to use membrane contactors. Membrane contactors bring the water into contact with an inert gas stream, such as nitrogen, to strip out dissolved oxygen. Membrane contactors have the advantage of being lower weight and compact enabling smaller system designs.
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Biogasoline Production ProcessBiogasoline is created by turning sugar directly into gasoline. In late March 2010, the world’s first biogasoline demonstration plant was started in Madison, WI by Virent Energy Systems, Inc. Virent discovered and developed a technique called Aqueous Phase Reforming (APR) in 2001. APR includes many processes including reforming to generate hydrogen, dehydrogenation of alcohols/hydrogenation of carbonyls, deoxygenation reactions, hydrogenolysis and cyclization.
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Use of trichlorosilane is a standard laboratory method. Industrial routes use phosgene or equivalent reagents, which produce chlorotriphenylphosphonium chloride, which is separately reduced. For chiral phosphine oxides, deoxygenation can proceed with retention or inversion of configuration. Classically, inversion is favored by a combination of trichlorosilane and triethylamine, whereas in the absence of the Lewis base, the reaction proceeds with retention. :HSiCl3 \+ Et3N ⇋ SiCl3− \+ Et3NH+ :R3PO + Et3NH+ ⇋ R3POH+ \+ Et3N :SiCl3− \+ R3POH+ → PR3 \+ HOSiCl3 The popularity of this method is partly attributable to the availability of inexpensive trichlorosilane. Instead of HSiCl3, other perchloropolysilanes, e.g. hexachlorodisilane (Si2Cl6), can also be used. In comparison, using the reaction of the corresponding phosphine oxides with perchloropolysilanes such as Si2Cl6 or Si3Cl8 in benzene or chloroform, phosphines can be prepared in higher yields. :R3PO + Si2Cl6 → R3P + Si2OCl6 :2 R3PO + Si3Cl8 → 2 R3P + Si3O2Cl8 Deoxygenation has been effected with boranes and alanes.
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The Wolff–Kishner reduction was discovered independently by N. Kishner in 1911 and Ludwig Wolff in 1912. Kishner found that addition of pre-formed hydrazone to hot potassium hydroxide containing crushed platinized porous plate led to formation of the corresponding hydrocarbon. A review titled “Disability, Despotism, Deoxygenation—From Exile to Academy Member: Nikolai Matveevich Kizhner” describing the life and work of Kishner was published in 2013. Scheme 2.
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The algae numbers are unsustainable and eventually most of them die. The decomposition of the algae by bacteria uses up so much of the oxygen in the water that most or all of the animals die, which creates more organic matter for the bacteria to decompose. In addition to causing deoxygenation, some algal species produce toxins that contaminate drinking water supplies. Different treatment processes are required to remove nitrogen and phosphorus.
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In alternative fashion, the conversion may be performed directly using thionyl chloride.[1] Some simple conversions of alcohols to alkyl chlorides Alcohols may, likewise, be converted to alkyl bromides using hydrobromic acid or phosphorus tribromide, for example: : 3 R-OH + PBr → 3 RBr + HPO In the Barton-McCombie deoxygenation an alcohol is deoxygenated to an alkane with tributyltin hydride or a trimethylborane-water complex in a radical substitution reaction.
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Structure of pyridine N-oxide Oxidation of pyridine occurs at nitrogen to give pyridine-N-oxide. The oxidation can be achieved with peracids: :C5H5N + RCO3H -> C5H5NO + RCO2H Some electrophilic substitutions on the pyridine are usefully effected using pyridine-N-oxide followed by deoxygenation. Addition of oxygen suppresses further reactions at nitrogen atom and promotes substitution at the 2- and 4-carbons. The oxygen atom can then be removed, e.g.
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This reductive coupling can be viewed as involving two steps. First is the formation of a pinacolate (1,2-diolate) complex, a step which is equivalent to the pinacol coupling reaction. The second step is the deoxygenation of the pinacolate which yields the alkene, this second step exploits the oxophilicity of titanium. A proposed mechanism when TiCl4 and Zn(Cu) are used for the coupling of benzophenone, as proposed in a reference.
