Photooxidation of Alkyl 4-Nitrophenyl Sulfides and Sulfoxides. Observation of Oxidative C-S Bond Cleavage and Rearrangement Reactions
摘要:
Alkyl 4-nitrophenyl sulfides and sulfoxides undergo a self-photoinduced, singlet oxygen oxidation to produce a variety of products, including sulfonates and carbonyl compounds formed by the oxidative cleavage of the C-S bond of the sulfides and sulfoxides. Structural rearrangements are observed in the resulting carbonyl compounds formed in the oxidative cleavage of the C-S bond in the tert-amyl and 2-phenylethyl sulfides. An overall mechanism is proposed which involves the formation of peroxysulfoxides and peroxysulfones which undergo heterolytic C-S bond cleavage to form ion pairs which recombine to form persulfenates or persulfinates which then undergo photo- and/or thermally-induced homolytic O-O bond cleavage to form alkoxy and sulfinyl or sulfonyl radicals. The alkoxy radicals undergo beta-scission, disproportionation, or recombination with the sulfonyl radical to form the observed products. These C-S oxidative cleavage reactions have only been rarely observed in the earlier studies on the singlet oxygen oxidation studies of dialkyl sulfides, and are attributed, in part, to the presence of the 4-nitro group on the aromatic ring which greatly affects the susceptibility of the sulfur atom of the sulfides and sulfoxides toward nucleophilic attack, and on the reactivity of the peroxysulfoxides and peroxysulfones toward heterolytic cleavage of the O-S bond.
In order to obtain information concerning the reaction mechanism of the pyrolysis of sulfonium ylides bearing a substituted phenyl group on the 2-position in the S-ethyl group of ethylphenylsulfonium ylide, (2-phenylethyl)phenylsulfonium bis(methoxycarbonyl)methylide (1) and dicyanomethylide (2) were subjected to pyrolysis in benzene. The reaction rates of 1 and 2 at 140 °C were 6.0- and 3.2-times faster than those of ethylphenylsulfonium bis(methoxycarbonyl)methylide and dicyanomethylide, respectively. The activation parameters for 1 were ΔH‡ = 125 kJ mol−1 and ΔS‡ = −3.8 J K−1 mol−1, while those for 2 were ΔH‡ = 124 kJ mol−1 and ΔS‡ = −2.5 J K−1 mol−1. Substituent effects on the β-phenyl groups in 1 and 2 afforded positive Hammett ρ-values: ρ = 0.49 (γ = 0.997) and ρ = 0.26 (γ = 0.993), respectively.From the obtained results, it was suggested that the pyrolysis proceeds through essentially a concerted intramolecular cis-elimination inclined toward a slightly carbanion-like type from an E1-like type by introducing a phenyl substituent at the 2-position of the ethyl group in the ethylphenylsulfonium ylide.
In order to obtain information concerning the reaction mechanism of the pyrolysis of a sulfoxidebearing an electron-withdrawing substituent on the β-position in the S-ethyl group of ethyl phenyl sulfoxide, 2-(substituted phenyl)ethyl aryl sulfoxides(1) and 2-cyanoethyl (substituted phenyl) sulfoxides(2) were pyrolyzed. The rate-enhancing effect of the β-phenyl group of 1 was small. The activation
The use of aminoiminomethanesulfinic acid (thiourea dioxide) under phase transfer conditions for generating organochalcogenate anions. Synthesis of sulfides, selenides and tellurides
quenched by alkyl and activated aryl halides to give the corresponding sulfides and selenides in high yield (77–97%). The aryltellurolates react with alkyl halides giving the aryl alkyl tellurides in 81–96% yield. The procedure could not be successfully used for the synthesis of dialkylselenides and dialkyl tellurides; low yields and mixture of products were formed.
Arylisothiocyanate for the regulation of plant growth
申请人:Ciba-Geigy Corporation
公开号:US04004907A1
公开(公告)日:1977-01-25
New arylisothiocyanates corresponding to the formula ##STR1## wherein R represents alkyl, alkoxy or halogen X represents oxygen or sulfur and P represents an integer of from 2 to 5 are disclosed. They can be used for the regulation of plant growth especially for the dessication and defoliation of unlignified parts of plants above the soil.
only in the fundamentals but also in the economic and ecological fingerprint of organic reactions. Here we show that few-layer black phosphorous (FL-BP), a recently discovered and now readily available 2D material, catalyzes different radical additions to alkenes with an initial turnover frequency (TOF0) up to two orders of magnitude higher than representative state-of-the-art metal complex catalysts