Atmospheric Pressure Of Carbon Dioxide Research Articles

Electrochemical carboxylation of bicyclo[ n.1.0]alkylidene derivatives

Electrochemical carboxylation of bicyclo[ n.1.0]alkylidene derivatives (ring-fused alkylidenecyclopropanes) in a suitable aprotic solvent using a one-compartment electrochemical cell equipped with a platinum plate cathode and a zinc plate anode under an atmospheric pressure of carbon dioxide afforded either mono- or dicarboxylic acid in moderate to good yields.

Response of Early Cretaceous carbonate platforms to changes in atmospheric carbon dioxide levels

During the Late Barremian and Early Aptian (about 120 million years ago) intense volcanic degassing and extremely rapid release of methane hydrates contained in marine sediments added high amounts of carbon to the ocean and atmosphere, and resulted most probably in rising atmospheric carbon dioxide pressure. In order to document the response of the shallow water carbonate-producing communities to this pronounced disturbance of the carbon cycle we studied a Late Barremian to Early Aptian neritic carbonate succession deposited on the northern Tethyan shelf (Swiss Alps). The sedimentological and stable carbon and oxygen isotope records of two sections located along a N–S transect from proximal to more distal shelf environments were investigated. The sediments correspond to outer-, mid-, and inner-ramp deposits of a homoclinal carbonate ramp. Vertical facies variations within the two studied sections feature three progradation phases of the platform. A highly resolved correlation of the shelf sediments with a pelagic succession from the Southern Alps (Northern Italy) is based on both δ 13C stratigraphy and biostratigraphy, and indicates that the drowning of the Helvetic carbonate platform coincided with a pronounced calcification crisis of calcareous nannofossils. The biocalcification crisis started before but culminated during the Aptian methane event recorded in a negative carbon-isotope spike. We propose that increased carbon dioxide concentrations in oceans and atmosphere related to volcanic activity and to sudden methane release reduced the marine calcium carbonate oversaturation and the calcification potential of benthic and planktonic organisms. Carbonate-producing shallow water communities on platforms and ramps suffering from additional environmental stress such as extreme temperatures or high nutrient levels could not survive during times of rising sea level, and, as a consequence, carbonate platforms drowned.

Cyclic Carbonate Formation from Carbon Dioxide and Oxiranes in Tetrabutylammonium Halides as Solvents and Catalysts.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Comparison of water column [CO2aq] with sedimentary alkenone‐based estimates: A test of the alkenone‐CO2proxy

The stable carbon isotopic compositions of alkenones have been used to interpret the long‐term history of the partial pressure of atmospheric carbon dioxide (pCO2). Although extensive water column and culture studies document the potential utility and limitations of this approach, to date the accuracy ofpCO2values derived from sedimentary alkenones remains untested. For this study we establish Holocene‐aged, alkenone‐based CO2aqestimates ([CO2aq]alk) from 20 sites along a central Pacific Ocean transect and compare them against both observed modern water column CO2aqand estimated preindustrial concentrations at the depth of alkenone production at each site. Although the [CO2aq]alktrack measured water column values, they are conspicuously lower than modern values across the subtropics. This offset likely reflects the contributions of anthropogenic CO2in modern surface waters relative to preindustrial concentrations at the time of alkenone production. When a model‐based estimate of anthropogenic CO2is removed from the modern observed values, a majority (84%) of [CO2aq]alkfalls within 20% of modeled preindustrial values. Consistency between the modeled and alkenone‐based estimates of preindustrial CO2levels points to the relative accuracy of the alkenone‐CO2method across a wide range of ocean and biogeographic regimes, provided that phosphate concentrations, at the depth of haptophyte production, are reasonably constrained. It further suggests that light‐limited growth and/or active carbon uptake, if they occur, have a negligible effect on reconstructed [CO2aq].

Cyclic carbonate formation from carbon dioxide and oxiranes in tetrabutylammonium halides as solvents and catalysts.

[reaction: see text] Epoxides dissolved in molten tetralkylammonium salts bearing halides as counterions are converted into cyclic carbonates under atmospheric pressure of carbon dioxide. The reaction rate depends on the nucleophilicity of the halide ion as well as the structure of the cation.

Facile Synthesis of α-Hydroxy-α-Methyl Carboxylic Acids by Electrochemical Carboxylation of Methyl Aryl Ketones

Electrochemical carboxylation of methyl aryl ketones in the presence of atmospheric pressure of carbon dioxide using platinum cathode and dissolved magnesium anode at constant current density of 10 mA/cm2 gave the corresponding α-hydroxy-α-methyl carboxylic acids in 79-84% isolated yields. The precursor of cicloprofen, α-hydroxy-α-methylfluorene-2-acetic acid (1a) and biprofen, α-hydroxy-α-methybiphenyl-4-acetic acid (2a) were readily obtained in good yield by a similar electrochemical carboxylation of 2-acetylfluorene (1) and 4-acetylbiphenyl (2). Cyclic voltammetric studies showed that the reaction is reversible indicating the preferential generation of stable anion radicals from methyl aryl ketones and that further addition of carbon dioxide does not take place in these electrochemical carboxylations.

