G. Toupance

Université Paris-Est Créteil Val de Marne - Université Paris 12, Créteil, Île-de-France, France

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Publications (18)56.46 Total impact

  • François Raulin · Didier Mourey · Gérard Toupance
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    ABSTRACT: Numerous experiments have already been performed, simulating the evolution of gaseous mixtures containing CH4 when submitted to energy flux. From their results, it appears that a variety of organic compounds, including unsaturated hydrocarbons and nitriles such as HCN, can be synthesized into noticeable amounts from CH4−N2 mixtures. In particular, systematic studies of the influence of the composition of the mixture on the nature and amount of synthesized compounds show that organic volatile nitriles, and particularly cyanoacetylene and cyanogen, are formed only in media rich in nitrogen. Those nitriles have been identified very recently in the atmosphere of Titan, and thus, data from such laboratory experiments may provide important indirect information on the organic chemistry occuring at the periphery of this satellite of Saturn. However, during these experiments, there is a continuous formation and accumulation of molecular hydrogen, which does not occur in the atmosphere of Titan, because of H2 escape. In order to reassess the data already available from this type of laboratory studies, experiments on CH4−N2 atmospheres, with and without H2 escape, have been recently performed. The influence of this parameter on the chemical evolution of the atmosphere and on the nature and relative quantities of organic compounds has been studied. After reviewing these experiments, implications of the obtained results on the organic chemistry at the periphery of Titan are discussed.
    No preview · Article · Sep 1982 · Origins of Life and Evolution of Biospheres
  • Alain R. Bossard · François Raulin · Didier Mourey · Gérard Toupance
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    ABSTRACT: The purpose of this paper is to compare the role of UV light and of electric discharges, the two most important sources of energy on the primitive earth, in the synthesis of organic compounds out of a reducing model of that atmosphere. Since Miller's experiments in 1953, most of the experimental simulations have been performed with electric discharges, and it has been assumed that UV radiations would give similar results. In order to check this assumption we have performed both experimental simulations in our laboratory. Experimental results indicate that this assumption was wrong in a large extent. Our four main conclusions are:1. Unlike electric discharges, UV light is not an efficient source for producing unsaturated carbon chains. 2. UV light is efficient for producing nitriles in CH4-NH3 mixtures when the mole fraction of NH3 is very low while electric discharges need a higher mole fraction of NH3. 3. UV light is not able to produce nitriles from CH4-N2 mixtures while electric discharges produce important quantities of diversified nitriles from these mixtures. 4. UV light is not very efficient for producing aldehydes from CH4-H2O model atmosphere, electric discharges seem to be able to produce them more efficiently.
    No preview · Article · Feb 1982 · Journal of Molecular Evolution
  • A. Bossard · F. Raulin · D. Mourey · G. Toupance
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    ABSTRACT: The purpose of this paper is to compare the role of UV light and electric discharges, the two most important sources of energy on the primitive earth, in the synthesis of organic compounds out of a reducing model of that atmosphere. Since Miller’s experiments in 1953, most of the experimental simulations have been performed with electric discharges, and it is frequently assumed that UV radiation would give similar results.
    No preview · Chapter · Jan 1981
  • Alain Bossard · Gérard Toupance
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    ABSTRACT: New photochemical data are reported on the effects of mole fraction of NH3 in CH4-NH3 mixtures used in the production of N-containing organics. The photolysis of these mixtures at 147 nm forms nitriles when the NH3 mole fraction is low, and produces amines when the fraction is high. It was concluded that: (1) significant amounts of nitriles may have been photoproduced on the primitive earth if a low partial pressure of NH3 remained, and (2) nitriles are the principal N-containing organics which can be photoproduced in the atmosphere of giant planets.
    No preview · Article · Nov 1980 · Nature
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    ABSTRACT: Organic photochemical syntheses in the Jovian atmosphere was simulated by irradiating, at 147 nm, gaseous mixtures of methane and ammonia with varying amounts of hydrogen. Some results relevant to the photochemistry of the Jupiter atmosphere at several tens of kilometers above the clouds were obtained: (1) a favorable effect of the pressure of high amounts of H2 on the yield of hydrocarbon synthesis when NH3 is mixed with CH4; (2) a very low yield of synthesis of unsaturated hydrocarbons in such conditions; and (3) the possibility of formation of detectable amounts of HCN and CH3CN.
    No preview · Article · Jul 1979 · Icarus
  • G. Toupance · D. Mourey · F. Raulin
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    ABSTRACT: Classical laboratory experiments simulating the evolution of planetary atmospheres, such as that conducted by Miller (1955), fail to take into account the fact that a large proportion of the evolved hydrogen escapes from the atmosphere. The accumulation of hydrogen in experiments of the Miller type leads to initial limits on the synthesis of certain hydrocarbons and HCN, and subsequently, when H2 content is high and CH4 content low, to stabilization of hydrocarbon and NH3 synthesis. In addition, H2 accumulation prevents an oxidized state from arising. An experimental apparatus for studying planetary atmosphere evolution with hydrogen escape is also described.
    No preview · Article · Jan 1979
  • F Raulin · S Bloch · G Toupance

