- Nucleophilic reactions at the sulfur of thiiranium and thiirenium ions. New insight in the electrophilic additions to alkenes and alkynes. Evidence for an episulfurane intermediate
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The thiiranium hexachloroantimonates 1a, 3, and 5a-c and the thiirenium hexachloroantimonates 6a-c and 7a with exocyclic S-R substituent (R = Me, Et, i-Pr) react at sulfur with dialkyl disulfides R″SSR″ (R″ = Me, Et and R″ ≠ R) in CD2Cl2 at 25°C to give S-R″ substituted ions. The reaction rates are affected by the steric hindrance of the substituents at sulfur and at ring carbons. t-2,t-3-Di-tert-butyl-r-1-methylthiiranium hexachloroantimonate (2) does not react, and the t-2-tert-butyl-c-3-phenyl-r-1-methylthiiranium (5a) reacts about 100 times faster than the c-2,t-3-di-tert-butyl-r-1-methylthiiranium ion (1a). The analysis of the kinetic data suggests that the sulfonium sulfur undergoes attack by the disulfide in the ring plane from a direction that is parallel to the C-C ring bond. This is also the direction which ensures the maximum overlap with the LUMO of thiiranium or thiirenium ions (determined at the RHF/3-21G*//RHF/3-21G* level). The combined consideration of the approach modality and of the maximum orbital overlap suggests that the nucleophilic substitution at sulfonium sulfur is not an SN2-like reaction but occurs via an intermediate with episulfurane-like structure. The principle of microscopic reversibility will dictate that this is also the first intermediate in the electrophilic sulfenylation of unsaturated C-C bonds.
- Fachini, Marco,Lucchini, Vittorio,Modena, Giorgio,Pasi, Manuela,Pasquato, Lucia
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Read Online
- Phosphine-catalyzed disulfide metathesis
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The reaction between disulfides and phosphines generates a reversible disulfide metathesis process. The Royal Society of Chemistry 2008.
- Caraballo, Remi,Rahm, Martin,Vongvilai, Pornrapee,Brinck, Tore,Ramstroem, Olof
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scheme or table
p. 6603 - 6605
(2009/04/20)
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- Thiophilic addition of organolithiums to trithiocarbonate oxides (sulfines). Synthesis of β-oxoketene dithioacetals, 1,4-dicarbonyl compounds, and allyl sulfoxides
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Reaction of trithiocarbonates with meta-chloroperoxybenzoic acid in CH2Cl2 at 0°C affords the corresponding S-oxides. These sulfines are relatively stable comppounds which can be purified by chromatography. They react readily with organolithiums in THF at -78°C in a thiophilic manner to give carbanions which are stabilized by three sulfur groups. Hydrolysis affords trithioorthoester oxides. The thermal behaviour of these hindered products has been investigated and new rearrangenrent processes have been evidenced. The former carbanions are soft nucleophiles: 1,4-addition of these intermediates to α-enones was achieved selectively to lead to β-oxo ketenedithioacetals, which are easily transformed into 4-oxoalkanethioates. This 'Umpolung' route allows the formal use of the (alkylthio)carbonyl anion. A thiophilic addition was also observed with allylsilanes in the presence of n-Bu4NF furnishing allyl sulfoxides.
- Leriverend, Catherine,Metzner, Patrick,Capperucci, Antonella,Degl'Innocenti, Alessandro
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p. 1323 - 1342
(2007/10/03)
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- SCAVENGING OF RADICALS FROM THE GAS PHASE BY FREEZING WITH DIMETHYL DISULFIDE: 2. RADICALS FROM DISCHARGES AND A FLAME OF ACETYLENE.
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The method of detecting radicals from low-pressure gas-phase systems by scavenging with dimethyl disulfide (DMD) has been applied to microwave discharges in C//2H//2/He mixtures and to a C//2H//2/O//2 flame. It was accomplished by condensing a supersonic nozzle beam from the reaction system together with a beam of DMD on a liquid-N//2 cooled surface. The scavenging products were measured by GC/MS after warming-up. Radicals measured in the discharge were C//2H, C//4H, C//6H, C//3H//2, C//2 besides H atoms. Preliminary measurements on the flame showed that C//6H//5 (phenyl), CH//2, C//3H//2, besides H and O atoms were prominent radicals at the end of the oxidation zone. The concentration of phenyl is of the same order as that of e. g. naphthalene.
- Kubitza,Schottler,Homann
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p. 695 - 700
(2007/10/02)
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- SCAVENGING OF RADICALS FROM THE GAS PHASE BY FREEZING WITH DIMETHYL DISULFIDE: 1. TEST OF THE METHOD FOR LIGHT RADICALS.
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H and O atoms and methyl radicals produced in microwave discharges of H//2/He, O//2/He and CH//4/He mixtures, respectively, were scavenged by supersonic nozzle probing with subsequent freezing and reaction with dimethyl disulfide on a liquid nitrogen cooled wall. The main reaction products for the three kinds of radicals were CH//3SH, CH//3S(O)SCH//3 and CH//3SCH//3, respectively. The scavenging efficiencies for the different radicals were determined and measured as a function of the gas phase radical concentration, the flow of scavenger molecules, the pressure in the vacuum chamber, and the conditions of the discharge and the flow through the sampling nozzle. It is concluded that this method is suitable for light radicals with reservations in the case of H atoms and can probably be used with still better success for heavier radicals.
- Schottler,Homann
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p. 688 - 694
(2007/10/02)
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- Gas-phase reactions of O(3P) atoms with methanethiol, ethanethiol, methyl sulfide, and dimethyl disulfide. 2. Reaction products and mechanisms
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In conjunction with the determinations of the rate constants of reactions of the ground-state oxygen atoms, O(3P), with methanethiol, ethanethiol, methyl sulfide, and dimethyl disulfide described in the preceding paper,3 a parallel study was carried out of the products and mechanisms of the same reactions at 300 K. Oxygen atoms were generated by the mercury-photosensitized decomposition of N2O, used in large excess, and the recovered products were analyzed by gas chromatography. The total pressure was varied from 300 to 1200 torr. Nitrogen formed in the photosensitized decomposition of N2O provided a direct measure of the number of O atoms generated and allowed determination of the yields of some of the products per oxygen atom reacting with the sulfur organic compounds. From a detailed analysis of the experimental results obtained with single sulfur organics and their mixtures, it is possible to derive substantial quantitative information on the reaction mechanisms. The postulated overall reaction mechanisms include some novel features common to the thiols, sulfide, and disulfide studied, which provide a simple explanation for some unexpected experimental trends observed.
- Cvetanovic,Singleton,Irwin
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p. 3530 - 3539
(2007/10/02)
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