Determination of Ethanol Based on Polarographic Catalytic Current of Sulfate Radical Anion Using Ethanol as Catalyst

ABSTRACT

A new method for the determination of ethanol is proposed based on the catalytic current of sulfate radical anion SO₄ ^?. In 0.1 mol/L KH₂PO₄–Na₂HPO₄ buffer (pH5.6±0.1)–1.6×10^?2 mol/L K₂S₂O₈ solution, the first order derivative peak current is proportional to ethanol concentration in the range of 1×10^?4～9×10^?4 (r = 0.9998). The limit of detection is 6×10^?5 mol/L. The proposed method is applied to determine ethanol directly content in ardent spirits. The fundamental principle of the proposed method is that ethanol is oxidized by sulfate radical anion SO₄ ^? electrogenerated on the electrode surface to ethanol α-radical, and the reduction of the ethanol α-radical produces a polarographic reduction wave.     

Proton chemical polarisation,autocatalysis and frontal kinetics of the oxidation of dialkylsulphides with nitric acid

The oxidation of dimethyl sulphide to dimethylsulphoxide with nitric acid displays CIDNP effects of protons and the phenomenon of frontal kinetics. The process is autocatalytic, with N₂O₄ as the catalyst and the primary oxidant of sulphide. In the presence of the inhibitor (methylmercaptan) the frontal reaction takes place: in purified samples—the usual volume reaction. The interaction of ethyl, n-propyl and n-butyl sulphides with NO₂ is accompanied by integral polarisation of the α-CH₂-protons. In all the cases sulphide is negatively polarised and sulphoxide positively polarised. The reaction mechanism proposed includes the formation of a radical pair during the interaction of sulphide with N₂O₄. Disproportionation of the radical pair leads to the formation of polarised sulphoxide and the decay results in re-generation of sulphide. The rate of oxidation of sulphide during the volume reaction is proportional to the product polarisation.     

Enhanced Recognition of Spin Trapped Radicals In Complex Mixtures: Deuterated Nitronyl Adducts Provide A Gas Chromatographic/Mass Spectrometric Marker

Abstract

The use of deuterated analogues of α-phenyl-N-tert-butyl nitrone (PBN) are reported for GC/MS analysis of spin trapping products. PBN-d₉ and PBN-d₄₁, deuterated in the tert-butyl group (the latter also deuterated in the phenyl ring), result in a more diagnostic fragment ion, C₄D₉ ⁺ (m/z = 66) which improves the recognition of PBN adducts in mixtures. This feature has helped identify a new 1,3-radical addition product of PBN-d₉ formed during azobis(isobutyronitrile) thermolysis (addition of 2-cyano-2-propyloxyl followed by 2-cyano-2-propyl radicals). the ¹³C-trichloromethyl radical adduct of PBN-d₁₄ produced during ¹³C-carbon tetrachloride incubation with rat liver micrcsomes was identified by GC/MS in a complicated biological extract mixture.     

Direct N−H Activation to Generate Nitrogen Radical for Arylamine Synthesis via Quantum Dots Photocatalysis

Represented herein is the first example of N-radical generation direct from N−H bond activation under mild and redox-neutral conditions. The in situ generated N-radical intercepts a reduced heteroarylnitrile/aryl halide for C−N bond formation under visible-light irradiation of quantum dots (QDs). A series of aryl and alkylamines with heteroarylnitriles/aryl halides exhibit high efficiency, site-selectivity and good functional-group tolerance. Moreover, consecutive C−C and C−N bond formation using benzylamines as substrates is also achieved, producing N-aryl-1,2-diamines with H₂ evolution. The redox-neutral conditions, broad substrate scope, and efficiency of N-radical formation are advantageous for organic synthesis.     

Modulative magnetic interaction in π-diradicals of directly meso-linked porphyrin dimers

