ChemInform Abstract: BASE-CATALYZED ISOTOPIC EXCHANGE OF MOLECULAR HYDROGEN. 4. HYDROGEN ISOTOPE EFFECTS IN THE DIMETHYL SULFOXIDE-WATER SYSTEM

1978 ◽  
Vol 9 (22) ◽  
Author(s):  
E. BUNCEL ◽  
E. A. SYMONS ◽  
R. A. MORE O'FERRALL
Keyword(s):  
Dimethyl Sulfoxide ◽  
Molecular Hydrogen ◽  
Hydrogen Isotope ◽  
Isotopic Exchange ◽  
Isotope Effects ◽  
Water System

Base-catalyzed Isotopic Exchange of Molecular Hydrogen. II. Rate Dependence on Basicity in the Dimethyl Sulfoxide–Water System

1973 ◽  
Vol 51 (11) ◽  
pp. 1673-1681 ◽  
Author(s):  
E. Allan Symons ◽  
Erwin Buncel
Keyword(s):  
Proton Transfer ◽  
Dimethyl Sulfoxide ◽  
Molecular Hydrogen ◽  
Isotopic Exchange ◽  
Water System ◽  
Medium Composition ◽  
Hydroxide Ion ◽  
Hydride Ion ◽  
Low Sensitivity ◽  
Concerted Reaction

Isotopic exchange of D2 has been determined in mixtures of dimethyl sulfoxide and water under catalysis by hydroxide ion. The rate of exchange increases by ca. 104 as the medium composition is changed from 0% DMSO to 99.6% DMSO at 65 °C. The unusually low sensitivity to medium basicity is reflected in abnormally low slope values for the plots of log kobs υs. H− or J−. When [Me4NOH] is varied at a given medium composition, the apparent order with respect to [Me4NOH] is greater than unity.These results are discussed in terms of (1) rate determining proton transfer from D2 to OH− with formation of hydride ion; (2) a concerted reaction of OH−, D2, and H2O; (3) addition of OH− to D2 to yield an intermediate adduct, [HODD]−; (4) a 6-centered process involving cation participation and electrophilic assistance by H2O in the reaction of OH− with D2.L'échange isotopique de D2 a été étudié dans des mélanges de sulfoxyde de diméthyle et d'eau sous l'effet d'une catalyse par l'ion hydroxyle. Le taux d'échange augmente d'environ 104 alors que la composition du milieu change de 0% en DMSO à 99.6% en DMSO à 65 °C. La sensitivité anormalement faible à la basicité du milieu est réflétée par des valeurs anormalement faibles de la pente dans les graphiques du log kobs υs. H− ou J−. Quand la concentration de Me4NOH est changée pour une composition donnée du milieu, l'ordre apparent en ce qui a trait à la [Me4NOH] est plus élevé que l'unité.

scholarly journals A consistent molecular hydrogen isotope chemistry scheme based on an independent bond approximation

2009 ◽  
Vol 9 (2) ◽  
pp. 5679-5751 ◽  
Author(s):  
G. Pieterse ◽  
M. C. Krol ◽  
T. Röckmann
Keyword(s):  
Molecular Hydrogen ◽  
Hydrogen Isotope ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Quantitative Information ◽  
Sensitivity Study ◽  
Reaction Scheme ◽  
Photochemical Oxidation ◽  
Oxidation Of Methane ◽  
The Individual

Abstract. The isotopic composition of molecular hydrogen (H2) produced by photochemical oxidation of methane (CH4) and Volatile Organic Compounds (VOCs) is a key quantity in the global isotope budget of (H2). The many individual reaction steps involved complicate its investigation. Here we present a simplified structure-activity approach to assign isotope effects to the individual elementary reaction steps in the oxidation sequence of CH4 and some other VOCs. The approach builds on and extends the work by Gerst and Quay (2001) and Feilberg et al. (2007b). The description is generalized and allows the application, in principle, also to other compounds. The idea is that the C-H and C-D bonds – seen as reactive sites – have similar relative reaction probabilities in isotopically substituted, but otherwise identical molecules. The limitations of this approach are discussed for the reaction CH4+Cl. The same approach is applied to VOCs, which are important precursors of H2 that need to be included into models. Unfortunately, quantitative information on VOC isotope effects and source isotope signatures is very limited and the isotope scheme at this time is limited to a strongly parameterized statistical approach, which neglects kinetic isotope effects. Using these concepts we implement a full hydrogen isotope scheme in a chemical box model and carry out a sensitivity study to identify those reaction steps and conditions that are most critical for the isotope composition of the final H2 product. The reaction scheme is directly applicable in global chemistry models, which can thus include the isotope pathway of H2 produced from CH4 and VOCs in a consistent way.

