926-09-0Relevant articles and documents
Keto-difluoromethylation of aromatic alkenes by photoredox catalysis: Step-economical synthesis of α-CF2H-substituted ketones in flow
Nakayama, Yoshiki,Ando, Gaku,Abe, Manabu,Koike, Takashi,Akita, Munetaka
, p. 6555 - 6563 (2019)
A step-economical method for synthesis of α-CF2H-substituted ketones from readily available alkene feedstocks has been developed. Radical difluoromethylation of aromatic alkenes combining DMSO oxidation and photoredox catalysis is a key to the successful transformation. Electrochemical analysis, laser flash photolysis (LFP), and density functional theory (DFT) calculations reveal that N-tosyl-S-difluoromethyl-S-phenylsulfoximine serves as the best CF2H radical source among analogous sulfone-based CF2H reagents. The present photocatalytic keto-difluoromethylation has been applied to flow synthesis and easily scaled up to gram-scale synthesis within a reasonable reaction time. Furthermore, potentials of the α-CF2H-substituted ketones for useful synthetic intermediates are shown; e.g., synthesis of the CF2H-containing α-hydroxyamide with the same carbon skeleton as that of the anticonvulsant active CF3-analogue, is disclosed. Additionally, mechanistic studies are also discussed in detail.
Reactions and products revealed by NMR spectra of deuterated dimethylsulfoxide with iodomethane in neutral and basic media
Avella-Moreno,Nu?ez-Dallos,Garzón-Tovar,Duarte-Ruiz
, p. 535 - 543 (2015/10/19)
Reactions occurring within each one of two mixtures, a mixture of deuterated dimethylsulfoxide, DMSO-d6, with CH3I (system I) and another mixture of DMSO-d6 with CH3I, NaOH and water (system II), were monitored by 1D and 2D nuclear magnetic resonance (1H, 13C, heteronuclear multiple quantum correlation, heteronuclear multiple bond correlation and diffusion-ordered NMR spectroscopy). The analysis of the spectra as a function of reaction time revealed the formation of methoxy-bis(trideuteromethyl)sulfonium iodide, 3; the precipitation of hexadeuterated trimethyloxosulfonium, 2a; a methyl exchange between DMSO-d6 and 2a to produce trideuterated dimethylsulfoxide, DMSO-d3, 4, and nona-deuterated trimethyloxosulfonium iodide, 2b; and the production of small quantities of methanol, 5, trideuterated dimethylsulfide, 6, and dimethyl ether, 7, in both systems. Only system II precipitated deuterated [Na4(DMSO-dx)15][(I3)3I], 1a, a green solid with metallic shine that corresponds to an isotopomer of 1, which is produced by the self-assembly of DMSO and CH3I in the presence of NaOH and water.
Reaction of OH with Dimethyl Sulfide (DMS). 1. Equilibrium Constant for OH + DMS Reaction and the Kinetics of the OH*DMS + O2 Reaction
Barone, Stephen B.,Turnipseed, Andrew A.,Ravishankara, A. R.
, p. 14694 - 14702 (2007/10/03)
The formation of a weakly bound adduct in the reaction of OH with DMS-d6 was observed between 217 and 240 K using the technique of pulsed laser photolysis/pulsed laser-induced fluorescence.The equilibrium constant for this process, OH + DMS-d6 OH*DMS-d6, was measured as a function of temperature.The bond strength of this adduct was determined to be 10.7 +/- 2.5 kcal mol-1.The weakly bound adduct was observed to react rapidly with O2.The rate constant for the reaction OH*DMS-d6 + O2 -> products was determined to be (1.00 +/- 0.33)E-12 cm3 molecules-1 s-1, independent of pressure and temperature.The atmospheric implications of the formation of this adduct and its reaction with O2 to the mechanism of DMS oxidation in the atmosphere are discussed.
A Mechanistic Study of the Reaction of OH with Dimethyl-d6 Sulfide. Direct Observation of Adduct Formation and the Kinetics of the Adduct Reaction with O2
Hynes, A. J.,Stoker, R. B.,Pounds, A. J.,McKay, T.,Bradshaw, J. D.,et al.