A series of directly meso-linked Zn(II) porphyrin dimers were prepared, and properties of their bis(π-radical cation)s were investigated. The redox potentials of the dimers bearing various meso-substituents are distributed in wide range although the potential difference (ΔE) between the first and the second oxidations were similar values. Among these dimers, di-tert-butylphenyl derivative and octyloxyphenyl derivative were chemically oxidized by the treatment with NaAuCl₄ in chloroform to afford mono(π-radical cation)s and bis(π-radical cation)s. In the mono(π-radical cation), the π-radical resides one of the porphyrin rings in view of the ESR hyperfine structure. The bis(π-radical cation)s of these dimers showed fine-structured ESR spectra due to triplet species, indicating that the orthogonal alignment of π-radicals leads a stable triplet state. The plots of the triplet ESR signal intensity of the bis(π-radical cation)s versus temperature showed an anomalous feature, in which slight change at lower temperatures and drastic change at higher temperatures were observed. The spectral behavior at lower temperatures was elucidated to be derived from the existence of several kinds of frozen dimers with various dihedral angles between two porphyrin rings. An abrupt increase of triplet signal intensity around 130–160 K can be rationalized by molecular motion around the meso–meso linkage. Such phenomena are comparable with spin-crossover. It also proved that the magnetic interaction in the π-diradical is modulated by the electron-donating ability of the meso-aryl substituents.     

Hyperpolarisation of Mirfentanil by SABRE in the Presence of Heroin

Mirfentanil, a fentanyl derivative that is a μ-opioid partial agonist, is hyperpolarised via Signal Amplification By Reversible Exchange (SABRE), a para-hydrogen-based technique. [Ir(IMes)(COD)Cl] (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazole-2-ylidene, COD=cyclooctadiene) was employed as the polarisation transfer catalyst. Following polarisation transfer at 6.5 mT, the pyrazine-protons were enhanced by 78-fold (polarisation, P=0.04 %). The complex [Ir(IMes)(H)₂(mirfentanil)₂(MeOH)]⁺ is proposed to form based on the observation of two hydrides at δ −22.9 (trans to mirfentanil) and −24.7 (trans to methanol). In a mixture of mirfentanil and heroin, the former could be detected using SABRE at concentrations less than 1 % w/w. At the lowest concentration analyzed, the amount of mirfentanil present was 0.18 mg (812 μM) and produced a signal enhancement of −867-fold (P=0.42 %). following polarisation transfer at 6.5 mT.     

Indoor corrosion of Pb: Effect of formaldehyde concentration and relative humidity investigated by Raman microscopy

In this work the effect of relative humidity (RH) and formaldehyde (H₂CO) concentration on Pb corrosion was investigated; a possible synergism between the aldehyde and CO₂ effects was also considered. Triphasic aqueous salt solutions were used to produce 54% and 75% RH that, together with the 100% RH condition, were combined with 0, 0.62, 55 and 2.0 10² mg m⁻³ formaldehyde concentrations to compose the wanted environments.The results pointed to the conclusion that even at low RH (54%) formates are produced at the metal surface as a consequence of formaldehyde adsorption, indicating that the aldehyde has an active role in Pb corrosion; formates were also observed at relatively low H₂CO concentration (0.62 mg m⁻³). No synergism between formaldehyde and carbon dioxide were observed as demonstrated by the Raman images from a corroded Pb coupon, showing that formate and carbonate contributions to the corrosion products were not spatially related.When compared to other volatile organic compounds (VOCs), formaldehyde harmful effect towards metals is frequently underestimated and the results here reported clearly indicate that, even at low RH, its concentration in indoor environments, where it tends to be produced and accumulated, has to be carefully controlled.     

Electrosynthesis of vanadophosphate by anodic oxidation of vanadium in phosphoric acid solutions

Anodic polarisation of vanadium has been studied in aqueous H₃PO₄ solutions. In all solutions, from 1 to 14 M H₃PO₄, vanadium oxidation occurred at +0.2 V/SCE. A passivation behaviour was observed. In all the cases, the polarisation curve showed a current peak followed by a current plateau. The peak current was dependent upon phosphoric acid concentration. It decreased with the increase of acid concentration. Current oscillations occurred for vanadium anode for lowest concentrated solutions. All the electrochemical observations agreed with the formation of an anodic electrodeposit of vanadophosphate. The yellowish product isolated after controlled potential oxidation has been identified to VOPO₄,2H₂O.     