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Ocean deoxygenation poses implications for ocean productivity, nutrient cycling, carbon cycling, and marine habitats. Studies have shown that oceans have already lost 1-2% of their oxygen since the middle of the 20th century, and model simulations predict a decline of up to 7% in the global ocean O2 content over the next hundred years. The decline of oxygen is projected to continue for a thousand years or more.
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The most frequent cause of autosplenectomy is sickle cell anemia which causes progressive splenic hypofunction over time. Increased deoxygenation causes sickling of red blood cells, which adhere to the spleen wall and splenic macrophages causing ischemia. This ischemia can result in splenic sequestration, where large amounts of blood pool in the spleen but do not flow within vasculature. This lack of blood flow can cause atrophy in the spleen and can lead to autosplenectomy.
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The selectivity in the reaction is due to the stronger electron withdrawing power of the esters compared to the ethers. A stronger electron withdrawing substituent leads to a greater destabilization of the oxocarbenium ion. This slows this reaction pathway, and allows for disaccharide formation to occur with the benzylated sugar. Other effective electron withdrawing groups that have shown selectivity are halogens and azido groups, while deoxygenation has been proven an effective tool in “arming” sugars.
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Molybdenum(IV) bromide is prepared by treatment of molybdenum(V) chloride with hydrogen bromide: ::2 MoCl5 \+ 10 HBr → 2 MoBr4 \+ 10 HCl + Br2 The reaction proceeds via the unstable molybdenum(V) bromide, which releases bromine at room temperature. MoCl5 is a good Lewis acid toward non-oxidizable ligands. It forms an adduct with chloride to form [MoCl6]−. In organic synthesis, the compound finds occasional use in chlorinations, deoxygenation, and oxidative coupling reactions.
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In the context of ocean deoxygenation, species experience the impacts of low oxygen at different levels and rates of oxygen loss, as driven by their thresholds of oxygen tolerance. Generally, we can expect mobile species to move away from areas of lethally low oxygen, but they also experience non- lethal effects of exposure to low oxygen. Further examples are included in the body of this page. Bioavailability will continue to change in a changing climate.
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WCl6 is soluble in carbon disulfide, carbon tetrachloride, and phosphorus oxychloride. Methylation with trimethylaluminium affords hexamethyl tungsten: : WCl6 +3 Al2(CH3)6 → W(CH3)6 \+ 3 Al2(CH3)4Cl2 Treatment with butyl lithium affords a reagent that is useful for deoxygenation of epoxides. The chloride ligands in WCl6 can be replaced by many anionic ligands including: Br−, NCS−, and RO− (R = alkyl, aryl). Reduction of WCl6 gives, sequentially, tungsten(V) chloride and tungsten(IV) chloride.
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A simplified illustration of the nitrogen and phosphorus cycles in a wetland (modified from Kadlec and Knight (1996), “Treatment Wetlands”; images from IAN, University of Maryland). Eutrophication is an enrichment of water by nutrient that lead to structural changes to the aquatic ecosystem such as algae bloom, deoxygenation, reduction of fish species. The primary source that contributes to the eutrophication is considered as nitrogen and phosphorus. When these two elements exceed the capacity of the water body, eutrophication occurs.
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A hydroxyl group is first derivitised into a stable and very often crystalline toluate derivative. The aromatic ester is submitted to a monoelectronical reduction, by the use of SmI2/HMPA or by electrolysis, to yield the a radical-anion which decomposes into the corresponding carboxylate and into the radical of the alkyl fragment. The Marko-Lam deoxygenation This radical could be used for further chemical reactions or can abstract a hydrogen atom to form the deoxygenated product.
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The Trust is encouraged by the appearance of Azolla carpets on sections of the Canning River as this fern is known to reduce the amount of sunlight available to the algae as well as absorbing large amounts of phosphorus and other nutrients from the water. However, it is possible that Azolla carpets can cause deoxygenation and emit a strong sulfur smell. Canning River without the Azolla in February 2006. Same location covered in a carpet of Azolla March 2007.
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A fish’s behavior in response to ocean deoxygenation is based upon their tolerance to oxygen poor conditions. Species with low anoxic tolerance tend to undergo habitat compression in response to the expansion of OMZs. Low tolerance fish start to habitate near the surface of the water column and ventilate at the top layer of the water where it contains higher levels of dissolved oxygen, a behavior called aquatic surface respiration. Biological responses to habitat compression can be varied.