, p. 16967 - 16975 (2007/10/02)
A pulsed laser photolysis-pulsed laser-induced fluorescence technique has been employed to study the detailed mechanism for the reaction of OH radicals with deuterated dimethyl sulfide .Equilibration of pulsed laser-generated OH with a (CD3)2S-OH adduct has been directly observed, thus confirming the existence of this controversial weakly bound species.Elementary rate coefficients for adduct formation and decomposition and, therefore, the equilibrium constant for OH + (CD3)S (CD3)2SOH have been determined as a function of temperature.From tte temperature dependence of the equilibrium constant over the relatively narrow temperature range 250-267 K, a 258 K adduct bond strength of 13.0 +/- 3.3 kcal mol-1 has been obtained (second law method).Alternatively, an entropy change calculated using standard statistical mechanical methods and ab initio theory (for determining the (CD3)2S and (CD3)2SOH structures) has been employed in conjunction with an experimental value for the equilibrium constant at a single temperature to obtain a 258 K adduct bond strength of 10.1 +/- 1.1 kcal mol-1 (third law method).Experiments in the presence of O2 confirm the previously reported dependence of the OH + DMS-d6 rate coefficient on the O2 partial pressure and are consistent with the previously proposed four-step mechanism involving hydrogen abstraction, addition of OH to the sulfur atom, and adduct decomposition in competition with an adduct + O2 reaction .The rate coefficient for the adduct + O2 reaction is found to be (8 +/-3 ) x 1E-13 cm3 molecule-1 s-1 independent of pressure (100-700 Torr of N2) and temperature (250-300 K).
THERMODYNAMICS OF S THEREFORE S2 sigma /1 sigma * THREE-ELECTRON BONDS AND DEPROTONATION KINETICS OF THIOETHER RADICAL CATIONS IN AQUEOUS SOLUTION.
Moenig,Goslich,Asmus
, p. 115 - 121 (2007/10/02)
These experiments on the determination of K//1 and the associated rate constants were conducted at various temperatures and thus provided for the first time experimentally determined thermodynamic parameters ( DELTA H** does not equal and DELTA S** does not equal ) for the unimolecular dissociation of the three-electron bond. This in turn will allow an experimental estimate for the sulfur-sulfur bond strength in (R//2S therefore SR//2)** plus . Up to now only a theoretical ab-initio value has been published, namely 130 kJ mol** minus **1 for the simplest congeneric species with all R equals H. The kinetic and thermodynamic results substantiate previous conclusions on the electronic structure and relative stability of S therefore S bonded radicals and corroborate some theoretical calculations.
RADICAL CATIONS OF ORGANIC SULPHIDES AND DISULPHIDES FORMED BY RADIOLYSIS: AN ELECTRON SPIN RESONANCE STUDY
Rao, Ramakrishna D. N.,Symons, M. C. R.,Wren B. W.
, p. 1681 - 1688 (2007/10/02)
Exposure of dilute solutions of various organic sulphides in fluorotrichloromethane at 77 K to 60Co γ-rays gave species identified by their e.s.r. spectra as the parent radical cations.The average β-proton coupling (R2CHS.R)+ of ca. 20 G is about half that for the corresponding ether cations, indicating greatly reduced ?-? delocalisation.However, the spread of g-values (ca. 2.032, 2.015, 2.00) is much greater than that for the ether cations.These cations readily react with other disulphide molecules to form (R2S.-SR2)+ dimer cations.The spectrum for tetrahydrothiophene (tetramethylene sulphide) exhibits a large coupling to two axial protons (ca. 42 G) and two equatorial protons (ca. 19 G), the coupling constants again being about half those for tetrahydrofuran cations.However, conformational inversion did not occur below the softening point of the solids (ca. 160 K) in marked contrast with the ether cations.The three-and four-membered ring cations (ethylene and trimethylene sulphide cations) gave very similar spectra with gx = gy, and four equivalent protons having an isotropic coupling of ca. 31 G.Thus their structures are similar to the normal R2S.+ cations, the equivalence of the g-values being interpreted in terms of effective C-S-C bond angles (θ) close to 90 deg.This, in turn, implies that θ > 90 deg for the unconstrained cations.It is noteworthy that the ethylene oxide (oxirane) cation exhibits a smaller coupling to its four protons (16 G).This implies a drastic change in structure for the oxirane cation which is clearly not the case for the sulphur analogue.Disulphides of structure R-S-CH2-S-R form cyclic ?* radicals with weak S-S bonding, in marked contrast with the oxygen analogues (acetal cations) which have ?-structures conferring very high spin-density onto the CH2 protons.Other molecules containing two RSR units form similar cyclic ?* radicals.Persulphides of structure RS-SR readily give the ?-cations (RS.SR)+, characterised by g-values in the region of 2.035, 2.018, 2.002.The smaller range of g values for (PhS.-SPh)+ cations is interpreted in terms of ca. 30percent spin-delocalisation into both the benzene rings.
