The quantum efficiency of the primary processes in formaldehyde photolysis at 3130 Å and 25°C

The mechanism of the photolysis of formaldehyde was studied in experiments at 3130 Å and in the pressure range of 1–12 torr at 25°C. The experiments were designed to establish the quantum yields of the primary decomposition steps (1) and (2), CH₂O + hν → H + HCO (1): CH₂O + hν → H₂ + CO (2), through the effects of added isobutene, trimethylsilane, and nitric oxide on Φ_CO and Φ. The ratio Φ_CO/Φ was found to be 1.01 ± 0.09(2σ) and (Φ + Φ_CO)/2 = 1.10 ± 0.08 over the range of pressures and a 12-fold change in incident light intensity. Isobutene and nitric oxide additions reduced Φ to about the same limiting value, 0.32 ± 0.03 and 0.34 ± 0.04, respectively, but these added gases differed in their effects on Φ_CO. With isobutene addition Φ_CO/Φ reached a limiting value of 2.3; with NO addition Φ_CO exceeded unity. The addition of small amounts of Me₃SiH reduced Φ to 1.02 ± 0.08 and lowered Φ_CO to 0.7. These findings were rationalized in terms of a mechanism in which the “nonscavengeable,” molecular hydrogen is formed in reaction (2) with ?₂ = 0.32 ± 0.03, while the “free radical” hydrogen is formed in reaction (1) with ?₁ = 0.68 ± 0.03. In the pure formaldehyde system these reactions are followed by (3)–(5): H + CH₂O → H₂ + HCO (3); 2HCO → CH₂O + CO (4); 2HCO → H₂ + 2CO (5). The data suggest k₄/k₅ ? 5.8. Isobutene reduced Φ by the reaction H + iso-C₄H₈ → C₄H₉ (20), and the results give k₂₀/k₃ ? 43 ± 4, in good agreement with the ratio of the reported values of the individual constants k₃ and k₂₀.     

Unusual H2-forming chain reaction in the 3130-Å photolysis of formaldehyde-oxygen mixtures at 25°C

A kinetic study has been made of the 3130-Å photolysis of CH₂O (8 torr) in O₂-containing mixtures (0.02–8 torr) and in the presence of added CO₂ (0–300 torr) at 25°C. Quantum yields of formation of H₂, CO, and CO₂ and the loss of O₂ were measured. Φ and Φ_CO were much above unity. In an explanation of these unexpected results, a new H-atom-forming chain mechanism was postulated involving HO₂ and HO addition to CH₂O: CH₂O + hν → H + HCO (1) H + CH₂O → H₂ + HCO (3) H + O₂ + M → HO₂ + M (6) HCO + O₂ → HO₂ + CO (8) HO₂ + CH₂O → (HO₂CH₂O) → HO + HCO₂H (15) HO + CH₂O → H₂O + HCO? (16); HCO? → H + CO (19) HO + CH₂O → H₂O + HCO (17) and HO + CH₂O → HCO₂H + H (18). When the results are rationalized in terms of this mechanism, the data suggest k₁₆ ? k₁₇ and k₁₆/k₁₈ ? 0.5. The data require that a reassessment of the relative rates of reactions (7) and (8) be made, since in the previous work HCO₂H formation was used as a monitor of the rate of reaction (7) HCO + O₂ + M → HCOO₂ + M (7). The present data from experiments at P = 8 torr and P = 1–4 torr give k₇[M]/(k₇[M] + k₈) ≥ 0.049 ± 0.017. These data coupled with the k₈ estimates of Washida and coworkers give k₇ ≥ (4.4 ± 1.6) × 10¹¹ l²/mol²·sec for M = CH₂O. The reaction sequence proposed here is consistent with the observed deterimental effect of O₂ addition on the laser-induced isotope enrichment in HDCO. In additional studies of CH₂O-O₂-isobutene mixtures it was found that Φ was equal to ?₂ as estimated in O₂-free CH₂O-isobutene mixtures. These results suggest that the increase in CO (ν = 1) product observed with O₂ addition in CH₂O photolysis does not result from perturbations in the fragmentation pattern of the excited CH₂O, but it is likely that it originates in the occurrence of the exothermic reaction HCO + O₂ → HO₂ + CO (ν = 1).     

