Atmospheric peroxy radicals: ROXMAS,a new mass-spectrometric methodology for speciated measurements of HO2 and ∑RO2 and first results

ROXMAS (ROx Chemical Conversion/CIMS), a novel method for atmospheric speciated measurements of HO₂ and the sum of organic peroxy radicals (∑RO₂) developed by MPI-K, has been successfully deployed in a field campaign on Monte Cimone, Italy, June-July 2000. The method relies on amplifying chemical conversion of peroxy radicals to gaseous sulfuric acid via the chain reaction with NO and SO₂ and detection of the sulfuric acid by CIMS. Speciated measurements have been realized by diluting atmospheric air in either N₂ or O₂ buffer, thus exploiting the dependence of the conversion efficiency of RO₂ to HO₂ on [O₂], [NO], and [SO₂]. Speciated measurements of HO₂ and RO₂ are required to provide further insight into radical partitioning and thus to elucidate further the mechanisms of the oxidation of volatile organic compounds in the troposphere. This methodology yields useful speciated results for atmospheric conditions where CH₃O₂ makes a major contribution to total RO₂. Under other conditions it gives an upper limit for [HO₂] and a lower limit for [∑RO₂].     

Kinetic studies of reactions of the nitrate radical (NO3) with peroxy radicals (RO2): an indirect source of OH at night?

A discharge-flow system, coupled to cavity-enhanced absorption spectroscopy (CEAS) detection systems for NO3 at lambda=662 nm and NO2 at lambda=404 nm, was used to investigate the kinetics of the reactions of NO3 with eight peroxy radicals at P approximately 5 Torr and T approximately 295 K. Values of the rate constants obtained were (k/10(-12) cm3 molecule-1 s-1): CH3O2 (1.1+/-0.5), C2H5O2 (2.3+/-0.7), CH2FO2 (1.4+/-0.9), CH2ClO2 (3.8(+1.4)(-2.6)), c-C5H9O2 (1.2(+1.1)(-0.5)), c-C6H11O2 (1.9+/-0.7), CF3O2 (0.62+/-0.17) and CF3CFO2CF3 (0.24+/-0.13). We explore possible relationships between k and the orbital energies of the reactants. We also provide a brief discussion of the potential impact of the reactions of NO3 with RO2 on the chemistry of the night-time atmosphere.     

Ruthenium-catalyzed oxidation of alkenes at room temperature: a practical and concise approach to α-diketones

The catalytic oxidation of alkenes to α-diketones is unprecedented. A new oxidation of alkenes, catalyzed by a ruthenium complex, which allows an efficient route to α-diketones using TBHP as an oxidant is described. This methodology is highly functional group tolerant, is practically convenient, requires no additional ligand, and operates under mild conditions with short reaction times. Based upon experimental observations, a plausible mechanism is proposed.     

Catalyst and solvent-free, ultrasound promoted rapid protocol for the one-pot synthesis of α-aminophosphonates at room temperature

An ultrasound promoted easy, efficient, and environment friendly process has been devised for the synthesis of α-aminophosphonates within seconds through a one-pot three-component condensation of the aldehydes, amines, and triethylphosphite. The desired products were obtained in excellent yields and in high purity under solvent-free and catalyst-free conditions. Study with various aldehydes and amines reveals that ultrasound radiation plays a key role in the direct synthesis of α-aminophosphonates.     

Polysilazane as the source of silica: the formation of dense silica coatings at room temperature and the new route to organic–inorganic hybrids

Xylene solutions of perhydropolysilazane (PHPS) were used as the coating solutions for preparing silica coatings at room temperature. The PHPS-to-silica conversion was achieved by exposing the spin-on coatings to the vapor from aqueous ammonia. In order to examine the significance of the mechanical properties of the PHPS-derived silica coatings, the pencil hardness was measured, which was compared with that of tetraethoxysilane (TEOS)-derived silica coatings. The pencil hardness was over 9H at a load of 1 kg, which was much higher than that of the TEOS-derived silica gel films, and was comparable to that of the TEOS-derived films heat treated at 300 °C. Second, poly(methyl methacrylate) (PMMA)–silica hybrid coatings were prepared from xylene solutions of PMMA and PHPS via exposure to the vapor from aqueous ammonia. Crack-free, optically transparent PMMA–silica hybrid coatings could be prepared, where PHPS-to-silica conversion was confirmed by infrared absorption spectroscopy. The refractive index was around 1.42–1.50, and the contact angle with water increased from 35 to 70° with increasing PMMA content. The pencil hardness greatly increased during the PHPS-to-silica conversion, and was much higher than that of the non-heat treated TEOS-derived hybrid coatings. The durability in tetrahydrofuran (THF) was also evaluated by measuring the reduction in thickness occurring during soaking in THF. The durability decreased with increasing PMMA content, but was much higher than that of the non-heat treated TEOS-derived hybrid coatings. Both the hardness and the durability were comparable to those of the TEOS-derived coatings heated at 300 °C. The hybrid coatings could also be deposited on poly(ethylene terephthalate) substrates, where no cracks were observed at high PMMA contents even when the substrate was bent.     