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Nosiheptide precursor peptide including 37 amino acid leader peptide and 13 amino acid structural peptide (shown). All moieties of the peptidyl backbone of nosiheptide were shown to originate exclusively from proteinogenic amino acids. The structural motifs include dehydroamino acids from the serine or threonine residues undergoing anti elimination of water, thiazoles from cysteine residues with cyclodehydration followed by deoxygenation, and the central hydroxypyridine produced by cyclization between two dehydroalanine acids with incorporation of an adjacent carbonyl group. Thiazole formation.
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The Permian Mass Extinction was thought to have been brought on by such ocean warming, stratification, deoxygenation, anoxia, and subsequent extinction of 96% of all marine species. Reduced vertical mixing and marine heatwaves have decimated seaweed ecosystems in many areas. Marine Permaculture mitigates this by restoring some vertical mixing and preserves these important ecosystems. By preserving and regenerating habitat offshore on a platform, Marine Permaculture employs natural processes to ensure conditions that regenerate an abundance of marine life.
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High respiration rates deplete the oxygen in the water column to concentrations of 2 mg/l or less forming the OMZ. OMZs are expanding, with increasing ocean deoxygenation. Under these oxygen-starved conditions, energy is diverted from higher trophic levels to microbial communities that have evolved to use other biogeochemical species instead of oxygen, these species include Nitrate, Nitrite, Sulphate etc. Several Bacteria and Archea have adapted to live in these environments by using these alternate chemical species and thrive.
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Biogasoline, or biopetrol (British English) is a gasoline produced from biomass such as algae. Like traditionally produced gasoline, it contains between 6 (hexane) and 12 (dodecane) carbon atoms per molecule and can be used in internal-combustion engines. Biogasoline is chemically different from biobutanol and bioethanol, as these are alcohols, not hydrocarbons. Companies such as Diversified Energy Corporation are developing approaches to take triglyceride inputs and through a process of deoxygenation and reforming (cracking, isomerizing, aromatizing, and producing cyclic molecules) producing biogasoline.
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The synthesis of hexacene has also been reported to yield a crystalline solid from a monoketone precursor, by solid state synthesis at 180 °C. The solid was reported stable in the dark for up to a month, stability attributed to its "herringbone" crystalline packing that prevented dimerization. In December 2016, the groups of Diego Peña and Francesca Moresco reported synthesis of hexacene in-situ, via deoxygenation of an air-stable precursor, and used scanning tunneling microscopy to produce orbital resonance images of a single hexacene molecule.
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Oxygen must be removed from the water because it promotes corrosion and growth of certain bacteria. Bacterial growth in the reservoir can produce toxic hydrogen sulfide, a source of serious production problems, and block the pores in the rock. A deoxygenation tower brings the injection water into contact with a dry gas stream (gas is always readily available in the oilfield). The filtered water drops into the de-oxygenation tower, splashing onto a series of trays, causing dissolved oxygen to be lost to the gas stream.
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The larger the differences in the properties between layers, the less mixing occurs between the layers. Stratification is increased when the temperature of the surface ocean or the amount of freshwater input into the ocean from rivers and ice melt increases, enhancing ocean deoxygenation by limiting supply. Another factor that can limit supply is the solubility of oxygen. As temperature and salinity increase, the solubility of oxygen decreases, meaning that less oxygen can be dissolved into water as it warms and becomes more salty.
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Coastal regions, such as the Baltic Sea, the northern Gulf of Mexico, and the Chesapeake Bay, as well as in large enclosed water bodies like Lake Erie, have been affected by deoxygenation due to eutrophication. Excess nutrients are input into these systems by rivers, ultimately from urban and agricultural runoff and exacerbated by deforestation. These nutrients lead to high productivity that produces organic material that sinks to the bottom and is respired. The respiration of that organic material uses up the oxygen and causes hypoxia or anoxia.
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The relationship between zooplankton and low oxygen zones is complex and varies by species and life stage. Some gelatinous zooplankton reduce their growth rates when exposed to hypoxia while others utilize this habitat to forage on high prey concentrations with their growth rates unaffected. The ability of some gelatinous zooplankton to tolerate hypoxia may be attributed to the ability to store oxygen in intragel regions. The movements of zooplankton as a result of ocean deoxygenation can affect fisheries, global nitrogen cycling, and trophic relationships.