Ultrafast SET‐LRP of methyl acrylate at 25 °C in alcohols

Alcohols are known to promote the disproportionation of Cu(I)X species into nascent Cu(0) and Cu(II)X. Therefore, alcohols are expected to be excellent solvents that facilitate the single‐electron transfer mediated living radical polymerization (SET‐LRP) mediated by nascent Cu(0) species. This publication demonstrates the ultrafast SET‐LRP of methyl acrylate initiated with bis(2‐bromopropionyloxy)ethane and catalyzed by Cu(0)/Me₆‐TREN in methanol, ethanol, 1‐propanol, and tert‐butanol and in their mixture with water at 25 °C. The structural analysis of the resulting polymers by a combination of ¹H NMR and MALDI‐TOF MS demonstrates the synthesis of perfectly bifunctional α,ω‐dibromo poly(methyl acrylate)s by SET‐LRP in alcohols. Moreover, this work provides an expansion of the list of solvents available for SET‐LRP. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2745–2754, 2008     

Analysis of quantum yields for the photolysis of formaldehyde at lambda > 310 nm

Experimental quantum yields of the photolysis of formaldehyde at lambda > 310 nm are combined with absolute and relative rate calculations for the molecular elimination H2CO --> H2 + CO (1), the bond fission H2CO --> H + HCO (2), and the intramolecular hydrogen abstraction H2CO --> H ... HCO --> H2 + CO (3) taking place in the electronic ground state. Temperature and pressure dependencies of the quantum yields are analyzed with the goal to achieve consistency between experiment and modeling. Two wavelength ranges with considerably different properties are considered: 340-360 nm, where channel 1 competes with collisional deactivation of excited molecules, and 310-340 nm, which is dominated by the competition between the formation of radical and molecular products. The close relation between photolysis and pyrolysis of formaldehyde, such as analyzed for the pyrolysis in the companion paper, is documented and an internally consistent treatment of the two reaction systems is provided. The quantum yields are modeled and represented in analytical form such that values outside the available experimental range can be predicted to some extent.     

Wavelength dependence of HCO formation in the photolysis of acetaldehyde

The wavelength dependence of HCO(0,0,0) formation in the photodissociation of acetaldehyde was measured using narrow (0.1 nm) bandwidth laser excitation and time-resolved intracavity laser detection (TRILD). A sharp energetic onset at 320 ± 1 nm (89.3 ± 0.3 kcal) for HCO(0,0,0) formation was found. The maximum concentration of HCO(0,0,0) occurs between 100 and 250 μs after excitation depending on the wavelength of excitation     

Dissociation Constants of P-Nitroanilinium Ion in Tetrahydrofuran-Water Mixtures at 25°C by Spectrophotometric Measurements

A spectrophotometric method has been used for the determination of the dissociation constant of P-nitroaniline indicator (which has a charge type A⁺B⁰) in various THF-water solvent mixtures at 25°_C. The dissociation constant is found to decrease with the addition of THF which indicates that the basicity of the medium is increased by the addition of the organic solvent. The relative basicity of the medium is compared with other aqueous-organic solvent mixtures and the trend of decreasing basicity is in the order THF-H₂O> DMF-H₂O > AN-H₂O > HAC-H₂O.     

Primary photochemical processes in the photolysis of alkyl nitrites at 366 NM and 23°c in the presence of 15NO

The alkyl nitrites, C₂H₅ONO, n-C₃H₇ONO, n-C₄H₉ONO, and i-C₄H₉ONO were photolyzed at 23°C in the presence of ¹⁵NO at 366-nm incident radiation. The quantum yields of the corresponding isotopically-enriched alkyl nitrites were measured by mass spectrometry. The results indicated that only part of the absorption leads to photodecomposition. The remainder forms an electronically excited state which isotopically exchanges with ¹⁵NO. The indicated reactions of the electronically excited state RONO*, are where k₃/k₂ = 0.50 ± 0.10, 0.62 ± 0.20, 0.42 ± 0.06, and 0.24 ± 0.03 torr, and that k_2a/k₂ = 1.0, 1.0, 0.64 ± 0.04, and 0.56 ± 0.03, respectively, for C₂H₅ONO, n-C₃H₇ONO, n-C₄H₉ONO, and i-C₄H₉ONO.     

SET‐LRP of vinyl chloride initiated with CHBr3 in DMSO at 25 °C

The development of Cu(0)/TREN/CuBr₂‐catalyzed SET‐LRP of VC initiated with CHBr₃ in DMSO at 25 °C is reported. The use of CuBr₂ additive allows for the first LRP of low molecular weight VC (target DP = 100), as well as lower Cu powder loading levels, improved I_eff and control in the synthesis of higher molecular VC, targeted degree of polymerization = 350, 700, 1,000, 1,400. ¹H NMR and HSQC confirm the bifunctionality of CHBr₃ as an initiator and suggest that deleterious side‐reactions such as the formation of allylic chlorides occur primarily at the onset of the reaction. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 4130–4140, 2009     

Surface tension of water at 100°C

The surface tensions of water samples of various degrees of purity were measured at 100°C using the Wilhelmy slide method. The purest water, obtained by constant redistillation and overflowing of the distillate surface assayed at 60.22 dyn/cm which may be compared with 58.74 dyn/cm (σ = 5.994 mg/mm) reported in the literature. Samples of distilled water of lesser purity gave values between σ = 59.48 dyn/cm and σ = 60.16 dyn/cm. It is concluded that the accepted value at 100°C for water should be increased by 2.5%.     

