Transient spectra and primary processes in the flash photolysis of CH3SSCH3, CH3SCH3, CH3SH and C2H5SH

. Can. J. Chem. 59,2750Chem. 59, (1981.The photolytic oxidation of methyl mercaptan, dimethyl sulphide, and dimethyl disulphide was studied in a batch photolysis apparatus. Short wavelength ultraviolet light was provided by a deuterium discharge lamp and monitored by a monochromator equipped with an extended response photomultiplyer tube. Sulphide concentrations were determined using a gas chromatograph equipped with a flame photometric detector having a sulphur response at 365 nm.The rate of photo-oxidation of methyl mercaptan was found to be a linear function of the photon absorption rate and exhibited a quantum yield of 12. The methyl mercaptan photo-oxidation rate was found to be unaffected by increased oxygen concentration, decreased atmospheric pressure, or the presence of sulphur dioxide.The quantum yield of dimethyl sulphide photo-oxidation was found to be dependent upon air pressure; the quantum yield of 4 at 1 atm pressure increased to 8 at batm.The quantum yield of dimethyl disulphide photo-oxidation in air was found to be 1. On trouve que la vitesse d'oxydation photochimique du methylmercaptan est lineaire en fonction de la vitesse d'absorption du photon et presente un rendement quantique de 12. On a trouve que la vitesse d'oxydation photochimique du methylmercaptan n'est pas affectee par une augmentation de la concentration en oxygene, par la diminution de la pression atmospherique ou par la presence du bioxyde de soufre.On a trouve que le rendement quantique de I'oxydation photochimique du sulfure de dimethyle depend de la pression d'air; le rendement quantique qui est de 4 a la pression atmospherique passe 8 une pression de 0,25 atmosphere.Dans le cas du disulfure de dimethyle le rendement quantique dans I'air est de 1.9 a la pression atmospherique pour une concentration en disulfure de 7,04 x M .[Traduit par le journal]

Section: (C) Irradiation Of Methyl Mercaptan In Airsupporting

confidence: 85%

Quantum yields in the photolytic oxidation of some sulphur compounds

Sheraton¹,

Murray²

1981

“…It has been suggested previously that this primary process characterizes the liquid phase photolysis (1, 2), the Hg-sensitized decomposition (5), and the gas phase photolysis in both a conventional system (3) and in flash photolysis (4).…”

Section: Discussionmentioning

confidence: 99%

“…Both are exothermic, 66 and 26 kcal/mol respectively, but the reaction forming methane and thioformaldehyde is more favored energetically. Furthermore, the absence of S2 in the flash photolysis of CH,SCH, (4) suggests that reaction 6 is not an important mode of decomposition of excited methyl sulfide molecules.…”

Section: Discussionmentioning

confidence: 99%

Reactions of Thiyl Radicals. VII. Photolysis of Methyl Sulfide Vapor

Rao¹,

Knight²

1972

The photolysis of methyl sulfide vapor has been investigated as a function of substrate pressure, exposure time, and temperature in the wavelength range 2000 to 2300 Å. The effects of added propane, sulfur hexafluoride, and 2-methylpentane have been studied. The principal products of the decomposition are CH4, C2H6, CH3SSCH3, and CH3SH. The data indicate direct C—S bond scission in the primary process giving rise to "hot" CH3 and CH3S radicals. A mechanism in which disproportionation of methylthiyl radicals is a very minor process is proposed.The reactions of CH3 and CH3S radicals with methyl sulfide have been examined also by photolyzing CH3SSCH3 and CH3COCH3 in the presence of CH3SCH3. Quantum yields at 2288 Å have been determined as a function of several variables. A number of rate parameters for the reactions of methyl radicals and methylthiyl radicals have been calculated.

“…spectrum of dilute thiol solutions in xenon further indicates that the primary photolytic process must be similar in both the vapor and the glassy state. This may be true for 2537 mercury excitation alone, since it has been shown in the vapor phase with the use of higher photon energies, that C-S bond rupture becomes the more probable decomposition route (19).…”

Section: A Photolysismentioning

confidence: 99%

“…The effect of radiation or of photolytic absorption on the pure mercaptans has been extensively studied in the gaseous state (11,12), in the solid polycrystalline state (13,14), and in single crystals such as cysteine (15,16). The metastable intermediates of chemical oxidation in dilute aqueous solutions have also been studied using fast flow techniques (17,18), flash photolysis (19), or pulse radiolysis methods (20), but until recently not much work had been done on the radiolysis and photolysis of thlols in dilute rigid solutions using inert or chemically indifferent organic matrices. We wish to report on some of the work done in this direction Can.…”

Section: Introductionmentioning

confidence: 99%

The Photolysis and Radiolysis of Simple Mercaptans in Dilute Glassy Matrices

Skelton¹,

Adam²

1971

The e.p.r. spectrum of thiyl radicals is obtained when dilute solutions of aliphatic mercaptans are photolyzed in a xenon matrix at 77 OK. No proton hyperfine structure is observed at low concentrations of thiol but it appears at higher concentrations due to the reaction of hot hydrogen atoms with solute mercaptan molecules. When small amounts of the thiols are dissolved in glassy hydrocarbon matrices such as 3-methylpentane, there is produced after photolysis hyperfine structure characteristic of the solvent as well as the thiyl resonance. The e.s.r. absorption due to the solvent species disappears when the matrix is warmed a few degrees above 77 "K but thiyl radicals are stable up to the melting point of the glass. The corresponding y-irradiated glasses do not give thiyl absorption, but two other species are produced along with solvent radicals. No thiyl radicals are observed following radiolysis, or upon photobleaching the new species. The spatial distribution of the neutral radicals in the glasses is discussed in view of these results.Le spectre de r.p.e. de radicaux thiyl est obtenu lors de la photolyse de solutions dilukes de mercaptans aliphatiques dans une matrice de xenon a 77 OK. On n'observe pas la structure hyperfine du proton en utilisant de faibles concentrations de thiol, mais elle apparait lorsqu'on utilise des concentrations plus ClevCes a cause de la reaction des atomes d'hydrogkne chauds avec les molCcules de mercaptan en solution. Si on dissout de petites quantites de thiol dans des matrices d'hydrocarbure vitreuses, tel le methylpentane-3, il se produit apres photolyse, une structure hyperfine qui est caracteristique du solvant aussi bien que de la resonance du thiyl. L'absorption r.p.e. due a l'espece solvant disparait quand la matrice est chauffee a quelques degris au-dessus de 77 OK, mais les radicaux thiyl demeurent stables jusqu'au point de fusion du verre. Les verres irradits aux rayons-y ne donnent pas d'absorption thiyl, mais deux autres especes sont produites en meme temps que les radicaux de solvant. On n'observe pas de radicaux thiyl apres radiolyse, ou pendant la photodCcoloration des nouvelles espkces. On discute de la distribution spatiale des radicaux neutres dans les verres pour arriver aces rksultats.