Production of radicals in the ozonolysis of propene in air

Radical production in the ozonolysis of propene in air was monitored directly by a peroxy radical chemical amplification (PERCA) instrument at room temperature (298±2 K) and atmospheric pressure (1×105 Pa). The ozonolysis reactions were conducted in a flow tube under pseudo-first-order conditions for ozone. The decay in ozone was calculated based on reaction time tr and effective rate constant keff (keff = k1[C3H6]0)) for the ozone-propene reaction. The total radical yields relative to consumed ozone were d...     

Cumulative yields of short-lived ruthenium isotopes in the thermal neutron induced fission of233U,235U and239Pu

Cumulative yields of short-lived ruthenium isotopes in the thermal neutron induced fission of²³⁵U,²³⁵U and²³⁹Pu have been determined using a fast radiochemical separation technique followed by gamma spectrometry. The cumulative yields of¹⁰⁷Ru and¹⁰³Ru in²³³U (n_th, f) and¹⁰⁷Ru and¹⁰⁹Ru in²³⁹Pu (n_th, f) are determined for the first time. The measured cumulative yields are converted to chain yields assuming normal charge distribution systematics for comparison with the literature data on chain yields.     

Application of non-thermal atmospheric pressure ac plasmas to the carbon dioxide reforming of methane

Methane conversions of 11.9%, yields of hydrogen as high as 23.3% and energy yields of 1.0 mol H₂/kWh have been achieved from CO₂ reforming of CH₄ in non-thermal, atmospheric pressure plasma reactors with Pt coated electrodes. Two reactors have been studied. A novel fan type reactor consisting of a movable rotor and immobile stator produced the highest yields in contrast to a tube type (silent discharge) reactor with a glass dielectric barrier. Conversions, yields of hydrogen and energy yields (expressed as mol H₂/kWh) were studied for CO₂/CH₄ concentrations of 1.1% and 5.0% in He as a function of flow rate and input voltage. Hydrogen yields are observed to increase as the input voltage is increased from 411 V to 911 V and the flow rate is decreased from 100 cc/min to 30 cc/min. Energy yields vary only slightly with input voltage and flow rate. Hydrogen yields show little dependence on CO₂/CH₄ concentrations, but energy yields are approximately five times greater for the 5.0% mixture than the 1.1% mixture. Selectivities to H₂, CO, coke, and low molecular weight hydrocarbons were also evaluated and compared to data obtained without CO₂ in the feed. Hydrogen selectivities of nearly 100% were obtained, with small amounts of ethane and propane as the only observed side products and the selectivites were approximately the same whether CO₂ was present or absent in the mixture. However, the reaction proceeds much more cleanly when CO₂ is present, producing CO. The syngas product has an H₂ : CO ratio of 1.5 with the fan type reactor and 0.67 with the tubular reactor. In the absence of CO₂, coke is the main carbonaceous product. Under all conditions studied the fan type reactor demonstrated higher methane conversions (up to 11.9%) and selectivities to hydrogen.     

Products distribution and gas release in pyrolysis of thermally thick biomass residues samples

The pyrolysis of thermally thick (approximately 75 g) biomass residues samples (i.e. brewer spent grains, fibreboard and coffee beans waste) has been investigated in an in-house designed and fabricated macro-TGA both by rapid sample introduction at reactor temperatures from 600 to 900 °C and by applying a constant heating rate of 10 K/min. The composition of the product gas is determined by simultaneous online use of a micro-GC and a FTIR analyser. The product yields (liquid, char and gas) and the gas composition show a clear dependence on temperature and heating rate. The main gas products are CO₂, CO, CH₄, H₂, C₂H₂, C₂H₆ and C₂H₄. The results show that a rise in temperature leads to increasing gas yields and decreasing liquid and char yields. Lower heating rates favour liquid and char yields. The release patterns of the gaseous species are also greatly affected by the temperature history of the sample.     

