Selective aerobic oxidation of alcohols catalyzed by iron chloride hexahydrate/TEMPO in the presence of silica gel

An environmentally friendly and efficient process whereby FeCl₃?6H₂O/2,2,6,6‐tetramethylpiperidine N‐oxyl (TEMPO)‐catalyzed oxidation of alcohols to the corresponding aldehydes and ketones is accomplished in the presence of silica gel using molecular oxygen or air as the terminal oxidant. The electron‐deficient benzyl alcohol was smoothly oxidized to the corresponding aldehydes with up to 99% isolated yield. It was found that silica gel not only could enhance the catalytic reaction rate but also increase the selectivity for the product. The high performance of FeCl₃?6H₂O/TEMPO catalyst system in the presence of silica gel might be attributed to the surface silanol groups. UV–visible spectra analysis showed that the Fe (III)–TEMPO complex could serve as the active intermediate species in the present catalytic system. A plausible mechanism of the catalytic system is proposed. Copyright © 2012 John Wiley & Sons, Ltd.     

Isomerization of oxygen-containing heterocycles in the presence of activated charcoal

Alky1-2,3-dihydrobenzofurans, octahydrobenzofuran, and chromans undergo skeletal isomerization, dehydroisomerization, cis-trans isomerization, and dehydrogenation in the presence of BAU-activated charcoal. An ionic mechanism including initial stripping of a hydride ion from the starting compounds is proposed for the reactions. It is shown by means of ESR spectroscopy that there is no correlation between the catalyst activity and the concentration of paramagnetic centers on it. It is assumed that quinoid groupings on the charcoal surface are the active centers.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 321–323, March, 1975.     

Kinetics of diethyl sulfide oxidation by hydrogen peroxide and peroxymonocarbonate in the presence of surfactants

We have studied the effect of different surfactants on the rate of diethyl sulfide (Et₂S) oxidation by hydrogen peroxide and peroxymonocarbonate (HCO ₄ ^- ) in aqueous solutions. In all the studied cases, the rate of the reaction between Et₂S and H₂O₂ decreases as the surfactant concentration increases. The reaction of Et₂S with HCO ₄ ^- is catalyzed by cationic surfactants and inhibited by neutral and anionic surfactants.Translated from Teoreticheskaya i Éksperimentalnaya Khimiya, Vol. 40, No. 6, pp. 368–372, November–December, 2004.     

Ozone oxidation of cysteine in optically trapped aqueous micro-droplets

The ozone (O₃) oxidation kinetics of cysteine in aqueous micro-droplets at different acidities is investigated in this study via aerosol optical tweezers coupled with Raman spectroscopy. This study exploits the O₃ oxidation of cysteine near the interface of micro-droplets as a model system to elucidate the oxidation damage of amino acids in biosurfaces. For each optically trapped micro-droplet, Raman spectroscopy is used to determine its droplet radius, concentrations of solutes, and droplet pH, as well as their time evolutions during the kinetics measurements. The bimolecular rate coefficients of the cysteine + O₃ reaction measured in micro-droplets are around 4 × 10⁵ M⁻¹ s⁻¹ and 2 × 10⁴ M⁻¹ s⁻¹ for pH ≈ 5 and 0.5, respectively. These results agree with the previous bulk measurements, indicating that the observed aerosol kinetics can be solely rationalized via diffusion-limited kinetics. The results also indicate that a high-ionic strength could enhance the cysteine + O₃ reaction, particularly for the zwitterion form of cysteine. The results imply that when surfactant proteins in lung fluids are exposed to ambient O₃, the cysteine residues in proteins will be attacked by O₃ at first due to the high reactivity of the thiol moiety in cysteine.     

Cucurbit[n]uril-calix[n]arene-based supramolecular frameworks assembled using the outer surface interactions of cucurbit[n]urils

Based on the crystal structures of two cucurbit[6]uril/calix[n]arene-based supramolecular frameworks reported by Long and co-workers,we further investigated the interactions of cucurbit[6]uril with 4-sulfocalix[4]arene and 4-sulfocalix[6]arene using ¹H NMR spectroscopy and isothermal titration calorimetry(ITC),respectively.Moreover,solid fluorescent materials were prepared via the adsorption of fluorescent dyes by these porous supramolecular frameworks,which exhibit a selective response to certain volatile organic compounds.     

Aerobic oxidation of primary alcohols in the presence of activated secondary alcohols

Chemoselective aerobic oxidation of primary alcohols in the presence of activated secondary alcohols was effected under irradiation of visible light by using (nitrosyl)Ru(salen) complex 6 that possesses bulky 1-ethyl-1-methylpropyl groups at C3, C3′, C5 and C5′, as catalyst. For example, oxidation of n-decanol was >50 times faster than oxidation of 1-phenylethanol at 10 °C.     

