Presence Of Hydrogen Acceptor Research Articles

Intermolecular C–H Silylation of Arenes and Heteroarenes with HSiEt3 under Operationally Diverse Conditions: Neat/Stoichiometric and Acceptor/Acceptorless

Efficient protocols for Rh-catalyzed intermolecular C–H silylation of unactivated arenes and heteroarenes are disclosed. The silylations are catalyzed by a Rh-complex (2 mol %) derived in situ from commercially available Rh(nbd)2BF4 and (S,S)-i-Pr-BPE (L3) with Et3SiH in the presence of hydrogen acceptor under either neat (excess of arene) or stoichiometric conditions. The regioselectivity is determined mainly by the steric bulk of the substituents and by the electronic effect as an ancillary factor. In addition, our preliminary result shows that the current protocol catalyzes the silylation of arenes in the absence of hydrogen acceptors.

Dramatic liquid-phase dehydrogenation rate enhancements using gas-phase hydrogen acceptors

The dehydrogenation of 1,2,3,4-tetrahydrocarbazole (THCZ) to form carbazole (CZ) over supported palladium catalysts was examined in the presence of hydrogen acceptors. As expected, liquid hydrogen acceptors increased the rate of reaction but, importantly, gaseous hydrogen acceptors also have been used. Ethene, propene, and but-1-ene showed up to a fivefold increase in the rate of dehydrogenation. Moreover, compared with the analogous liquid systems, the gaseous alternatives are a potentially more economic method of enhancing the activity and provide a simpler workup. The mechanism for the increase in rate was examined by density functional theory calculations, which showed that the propene hydrogenation competes effectively with the back-hydrogenation of the intermediates formed during the THCZ dehydrogenation, resulting in a shift in the equilibrium toward to the formation of CZ.

Effect of Hydrogen Acceptors on pKa of Phenolic Resins: Link to Dissolution Inhibition

Dissolution inhibition in positive resists is brought about by an inductive polarization effect of strong hydrogen acceptors, which creates hydrogen-bonded strings of OH groups. The acidity of the OH groups bound in the strings is considerably lower than that of phenols in the bulk of the system. It is the reduction in the concentration of protons in equilibrium with the various parts of the resin that lowers the rate of phenol deprotonation and with it the rate of resin dissolution. Here we describe changes in the pKa of the resin in the presence of hydrogen acceptors (dissolution inhibitiors) and we demonstrate the existence of a quantitative link between acidity changes and inhibition factors.

Formation of an active surface on oxide systems containing vanadium used for dehydrogenation of hydrocarbons in the presence of hydrogen acceptors. 4. Catalytic and physicochemical properties of vanadium-zirconium and vanadium-titanium catalysts for the oxidative dehydrogenation of ethylbenzene in the presence of nitrobenzene

A study has been made of the catalytic and physicochemical properties of vanadium-zirconium and vanadium-titanium oxide systems in the oxidative dehydrogenation of ethylbenzene in the presence of nitrobenzene. The degree of conversion to styrene was less than 10% and to aniline 60%. The methods used to study the physicochemical properties of the catalysts were diffuse reflection electron spectroscopy (DRES), x-ray and differential thermogravimetric analysis. The presence of surface VTd5+, VOh5+, and VQ4+ ions has been established, their ratios depending on the initial vanadium concentrations, the nature of the carrier, and the thermal treatment conditions. In the vanadium—zirconium systems VTd5+ predominate, but in the vanadium-titanium ones VQ4+. The VOh5+ ions appear to be present in the form of clusters. A chemical compound between the active components and ZrO2 and a V2O5 phase have been detected, which take no part in the dehydrogenation reaction.