Esterification of alcohols with acetic anhydride in Br?nsted acidic ionic liquids at room temperature

Br?nsted acidic ionic liquids were employed as a series of efficient catalysts and solvents in the esterification of alcohols with acetic anhydride at room temperature. Good yields, mild reaction conditions, short reaction time and no side reactions were achieved. The ionic liquids could be recycled easily without obvious decline in catalytic activities.     

The effect of inclusion inβ-cyclodextrin on the chemistry of peroxides: Reactions of radicals withβ-cyclodextrin

Studies by electron paramagnetic resonance (EPR), differential scanning calorimetry, thermogravimetric analysis, HPLC and NMR showed that radicals produced by thermolysis and photolysis of benzoyl peroxide,t-butyl peroxide and cumene hydroperoxide included in-cyclodextrin (-CD), undergo significant reaction with the-CD. The formation of-CD radicals was observed by EPR. Products formed by addition of radicals to-CD were also observed. Such host:guest radical reactions explain the reported stabilization of peroxides, found with-CD inclusion, as being primarily due to the interruption of chain reactions by trapping of the chain carriers. A small increase in activation barrier for cleavage of the included peroxide in-CD was also observed.     

Colloid and nanosized catalysts in organic synthesis: V. Reactions of alkyl halides and alcohols with β-diketones in the presence of metal nanoparticles

Reaction of copper, nickel, and iron nanoparticles with β-diketones directly yields corresponding metal β-diketonates. Reaction of alkyl halides, β-diketones, and nanodispersed metals leads to a mixture of monoketone and the alkylated β-diketone. When alcohol is used as the alkylating agent instead of alkyl halide, corresponding ester is formed.     

Suzuki reaction with aryl bromides at room temperature in the presence of a simple “ligand-free” catalytic system

Possibility was examined of using the simplest catalytic system (palladium salt and NaOH) in ethanol or in a mixture of ethanol and water as a catalyst precursor in order to obtain high product yields in the Suzuki reaction with nonactivated aryl bromides at room temperature without an inert atmosphere or ligand additives.     

Unique copper–salen complex: an efficient catalyst for N-arylations of anilines and imidazoles at room temperature

We have reported here the catalytic activity of a unique Cu–salen type complex in N-arylation of anilines with arylboronic acids in water. The protocol is found to be applicable for a wide range of electronically diversified arylboronic acids and anilines with excellent yields of the isolated product. Further the scope of this protocol has been extended to the synthesis of various N-aryl imidazoles in iso-propanol.     

Heterogeneous reusable catalyst,ultrasound energy,and no solvent: a quick and green recipe for one-pot synthesis of β-phosphonomalononitriles at room temperature

Clay-supported heteropolyacid catalyst has been prepared and investigated as a novel heterogeneous, reusable and efficient catalyst for the one-pot synthesis of β-phosphonomalononitriles under ultrasound irradiation at room temperature. Compared with traditional methods, the present method is solvent-free, works under milder and cleaner conditions, furnishes products with higher purity and yields, needs shorter reaction time, easier work-up procedure, and generates less waste. No column purification is required and the products can be purified by simple crystallization. The catalyst can be easily recovered and reused several times without significant loss of its catalytic activity. The catalyst was characterized by scanning electron microscopy, X-ray powder diffraction, and thermal gravimetric, surface area, and elemental analyses.     

Synergistic role of Brønsted and Lewis acidity in alkali metal-exchanged heteropolyacid catalysts for esterification of acetic acid at room temperature