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These anchovy runs into the Yacht Harbor occur regularly and the Santa Cruz takes steps to mitigate deoxygenation and mass die-off through mechanical aeration machines located at the end of several of the docks throughout the harbor. The 1970s saw Santa Cruz and the yacht club come to the forefront of the Ultra Light Displacement Boat (ULDB) movement that revolutionized yacht racing. In 1977 Bill Lee’s “Merlin” shattered the Trans Pacific Race record and Santa Cruz ULDBs of all sizes became the boats to beat. Merlin’s record stood for 20 years.
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VOCl3 arises by the chlorination of V2O5. The reaction proceeds near 600 °C: :3 Cl2 \+ V2O5 → 2 VOCl3 \+ 1.5 O2 Heating an intimate (well-blended with tiny particles) mixture of V2O5, chlorine, and carbon at 200–400 °C also gives VOCl3. In this case the carbon serves as a deoxygenation agent akin to its use in the chloride process for the manufacturing of TiCl4 from TiO2. Vanadium(III) oxide can also be used as a precursor: :3 Cl2 \+ V2O3 → 2 VOCl3 \+ 0.5 O2 A more typical laboratory synthesis involves the chlorination of V2O5 using SOCl2.
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In August 2013, a long period of hot dry weather followed by heavy rain washed polluted road run-off water into the Lower Lea, causing deoxygenation of the water. The role of the canalisation of the Bow Back Rivers in and around the Olympic Park, with its consequences for tidal flow have been implicated in the considerable levels of fish kill which resulted from the incident."Fish killed in the River Lea. Pushed to their limits by environmental mismanagement" (Martin Slavin, Gamesmonitor, July 2013) accessed 11 August 2013.
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Vacuum and gas manifolds often have many ports and lines, and with care, it is possible for several reactions or operations to be run simultaneously. When the reagents are highly susceptible to oxidation, traces of oxygen may pose a problem. Then, for the removal of oxygen below the ppm level, the inert gas needs to be purified by passing it through a deoxygenation catalyst.C. R. McIlwrick and C. S. Phillips The removal of oxygen from gas streams: applications in catalysis and gas chromatography, Journal of Physics E: Scientific Instruments, 1973, 6:12, 1208–10.
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This radical reacts with the xanthate 2 to S-methyl-S-methyl dithiocarbonate 7 and the radical intermediate 5. The (CH3)3B.H2O complex 3 provides a hydrogen for recombining with this radical to the alkane 6 leaving behind diethyl borinic acid and a new methyl radical. Barton-McCombie deoxygenation reaction mechanism It is found by theoretical calculations that an O-H homolysis reaction in the borane-water complex is endothermic with an energy similar to that of the homolysis reaction in tributylstannane but much lower than the homolysis reaction of pure water.
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Natural currents and weather were expected to eventually dilute and flush the molasses out of the harbor and a nearby lagoon. Divers in the harbor area reported that all sea life in the area was killed by the molasses, which instantly sank to the bottom of the harbor and caused widespread deoxygenation. Members of various coral species were injured or killed, and more than 26,000 fish and members of other marine species suffocated and died. The Hawaiian Commercial & Sugar Co. on Maui produces molasses from sugar cane, and ships it to the mainland to be processed and sold.
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Another approach of preparing carbenes has relied on the desulfurisation of thioureas with potassium in THF. A contributing factor to the success of this reaction is that the byproduct, potassium sulfide, is insoluble in the solvent. The elevated temperatures suggest that this method is not suitable for the preparation of unstable dimerising carbenes. A single example of the deoxygenation of a urea with a fluorene derived carbene to give the tetramethyldiaminocarbene and fluorenone has also been reported: Preparation of carbenes by dechalcogenation The desulfurisation of thioureas with molten potassium to give imidazol-2-ylidenes or diaminocarbenes has not been widely used.