Calorimetric study of the ionization process for 2,4-dinitrophenol in water—dimethylsulphoxide mixtures at 25°C

The ionization and solution enthalpies of 2,4-dinitrophenol were measured calorimetrically at 25°C in water—DMSO mixtures ranging from 0.1 to 0.8 mole fraction of DMSO.

The greater acidity of 2,4-dinitrophenol with respect to 2,5-dinitrophenol is explained on the basis of the observation that in the anion the π-withdrawing resonance effect of the para nitro group stabilizes the benzene ring while in the undissociated molecule the contrary is true.     

Calorimetric study of the ionization process for 2,5-dinitrophenol in water—dimethylsulfoxide mixtures at 25°C

The ionization and solution enthalpies of 2,5-dinitrophenol were measured calorimetrically at 25°C in water—DMSO mixtures ranging from 0.1 to 0.8 mole fraction of DMSO.

The effect of the nitro group in the ortho position seems to prevail over that of the nitro group in the meta position.

The greater acidity of dinitrophenol with respect to the mononitro isomers is explained on the basis of the interference of the nitro group in the metaposition on the interactions between the nitro group in the ortho position and the hydroxyl group or phenolate oxygen.     

Determination of activity coefficients in aqueous solutions of trichloroacetic acid from emf measurements at 25°C

Values of the emf for the cell: Na-glass|Na₂Succ(m), Hg₂Succ|Hg, have been measured. These values of E have been used with Hückel's extended Debye and Hückel equation to obtain the mean ionic activity coefficient values for Na₂Succ in aqueous solutions of several concentrations, m. The values of γ_± thus obtained have been adjusted to Pitzer's equation, with b = 1.2 and α = 2.0 to find Pitzer's parameters and then the values for both the osmotic coefficients and the activity of water. Finally, the standard potential of the Hg₂Succ|Hg electrode has been determined and from this value the solubility-product equilibrium constant for mercurous succinate has also been calculated.     

Transport of hexane vapor in polystyrene at 25°C I. Analysis of integral sorption data

A series of measurements of integral n-hexane vapor sorption at 25°C and moderate activity, in polystyrene microspheres of varying radii, exhibits typical non-Fickian behavior: nonoverlap of curves of fractional uptake versus (square root of time)/radius. The data are examined in light of a sorption isotherm indicating hexane solubility in excess of that predicted by the Flory–Huggins equation, up to the hexane activity at which the glass transition apparently occurs. A transport analysis is developed based on the assumption that below the transition temperature T_g the rate of sorption is limited by the rate of polymer chain relaxations induced by the penetrant, which facilitate hexane entry into, and immobilization in, glassy microvoids.     

Wavelength dependence of nitrate radical quantum yield from peroxyacetyl nitrate photolysis: experimental and theoretical studies

The photolysis wavelength dependence of the nitrate radical quantum yield for peroxyacetyl nitrate (CH(3)C(O)OONO(2), PAN) is investigated. The wavelength range used in this work is between 289 and 312 nm, which mimics the overlap of the solar flux available in the atmosphere and PAN's absorption cross section. We find the nitrate radical quantum yield from PAN photolysis to be essentially invariant; Phi(NO3)(PAN) = 0.30 +/- 0.07 (+/-2sigma) in this region. The excited states involved in PAN photolysis are also investigated using ab initio calculations. In addition to PAN, calculations on peroxy nitric acid (HOONO(2), PNA) are performed to examine general photochemical properties of the -OONO(2) chromophore. Equation of motion coupled cluster calculations (EOM-CCSD) are used to examine excited state energy gradients for the internal coordinates, oscillator strengths, and transition energies for the n --> pi* transitions responsible for the photolysis of both PNA and PAN. We find in both molecules, photodissociation of both O-O and O-N bonds occurs via excitation to predissociative electronic excited states and subsequent redistribution of that energy as opposed to directly dissociative excitations. Comparison and contrast between experimental and theoretical studies of HOONO(2) and PAN photochemistry from this and other work provide unique insight on the photochemistry of these species in the atmosphere.     

