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  • Springer  (59)
  • Institute of Physics  (13)
  • American Institute of Physics (AIP)  (11)
  • 11
    Electronic Resource
    Electronic Resource
    Diffusion-influenced controlled reaction in an inhomogeneous medium: Small concentration of reagents (2000)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 112 (2000), S. 8495-8501 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We report a computer simulation study of diffusion influenced reactions in a disorder medium constituting by immobile spherical obstacles when the concentration of reagents is smaller than the concentration of obstacles. We found that the compartmentalization of the embedding medium leads to a strong decrease of the rate of the first collision between reagents and a strong increase of the rate of recollision after a no-reactive encounter. The behavior of the full rate of reaction depends on the probability that a collision leads to reaction (value of the activation energy) and on the relationship between the decrease of the rate of collision and the increase of the rate of recollision. Thus, totally diffusion controlled reactions are always unfavored in these mediums, while partially diffusion controlled reactions with very high activation energy are more favored in mediums with a bigger degree of compartmentalization. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.481452
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  • 12
    Electronic Resource
    Electronic Resource
    Influence of the fractal geometry of trajectories on the rate of diffusion-controlled bulk ion recombination (1988)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 88 (1988), S. 7478-7480 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Analysis of the influence of the differential fractal dimension of reagent trajectories on the rate of diffusion-controlled bulk ion recombination provides explanations of both Tachiya's recent Monte Carlo results on the dependence of the rate constant on the mean free path and Nakamura's results on electron-ion recombination in liquid methane.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.454312
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  • 13
    Electronic Resource
    Electronic Resource
    Kinetische Untersuchungen zur Bildung von N-Nitrosoverbindungen II. Entstehung von N-Nitroso-N-methylharnstoff in wäßriger Perchlorsäurelösung (1979)
    Springer
    Monatshefte für Chemie 110 (1979), S. 1331-1344 
    Details
    ISSN: 1434-4475
    Keywords: Kinetic study ; N-Methylurea ; Nitrosation ; N-Nitroso-N-methylurea
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The kinetics of nitrosation of Methylurea (MU) in aqueous perchloric solution has been studied using two techniques: a dynamic spectrophotometric and a stopped-flow technique. The rate law obtained, whenpH was varied in the range 0.27–3.22, is $$---d[nitrite]/dt = f[MU][nitrite][H^ + ]/(1 + g/[H^ + ])$$ where [MU] and [nitrite] represent stoichiometric concentrations. At 288.0 K and μ=1.0M,f=(15.6±0.5)M −2s−1 andg=(1.06±0.08) 10−3 M. This rate law becomes independent of the acidity of the solution when this is increased ([ClO4H])〉1.00M). These results together with the activation of the nitrosation rate by the ionic strength and the negative value of the activation entropy shown that only the NO2H2 + or NO+ is the effective carrier for the nitrosation. Comparisons with the nitrosation of dimethylamine were also made leading to the conclusion that there is no simple explanation for the fact that the nitrosation via NO2H2 +/NO+ disappears when the nitrosable compound is of increased basicity.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00938290
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  • 14
    Electronic Resource
    Electronic Resource
    Kinetic studies on the formation ofN-nitroso compounds. IV. Formation of mononitrosopiperazine and general discussion ofN-nitrosation mechanisms in aqueous perchloric solution (1981)
    Springer
    Monatshefte für Chemie 112 (1981), S. 1221-1238 
    Details
    ISSN: 1434-4475
    Keywords: Kinetics ; Mechanism ; Mononitrosopiperazine ; N-Nitrosation ; Piperazine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Der Mechanismus der Bildung vonN-Nitroso-Verbindungen, die als potentielle carcinogene Substanzen gelten, wurde untersucht. Die Kinetik der Nitrosierung von Piperazin (PIP) in wäßriger Perchlorsäurelösung wurde mittels einer differentiellen spektrophotometrischen Methode verfolgt. Es ergab sich für denpH-Bereich 0,85–4,36 folgendes Zeitgesetz: $$v_0 = \left[ {nitrite} \right]_0 2 \left[ {PIP} \right]_0 /\left( {1 + f/\left[ {H^ + } \right]} \right)^2 \left( {g \left[ {PIP} \right]_0 + h + j\left[ {H^ \div } \right]} \right)$$ wobei [Nitrit]0 und [PIP]0 die anfänglichen stöchiometrischen Konzentrationen bedeuten. Bei 298,2 K und μ=1,0M,f=(1,17±0,11) 10−3 M,g=(3,5±0,7)·10−2 M s,h=2,6·10−6 M 2 s andj=(0,95±0,04)M s. Bei Erhöhung der Acidität ([HClO4]≥1M) tritt ein neuer kinetischer Term auf: $$v_0 ' = p\left[ {Nitrit} \right]_0 \left[ {PIP} \right]_0 $$ Bei 298,2 K und μ=3,0M,p=(1,9±0,2) 10−3 M −1 s−1. Es wird ein genereller Mechanismus für die Nitrosierung jedesN-nitrosierbaren Substrates in wäßriger Perchloratlösung vorgeschlagen, wobei als nitrosierende Agentien ausschließlich N2O3 und H2NO2 +/NO+ auftreten. Es werden die Besonderheiten dieses Mechanismus bezüglich derpK-Werte derN-nitrosierbaren Substrate diskutiert.
