Reactions of thiyl radicals. II. The photolysis of methyl disulfide vapor

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The photolysis of ethanethiol vapor in the pressure range 10 to 350 Torr and the effect of % decomposition, wavelength, and of added inert gas and ethylene on the rate of formation of the products has been determined. In addition, the effect of temperature on the photolysis of methanethiol-ethylene -inert gas and ethanethiol -ethylene -inert gas systems has been studied.For the pure substrate, the primary process is S-H bond cleavage and the hydrogen atom produced abstracts the sulfyhydryl hydrogen of the substrate. The quantum yield of molecular hydrogen formation is unity, independent of pressure. C,H5S radicals, formed either in the primary process or as a result of abstractive attack by H atoms or radicals on the substrate, combine to form an excited disulfide molecule.The major condensable product, C,H5SSC,H,, arises via collisional deactivation of this excited species which can also sensitize the decomposition of the substrate to give C2H4, C2H6, and H,S, the other products observed. With added inert gas the rates of formation of the mlnor products decrease whereas hydrogen and disulfide remain unchanged.With added ethylene, the major products are H,, C2H5SSC2F15, and C2H,SCZH,, the addition product. Diethyl sulfide is forrned in a chain reaction by the attack of C2H5S on the olefinic double bond to form the con~posite radical, followed by H abstraction from the substrate. The hydrogen rate decreases due to the addition of H atoms to ethylene. Thc rate constant ratio, kzzlk4, for the reactions [22] and [4], respectively,is pressure dependent, indicative of the formation of hot hydrogen atoms in the primary process of the photolysis of methanethiol and ethanethiol. The Arrhenius parameters A,Z/A4 and E,, -E, for the methanethiol-ethylene and ethanetl~iol-ethylene systems have been determined. Kinetic treatments of the proposed mechanisms have been undertaken.

Section: Natlrre Of the Prin~ary Process A~d Fates Of Thementioning

confidence: 99%

Section: Natlrre Of the Prin~ary Process A~d Fates Of Thementioning

confidence: 99%

mentioning

confidence: 99%

See 1 more Smart Citation

Reactions of thiyl radicals. VI. Photolysis of ethanethiol

Steer¹,

Knight²

1969

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“…In Part I1 of this series (5) it was shown that in the gas phase methyl disulfide photolyzes with S-S bond scission. The main fate of the CH,S radicals produced at substrate pressures between 2 and 25 Torr is recombination to reform the substrate.…”

Section: Introductionmentioning

confidence: 99%

Reactions of thiyl radicals. III. Photochemical equilibrium in the photolysis of liquid disulfide mixtures

Sayamol¹,

Knight²

1968

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The photolysis of mixtures of liquid methyl disulfide and ethyl disulfide at room temperature at wavelengths greater than 2300 A has been investigated. The sole detectable product is methyl ethyl disulfide which reaches a photostationary state concentration after relatively short irradiation periods. For various initial mixtures, the concentration of the three disulfides in the photostationary state can be

“…The photolyses were conducted in a conventional high vacuum system described previously (3). The light source was a Hanovia 30620 medium pressure mercury lamp filtered to remove wavelengths less than 2000 A.…”

Section: Introductionmentioning

confidence: 99%

Reactions of Thiyl Radicals. VIII. Photolysis of Methyl Ethyl Sulfide Vapor

Tycholiz¹,

Knight²

1972

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Methyl ethyl sulfide has been photolyzed in the vapor phase with wavelengths between 2000 and 2350 A and the effects of pressure, temperature, and exposure time investigated. The vapor phase absorption spectrum of the sulfide has been determined and the variation in the nature and rates of formation of products in the presence of C 0 2 , CF,, propylene, and 2-pentene measured. Quantum yields of products from the decomposition of the pure substrate were determined at 2288 A.The products of the reaction are, in order of decreasing importance, C2H6, CH3SSC2H,, C,H,SSC,H,, CH,, CH3SCH3, C2H,SC2H,, C3Hs, C2H,, CH3SSCH3, C,Hlo, C,H,SH, and CH,SH. Acarbon/sulfur mass balance is obtained at all substrate pressures at 25 "C, and at the single substrate pressure examined at 120 "C. In the presence of propylene four additional products, n-C,H,,, CH,S(CH,),CH,, (CH,CH,CH,),S, and CH,=CH-CH2SC2H5, were found. Only a small fraction of photochemically excited methyl ethyl sulfide molecules undergoes chemical decomposition. The two primary processes and subsequent reactions of the radicals so formed account for the observed products. R,,,/R,, has a value of 1.32 at 25 "C.