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Though the use of hydrogen is not strictly necessary in these reactions, it does facilitate the production of higher yields of hydrocarbon products. However, with Ni-based catalysts there is a limit to this effect; if the partial pressure of hydrogen is too high, it will decrease the yield of desired products. The rate at which the reaction occurs is highly dependent upon the reaction conditions and the catalyst utilized. Though it is known that deoxygenation via deCOx generally proceeds at a higher rate with increased temperatures, alternate reactions may also occur which could lead to catalyst deactivation.
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Fennel's research focuses on the development and use of computational models to predict and understand marine ecosystems, particularly the causes and effects of changes in oxygen and carbon levels. Her publications have been cited thousands of times. Her work was part of a 2018 publication in Nature Climate Change that found a link between current flows and rapid deoxygenation of the Gulf of St. Lawrence, which the team attributed to broader changes in ocean flows as part of climate change. Fennel is co-editor-in-chief of Biogeosciences, an open access journal covering the earth sciences.
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Oxophilic reagents are often used to extract or exchange oxygen centers in organic substrates, especially carbonyls (esters, ketones, amides) and epoxides. The highly oxophilic reagent generated from tungsten hexachloride and butyl lithium is useful for the deoxygenation of epoxides. Such conversions are sometimes valuable in organic synthesis. In the McMurry reaction, ketones are converted into alkenes using oxophilic reagents: :2 R2CO + "Ti" → R2C=CR2 \+ TiO2 Similarly, Tebbe's reagent is used in olefination reactions: : Cp2TiCH2AlCl(CH3)2 \+ R2C=O → "Cp2TiO" + 0.5 (AlCl(CH3)2)2 \+ R2C=CH2 Oxophilic main group compounds are also well known and useful.
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Ph3PO is a byproduct of many useful reactions in organic synthesis including the Wittig, Staudinger, and Mitsunobu reactions. It is also formed when PPh3Cl2 is employed to convert alcohols into alkyl chlorides: :Ph3PCl2 \+ ROH -> Ph3PO + HCl + RCl Triphenylphosphine can be regenerated from the oxide by treatment with a variety of deoxygenation agents, such as phosgene or trichlorosilane/triethylamine: :Ph3PO + SiHCl3 -> PPh3 \+ 1/n (OSiCl2)n \+ HCl Triphenylphosphine oxide can be difficult to remove from reaction mixtures by means of chromatography. It is poorly soluble in hexane and cold diethyl ether. Trituration or chromatography of crude products with these solvents often leads to a good separation of triphenylphosphine oxide.
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Studies of successful decarboxylation over nickel and palladium based catalysts were first reported by Wilhelm Maier et al. in 1982. These authors achieved the deoxygenation of several carboxylic acids via decarboxylation under a hydrogen atmosphere – including the conversion of aliphatic acids (such as heptanoic and octanoic acids) to alkanes (namely hexane and heptane) – a reaction in which Pd catalysts afforded the best results (close to quantitative yields). This reaction can be written as: RCO2H → RH + CO2 In 2006, Dmitry Murzin produced a patent with Neste Oil to manufacture hydrocarbons in the diesel fuel range from renewable feedstock with decreased consumption of hydrogen using Group VIII metals.
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In organic chemistry, the Myers allene synthesis is a chemical reaction that converts a propargyl alcohol into an allene by way of an arenesulfonylhydrazine as a key intermediate. This name reaction is one of two discovered by Andrew Myers that are named after him; both this reaction and the Myers deoxygenation reaction involve the same type of intermediate. The reaction is a three-step process in which the alcohol first undergoes a Mitsunobu reaction with an arenesulfonylhydrazine in the presence of triphenylphosphine and diethyl azodicarboxylate. Unlike hydrazone-synthesis reactions, this reaction occurs on the same nitrogen of the hydrazine that has the arenesulfonyl substituent.
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In OMZs oxygen concentration drops to levels <10nM at the base of the oxycline and can remain anoxic for over 700m depth. This lack of oxygen can be reinforced or increased due to physical processes changing oxygen supply such as eddy-driven advection, sluggish ventilation, increases in ocean stratification, and increases in ocean temperature which reduces oxygen solubility. At a microscopic scale the processes causing ocean deoxygenation rely on microbial aerobic respiration. Aerobic respiration is a metabolic process that microorganisms like bacteria or archaea use to obtain energy by degrading organic matter, consuming oxygen, producing CO2 and obtaining energy in the form of ATP.