    Notes: Abstract The mechanism of formation ofN-nitroso compounds, which are considered as potential chemical carcinogens was studied. The kinetics of nitrosation of piperazine (PIP) in aqueous solution of perchloric acid have been investigated using a differential spectrophotometric technique. Based on our experimental results, the following rate law, in thepH-range 0.85 4.36, is proposed: $$v_0 = \left[ {nitrite} \right]_0 2 \left[ {PIP} \right]_0 /\left( {1 + f/\left[ {H^ + } \right]} \right)^2 \left( {g \left[ {PIP} \right]_0 + h + j\left[ {H^ \div } \right]} \right)$$ where [nitrite]0 and [PIP]0 represent initial stoichiometric concentrations. At 298.2K and μ=1.0M,f=(1.17±0.11) 10−3 M,g=(3.5±0.7) 10−2 M s,h=2.6×10−6 M 2 s andj=(0.95±0.04)M s. When the acidity is increased ([HClO4]≥1M), a new kinetic term comes into play: $$v_0 ' = p\left[ {nitrite} \right]_0 \left[ {PIP} \right]_0 $$ At 298.2 K and μ=3.0M,p=(1.9±0.2) 10−3 M −1 s−1. A general mechanism for the nitrosation of anyN-nitrosable substrate in aqueous perchloric solution in which the only nitrosating agents are N2O3 and H2NO2 +/NO+ is proposed. Also, the various particularities of this mechanism, according to thepK of theN-nitrosable substrate, are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00904675
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  • 15
    Electronic Resource
    Electronic Resource
    Synthesis of pyrimido[4′,5′:4,5]thieno[2,3-c]-pyridazine derivatives (1996)
    Springer
    Monatshefte für Chemie 127 (1996), S. 537-547 
    Details
    ISSN: 1434-4475
    Keywords: Thieno[2,3-c]pyridazine-6-carboxamide ; 5,6,7,8-Tetrahydropyrimido[4′,5′:4,5]-thieno[2,3-c]pyridazines ; 7,8-Dihydropyrimido[4′,5′:4,5]thieno[2,3-c]pyridazines ; Pyrimido[4′,5′:4,5]thieno-[2,3-c]pyridazines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Einfache Synthesen von 3,4-Diphenyl-8-oxo-6-substituierten-5,6,7,8-tetrahydropyrimido[4′,5′:4,5]thieno[2,3-c]pyridazinen (4a-g), 3,4-Diphenyl-8-oxo-6-substituierten-7,8-dihydropyrimido[4′,5′:4,5]thieno[2,3-c]pyridazinen (5a-g), 8-Chlor-3,4-diphenyl-6-substituierten Pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazinen (6a-g) und 3,4,6-Triphenyl-8-substituierten-pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazinen (7a-f) aus 4-Cyano-5,6-diphenylpyridazin-3(2H)-thion (1)via 5-Amino-3,4-diphenylthieno[2,3-c]pyridazin-6-carboxamid (3) werden beschrieben.