Kinetics and mechanism of the oxidation of arenes in the presence of heteropoly acids and palladium(II) complexes supported on silica gel

Pd(II) complexes and twelfth-series heteropoly acids (HPA) H₉[PMo₆V₆O₄₀] and H₃[PMo₁₂O₄₀] supported on silica gel oxidize benzene and toluene at 95°C. The formation of methyldiphenylmethane in the oxidation of toluene on HPA/SiO₂ and (PdCl₂−HPA)/SiO₂ catalysts, KIE>1 for the toluene/toluene-d₈ pair, and greater rate for toluene than for benzene are in accord with a one-electron transfer mechanism. L. M. Litvinenko Institute of Physical Organic and Coal Chemistry, National Academy of Sciences of Ukraine, 70 R. Lyuksemburg ul., Donetsk 340114, Ukraine. Translated from Teoreticheskaya i éksperimental'naya Khimiya, Vol. 35, No. 4, pp. 249–252, July–August, 1999.     

Comparison of phenyl- and octadecyl-modified silica gel as stationary phase for the prediction of n-octanol-water partition coefficients by high-performance liquid chromatography

The correlation between the retention of 29 aromatic compounds on phenyl and octadecyl silica gel with their n-octanol-water partition coefficients has been studied. The work also covered the influence of mobile phase buffers and the effect on the correlation of using k′ values extrapolated to 100% water. The results show that the retention on phenyl silica correlates significantly better than that on octadecyl silica. The error in the prediction of log P, ranging from 1 to 8, from retention data on phenyl silica at a 95% confidence limit was found to be ±0.04 log units at log P = 4, and ±0.07 log units at log P = 7 when extrapolated k′ values were used. When k′ values measured at one fixed mobile phase composition were used, the error was found to be ±0.10 and ±0.16 log units at log P = 4 and 7, respectively.     

Decay kinetics of benzophenone oxide in the liquid phase

The kinetics of self-termination of benzophenone oxide (BPO) in the liquid phase was studied by flash photolysis. The extinction coefficient of BPO (ε) was found to be virtually independent of the solvent nature, ε=(1.9±0.1)·10³ L mol⁻¹ cm⁻¹. The rate constant of the BPO self-temination increases from 1.8·10⁷ (MeCN) and 7.4·10⁷ (C₆H₆) to 1.5·10⁹ (n-decane) and 2.0·10⁹ L mol⁻¹ s⁻¹ (n-pentane) at 293±2 K. Solvation of BPO promotes a polar state of the molecule in MeCN and C₆H₆. In nonpolar hydrocarbons, a great contribution is made by the biradical structure resulting in an increase in the rate constant and a shift of the absorption maximum to the long-wave region (from 410 nm in MeCN to 425 nm inn-pentane). In solutions of benzene and acetonitrile, benzophenone oxide reacts with the parent diazo compound with a rate constant of (2–4)·10⁵ L mol⁻¹ s⁻¹ (293±2 K) along with the self-termination. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1329–1332, July, 1998.     

Nitric acid in the presence of supported P2O5 on silica gel: an efficient and novel reagent for oxidation of sulfides to the corresponding sulfoxides

This paper describes an efficient and easy method for oxidation of sulfides 1 to their corresponding sulfoxides 2 with nitric acid in the presence of supported P₂O₅ on silica gel under solvent-free conditions in high yields.     

Microgravity experiments on colloidal crystallization of silica spheres in the presence of sodium chloride

 Rate coefficients (k) in the colloidal crystallization of monodispersed silica spheres in the presence of sodium chloride are studied in microgravity achieved by parabolic flights of an aircraft. Time-resolved reflection spectroscopy is made with a continuous circulating-type stopped-flow cell system. The k values decrease as the salt concentration increases both at 0 and 1 G and those in microgravity are smaller than those in normal gravity by 16% (maximum), especially in water and in the presence of a small amount of the salt lower than 2 × 10⁻⁶ mol/l. The rates in flight at 1 G are larger by 15% (maximum) compared with those at 1 G on the ground. The k values obtained at 0 G, 1 G in flight and 1 G on the ground agree excellently with each other for the suspensions with 3 × 10⁻⁶ and 4 × 10⁻⁶ mol/l sodium chloride. Disappearance of the downward diffusion of spheres and no convection of the suspensions are important for retardation in microgravity. Received: 20 January 2000 Accepted: 9 March 2000     

On the mechanism of the OH initiated oxidation of acetylene in the presence of O2 and NO x

The mechanism of the oxidation of acetylene, in the presence of O₂ and NO _x , has been studied. Different levels of theory have been tested for the first step of the mechanism: the acetylene + OH radical reaction. Based on these results the meta-hybrid functional MPWB1K has been chosen for modeling all the other steps involved in the oxidation of acetylene. Different reaction paths have been considered and the one leading to glyoxal formation and OH regeneration is predicted to be the main channel, independently of the presence of NO _x . Two different mechanisms were modeled to account for formic acid formation, both of them involving cyclic intermediates. According to the computed activation free energies, the three-membered intermediate seems to be more likely to occur than the four-membered one. However, reaction barriers are very high and only a very small proportion of formic acid is expected to be formed through such intermediates. In the presence of NO _x , considered in this work for the first time, the main product of the tropospheric oxidation of acetylene is also expected to be glyoxal.     

