Direkte Photolyse von Kohlenoxidsulfid in Alkoholen und Acetonitril in Gegenwart von Olefinen. Reaktionen von Triplett‐Schwefelatomen mit Norbornen in Äthanol und 1.4‐Dioxan
Abstract:Die COS-Photolyse fiihrt in Methanol wie auch in Acetonitril in Gegenwart von Cyclohexen bzw. Octen-(I) zur Bildung der Episulfide durch Reaktion von S(3P)-Atomcn mit dcn Olefinen. Mit Norhornen dagegen wird keine Episulfidbildung heobachtet ; die COS-Photolyse in Athanol liefert ausschlieRlich die beiden diastereomeren Dinorhornylsulfide 1 a und 1 h, wiihrend in 1.4-Dioxan aunerdem noch [Norbornyl-(2)]-[l.4-dioxanyl]-sulfid (5) entsteht. Die Bildungsweisen dieser Verbindungen werden diskutiert.
“…290 and 390 nm. The more complex transient behavior displayed by carbonyl sulfide is supposedly due to the intervention of both excited singlet ( 1 D 2 ) and triplet ground state ( 3 P J ) sulfur atoms and their competing followup reactions. − ,,,,, …”
Section: Resultsmentioning
confidence: 99%
“…While the direct photolysis of OCS affords primarily S( 1 D 2 ) with unit quantum yield, , the addition of the triplet sensitizer mercury, or of deactivating colliders like CO 2 , or noble gases, rendered the photolysis of OCS in the gas phase a selective source for ground state ( 3 P J ) atoms . Similarly, when the OCS photolysis was carried out in alcohols, acetonitrile, or aromatic solvents, no evidence for the reactions of excited S( 1 D 2 ) atoms could be obtained, but only the characteristic ground state S( 3 P J ) reactions were observed. , …”
Section: Introductionmentioning
confidence: 99%
“…It is well-known that S( 1 D 2 ) atoms react with paraffins to undergo C−H insertion reactions and deactivation, ,, while S( 3 P J ) atoms do not efficiently undergo this reaction with paraffins, alcohols, and acetonitrile (eq 6). , Several relative 33,34,42,51-53 and absolute − rate constants for the vapor reactions of S( 1 D 2 ) have been reported over the years. The majority of the known absolute rate constants for sulfur atoms, however, refer to the gas phase reactions of ground state atoms S( 3 P J ) with alkenes 17,18,57-59 and some halogenated olefins, alkynes, ethylene episulfide, ,, carbon disulfide, and carbonyl sulfide. , The absolute reaction rate constant between atomic sulfur and molecular oxygen in the gas phase has also received considerable attention 43,62,63 due to its importance as an elementary process in the oxidation and combustion of sulfur compounds at elevated temperatures.…”
The 248-nm laser flash photolysis of methyl isothiocyanate (MeNCS) was used to generate S( 3 P J ) ground state atoms in acetonitrile solution. The reaction of S( 3 P J ) atoms with the MeNCS precursor produces molecular diatomic sulfur S 2 ( 3 Σ g -) in its ground state, which possesses an absorption at ca. 270 nm. The first-order growth of this absorption was used to monitor the decay kinetics of the sulfur ( 3 P J ) atoms and to measure the rate constants for their reactions with additives. The rate constants obtained for a number of olefins, e.g., 9.7 × 10 7 M -1 s -1 for ethyl vinyl ether, hydrogen donors, e.g., 3.1 × 10 9 M -1 s -1 for tributyltin hydride, sulfur atom donors, e.g., 5.0 × 10 7 M -1 s -1 for carbon disulfide, and nucleophiles, e.g., 1.3 × 10 9 M -1 s -1 for chloride ions, demonstrate that S( 3 P J ) atoms behave as reactive, yet very selective, intermediates in solution; the highest reactivity was observed toward nitrogen and phosphorus nucleophiles, e.g., 1.2 and 2.1 × 10 10 M -1 s -1 for hydrazine and triethyl phosphite. The comparison with known nucleophilicity constants, e.g., for methyl iodide as electrophile, suggests further that S( 3 P J ) atoms act as potent but relatively soft electrophiles. The reaction modes between S( 3 P J ) atoms and the additives are assumed to involve abstractions of single atoms or addition to double bonds or lone electron pairs. The reaction rate constants for atomic sulfur S( 3 P J ) in solution are compared with previous gas phase data for S( 3 P J ) atoms and with the data for oxygen ( 3 P J ) atoms in solution.