Chemistry of peroxyacyl nitrates. Part III. The oxidation of thioethers by peroxyhexanoyl nitrate
Noort, Paul C. M. van,Vermeeren, Hans P. W.,Louw, Robert
, p. 312 - 321 (2007/10/02)
The reaction of peroxyhexanoyl nitrate, 1a, a homologue of the atmospheric pollutant "PAN", 1b, with some twenty thioethers, is described.At 0-25 deg C, common thioethers such as Et2S or PhSMe are rapidly converted into sulfoxides in high yields in a variety of solvents, ranging from pentane and chloroform to acetic acid, methanol and aqueous acetonitrile.Rates are essentially solvent-independent, although the reaction is subject to marked steric hindrance.Relative rates for five p-substituted thioanisoles in MeOH at 22 deg C, leading to a Hammett ρ-value of -1.7, show that the sulfur atoms display nucleophilic character.Electron-attracting groups on α-carbon, such as in PhSCCl3 and in MeSCH2OC(O)Ph, inhibit the formation of sulfoxide.Addition of EtSH lowers the yield of sulfoxide, producing instead EtSSEt and EtSNO.Oxidation of Me2S by 1a with the NO2 group labelled by 18O does not give rise to 18O-enriched DMSO.Comparison of (CH3)2S with (CD3)2S revealed an inverse kinetic H/D isotope effect.The products obtained from 1a vary with solvent.In the presence of water or EtSH, hexanoic acid is formed, while methanol gives rise to methyl hexanoate, and in pentane/hexanoic acid, hexanoic anhydride is produced.In aprotic solvents, significant amounts of CO2 are formed.These observations can best be rationalized on the basis of an intermediate sulfurane R1R2S(ONO2)(OCOR), (I), produced from thioether R1SR2 and 1a, in the first step.The fate of (I) under various conditions is discussed.Finally, the features of the oxidation of thioethers by peroxyacylnitrate are compared with those of acyl peroxides and peroxy esters.It is suggested that in each case formation of a sulfurane may well be the first step.
REACTION OF NUCLEOPHILES WITH ELECTRON ACCEPTORS BY SN2 OR ELECTRON TRANSFER (ET) MECHANISMS: TERT-BUTYL PEROXYBENZOATE/DIMETHYL SULFIDE AND BENZOYL PEROXIDE/N,N-DIMETHYLANILINE SYSTEMS.
Pryor,Hendrickson Jr.
, p. 7114 - 7122 (2007/10/02)
This study is one of a series that probes the reactions of nucleophiles with peroxides, reactions that can occur either by an initial S//N2 reaction or by an electron-transfer (ET) reaction. The products and kinetics are reported for the reaction of dimethyl sulfide and a series of ring-substituted aryl methyl sulfides with tert-butyl peroxybenzoate (TBP) and four ring-substituted TPB's. Kinetic analysis allows the separation of the rate constants for unimolecular homolysis (k//1) and those for the decomposition of the TBP by the sulfide (k//2). The bimolecular reaction is accelerated by electron-withdrawing substituents in the TBP; for example, when 3,5-(NO//2)//2-TBP is used, k//2/k//1 is 12,000. The products that are formed are consistent with a radical process; however, this evidence is not regarded as conclusive.