Formation and characterization of different ceria/silica composite materials via dispersion of ceria gel or soluble ceria precursors in silica sols

Composite ceria/silica materials of 10 and 20% (w/w) were prepared by calcination, at 650 degrees C for 3 h, of the xerogels obtained by mixing the corresponding amount of a ceria precursor with freshly prepared sols of spherical silica particles (Stober particles) in their mother liquors. Two different ceria precursors were examined in this investigation. The first was a gel produced by the prehydrolysis of cerium(IV) isopropoxide in isopropanol medium, and the second was an aqueous solution of cerium(IV) ammonium nitrate. Different textural and morphological characteristics that developed by calcination were investigated by TGA, FTIR, XRD, SEM, and analyses of N2 adsorption isotherms. The results indicated that ceria dispersion and formation of mesoporous textural composite materials produced by the second precursor, cerium(IV) ammonium nitrate, are better than those produced by the first precursor, prehydrolyzed cerium(IV) isopropoxide. The results are discussed in terms of the effect of precursors and mixing media on nucleation and growth of ceria particles and their protection from sintering on calcination at the test temperature.     

Laser flash photolysis study of the decay kinetics of carbocations of 1,2,2,4-tetramethyl-1,2-dihydroquinoline in the porous glass in the presence of methanol

The efficiency of formation and the decay kinetics of carbocations formed under the photolysis of 1,2,2,4-tetramethyl-1,2-dihydroquinoline in methanol and in a porous glass filled with methanol or dried in air or in vacuo were studied by the laser flash photolysis techniques. In MeOH, the carbocations recombine via the second-order law in the reaction with the MeO⁻ anion formed in an equimolar amount and decay via the first-order law in the reaction with the solvent with rate constants of 3·10⁸ L mol⁻¹ s^{− 1} and 1.4·10³ s⁻¹, respectively. When the solution is placed into the porous glass, no recombination of the carbocations with MeO⁻ is observed, and the reaction with the solvent is somewhat inhibited (rate constant 8·10² s⁻¹). More than tenfold inhibition of the reaction of the carbocations with methanol is observed on going to a monolayer of MeOH on the surface. The main route of carbocation decay in the porous glass dried in vacuo is the geminate recombination with the SiO groups. The corresponding kinetics is described in terms of the model of freely diffusing reactants. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2239–2243, October, 2005.     

Functionalization of silica (II) - oxidation of cyclohexanes in the presence of functionalized silica complexed by iron and copper

Silica gel was modified with (N,N-dimethyl-3- aminopropyl)trimethoxysilane and the functionalized silica catalysts thus prepared complexed with iron and copper to produce FS-1{Fe},FS-1{Cu}. 11.2% of methylcyclohexane was oxidized in the presence of oxygen with FS-1(Fe) at 60°C. 2-Hydroxymethylcyclohexane was obtained in 59% yield. The structural differences between FS-1 (Fe)and FS-1 {Cu} are discussed.     

Preparation of crown compounds containing allyloxymethyl or butenyl groups for attachment to silica gel or containing long chain lipophilic groups for use in liquid membrane systems

Several new macrocyclic polyether ligands have been prepared for use in the separation of metal ions from aqueous solutions. Four of the crown ethers reported contain 1,2,4-triazole or 4-pyridone protonionizable subcyclic units and lipophilic groups. The remaining crown ethers are not proton-ionizable but contain alkene groups and were prepared for attachment to silica gel. The crowns were prepared by reacting the appropriate glycols with the appropriate ditosylates or dichloride in the case of the 1,2,4-triazole subcyclic unit. The crowns with proton-ionizable and lipophilic substituents were tested in liquid membrane transport systems and some of the crowns with alloxymethyl or butenyl substituents were attached to silica gel. The log K values for the interaction of these silica gel-bound macrocycles with certain metal ions were nearly the same (± 10%) as those for the association of the unbound macrocycles with the same metal ions.     

Selective water sorbents for multiple applications, 4. CaCl2 confined in silica gel pores: Sorption/desorption kinetics

This paper presents experimental data on water sorption/desorption kinetics on composite SWS-1L and SWS-1S materials, bulk aqueous CaCl₂ solutions and pure KSKG silica gel. Desorption kinetic curves are measured in the temperature range of 328–363 K at different vapor pressures. First order kinetics is found for both SWS materials and the bulk aqueous solution with the apparent activation energies of the water desorption equal to 23.5 kJ/mol and 48.6 kJ/mol, respectively. The difference in the kinetic behavior of the bulk and disperse systems is discussed.