Gas phase photolysis of CF2Cl2, CFCl3 and CCl4 in the presence of bromine at 213.9, 163.3, 147.0 and 123.6 nm

CF₂Cl₂Br₂, CFCl₃Br₂ and CCl₄Br₂ mixtures were photolyzed at 213.9, 163.3 and 147.0 nm. The first two mixtures were also photolyzed at 123.6 nm. In the CF₂Cl₂Br₂ system the quantum yields for the formation of CF₂Cl radicals (as determined by the formation of CF₂ClBr) were 1.0 ± 0.1, 0.67 ± 0.07, 0.05 ± 0.02 and not more than 0.02 respectively. For the CFCl₃Br₂ system the quantum yields of formation of CFCl₂ radicals (as CFCl₂Br) were 1.0 ± 0.1, 0.53 ± 0.05, 0.02 ± 0.01 and 0.03 ± 0.02 respectively. In the CCl₄Br₂ experiments the quantum yields of formation of CCl₃ radicals (as CCl₃Br) were 1.0 ± 0.1, 0.41 ± 0.04 and 0.02 ± 0.01 at the wavelengths 213.9, 163.3 and 147.0 nm respectively. These results are in excellent agreement with some earlier determinations which utilized a different technique. In all such cases the quantum yields, determined by the bromine addition technique for such fragments as CF₂, CFCl, CCl₂, CF and CCl, can only be used to set lower limits for the quantum yields of formation of these radicals. There are complications in this method for these fragments which cannot at present be taken entirely into account.     

Gas phase photolysis of CF2Cl2, CFCl3 and CCl4 in the presence of bromine at 213.9, 163.3, 147.0 and 123.6 nm

CF₂Cl₂Br₂, CFCl₃Br₂ and CCl₄Br₂ mixtures were photolyzed at 213.9, 163.3 and 147.0 nm. The first two mixtures were also photolyzed at 123.6 nm. In the CF₂Cl₂Br₂ system the quantum yields for the formation of CF₂Cl radicals (as determined by the formation of CF₂ClBr) were 1.0 ± 0.1, 0.67 ± 0.07, 0.05 ± 0.02 and not more than 0.02 respectively. For the CFCl₃Br₂ system the quantum yields of formation of CFCl₂ radicals (as CFCl₂Br) were 1.0 ± 0.1, 0.53 ± 0.05, 0.02 ± 0.01 and 0.03 ± 0.02 respectively. In the CCl₄Br₂ experiments the quantum yields of formation of CCl₃ radicals (as CCl₃Br) were 1.0 ± 0.1, 0.41 ± 0.04 and 0.02 ± 0.01 at the wavelengths 213.9, 163.3 and 147.0 nm respectively. These results are in excellent agreement with some earlier determinations which utilized a different technique. In all such cases the quantum yields, determined by the bromine addition technique for such fragments as CF₂, CFCl, CCl₂, CF and CCl, can only be used to set lower limits for the quantum yields of formation of these radicals. There are complications in this method for these fragments which cannot at present be taken entirely into account.     

By-product formation in spark breakdown of SF6/O2 mixtures

The yields of SOF₄, SO₂F₂, SOF₂, and SO₂ have been measured as a function of O₂ content in SF₆/O₂ mixtures, following spark discharges. All experiments were made at a spark energy of 8.7 J/spark, a total pressure of 133 kPa, and for O₂ additions of 0, 1, 2, 5, 10, and 20% to SF₆. Even for the case of no added O₂, trace amounts of O₂ and H₂O result in the formation of the above by-products. However, addition of O₂ significantly increases the yields of SOF₄ and SO₂F₂, while SOF₂ is only slightly affected. The net yields for SOF₄ and SO₂F₂ formation range from 0.18×10^–9 and 0.64×10^–10 mol·J^–1, respectively, at 1% O₂ content to 10.45×10^–9 and 7.15×10^–10 mol·J^–1, respectively, at 20% O₂ content. The mechanism for SOF₄ production appears to involve SF₄, an important initial product of SF₆, as a precursor. Comparison of the SOF₄ and SO₂F₂ yield from spark discharges (arc and corona) shows that the yields from other discharges (arc and corona) shows that the yields can vary by at least three orders of magnitude, depending on the type of discharge and on other discharge parameters.     

Primary photochemical process in norbornadienechromium tetracarbonyl

Low-temperature photolysis of NbdCr(CO)₄(I) (Nbd  norbornadiene) in the presence of triphenylphosphine yields trans-NbdCr(CO)₃[P(C₆H₅)₃]. The quantum yields of the room-temperature photoinduced conversion of I in the presence of H₂, of P(C₆H₅)₃ and of both reagents, are respectively 0.140, 0.105 and 0.104. Primary photoinduced formation of monodentate I is shown to account for these observations.     