    Notes: Summary Convenient syntheses of 3,4-diphenyl-8-oxo-6-substituted-5,6,7,8-tetrahydropyrimido[4′,5′:4,5]thieno[2,3-c]pyridazines (4a-g), 3,4-diphenyl-8-oxo-6-substituted-7,8-dihydropyrimido[4′,5′:4,5]thieno[2,3-c]pyridazines (5a-g), 8-chloro-3,4-diphenyl-6-substituted-pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazines (6a-g), and 3,4,6-triphenyl-8-substituted-pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazines (7a-f) from 4-cyano-5,6-diphenylpyridazine-3(2H)-thione (1)via 5-amino-3,4-diphenyl-thieno[2,3-c]pyridazine-6-carboxamide (3) are reported.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807079
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  • 16
    Electronic Resource
    Electronic Resource
    A general route for the synthesis of pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazine derivatives (1996)
    Springer
    Monatshefte für Chemie 127 (1996), S. 739-745 
    Details
    ISSN: 1434-4475
    Keywords: Pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazine derivatives ; Thieno[2,3-c]pyridazine-6-carbonitrile ; N,N-Dimethyldichloromethyleniminium chloride ; Enaminonitrile
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurde ein einfacher Syntheseweg für 8-substituierte Pyrimido[4′,5′:4,5]thieno-[2,3-c]pyridazine entwickelt. Die Reaktion verläuft über den Ringschluß eines heterocyclischen Aminonitrilvorläufers (3) nach Umsetzung mit Dichlormethylen-dimethylammoniumchlorid.
    Notes: Summary A facile synthesis of 8-substituted pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazines (6a–i) has been accomplished. The sequence involves the ring closure of a heterocyclic aminonitrile precursor (3) after reaction with (dichloromethylene)-dimethylammonium chloride.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00817265
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  • 17
    Electronic Resource
    Electronic Resource
    Synthesis of new pyridazino[4′,3′:4,5]-thieno[3,2-d]-1,2,3-triazine and pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazine derivatives (1996)
    Springer
    Monatshefte für Chemie 127 (1996), S. 1037-1043 
    Details
    ISSN: 1434-4475
    Keywords: Thieno[2,3-c]pyridazine-6-carboxamide ; Pyridazino[4′,3′:4,5]thieno[3,2-d]1,2,3-triazines ; Pyrimido[4′,5′:4,5]thieno[2,3-c]pyridazines ; Pyridazines ; 1,2,3-Triazines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Folgende Verbindungen wurden ausgehend von 5-Amino-3,4-diphenylthieno[2,3-c]pyridazin-6-carboxamid (1) synthetisiert: 8,9-Diphenylpyridazino[4′,3′:4,5]thieno[3,2-d]-1,2,3-triazin-4(3H)-on (2), 3-substituierte 8,9-Diphenylpyridazino[4′,3′:4,5]thieno[3,2-d]-1,2,3-triazin-4(3H)-one (3a–c), 3,4-Diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin-8[7H]-on (4), 8-Chlor-3,4-diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin (5), 8-substituierte 3,4-Diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazine (6a–h) und 7-substituierte 3,4-Diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin-8(7H)-one (7a–c).