    No preview · Article · Nov 1977 · Origins of Life
  • G Toupance · A Bossard · F Raulin
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    ABSTRACT: UV light has been the most important energy source on the primitive Earth. However, very few experiments have been performed to test directly the possible role of this energy source on the chemical evolution of the primitive atmosphere, mainly on account of experimental difficulties. Experiments are generally performed with other excitations, mainly electric discharge, and it is frequently assumed that UV irradiation would give similar results. As theoretical considerations make this assumption questionable, direct experimental controls have been undertaken: Model primitive atmospheres have been submitted to 147 nm UV light and the gaseous phase has been analysed. Preliminary qualitative results concerning CH4-NH3 atmospheres are reported. Irradiation of pure CH4 gives rise to the synthesis of a large number of hydrocarbons, mainly saturated hydrocarbons but including also unsaturated ones as, C2H2, C2H4, C3H6, C3H4. These insaturated hydrocarbons are synthetized at a very low rate when ammonia is present in the medium. Irradiations of CH4-NH3 mixtures give rise, in addition to hydrocarbons, to important amounts of HCN (about 0.1%) and to lesser amounts of CH3CN and C2H5CN. No unsaturated nitriles such as acrylonitrile and cyanoacetylene have been detected. Search for amines is in progress. These results evidence that UV irradiation may contribute largely to synthesis of HCN in CH4-NH3 atmospheres and, consequently to the synthesis of many biochemical compounds that can be derivated from HCN. However, synthesis of other compounds, such as pyrimidines, which can derivate from other nitriles, such as cyanoacetylene, cannot be initiated only by UV light, contrary to electric discharges. In addition, if electric discharges are very efficient for synthesis of nitriles in CH4-N2 atmospheres, there is not yet evidence that UV light is able to do so.
    No preview · Article · Nov 1977 · Origins of Life
  • François Raulin · Suzanne Bloch · Gérard Toupance
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    ABSTRACT: In order to evidence new reactions of prebiotic synthesis in aqueous solution between the S-containing compounds, such as alkanethiols, which can be obtained in gaseous phase during the simulation of the evolution of primitive atmosphere, and the malonic nitriles which are generally considered as important intermediates in the Chemical Evolution, a kinetic study on the eventual reactions of ethanethiol with cyanoacetaldehyde and malononitrile has been carried out. It appears that ethanethiol does not react directly in aqueous solution with cyanoacetaldehyde, but it gives an addition reaction with the double bond of the crotonic dimer of this malonic compound giving a thioether. With malononitrile, ethanethiol reacts directly by addition reaction on the CN group of the monomer, producing an iminothioester. These two reactions are equilibrated. The specific rate constants and the apparent equilibrium constants for these two reactions have been simultaneously studied by UV spectrophotometry at room temperature as a function of pH. The conditions for the formation of iminothioester will be discussed in terms of the respective pKa values of the thiol and of the malonic nitrile. These two addition products, principally the iminothioesters, because of their hydrolysis in thioesters may have played an important role in the prebiochemical evolution.
    No preview · Article · Sep 1977 · Origins of Life and Evolution of Biospheres
  • F Raulin · G Toupance
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    ABSTRACT: Sulphur may have played an important role, mainly as an energy converter, during the initial steps of Chemical Evolution. In atmospheric processes, sulphur, in the form of H2S might have been a primary energy acceptor and a source of hot hydrogen atoms. The presence of H2S in the primeval earth atmosphere with a molar ratio of about 10-2 could have allowed the formation of several volatile S-containing compounds without inhibiting the synthesis of the reactive products which are formed in the absence of H2S. An evaluation of the quantity of H2S which could have been included in the primeval atmosphere suggests that such a molar ratio may have been reached. In the primitive soup, the thiols and sulphides formed in the gaseous phase may have evolved, giving rise to various prebiotic syntheses. Studies on the addition reaction of alkanethiols on malonic nitriles in aqueous solutions show two different condensation processes: the formation of thioethers and the formation of iminothioesters. Taking into account the values of the specific rate constants for the two reactions, it is shown that these reactions may have taken place in the primitive earth conditions. These two compounds may have played an important role in the prebiochemical evolution. In particular, iminothioesters can be considered as the immediate precursors of thioesters.
    No preview · Article · Sep 1977 · Journal of Molecular Evolution
  • F Raulin · G Toupance
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    ABSTRACT: H2S has been often invoked as the initial source of sulfur in prebiotic evolution, and several sulfur-containing compounds have been proposed as intermediates in the primordial synthesis of biologically relevant sulfur-containing chemicals. The possibilities of synthesis of the principal key intermediates by glow discharges in CH4-N2-H2S mixtures is studied. It is shown that synthesis of important intermediates such as HCN, (CN)2, CHCCN and CH3SH is possible from such mixtures if the amount of H2S is not more than 10%. For higher amounts of H2S, the syntheses are strongly inhibited.
    No preview · Article · Nov 1975 · Origins of Life
  • F. Raulin · G. Toupance
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    ABSTRACT: In order to understand the role of sulfur in the primitive atmosphere, we have studied the action of a silent discharge on mixtures of CH4 and H2S at low pressure. The nature of the products formed in the gaseous phase, and the influence of several parameters, especially the H2S percentage, on the yield of the products are reported. The analysis of the products is carried out by gas liquid chromatography and infrared spectrometry. The formation of sulfur-containing compounds, such as thiols and sulfides, is reported. CS2 is formed in high yield (a few percent) in mixtures containing 40–50% of H2S, while the maximum concentration of thiols (i.e., CH3SH and C2H5SH) is reached with lower percentages of H2S. The formation of hydrocarbons decreases rapidly with increasing proportions of H2S. These results show the important inhibitor effect of H2S on the formation of hydrocarbons and the possibility of occurrence of many sulfur compounds in prebiological evolution.
    No preview · Article · Dec 1974 · Origins of Life and Evolution of Biospheres
  • G. Toupance · F. Raulin · R. Buvet
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    ABSTRACT: In order to understand the formation of organic compounds in the primitive atmosphere, the first steps of evolution in models of the primitive atmosphere were investigated. Mixtures containing C–H–N elements were subjected to a low pressure silent electric discharge for several seconds, and the resulting effluents were analysed mainly by gas chromatography, infrared spectrometry and chemical analysis. The formation of hydrocarbons (i.e. ethylene, acetylene, methylacetylene) and of nitrogen containing compounds (i.e. hydrogen cyanide, cyanogen, saturated nitriles, acrylonitrile, cyanoacetylene) is reported. The influence of the initial mixture composition on the amount of compounds formed was systematically studied. The nature of the nitrogen source (N2 or NH3) in the primitive atmosphere has a great influence on the amount and on the very nature of the synthesized products. It is shown that important precursors such as cyanogen and cyanoacetylene are formed only in very rich N2 mediums. There results show the important role played by the nature of the primitive atmosphere in the determination of the chemical evolution pathways.
    No preview · Article · Dec 1974 · Origins of Life and Evolution of Biospheres
  • F. Raulin · G. Toupance