Direct Spectroscopic Evidence for 1ΔgO2 Production from the Photolysis of Vanadium(V)-Peroxo Complexes in Aqueous Solution

The chemiluminescence of ¹DL_gO₂ expelled from the UV photolysis of vanadium(V)-peroxo (VP) complexes in aqueous solution was observed for the first time. Using phenalenone photosensitization as a standard reference, the ¹O₂ quantum yields from the photolysis of 12 VP complexes were measured. No good correlation was found between the relative DNA-photocleavage activities and the ¹O₂ quantum yields of these complexes. This lack of correlation underscores the significant contribution of the complex-DNA binding interaction in determining the observed DNA-photocleavage activity of the complex. The small ¹O₂ quantum yields observed in these complexes were interpreted in terms of the minor ¹O₂ pho-toelimination channel relative to other more efficient relaxation processes.     

An efficient and chemoselective method for protection of thiols catalyzed by aluminumdodecatungstophosphate (AlPW12O40), as a highly water tolerant Lewis acid catalyst

Protection of various thiols with diphenylmethanol was achieved in high yields at room temperature using catalytic amounts of AlPW₁₂O₄₀ in CH₂Cl₂. In the presence of this catalyst, protection of SH versus OH was achieved with high chemoselectivity and yields. The catalyst can be easily recovered and reused. Deprotection of DPM thioethers was also achieved using molecular iodine at reflux in CH₂Cl₂ in high yields.     

The photolysis of bis(acetonitrile)tetrachlorotungsten in acetonitrile

When WCl₆ is dissolved in CH₃CN it is reduced to WCl₄(CH₃CN)₂ in a first-order process with a half-life of 52 s. Irradiation of the WCl₄(CH₃CN)₂ solution at 365 nm yields WO₂Cl₂(CH₃CN)₂. Further irradiation of this solution with access to air yields a blue, partially reduced form of WO₃ · 2H₂O, which eventually precipitates.     

Methylation of tin(II) and lead(II) in sediment by carbanion donors

A factorial experimental design determined separate and combined effects of MeCoB₁₂ (methylcobalamin) and Me₂Co(N₄)⁺ (a methylcobalamin model) on methylation of Sn(II) and Pb(II) in sediment matrices. Total methyltin yields ranged from 1.4% to 3.2%, and total methyllead yields varied from 0.037% to 0.11%. No methylmetal products occurred in the absence of Me₂Co(N₄)⁺.     

Variation of xanthene-based bidentate ligands in the palladium-catalyzed arylation of ureas

A series of xanthene-based bidentate ligands containing various substituents on diphenylphosphino groups were synthesized and tested in the palladium-catalyzed arylation reaction of urea with unactivated aryl bromides. It was found that both steric and electronic properties of the ligands have a pronounced effect on the yields and ratios of the products. Arylation of urea and phenylurea with unactivated aryl bromides in the presence of Pd₂dba₃·CHCl₃/3,5-(CF₃)₂Xantphos and Cs₂CO₃ as base in dioxane at 100°C gave the corresponding N,N′-diarylureas in 62-98% yields.     

Yields of light products in radiolysis of binary mixture isooctane-benzene and isooctane-hexafluoro-benzen

Radiolysis of binary mixtures isooctance-benzene and isooctane-hexafluorobenzene has been studied. The yields of light products of isooctane radiolysis, namely, G/H₂/, G/CH₄/, G/C₄H₁₀/ and G/C₄H₈/, have been determined for various electron ratios of benzene- and hexafluorobenzene. The acceptance of positive charges with benzene and of electrons with hexafluorobenzene is reponsible for deviations of radiation-chemical yields towards negative side from the additivity rule. Positive deviation of G/CH₄/, G/C₄H₁₀/ and G/C₄H₈/ yields at is attributed to indirect ionization of isooctane. Monomolecular reactions of C₈H ₁₈ ⁺ have been discussed.     