    Notes: Summary 8,9-Diphenylpyridazino[4′,3′:4,5]thieno[3,2-d]-1,2,3-triazin-4(3H)-one (2), 3-substituted 8,9-diphenylpyridazino[4′,3′:4,5]thieno[3,2-d]-1,2,3-triazin-4(3H)-ones (3a–c), 3,4-diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin-8(7H)-one (4), 8-chloro-3,4-diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazine (5), 8-substituted 3,4-diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazines (6a–h) and 7-substituted 3,4-diphenylpyrimido[4′,5′:4,5]thieno[2,3-c]pyridazin-8(7H)-ones(7a–c) were synthesized from 5-amino-3,4-diphenylthieno[2,3-c]pyridazine-6-carboxamide (1).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00807576
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  • 18
    Electronic Resource
    Electronic Resource
    Experimental and computational patterns in convection instability of microemulsions (1991)
    Springer
    Naturwissenschaften 78 (1991), S. 224-226 
    Details
    ISSN: 1432-1904
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology , Natural Sciences in General
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01136086
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  • 19
    Electronic Resource
    Electronic Resource
    Kinetic studies on the formation ofN-nitroso compounds VI. The reactivity of N2O3 as a nitrosating agent (1983)
    Springer
    Monatshefte für Chemie 114 (1983), S. 639-646 
    Details
    ISSN: 1434-4475
    Keywords: Dinitrogen trioxide ; Kinetics of nitrosation ; N-Nitrosation ; Secondary amines
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurde mittels einer differentiellen spektrophotometrischen Methode die Reaktionsgeschwindigkeit derN-Nitrosierung von sekundären Aminen unter Bedingungen untersucht, bei denen N2O3 als nitrosierendes Agens angesehen wird. Der wahre Reaktionsgeschwindigkeitskoeffizientk für denN-Nitrosierungsschritt — sowohl für die oben genannten als auch andere erneut berechnete Systeme mit aliphatischen und aromatischen Substraten mitpK a 〉5 — ergab immer die gleiche Größenordnung von 108 M −1s−1. Dieser Befund zeigt an, daß der Angriff von N2O3 auf die freien Amine diffusionskontrolliert erfolgen muß, wobei diese Annahme auch von den experimentellen Aktivierungsenthalpien von 10–20 kJ/mol gestützt wird.
    Notes: Abstract Using a differential spectrophotometric technique in water at 25°C measurements were made of the reaction rate in the nitrosation of a number of secondary amines in conditions in which the effective nitrosating agent is thought to be dinitrogen trioxide. Analysis of the rate data leads to values ofk, the true rate coefficient for theN-nitrosation step, which, like the values recalculated here for other systems involving aliphatic and aromatic substrates ofpK a 〉5, exhibit the same unvarying order of magnitude, 108 M −1s−1. This figure together with the invariance already mentioned indicates that the attack of the N2O3 upon free amines must be diffusion controlled; this hypothesis is supported by the values found for the enthalpies of activation (10–20 kJ/mol).
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01134177
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  • 20
    Electronic Resource
    Electronic Resource
    Kinetic studies on the formation ofN-nitroso compounds VII. Nitrosation of morpholine in acetate buffer (1983)
    Springer
    Monatshefte für Chemie 114 (1983), S. 647-660 
    Details
    ISSN: 1434-4475
    Keywords: Acetate buffer ; Kinetics of nitrosation ; Morpholine ; N-Nitrosomorpholine
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Description / Table of Contents: Zusammenfassung Es wurde die Kinetik der Nitrosierung von Morpholin in Acetat-Puffer untersucht. Unter den gewählten Reaktionsbedingungen ist das effektive Agens N2O3, dessen Bildung von Acetat-Ionen im Einklang mit dem gezeigten Schema gefördert wird: Zwischen Nitrosylacetat und Amin wurde keine Reaktion beobachtet, vermutlich wegen der niederen Konzentration des ersteren. Der vorgeschlagene Mechanismus erklärt, daß keine Katalyse mittels Puffer unter Bedingungen zu beobachten ist, wo der geschwindigkeitsbestimmende Schritt die Reaktion von N2O3 mit dem Amin ist und daß der katalytische Effekt nur dann beobachtet wird, wenn die Bildung des Nitrosierungsagens geschwindigkeitsbestimmend ist. Gleichgewichts- und kinetische Konstanten, die für den Mechanismus von Bedeutung sind, wurden ermittelt.
    Notes: Abstract The kinetics of the nitrosation of morpholine in acetate buffer have been studied. It was found that in the experimental conditions used the effective nitrosating agent is dinitrogen trioxide, whose formation is promoted by the acetate ion in accordance with the scheme: No reaction between nitrosyl acetate and the a mine was observed, probably owing to the low concentration of the former. The proposed mechanism explains the experimental facts that no catalysis by the buffer is observed in conditions in which the rate controlling step is the reaction of N2O3 with the amine, and that the catalytic effect has only been observed when the formation of the nitrosating agent is also rate controlling. Values have been calculated for several equilibrium and kinetic constants involved in the mechanism proposed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01134178
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