Relationships in formation of the active surface of vanadium-containing oxide systems for hydrocarbon dehydrogenation reactions in the presence of hydrogen acceptors

Relationships in formation of the active surface of vanadium-containing oxide systems for hydrocarbon dehydrogenation reactions in the presence of hydrogen acceptors

Relationships in formation of the active surface of vanadium-containing oxide systems for hydrocarbon dehydrogenation reactions in the presence of hydrogen acceptors

Diffuse reflection electronic spectroscopy and ESR spectroscopy have been used in a study of the valence and coordination state of vanadium ions in vanadium-alumina and vanadium-magnesia catalytic systems that are effective in the oxidative dehydrogenation of hydrocarbons. On the surface ofγ-Al2O3, vanadium ions in octahedral coordination with the oxygen of the immediate surtoundings may be grouped primarily in clusters of 10–12 ions, providing stability of the V5+ ions against reduction to lower degrees of oxidation, and also providing easy reoxidizability of V4+ at ∼20°C. On the surface of MgO, the vanadium ion clusters that are formed are mostly small — two or three ions. Modification with KOH, K2SO4 and CdO tends to stabilize the V5+ under the reaction conditions in the oxidative dehydrogenation of ethylbenzene to styrene in the presence of nitrobenzene.

Relationships in formation of the active surface of vanadium-containing oxide systems for hydrocarbon dehydrogenation reactions in the presence of hydrogen acceptors

Relationships in formation of the active surface of vanadium-containing oxide systems for hydrocarbon dehydrogenation reactions in the presence of hydrogen acceptors

Solid state photochemistry at 4.2 K: The photocyclization of [5] helicene to dihydrobenzoperylene in hpolskii matrices

The reversible photocyclization reaction of [5]helicene to dihydrobenzoperylene (DHBP) was studied in the Shpolskii matrices n-pentane and n-hexane at 4.2 K. The well-resolved transitions from the photochemical product are attributed to DHBP, occupying a distinct site in n-hexane. The photoinduced formation of DHBP at 4.2 K was monitored during illumination by sequentially recording fluorescence spectra. The multiplet structure of [5]helicene and DHBP in fluorescence and in phosphorescence in n-pentane were determined by high-resolution total luminescence spectroscopy (TLS). The subsequent dehydrogenation of DHBP to benzoperylene (BP), which occurs rapidly at higher temperatures in fluid media and in the presence of hydrogen acceptors, was found to be inhibited in solid matrices.

Influence of water vapor on the dehydrogenation of ethylbenzene in the presence of various hydrogen acceptors

1. Water vapor influences the activity and selectivity of a vanadium-magnesium catalyst during the dehydrogenation of ethylbenzene in the presence of hydrogen acceptors, viz., oxygen, nitrobenzene, and sulfur dioxide, reducing the formation of carbon on the surface of the catalyst and promoting elongation of the operation of the catalyst without regeneration. 2. Water vapor provides for the formation of the optimally active catalyst surface, which contains vanadium ions in high oxidation states with octahedral coordination.

Influence of hydrogen acceptors on growth and energy production ofProteus mirabilis

The generation time ofP. mirabilis in defined and in complex medium is shorter in the presence of hydrogen acceptors than in their absence. In the presence of hydrogen acceptors the molar growth yield for glucose and the acetate production are strongly increased. From the molar growth yield and the acetate production YATP in defined medium was calculated as 5.5 g/mole, whereas in complex medium a value of 12.6 g/mole was obtained. The molar growth yield, the acetate production, the amount of hydrogen acceptor reduced and YATP were used to calculate P/2e−ratios for phosphorylation coupled to electron transfer to oxygen, nitrate and tetrathionate as respectively 2.80; 1.48 and 1.23 in defined medium. Under anaerobic conditions in the presence of nitrate or tetrathionate as hydrogen acceptor in complex medium a bend in the growth curve is observed. In the period of rapid growth the P/2e−ratio for nitrate reduction is of the same magnitude as that in defined medium, however much lower P/2e−ratios are found during the subsequent period of slow growth. The P/2e−ratios for tetrathionate reduction in complex medium for both growth periods are lower than those in defined medium. Most probably these results indicate that during this period growth and energy production are uncoupled. Under aerobic conditions in complex medium a constant YO value of 32.2 g/atom O is found during a short period of the growth curve. Afterwards when the cell density increases a steady decrease of YO is observed.