“…290 and 390 nm. The more complex transient behavior displayed by carbonyl sulfide is supposedly due to the intervention of both excited singlet ( 1 D 2 ) and triplet ground state ( 3 P J ) sulfur atoms and their competing followup reactions. − ,,,,, …”
Section: Resultsmentioning
confidence: 99%
“…While the direct photolysis of OCS affords primarily S( 1 D 2 ) with unit quantum yield, , the addition of the triplet sensitizer mercury, or of deactivating colliders like CO 2 , or noble gases, rendered the photolysis of OCS in the gas phase a selective source for ground state ( 3 P J ) atoms . Similarly, when the OCS photolysis was carried out in alcohols, acetonitrile, or aromatic solvents, no evidence for the reactions of excited S( 1 D 2 ) atoms could be obtained, but only the characteristic ground state S( 3 P J ) reactions were observed. , …”
Section: Introductionmentioning
confidence: 99%
“…It is well-known that S( 1 D 2 ) atoms react with paraffins to undergo C−H insertion reactions and deactivation, ,, while S( 3 P J ) atoms do not efficiently undergo this reaction with paraffins, alcohols, and acetonitrile (eq 6). , Several relative 33,34,42,51-53 and absolute − rate constants for the vapor reactions of S( 1 D 2 ) have been reported over the years. The majority of the known absolute rate constants for sulfur atoms, however, refer to the gas phase reactions of ground state atoms S( 3 P J ) with alkenes 17,18,57-59 and some halogenated olefins, alkynes, ethylene episulfide, ,, carbon disulfide, and carbonyl sulfide. , The absolute reaction rate constant between atomic sulfur and molecular oxygen in the gas phase has also received considerable attention 43,62,63 due to its importance as an elementary process in the oxidation and combustion of sulfur compounds at elevated temperatures.…”
The 248-nm laser flash photolysis of methyl isothiocyanate (MeNCS) was used to generate S( 3 P J ) ground state atoms in acetonitrile solution. The reaction of S( 3 P J ) atoms with the MeNCS precursor produces molecular diatomic sulfur S 2 ( 3 Σ g -) in its ground state, which possesses an absorption at ca. 270 nm. The first-order growth of this absorption was used to monitor the decay kinetics of the sulfur ( 3 P J ) atoms and to measure the rate constants for their reactions with additives. The rate constants obtained for a number of olefins, e.g., 9.7 × 10 7 M -1 s -1 for ethyl vinyl ether, hydrogen donors, e.g., 3.1 × 10 9 M -1 s -1 for tributyltin hydride, sulfur atom donors, e.g., 5.0 × 10 7 M -1 s -1 for carbon disulfide, and nucleophiles, e.g., 1.3 × 10 9 M -1 s -1 for chloride ions, demonstrate that S( 3 P J ) atoms behave as reactive, yet very selective, intermediates in solution; the highest reactivity was observed toward nitrogen and phosphorus nucleophiles, e.g., 1.2 and 2.1 × 10 10 M -1 s -1 for hydrazine and triethyl phosphite. The comparison with known nucleophilicity constants, e.g., for methyl iodide as electrophile, suggests further that S( 3 P J ) atoms act as potent but relatively soft electrophiles. The reaction modes between S( 3 P J ) atoms and the additives are assumed to involve abstractions of single atoms or addition to double bonds or lone electron pairs. The reaction rate constants for atomic sulfur S( 3 P J ) in solution are compared with previous gas phase data for S( 3 P J ) atoms and with the data for oxygen ( 3 P J ) atoms in solution.
“…Be this as it may, the use of triplet atomic sulfur for stoichiometric preparative episulfidation is of little interest for the following reasons: (a) the photolysis of COS is conducted at wavelengths around 254 nm, and under these reaction conditions the thiiranes do not persistent sufficiently, since the small absorption coefficient of COS requires prolonged reaction times; and (b) the catenation propensity of triplet sulfur atoms leads to S 8 formation, which may only be suppressed at low COS pressure and becomes impractical at the preparative scale . A strategy to overcome these drawbacks was to conduct the reaction in the liquid phase in solvents such as aromatic hydrocarbons, cyclohexene, , alcohols, and acetonitrile; nevertheless, the episulfide yields were usually below 20%. The use of isothiocyanates as direct precursor to triplet atomic sulfur raised the yield of the episulfide up to 45% at 76% conversion of the alkene, as illustrated for cyclohexene (Scheme ) 25a.…”
Die COS‐Photolyse führt in Methanol und auch in Acetonitril in Gegenwart von Cyclohexen bzw. Octen‐(1) zur Bildung der entsprechenden Alkanepisulfide durch Reaktion von S(3P)‐Atomen mit den Olefinen.
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