scholarly journals A consistent molecular hydrogen isotope chemistry scheme based on an independent bond approximation

2009 ◽  
Vol 9 (21) ◽  
pp. 8503-8529 ◽  
Author(s):  
G. Pieterse ◽  
M. C. Krol ◽  
T. Röckmann
Keyword(s):  
Molecular Hydrogen ◽  
Hydrogen Isotope ◽  
Isotope Composition ◽  
Isotope Effects ◽  
Quantitative Information ◽  
Sensitivity Study ◽  
Reaction Scheme ◽  
Photochemical Oxidation ◽  
Oxidation Of Methane ◽  
The Individual

Abstract. The isotopic composition of molecular hydrogen (H2) produced by photochemical oxidation of methane (CH4) and Volatile Organic Compounds (VOCs) is a key quantity in the global isotope budget of (H2). The many individual reaction steps involved complicate its investigation. Here we present a simplified structure-activity approach to assign isotope effects to the individual elementary reaction steps in the oxidation sequence of CH4 and some other VOCs. The approach builds on and extends the work by Gerst and Quay (2001) and Feilberg et al. (2007b). The description is generalized and allows the application, in principle, also to other compounds. The idea is that the C-H and C-D bonds – seen as reactive sites – have similar relative reaction probabilities in isotopically substituted, but otherwise identical molecules. The limitations of this approach are discussed for the reaction CH4+Cl. The same approach is applied to VOCs, which are important precursors of H2 that need to be included into models. Unfortunately, quantitative information on VOC isotope effects and source isotope signatures is very limited and the isotope scheme at this time is limited to a strongly parameterized statistical approach, which neglects kinetic isotope effects. Using these concepts we implement a full hydrogen isotope scheme in a chemical box model and carry out a sensitivity study to identify those reaction steps and conditions that are most critical for the isotope composition of the final H2 product. The reaction scheme is directly applicable in global chemistry models, which can thus include the isotope pathway of H2 produced from CH4 and VOCs in a consistent way.

scholarly journals Unravelling the process of petroleum hydrocarbon biodegradation in different filter materials of constructed wetlands by stable isotope fractionation and labelling studies

2021 ◽  
Author(s):  
Andrea Watzinger ◽  
Melanie Hager ◽  
Thomas Reichenauer ◽  
Gerhard Soja ◽  
Paul Kinner
Keyword(s):  
Stable Isotope ◽  
Constructed Wetlands ◽  
Hydrogen Isotope ◽  
Petroleum Hydrocarbon ◽  
Isotope Fractionation ◽  
Isotope Effects ◽  
Filter Material ◽  
Hydrocarbon Biodegradation ◽  
Stable Isotope Fractionation ◽  
Filter Materials

AbstractMaintaining and supporting complete biodegradation during remediation of petroleum hydrocarbon contaminated groundwater in constructed wetlands is vital for the final destruction and removal of contaminants. We aimed to compare and gain insight into biodegradation and explore possible limitations in different filter materials (sand, sand amended with biochar, expanded clay). These filters were collected from constructed wetlands after two years of operation and batch experiments were conducted using two stable isotope techniques; (i) carbon isotope labelling of hexadecane and (ii) hydrogen isotope fractionation of decane. Both hydrocarbon compounds hexadecane and decane were biodegraded. The mineralization rate of hexadecane was higher in the sandy filter material (3.6 µg CO2 g−1 day−1) than in the expanded clay (1.0 µg CO2 g−1 day−1). The microbial community of the constructed wetland microcosms was dominated by Gram negative bacteria and fungi and was specific for the different filter materials while hexadecane was primarily anabolized by bacteria. Adsorption / desorption of petroleum hydrocarbons in expanded clay was observed, which might not hinder but delay biodegradation. Very few cases of hydrogen isotope fractionation were recorded in expanded clay and sand & biochar filters during decane biodegradation. In sand filters, decane was biodegraded more slowly and hydrogen isotope fractionation was visible. Still, the range of observed apparent kinetic hydrogen isotope effects (AKIEH = 1.072–1.500) and apparent decane biodegradation rates (k = − 0.017 to − 0.067 day−1) of the sand filter were low. To conclude, low biodegradation rates, small hydrogen isotope fractionation, zero order mineralization kinetics and lack of microbial biomass growth indicated that mass transfer controlled biodegradation.

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