Efficient Electrochemical Dicarboxylation of Phenyl-substituted Alkenes: Synthesis of 1-Phenylalkane-1,2-dicarboxylic Acids

Electrochemical dicarboxylation of phenyl-substituted alkenes in the presence of atmospheric pressure of carbon dioxide with a platinum plate cathode and a magnesium rod anode readily took place efficiently in a DMF solution containing 0.1 M Et4NClO4 to give the corresponding 1,2-dicarboxylic acids in high yields.

Synthesis of 2-arylpropionic acids by electrocarboxylation of benzylchlorides catalysed by PdCl 2(PPh 3) 2

Electrochemical carboxylation of benzylchlorides catalysed by Pd(II) complex afforded 2-arylpropionic acids in good yields under atmospheric pressure of carbon dioxide at constant current of 10 mA cm −2. Mechanistic and electrochemical studies revealed the cooperative role of reduced palladium species in the activation of carbon dioxide.

Climate change as the dominant control on glacial-interglacial variations in C3 and C4 plant abundance.

Although C4 plant expansions have been recognized in the late Miocene, identification of the underlying causes is complicated by the uncertainties associated with estimates of ancient precipitation, temperature, and partial pressure of atmospheric carbon dioxide (PCO2). Here we report the carbon isotopic compositions of leaf wax n-alkanes in lake sediment cores from two sites in Mesoamerica that have experienced contrasting moisture variations since the last glacial maximum. Opposite isotopic trends obtained from these two sites indicate that regional climate exerts a strong control on the relative abundance of C3 and C4 plants and that in the absence of favorable moisture and temperature conditions, low PCO2 alone is insufficient to drive an expansion of C4 plants.

Divergent electrochemical carboxylation of vinyl triflates: new electrochemical synthesis of phenyl-substituted α,β-unsaturated carboxylic acids and aliphatic β-keto carboxylic acids

Electrochemical carboxylation of vinyl triflates using a magnesium anode, as a reactive metal electrode, was investigated. Alkyl-substituted vinyl triflates were electrolyzed in the presence of an atmospheric pressure of carbon dioxide to give β-keto carboxylic acids as a sole products. On the other hand, electrochemical carboxylation of phenyl-substituted vinyl triflates gave α,β-unsaturated carboxylic acids exclusively. These divergent electrochemical carboxylation resulted from chemoselective cleavage of O–S or C–O bond of vinyl triflate, which was affected by the presence or absence of phenyl substituents in the structure of starting vinyl triflates.

A chemical model for evaporites on early Mars: Possible sedimentary tracers of the early climate and implications for exploration

Martian geomorphology seems to indicate extensive hydrological activity during the Noachian era. Liquid water at the surface would require a large greenhouse effect that is widely hypothesized to have been caused by a high partial pressure of atmospheric carbon dioxide,PCO2. A sedimentation model driven by sequential evaporation is used to calculate the evaporite mineral sequence in a closed basin lake subject to highPCO2. The initial fluid is derived from weathered igneous rock similar to Martian meteorite basalts. Siderite (FeCO3) is always the first major carbonate to precipitate. Thus siderite is predicted to be an important fades component in ancient Martian sediments along with silica, which is also an early precipitate. These would form varves in lakes that undergo cycles of evaporation and water recharge. After silica and siderite, the sequence is magnesian calcite, nearly pure hydromagnesite, and gypsum, followed by highly soluble salts like NaCl. The presence of siderite sediments generally requires an atmosphericPCO2level in excess of ∼0.1 bar, otherwise iron silicates (such as greenalite) would form. This may be used in exploration as an observational test on the past atmospheric composition of Mars, subject to consideration of the depositional environment. AtPCO2of approximately several bar, gypsum precipitation could occur before calcite upon evaporation if the initial SO42−:Ca2+ratio is high and there is no water recharge. The predicted carbonate sequence upon evaporation is generally consistent with recent hypotheses suggesting traces of evaporite carbonates in some Martian meteorites. Several mechanisms destroy or obscure carbonates at the Martian surface. Consequently, in situ analysis of the interior of ejecta from recent impact craters lying within sedimentary basins may offer the most practical approach to future exploration of ancient carbonate sediments.

Infrared matrix‐assisted laser desorption/ionization mass spectrometry with a transversely excited atmospheric pressure carbon dioxide laser at 10.6 µm wavelength with static and delayed ion extraction

Infrared matrix‐assisted laser desorption/ionization mass spectrometry with a transversely excited atmospheric pressure carbon dioxide laser at 10.6 µm wavelength with static and delayed ion extraction

Infrared matrix-assisted laser desorption/ionization mass spectrometry with a transversely excited atmospheric pressure carbon dioxide laser at 10.6 µm wavelength with static and delayed ion extraction

Infrared matrix-assisted laser desorption/ionization mass spectrometry with a transversely excited atmospheric pressure carbon dioxide laser at 10.6 µm wavelength with static and delayed ion extraction

New electrochemical carboxylation of vinyl triflates. Synthesis of β-keto carboxylic acids

Electrochemical reduction of alicyclic vinyl triflates ( 1a-1e) in a DMF solution containing 0.1 M Bu 4NBF 4 under an atmospheric pressure of carbon dioxide with a platinum cathode and a magnesium anode resulted in the cleavage of an oxygen-sulfur bond of 1 to give the corresponding β-keto carboxylic acids ( 2a-2e) in yields of 28–77%.

