1,721,000 research outputs found
Methylbenzene cation radical a-fragmentation selectivities revealed in SET-photoadditions of p-xylene derivatives to 1,4-dicyanonaphthalene
No full textPhotochemical reaction of arenecarbonitriles in the presence of alkylsilanes, silyl ethers and silyl amines
No full textThe irradn. of benzene-1,2,4,5-tetracarbonitrile, and benzene-1,2,4- as well as benzene-1,3,5-tricarbonitrile in the presence of various tetraalkylsilanes, alkoxytrialkylsilanes, hexamethyldisiloxane or heptamethyldisilazane leads to alkylation of the aromatics
Palladium nanoparticles, stabilized by lignin, as catalyst for cross-coupling reactions in water
No full textPalladium nanoparticles of a definite shape (spherical) and dimension (8–14 and 16–20 nm) were prepared employing two water soluble lignin samples as both reducing and stabilizing agent in definitely green experimental conditions, namely aqueous solution, aerobic conditions, moderate temperature,
short times. The above nanoparticles were employed as catalyst for a series of carbon–carbon coupling reactions carried out in water at mild conditions. Heck and Suzuki reactions were performed for several substrates, by changing the nature of halogen, the substituents at the aromatic ring, the bases employed and the temperature. Product yields were satisfactory and selectivities very good. Other two cross coupling reactions, namely Sonogashira and Stille, were also tested: iodine derivatives showed always the best reactivity, while chlorine derivatives did not react
Photodegradation of cyclohexanol sensitized by Fe(III) species in alkaline aqueous media
No full textThe degradation of cyclohexanol that can be photoinduced by Fe(III) derivatives (e.g. nitrate, pyrophosphate and sulfate) has been investigated
in aqueous media at room temperature and under neutral to alkaline conditions with continuous irradiation at 254, 366 and around 500 nm for
24 h. The conditions chosen are those putative to the Martian soil, and the experiments were relevant in view of the Viking experiments. The
conventional homogenous photocatalytic process that is based on the reduction of Fe(III) into Fe(II) and that is responsible for the continuous
production of hydroxyl radicals also occurs under the alkaline conditions used. During the oxidation of cyclohexanol, cyclohexanone was formed
in reasonable amounts in the presence of the nitrate salt, while with the other two iron salts it was present in negligible amounts, and carbon dioxide
was instead the dominant reaction product. Together with cyclohexanone, some unusual dihydroxylated and ketohydroxylated cyclic products
were also formed. The full product distribution allows us to infer the mechanism involved: the nitrate salt produces a large amount of HO• that
leads to an unselective reaction pathway, with the formation of a several cyclohexyl reaction products, while with iron pyrophosphate and iron sulfate, mineralization to CO2 is the dominant pathway, although there remains a minor conversion pathway to cyclohexanol (35% versus 85% of the aqueous cyclohexanol nitrate salt)
Oxidation of C1–C4 alcohols by iron- and ruthenium-sulfophthalocyanine precatalysts with hydrogen peroxide or mono-persulfate in water
No full textA catalytic system consisting of iron- or ruthenium-sulfophthalocyanine and hydrogen peroxide or mono-persulfate was
effective in the oxidation of simple primary and secondary alcohols as well as of simple ketones. The oxidation reactions
were conducted in aqueous media with turnover rates, defined as moles of product per mole of catalyst per minute, up to 5.
Primary alcohols, including methanol, were selectively oxidized into the corresponding carboxylic acids. Secondary alcohols
were transformed into the corresponding ketones, which were found to undergo further oxidation to esters via Baeyer–Villiger
reaction, followed by hydrolysis or alternatively in the case of acetone via direct oxidation to acetic acid and CO2. Moreover,
t-butyl alcohol was also found to be slowly oxidized into acetone and methanol. Analysis of the oxidation reaction of
cyclobutanol indicated an ionic mechanism; no deuterium kinetic isotope effect was measured in the cases of methanol and
ethanol. The mechanistic origin of the catalytic efficiency is also discussed
One-pot synthesis of lignin-stabilised platinum and palladium nanoparticles, and their catalytic behaviour in oxidation and reduction reactions
No full textA one-pot green method to synthesise Pt and Pd nanoparticles is reported. Two natural aromatic
polymers, lignin and fulvic acid, were used as both reducing and stabilising agents at moderate
temperature (80 °C) in water and under aerobic conditions. Full characterisation was performed using
TEM, UV-vis, XRD, 195Pt and 1H NMR, FT-IR and GC-MS techniques. In the TEM images, we
observed spherical nanoparticles of diameters in the range of 16 nm to 20 nm, in the case of Pd, and
smaller ones of not so well defined shapes for Pt. GC-MS of the organic fractions formed during the
preparation of the nanoparticles showed defined amounts of vanillin, a well known degradation product of
these polymers. This finding indicates that the active participation of lignins and fulvic acids in the metal
reduction step. The catalytic activity of the nanoparticles was tested for the NaBH4 reduction of
4-nitrophenol and for the aerobic oxidation of alcohols, reactions that are always conducted under green
conditions. Both Pt and Pd nanoparticles show good catalytic activity in the reduction reaction, while in
the aerobic oxidation reaction only the Pt nanoparticles were effective
Evidence for a Charge-Transfer Intermediate in the Catalytic Epoxidation of Alkenes by Ruthenium Complexes: a Comparison between Electrochemical and Kinetic Data
No full textEvidence for a charge-transfer intermediate in the catalytic epoxidation of alkenes by ruthenium complexes: a comparison between electrochemical and kinetic data.
No full text
Direct Synthesis of Adipic Acid by Mono-Persulfate Oxidation of Cyclohexane, Cyclohexanone or Cyclohexanol Catalyzed by Water-Soluble Transition-Metal Complexes
No full textA catalytic system consisting of water-soluble metal sulfophthalocyanines (MPcS) or various ruthenium complexes and mono-persulfate as the oxidant was e.ective in the oxidation of cyclohexanone, cyclohexanol and cyclohexane to adipic acid with di.erent yields and selectivity. Oxidations were conducted at room temperature and under atmospheric pressure in aqueous media (or, in the case of cyclohexane, in a waterÈneat substrate double phase).
The oxidation of cyclohexanol involved step-by-step formation of cyclohexanone, e-caprolactone and
6-hydroxyhexanoic acid, all of which have been identiÐed in the reaction mixtures; in selected cases moderate over-oxidation of adipic acid to glutaric and succinic acid was also observed. Various MPcS catalysts were examined (M\Fe, Co, Ni, Cu and Ru), and the ruthenium derivative exhibited the best performances in terms of rate and selectivity. Mono-persulfate was found to be a more convenient oxidizing reagent than hydrogen peroxide; related patterns were observed when H was used, however extended dismutation of the oxidant limited the 2O2 overall yields. Cyclohexane underwent slow oxidation when reacted with persulfate (waterÈsubstrate double phase) in the presence of the water-soluble metal catalysts ; adipic acid was selectively produced (95%) in the presence of RuPcS catalyst with yields as high as 21% (48 h). The catalytic performance of simpler ruthenium derivatives, such as [RuCl (RuDMS) and (RuPW), was also examined for comparison purposes. A 2(DMSO)4] K5[Ru(H2O)P11O39] kinetic scheme for cyclohexane oxidation is proposed
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