A series of Cs exchanged phosphotungstic acid (PTA) catalysts were synthesized by the ion exchanged method and were characterized by X-ray diffraction, FT-IR spectroscopy, pyridine adsorbed FT-IR spectroscopy, SEM, BF-TEM, ICP-OES and BET surface area analysis. For comparison purposes, K exchanged PTA, Cs and K exchanged phosphomolybdic acid (PMA) catalysts were also prepared. XRD diffractograms showed that the crystallites of the Keggin ion are maintained, while FT-IR spectra also revealed the characteristic bands of the Keggin ion at all metal loadings of all the catalysts. From pyridine adsorbed FT-IR spectroscopy, it was observed that the Brønsted and Lewis acidity were significantly maintained at lower metal loadings, whereas STEM analysis showed a uniform distribution of the elements which correlated well with the theoretical atomic values of the loaded metals for all the catalysts, which were verified by ICP results. The efficiency of various metal-exchanged heteropolyacid catalysts was assessed for the esterification reaction using various substrates, and the Cs exchanged phosphotungstic acid catalysts showed superior activity compared to the other catalysts. In particular, the Cs exchanged phosphotungstic acid with a 1 wt% loading showed the highest activity and was most tolerant to the presence of water that was produced in the reaction. The catalytic activity correlates well with the Brønsted and Lewis acidity, as well as Keggin ion density of the catalysts.     

Phosphorylated 2-Chloroethynes in the Reactions with Malonic Acid Derivatives: Azirine or Oxazole?

Russian Journal of General Chemistry - The reactions of (2-chloroethynyl)diphenylphosphine oxide with diethyl 2-aminomalonate and of dimethyl (2-chloroethynyl)phosphonate with...     

Reactions of hole species in γ-irradiated KCl,KBr and KI with the emulsion of aniline and water

-Irradiated KCl, KBr and KI are dissolved separately in the emulsion of water and aniline. Halogens as radiolytic products are extracted in aniline forming stable halogen-aniline complexes. Hole species from V₂ and V₃ centers and free halogens trapped in crystalline salts are solvated first in water phase during dissolution and immediately form complexes with aniline. A typical vibrational structure of absorption bands around 300 nm is observed. The yields of halogens and thereby complexes are found to depend upon the concentration of F and hole centers and the mesh of the salt.     

Reactions in a Mixture of CH_4 and CO_2 under the Action of Microwave Discharge at Atmospheric Pressure

Reactions between CH_4 and CO_2 under the action of continuous microwave discharge at atmospheric pressure were studied in a special homemade reactor. The main products were CO and H2, while acetylene and ethylene were also found in the products. Experimental results show that conversions of CH4 and CO2 could be higher than 90% without the presence of any catalyst. Effects of CO2/CH4 molar ratio and total flow rate of the feed gas on the reaction were also investigated.     

Reactions of HBr+ ions in the 2Π i , v + quantum states with H2 and HBr molecules

The mechanisms and kinetics of low-temperature ion-molecular reactions between the Br⁺, HBr⁺, and DBr⁺ions and the HBr, DBr, H₂, and D₂ molecules were studied. The HBr⁺ (i,v ⁺) and DBr⁺(i,v ⁺) ions were prepared in separate spin-orbit (i) and vibrational (v ⁺) states by resonance multiphoton ionization in a free flow of halogen halides (HBr and/or DBr) with hydrogen, deuterium, or inert gases (Ar, He). The effectiveness of various reaction channels, including the exchange of charges, H and D atoms, and H⁺andD⁺ ions, was studied. The quantitative data on the kinetics of these reactions were obtained for separate quantum states of the ions. The resonance ionization of one of the two ion isotopomers H⁷⁹Br⁺(D⁷⁹Br⁺) or H⁸¹Br⁺(D⁸¹Br⁺) was used to study and compare the effectiveness of various ion-molecular reaction channels.     

Reactions in a Mixture of CH4 and CO2 under the Aciton of Microwave Discharge at Atmospheric Pressure

Reactions between CH4 and CO2 under the action of continuous microwave discharge at atmospheric pressure were studied in a special homemade reactor,The main products were CO and H2,while acetylene and ethylene were also found in the products.Experimental results show that conversions of CH4 and CO2 could be higher than 90% without the presence of any catalyst,Effects of CO2/CH4 molar ratio and total flow rate of the feed gas on the reaction were also investigated.     

Calorimetric studies of interactions of some peptides with electrolytes,urea and ethanol in water at 298.15 K

The standard molar enthalpies of solution at infinite dilution \Updelta_\textsol H_\textm^￥ \Updelta_{\text{sol}} H_{\text{m}}^{\infty } of glycylglycine, dl-alanyl-dl-alanine and glycylglycylglycine in aqueous solutions of potassium chloride and ethanol as well as of glycylglycine and glycylglycylglycine in the solutions containing urea and water have been determined by calorimetry at the temperature 298.15 K. Changes of solution enthalpy, expressed in a form so-called heterotactic interaction coefficients, h_\textxy h_{\text{xy}} were used for analysis of interactions occurring between the investigated solutes in water. The group contributions illustrating the interactions of KCl, urea and ethanol with selected functional groups in the peptide molecules, namely CH₂, “pep,” and “ion” groups, were calculated and discussed.