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In organic chemistry, the Myers deoxygenation reaction is an organic redox reaction that reduces an alcohol into an alkyl position by way of an arenesulfonylhydrazine as a key intermediate. This name reaction is one of two discovered by Andrew Myers that are named after him; both this reaction and the Myers allene synthesis reaction involve the same type of intermediate. :R–CH2OH + H2NNHAr -> R–CH2N(Ar)NH2 -> R–CH2N=NH -> R–CH3 \+ N2 The reaction is a three-step one-pot process in which the alcohol first undergoes a Mitsunobu reaction with ortho-nitrobenzenesulfonylhydrazine in the presence of triphenylphosphine and diethyl azodicarboxylate. Unlike hydrazone-synthesis reactions, this reaction occurs on the same nitrogen of the hydrazine that has the arenesulfonyl substituent.
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Ocean deoxygenation has led to suboxic, hypoxic, and anoxic conditions in both coastal waters and the open ocean. Since 1950, more than 500 sites in coastal waters have reported oxygen concentrations below 2 mg liter−1, which is generally accepted as the threshold of hypoxic conditions. Several areas of the open ocean have naturally low oxygen concentration due to biological oxygen consumption that cannot be supported by the rate of oxygen input to the area from physical transport, air-sea mixing, or photosynthesis. These areas are called oxygen minimum zones (OMZs), and there is a wide variety of open ocean systems that experience these naturally low oxygen conditions, such as upwelling zones, deep basins of enclosed seas, and the cores of some mode-water eddies.
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The rate and total content of oxygen loss varies by region, with the North Pacific emerging as a particular hotspot of deoxygenation due to the increased amount of time since its deep waters were last ventilated (see thermohaline circulation) and related high apparent oxygen utilization (AOU) (. Estimates of total oxygen loss in the global ocean range from 119 to 680 T mol decade−1 since the 1950s. These estimates represent 2% of the global ocean oxygen inventory. Modeling efforts show that global ocean oxygen loss rates will continue to accelerate up to 125 T mol year−1 by 2100 due to persistent warming, a reduction in ventilation of deeper waters, increased biological oxygen demand, and the associated expansion and shoaling of OMZs.
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Coral reefs are not the only framework organisms, organisms that build physical structures that form habitats for other sea creatures, affected by climate change: mangroves and seagrass are considered to be at moderate risk for lower levels of global warming according to a literature assessment in the Special Report on the Ocean and Cryosphere in a Changing Climate. Marine heatwaves have seen an increased frequency and have widespread impacts on life in the oceans, such as mass dying events. Harmful algae blooms have increased in response to warming waters, ocean deoxygenation and eutrophication. Between one-quarter and one- third of our fossil fuel emissions are consumed by the earth's oceans and are now 30 percent more acidic than they were in pre-industrial times.
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As atomic carbon is an electron-deficient species, it spontaneously autopolymerises in its pure form, or converts to an adduct upon treatment with a Lewis acid or base. Oxidation of atomic carbon gives carbon monoxide, whereas reduction gives λ2-methane. Non-metals, including oxygen, strongly attack atomic carbon, forming divalent carbon compounds: :2 [C] + → 2 CO Atomic carbon is highly reactive, most reactions are very exothermic. They are generally carried out in the gas phase at liquid nitrogen temperatures (77 K). Typical reactions with organic compounds include:Reactive Intermediate Chemistry, Robert A. Moss, Matthew S. Platz and Maitland Jones Jr., Wiley-Blackwell, (2004), :Insertion into a C-H bond in alkanes to form a carbene :Deoxygenation of carboxyl groups in ketones and aldehydhdes to form a carbene, 2-butanone forming 2-butanylidene.