Synthesis of α,β-Unsaturated Carboxylic Acids by Nickel(II)-Catalyzed Electrochemical Carboxylation of Vinyl Bromides

Abstract Electrochemical carboxylation of alkyl-substituted vinyl bromides (1a-1g) in the presence of 20 mol% of NiBr2•bpy under an atmospheric pressure of carbon dioxide with a platinum cathode and a magnesium anode gave the corresponding α,β-unsaturated carboxylic acids (2a-2g) in yields of 53-82%.

A geochemical model for the formation of hydrothermal carbonates on Mars.

It is often argued that substantially more carbon dioxide and water were degassed from the martian interior than can be found at present in the atmosphere, polar caps and regolith. Calculations have shown that atmospheric escape cannot account for all of the missing volatiles. Suggestions that carbon dioxide is stored as marine or lacustrine deposits, are challenged by Earth-based and spacecraft remote-sensing data. Moreover, recent modelling of the martian atmosphere suggests that rainfall or open bodies of water are in any case unlikely to have persisted for extended periods of time. Hydrothermal carbonates therefore provide a possible solution to this dilemma. Using an accessible terrestrial system (Iceland) as a guide to the underlying processes, and a host rock composition inferred from the least-altered martian meteorite, we present a geochemical model for the formation of carbonates in possible martian hydrothermal systems. Our results suggest that an extensive reservoir of carbonate minerals--equivalent to an atmospheric pressure of carbon dioxide of at least one bar--could have been sequestered beneath the surface by widespread hydrothermal activity in the martian past.

Hard tissue laser ablation mechanisms

The aim of this work is the experimental and theoretical investigation of the influence of variable laser parameters (wavelength, fluence, pulse repetition rate) and of the optical and thermophysical properties of bone tissue (absorption coefficient, tissue inhomogeneity) as well as of the sample thickness on ablation thresholds and ablation rate. Ablation and perforation experiments were conducted using a semiconductively pre-ionized transverse excitation atmospheric pressure (TEA) carbon dioxide (CO2) laser (10.6Μm and a sliding discharge TEA [hydrogen fluoride (HF)] laser (2.9Μm). The experimental data are discussed with respect to the following ablation mechanisms: thermal melting and vaporization process, pressure oscillation of gases released by the thermal decomposition of collagen and/or apatite, stresses due to the expansion of superheated water.

Regioselective synthesis of β,γ-unsaturated acids by the electrochemical carboxylation of allylic bromides using a reactive-metal anode

Electrolysis of γ-mono and disubstituted allylic bromides in the presence of atmospheric pressure of carbon dioxide using a platinum cathode and a magnesium anode gave regioselectively the corresponding γ-mono and disubstituted β,γ-unsaturated carboxylic acids in 34–71% yields.

Lipid Composition of Hexane and Supercritical Carbon Dioxide Reduced Cholesterol Dried Egg Yolk , ,

Cholesterol was extracted from commercially spray-dried egg yolk using hexane at atmospheric pressure or supercritical carbon dioxide (SCCO2) (45 C, 238 atm; 45 C, 306 atm; 55 C, 374 atm). The effects of the different extraction methods on the lipid composition of the cholesterol-reduced yolks were evaluated. Polar lipids were separated into seven fractions using HPLC. Fractions 4, phosphatidylethanolamine (PE), and 5, phosphatidylcholine plus lysophosphatidylethanolamine (PC+LPE), accounted for almost 85% of the phospholipid (PL). As SCCO2 temperature and pressure increased, total lipid remaining decreased from 64.9 to 35.1%, but the PL content (15%) remained unaffected. The proportions of PE (12%) and PC+LPE (72%) of the PL fraction were constant. There was little effect on the fatty acid composition of the phospholipid fractions due to the SCCO2 treatments. However, the unsaturated fatty acids in the neutral lipids (NL) appeared to be effected by SCCO2 treatments. Hexane extracted a larger amount of total lipid (66%) and the NL fraction was decreased more than the PL fraction. Supercritical carbon dioxide was more efficient in removing cholesterol without major effects on the PL.

Ions in carbon dioxide at an atmospheric pressure—II. Effect of CO and O 2 addition

The formation and the subsequent reactions of positive and negative ions were observed by a TRAPI in an atmospheric pressure carbon dioxide added with small amounts of carbon monoxide and oxygen. A relatively stable ion of (44 × n) + ( n ≥ 2) having a different reactivity from that of (CO 2) + n was found to be one of major ionic species in this gas system. This species was tentatively assigned as [O 2(CO) 2] + (CO 2) n-2 . A new reaction sequence of positive ions is proposed which can be operative in the radiolysis of carbon dioxide at 1 atm.