Acceleration and Selective Monomer Addition during Aqueous RAFT Copolymerization of Ionic Monomers at 25 °C

An acceleration effect and selective monomer addition during RAFT copolymerization of the oppositely‐charged ionic monomers in dilute aqueous solution at 25 °C are reported. The reaction is conducted using a non‐ionic water‐soluble polymer as a macromolecular chain transfer agent under visible light irradiation. A fast iterative polymerization can be induced, even in dilute solution, by the favorable ionic interactions and in situ self‐assembly of zwitterionic growing chains. Selelctive monomer addition is achieved in the statistical copolymerization due to the ion‐pairing of the oppositely‐charged monomers, such as precisely the same reaction rates at a 1:1 of monomer ratio, otherwise a faster reaction of the minor monomer component over the major one. These behaviors open up an avenue towards the rapid synthesis of sequence‐controlled zwitterionic polyelectrolytes that can satisfy the demands of emerging biological applications.

     

Kinetic simulation of single electron transfer–living radical polymerization of methyl acrylate at 25 °C

A mechanistic comparison of the ATRP and SET‐LRP is presented. Subsequently, simulation of kinetic experiments demonstrated that, in the heterolytic outer‐sphere single‐electron transfer process responsible for the SET‐LRP, the activation of the initiator and of the propagating dormant species is faster than of the homolytic inner‐sphere electron‐transfer process responsible for ATRP. In addition, simulation experiments suggested that in both polymerizations the rate of deactivation is similar. In SET‐LRP, the Cu(II)X₂/L deactivator is created by the disproportionation of Cu(I)X/L inactive species, while in ATRP its concentration is mediated by the bimolecular termination. The combination of higher rate of activation with the creation of deactivator via disproportionation provides, via SET‐LRP, an ultrafast synthesis of polymers with very narrow molecular weight distribution at room temperature. SET‐LRP is mediated by a catalytic amount of Cu(0), and under suitable conditions, bimolecular termination is virtually absent. Kinetic and simulation experiments have also demonstrated that the amount of water available in commercial solvents and monomers is sufficient to induce the disproportionation of Cu(I)X/L into Cu(0) and Cu(II)X₂/L and, subsequently, to change the polymerization mechanism from ATRP to SET‐LRP. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1835–1847, 2007.     

Crystallographic data for KNO2III at −35 °C and KNO2VII at −100°C

KNO₂ III below ?13°C is monoclinic, space group P2₁ or P2₁/m, with a₀, b₀, c₀ = 4.677, 9.650, 6.395 Å, β = 93.8° at ?35°C. There is a further phase transformation between ?35°C and ?100°C to a new phase KNO₂ VII, which is also monoclinic, space group P2₁ or P2₁/m: with a₀, b₀, c₀ = 8.397, 4.773, 7.644 Å, β = 112° at ?100°C. Both these phases appear to be ordered.     

金属离子对氯过氧化物酶在25℃到55℃激活作用以及机理的研究

基于氯过氧化物酶（CPO）的卤化活性分析,发现某些碱土金属（Ca2+, Mg2+）和过渡金属（Co2+, Ni2+）对CPO具有明显的激活及稳定化作用。例如25 ºC时与CPO在纯缓冲溶液中相比,在75 μmol·L-1 Ca2+,90 μmol·L-1 Mg2+,90 μmol·L-1 Ni2+及105 μmol·L-1 Co2+存在时CPO可分别获得1.33,1.37,1.34 及1.27倍的最大相对活性。而在55 ºC,没有金属离子存在时,CPO 30分钟后仅能保留40%的活性,但在Ca2+,Mg2+离子的介质中,CPO的活性可分别保留81% 和 75%。推测这是由于金属离子结合在CPO活性中心周围的酸-碱催化位点Glu183, His105 and Asp106上,通过底物浓集和诱导有利构象来激活CPO. 同时动力学研究表明金属离子对CPO的激活归因于催化效率（kcat）的提高,以及CPO对底物亲和性及选择性的改善。     

Potentiometric study of chloro complexes of some divalent transition metal cations in dimethyl sulphoxide at 25°C

Formation of the chloro complexes of manganese(II), cobalt(II), nickel(II), copper(II) and zinc(II) in DMSO has been studied potentiometrically at 25°C. The con- centration stability constants for the ionic strength of 0.1 mol kg are derived and discussed. The stability of the divalent transition metal cations towards the chloride anion follows the sequence Mn &> Co &> Ni << Cu &> Zn disobeying the Irving-Williams series.