Carbon isotopic exchange

Horita J (2001) Carbon isotope exchange in the system CO2-CH4 at elevated temperatures. Geochim Cosmochim Acta 65 1907-1919... 

Malinin SD, Kropotiva 01, Grinenko VA (1967) Experimental determination of equihbrium constants for carbon isotope exchange in the system C02(gas)-HC03 (sol) under hydrothermal conditions. Geochem Int l 4 764-771... 

Catalyzed gaseous systems. The reaction between CO and CO2 at elevated temperatures ( 860-920°C) represents a classic example of carbon isotope exchange enhanced by catalysis with surfaces such as quartz, gold and silver (Brander and Urey 1945, Hayakawa 1953). In addition to rate enhancement on catalytic metal or oxide surfaces, Brander and Urey (1945) also observed an increase in rate in the presence of H2 or H20(v). They tested a variety of mechanisms to explain their experiments which involved reaction of C-enriched CO2 with normal CO as a function of temperature, gas... 

The work of Sackett and Chung (1979) demonstrated that at 500°C for up to 10.5 days, no observable carbon isotope exchange occurred between CO2 and CH4 reacted in the presence of water and montmorillonite. In similar experiments, Halting and Maass (1980) observed very limited carbon isotope exchange between normal isotopic CO2 and 66% CH4 at temperatures between 500 and 680°C up to 16 hours, also in the presence of montmorillonite and water (probably as water vapor ). The second order rate constants (k2) reported by Hailing and Maass (1980) were derived from the relationships... 

Horita J (1988b) Hydrogen isotope analysis of natural waters using an H2-water equilibration method A special implication to brines. Chem Geol (Isotope Geosci Section) 72 89-94 Horita J (2001) Carbon isotope exchange in the system CO2-CH4 at elevated temperatures. Geochim Cosmochim Acta 65 1907-1919... 

Bergfeld D, Nabelek PI, Labotka TC (1996) Carbon isotope exchange during polymetamorphism in the Panamint Mountains, California, USA. JMetamor Geol 14 199-212... 

Sackett W. M. and Chung H. M. (1979) Experimental confirmation of the lack of carbon isotope exchange between methane and carbon oxides at high temperatures. Geochim. Cosmochim. Acta 43, 273-276. 

Oceans play a significant role in the exchange of CO2 between the atmosphere and biosphere. Carbon isotope exchange between CO2 in the air and HCO3 in the oceans results in C enrichment of the latter. CO2 in air is well mixed globally and currently has a <5 C value of - 84 V-PDB compared to marine limestones at 04 V-PDB. Freshwater carbonates have much more variable and lower values due to the oxidation of C depleted organic matter and subsequent formation of HCOj. 

To extend the study of the apparent decomposition recombination reaction, and specifically to determine if the carbon atoms exchange with other atoms in other acetylene molecules, tests using carbon isotopes were conducted. A mixture of 50% regular acetylene, C2H2, and 50% heavy acetylene. 

Cya.nideExcha.nge, Acetone cyanohydrin and methyl isobutyl ketone cyanohydrin [4131 -68-4] dissolved in an organic solvent, such as diethyl ether or methyl isobutyl ketone, undergo cyanide exchange with aqueous cyanide ion to yield a significant cyanide carbon isotope separation. The two-phase system yields cyanohydrin enriched in carbon-13 and aqueous cyanide depleted in carbon-13. Fquilibrium is obtained in seconds. 

In this chapter it is clearly impossible to do more than sample the extensive literature on the carbon acidity of sulfinyl and sulfonyl compounds, as it illuminates the electronic effects of these groups, particularly in connection with linear free-energy relationships. There are three main areas to cover first, as already indicated, equilibrium acidities (pKa values) second, the kinetics of ionization, usually studied through hydrogen isotopic exchange and finally, the kinetics of other reactions proceeding via carbanionic intermediates. 

The most abundant isotope is which constitutes almost 99% of the carbon in nature. About 1% of the carbon atoms are There are, however, small but significant differences in the relative abundance of the carbon isotopes in different carbon reservoirs. The differences in isotopic composition have proven to be an important tool when estimating exchange rates between the reservoirs. Isotopic variations are caused by fractionation processes (discussed below) and, for C, radioactive decay. Formation of takes place only in the upper atmosphere where neutrons generated by cosmic radiation react with nitrogen ... 

We have previously assumed that the principle diagenetic process is attributable to exchange or interaction of (depleted) browser apatite values with (enriched) sedimentary matrix values (Lee-Thorp and van der Merwe 1987). Another possibility is ionic or isotopic exchange with soil CO2 however in most cases soil CO2 values will be closely related to matrix carbonate values. If the former is the case, one would expect enriched grazer values (near 0%o)... 

Haul, RA.W. and Stein, L.H. 1955 Diffusion in calcite crystals on the basis of isotope exchange with carbon dioxide. Faraday Society Transactions 51 1280-1290. 

Bottinga, Y. 1969 Calculated fractionation factors for carbon and hydrogen isotope exchange in the system calcite-carbon dioxide-graphite-methane-hydrogen-water vapour. Geochimica et CosmochimicaActa 33 49-64. 

Evans, J.R., Sharkey, T.D., Berry, J.A. Farquhar, G.D. (1986). Carbon isotope discrimination measured concurrently with gas exchange to investigate CO2 diffusion in leaves of higher plants. Australian Journal of Plant Physiology 13,281-92. 

The kinetics of deuterium isotope exchange between diphenyl phosphine and t-butylthiol have been studied by H n.m.r. spectroscopy.274 A negative temperature coefficient was observed for the reaction of a perf1uoroalky1 phosphite with a fluorinated aldehyde.275 The kinetics for the reaction of alcohols with phosphoryl trichloride bore strong similarities to those of carboxylic acid derivatives.276 An interesting report desribed the solvolysis of ary 1 hydroxymethyl-phosphonates. It was shown that a phosphoryl group does not prevent carbocation formation on an immediately adjacent carbon atom.277... 

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