Systematic study of lanthanoid endohedral metallofullerenes: Production yields, HPLC retention time and reactor irradiation effects

We made systematic studies of lanthanoid metallofullerenes on the following three properties using the radiochemical method: (1) the relative production yields of metallofullerene species, (2) variation of the HPLC retention time among M(III)@C₈₂ species, and (3) the effects of the reactor irradiation on the survival yields of each metallofullerene species. The production yields of M@C₈₂ relative to La@C₈₂ were found to decrease as the atomic number of M became larger and as the number of atom ratio, M/C, in the carbon rod became larger. On the other hand, the production yields of M₁M₂@C₈₂, relative to that of LuM@C₈₂ were found to increase for the larger atomic number. The retention time for the M(III)@C₈₂ species in the Buckyprep column was found to become slightly longer for the larger atomic number but it becomes abruptly larger for Gd, and Tb by about 5%. The overall effects of the reactor irradiation on the survival yields (or retention yields) of M@C₈₂ species were found to be (19.7±2.1)%.     

Synthesis of cross-linked polymer microspheres in supercritical carbon dioxide

Herein we report the synthesis of highly cross-linked polymers based on divinylbenzene by heterogeneous polymerization in supercritical CO₂ (scCO₂). The polymers were isolated in the form of discrete microspheres (diameter = 1.5–5 μm) in good yields (≥90%), in the absence of any stabilizers. In the presence of a CO₂-soluble polymeric stabilizer, much smaller particles (diameter <0.5 μm) were formed in high yields (≥95%) by emulsion polymerization in scCO₂.     

Radiation decomposition of Co(acac)3 in alcohol-water matrices

The reduction yields of Co(acac)₃ in methanol-water (11) solutions and also the formation yields of the radiolysis products Co(acac)₃Co(acac)₂ + acac have been determined. These yields were found to depend considerably on the acidity and also on the initial complex concentration. Solvated electrons, transformed in acidic solutions into atomic hydrogen, less effective in reducing acetyloacetonate, are of basic significance in the reduction process of Co(acac)₃. Studies of the methanol-glycol Co(acac)₃ solutions showed that the type of radiolytic products formed depends on the composition of the matrix.     

Temporary Protection and Activation in the Regioselective Synthesis of Saccharide Sulfates

Regioselective sulfation with Et₃N · SO₃ of partially protected or unprotected glycosides via stannanediyl acetals or stannyl ethers, combined with persistent or temporary protecting groups is described. Stannylation of phenylboronates, followed by sulfation and aqueous workup, is an efficient way for the synthesis of monosulfated monosaccharides. The stannanediyl acetal 2 led in high yields to 3a , while sulfation of the diol 1 proceeded more slowly and led in lower yield to a mixture 1/3a/4a/5a (Scheme 1). The trehalose disulfate 8a was obtained in high yields from 7 ; reducing the amount of sulfating agent led to a mixture 6/8a/9a . Stannylation and sulfation of the galactoside 11 afforded 13a , while direct sulfation of 11 gave a mixture of the 2-and 3-sulfates 13a/14a besides some disulfate 15a . Sulfation of the lactose derivative 16 and the stannanediyl acetal 17 gave the 3-sulfate 18a , with some disulfate 19a being formed from 16 . The mannopyranoside 21 was selectively sulfated at OH–C(2), leading to 22a , while the corresponding diol 20 yielded mostly the isomer 23a and some disulfate 24a . Sulfation of the stannyl ethers derived from the gluco-and galactopyranosides 25 and 28 and (Bu₃Sn)₂O afforded high yields of the 2,6-disulfate 26a and the 3,6-disulfate 29a , respectively. Stannylation of 25 and 28 with Bu₂SnO and sulfation proceeded less satisfactorily. Stannylation of the phenylboronate 32 (Bu₂SnO) and sulfation gave good yields of the 2-sulfate 27a ; stannylation and benzoylation yielded the 2-benzoate 34 (Scheme 2). Similarly, the galactose-derived 37 provided high yields of the 3-sulfate 30a and of the 3-benzoate 39 . Direct sulfation of the phenylboronates 32 and 37 proceeded in lower yields and gave mixtures.     

A green and highly efficient alkylation of thiols in water

An environmentally benign and efficient process for the preparation of thioethers was developed by simple and practical reactions of alkyl halides and thiols in water in the presence of K₂CO₃ or Et₃N in very high yields. The reaction of aryl, alkyl, aliphatic and hindered thiols with various alkyl halides gave the corresponding products with significant advantages such as high conversions, short reaction time, mild reaction conditions, and low cost, simple workup with good to quantitative yields.