    No preview · Article · Mar 1974 · Journal of Chromatography A
  • F Raulin · G Toupance
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    ABSTRACT: In order to understand the role of sulfur in the primitive atmosphere, we have studied the action of a silent discharge on mixtures of CH4 and H2S at low pressure. The nature of the products formed in the gaseous phase, and the influence of several parameters, especially the H2S percentage, on the yield of the products are reported. The analysis of the products is carried out by gas liquid chromatography and infrared spectrometry. The formation of sulfur-containing compounds, such as thiols and sulfides, is reported. CS2 is formed in high yield (a few percent) in mixtures containing 40-50% of H2S, while the maximum concentration of thiols (i.e., CH3SH and C2H5SH) is reached with lower percentages of H2S. The formation of hydrocarbons decreases rapidly with increasing proportions of H2S. These results show the important inhibitor effect of H2S on the formation of hydrocarbons and the possibility of occurrence of many sulfur compounds in prebiological evolution.
    No preview · Article · · Origins of Life
  • G. Toupance · F. Raulin · R. Buvet

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  • F. Raulin · G. Toupance

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  • G Toupance · F Raulin · R Buvet
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    ABSTRACT: In order to understand the formation of organic compounds in the primitive atmosphere, the first steps of evolution in models of the primitive atmosphere were investigated. Mixtures containing C-H-N elements were subjected to a low pressure silent electric discharge for several seconds, and the resulting effluents were analysed mainly by gas chromatography, infrared spectrometry and chemical analysis. The formation of hydrocarbon (i.e. ethylene, acetylene, methylacetylene) and of nitrogen containing compounds (i.e. hydrogen cyanide, cyanogen, saturated nitriles, acylonitrile, cyanoacetylene) is reported. The influence of the initial mixture composition on the amount of compounds formed was systematically studied. The nature of the nitrogen source (N2 or NH3) in the primitive atmosphere has a great influence on the amount and on the very nature of the synthesized products. It is shown that important precursors such as cyanogen and cyanoacetylene are formed only in very rich N2 mediums. These results show the important role played by the nature of the primitive atmosphere in the determination of the chemical evolution pathways.
    No preview · Article · · Origins of Life