Pyrolysis selenium oxides

Shock-tube experiments on the decomposition of hydrogen sulphide have been performed but were unsuccessful because traces of oxygen and other oxidizers could not be removed from the reactant24. No data are available on the homogeneous decomposition of hydrogen polysulphides, nor have the kinetics of pyrolysis of selenium and tellurium hydrides been studied. 

Subsequent epidemiological studies have supported the association between better health and long-term consumption of diets rich in foods of plant origin. " However, whether this is because such diets minimize exposure to deleterious substances (e.g., oxidized cholesterol, pyrolysis mutagens, salt, saturated fat, etc.), or maximize intake of certain beneficial nutrients (e.g., isothiocyanates and other sulfur-containing plant constituents, mono-unsaturated fatty acids, and poly-unsaturated fatty acids, PPT, poly acetylenes, selenium, terpenes, etc.) or some combination as advocated in the Polymeal concept, remains unknown. " An in vitro study indicates that there may be mechanistic basis for true synergy between PPT and isothiocyanates. ... 

A second proof of the ring system was the formation of anhydro-methylpseudolycorine (LVIIIa) in the pyrolysis of galanthine. This product and its phenanthridone (LVIIa) were identical with material obtained in a similar fashion from methylpseudolycorine. Galanthine was oxidized by selenium dioxide to a quaternary base (LXIV) which... 

Selenium dioxide oxidation of aryl ketone semicarbazones (4) in acetic acid affords 1,2,3-selenadiazoles (5). Pyrolysis of the latter gives selenium and the arylacetylenes (6) in good yield. The same procedure has been used to prepare cyclo-octyne in 34% yield. ... 

Oxidation of 2-methoxycarbonylcyclopentan-2-one with selenium dioxide in refluxing dioxan gives (323) in 45% yield.The latter is thought to be the first simple cyclopentenone containing an electron-withdrawing substituent in position 2, a situation which probably enhances the readiness to polymerization exhibited by cyclopentenone. Indeed attempts at purification of (323) result in rapid polymerization. However, (323) may be trapped by formation of Diels-Alder adducts, in particular the adduct with cyclopentadiene on pyrolysis at 438 °C gave a pure sample of (323) which was trapped at —10 °C. 

Meier has provided an excellent review of medium- and large-ring cyclic acetylenes. Cycloheptyne and cyclo-octyne may be obtained by pyrolysis of (144 n = 7 or 8), which can be readily obtained by selenium dioxide oxidation of the corresponding semicarbazones the photochemistry of cyclo-octyne in the presence of molybdenum hexacarbonyl is discussed. Compound (145) reacts with sodium methoxide to give (146) the acetylene (147) is proposed as an intermediate. 

The general synthetic methods for [2.2] CPs have been already estabhshed. Most of them employ the ring contraction reactions of the 2,11-diheteroatom-substituted [3.3]CPs. Photochemical ehmination of sulfur or selenium atoms from [3.3] CP-2,11-disulfide or diselenide and flash vacuum pyrolysis of sulfur dioxide obtained by the oxidation of the corresponding sulfides are the most general methods. 2,11-Diaza[3.3]CPs are converted to the corresponding [2.2]CPs via their nitroso derivatives by reductive elimination of nitrogen. " Photoextrusion reactions of COj from cychc diesters can also be appHed to the synthesis of [2.2]paracyclophanes (PCPs)"- and [2.2]heterophanes, as described below. "... 

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