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A variation of this reaction was used as one of the steps in the total synthesis of azadirachtin:Synthesis of Azadirachtin: A Long but Successful Journey Gemma E. Veitch, Edith Beckmann, Brenda J. Burke, Alistair Boyer, Sarah L. Maslen, and Steven V. Ley Angew. Chem. Int. Ed. 2007, :Azadirachtin reaction sequence In another variation the reagent is the imidazole 1,1'-thiocarbonyldiimidazole (TCDI), for example in the total synthesis of pallescensin B.The first total synthesis of (±)-pallescensin B Wen-Cheng Liu and Chun-Chen Liao Chem. Commun., 1999, 117–118 117 Article TCDI is especially good to primary alcohols because there is no resonance stabilization of the xanthate because the nitrogen lonepair is involved in the aromatic sextet. :Barton deoxygenation Wen-Cheng Liu 1999 The reaction also applies to S-alkylxanthates.
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Most recently, her studies have focused on the looming problem of the deoxygenation of the oceans as a result of global climate change. In addition to her studies of otoliths, early in her career, Limburg contributed to a now seminal study led by Robert Costanza that was one of the first to attempt to place a value on worldwide ecosystem services that still continues to be frequently invoked in discussions of conservation biology. In a later paper lead by Limburg, she and her coauthors argued that economic decisions need to be made in light of an understanding of ecosystem dynamics, including the potential for nonlinearity. Building upon the conceptual foundation of their earlier publications, in 2010 Limburg, Costanza, and Ida Kubiszewski edited the inaugural edition of the Annals of the New York Academy of Sciences Ecological Economics Reviews.
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Ocean deoxygenation is the reduction of the oxygen content of the oceans due to human activities as a consequence of anthropogenic emissions of carbon dioxide and eutrophication driven excess production. It is manifest in the increasing number of coastal and estuarine hypoxic areas, or dead zones, and the expansion of oxygen minimum zones in the world's oceans. The decrease in oxygen content of the oceans has been fairly rapid and poses a threat to all aerobic marine life, as well as to people who depend on marine life for nutrition or livelihood.Oceans suffocating as huge dead zones quadruple since 1950, scientists warn The Guardian, 2018Ocean's Oxygen Starts Running LowFinding forced trends in oceanic oxygenHow global warming is causing ocean oxygen levels to fall Oceanographers and others have discussed what phrase best describes the phenomenon to non-specialists.
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Researchers had previously claimed that either one or the other of the two factors was responsible for initiating crevice corrosion, but recently it has been shown that it is a combination of the two that causes active crevice corrosion. Both the potential drop and the change in composition of the crevice electrolyte are caused by deoxygenation of the crevice and a separation of electroactive areas, with net anodic reactions occurring within the crevice and net cathodic reactions occurring exterior to the crevice (on the bold surface). The ratio of the surface areas between the cathodic and anodic region is significant. Some of the phenomena occurring within the crevice may be somewhat reminiscent of galvanic corrosion: ;galvanic corrosion: two connected metals + single environment ;crevice corrosion: one metal part + two connected environments The mechanism of crevice corrosion can be (but is not always) similar to that of pitting corrosion.
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Starting point for the Woodward synthesis was the hydroquinone 1 that was converted to cis-bicycle 2 in a Diels-Alder reaction with butadiene. Conversion to the desired trans isomer 5 was accomplished by synthesis of the sodium enolate salt 4 (benzene, sodium hydride) followed by acidification. Reduction (lithium aluminum hydride) then gave diol 6, a dehydration (HCl/water) gave ketol 7, deoxygenation of its acetate by elemental zinc gave enone 8, formylation (ethyl formate) gave enol 9, Michael ethyl vinyl ketone addition (potassium t-butoxide/t-butanol) gave dione 11 which on reaction with KOH in dioxane gave tricycle 12 in an aldol condensation with elimination of the formyl group. In the next series of steps oxidation (osmium tetroxide) gave diol 13, protection (acetone/copper sulfate) gave acetonide 14, hydrogenation (palladium-strontium carbonate) gave 15, formylation (ethyl formate) gave enol 16 which protected as the enamine 17 (N-methylaniline/methanol) gave via the potassium anion 18, carboxylic acid 19 by reaction with cyanoethylene using triton B as the base. Cholesterol synthesis Woodward 1 Acid 19 was converted to lactone 20 (acetic anhydride, sodium acetate) and reaction with methylmagnesium chloride gave tetracyclic ketone 21. Treatment with periodic acid (dioxane) and piperidine acetate (benzene) gave aldehyde 24 through diol 22 (oxidation) and dialdehyde 23 (aldol condensation).
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