Sea salt deliquescence and crystallization in atmosphere: an in situ investigation using x‐ray phase contrast imaging

X‐ray phase contrast imaging (PCI) based on synchrotron radiation was introduced for the first time as an in situ imaging way to investigate sea salt phase change, i.e. deliquescence and crystallization in atmospheric environment. A performance on the deliquescence of pure NaCl, which is the dominant component in sea salt, demonstrated that this technique can directly observe the change of core particle and differentiate the outer water layer clearly in solid‐aqueous system of ~100 µm scale. The imaging results showed that sea salt particle deliquesced on a large scale of relative humidity (RH) between 34 and 97% RH as a solid–liquid drop, while no clear deliquescence RH was observed during the process. According to the drop size growth curve, sea salt deliquescence can be divided into three steps, namely water accumulating step (34–75% RH), bulk melting step (75–86% RH) and delay dissolving step (>86% RH), which are most probably dominated by grouped components as MgCl₂/CaCl₂/MgSO₄, NaCl and Na₂SO₄/KCl/K₂SO₄, respectively. Instead at a sole RH, the crystallization of sea salt solution occurred at a range of 46–58% RH, which well agreed with the theory proposed by Ge et al. The aqueous‐solid condition provided by sea salt deliquescence and crystallization may greatly enhance the heterogeneous chemical reactions in atmosphere. Copyright © 2012 John Wiley & Sons, Ltd.     

Ground electronic state and geometry of SF3

Ab initio LCAO MO SCF calculations with DZ + 3d(S) basis functions show that the sulphur trifluoride radical is a planar π-radical having a ²B₁ ground state. Like ClF₃, it has an umbrella-structure. However, it becomes Y-shaped in its first ²A₁ excited state which has been calculated to lie only ≈ 2.4 eV above the ²B₁ ground state.     

Kinetic modelling and inverse treatment of the radical mechanism of the liquid-phase autoxidation of 1,2,3,4-tetrahydronaphthalene

A kinetic model to account for the overall radical mechanism of the self-initiated liquid-phase autoxidation of 1,2,3,4-tetrahydronaphthalene (tetralin RH₂) without solvent and without catalyst at 60°C under normal pressure is presented. The model was constructed following a heuristic approach and it consists of 16 elementary steps and a species space including 6 radical and 7 nonradical compounds. Applying inverse computations, the model can be assigned to experimentally observed data within very good agreement where most of the computed values for the kinetic parameters are found to be close to literature values. The respective experimental data is characterized by an autocatalytic time-evolution of tetralin hydroperoxide (HROOH) and of α-tetralone (RO) where in the first stage of autoxidation a remarkable very slow rate of the RO formation in respect to that of the HROOH formation can be observed. This effect is explicitly expressed by the transformation process of tetralyloxy radicals (HRO˙) into α-tetralol radicals (˙ROH) which react with oxygen yielding RO. The transformation is suggested to be catalyzed by α-tetralol (HROH) which accumulates autocatalytically during the radical chain process. Hence, the nonlinear formation of HROH leads to a switching in the transformation of HRO˙ into ˙ROH radicals which causes a growing rate of RO evolution. The autocatalytic nature of the overall process is explained by degenerate branching of one molecule of HROOH yielding radical species finally resulting into 2 tetralyl radicals (RH˙). This process leads to a growing number of chain propagating reaction sequences involving RH˙ and tetralylperoxy radicals (HROO˙) in which RH₂ and O₂ are consumed and HROOH is formed. Based on the fitting of experimental data the suggested general dynamic structure of the model is validated by computing the reaction fluxes vs. time of several mechanistic key steps. By computer simulations the model is also shown to predict the increase of product accumulation which can be observed experimentally if the autoxidation of RH₂ is started after an initial addition of HROH. © 1996 John Wiley & Sons, Inc.     

The electrodissolution of magnetite: Part I. The electrochemistry of Fe3O4/C discs-potentiodynamic experiments

A simple technique is reported for the preparation of Fe₃O₄ compact electrodes by cold pressing of powdered magnetite admixed with carbon. The electrochemical behaviour of these compacts was shown to be similar with that of polycrystalline magnetite in respect of their potentiodynamic polarisation response. The variation of rest potential with solution composition is complex and indicates that there is oxidation of the surface to Fe₂O₃. Linear potentiodynamic polarisation curves are reported corresponding to unit concentration of ions for the pH range 3–9. The results provide evidence of an electrode process which is an irreversible single electron redox reaction. The current passing through the electrode is generally controlled by a solid-state diffusion process. It is postulated that the diffusing species is the H⁺ ion.     

Radiation synthesis of iron(II) and ruthenium(II) alkylnitroso complexes

The radiolysis of deoxygenated aqueous solutions of Ru(NH₃)₅NO³⁺ and Fe(CN)₅NO²⁻ in the presence of organic compounds (RH) generates alkylnitroso complexes of the form Ru(NH₃)₅N(O)R²⁺ and Fe(CN)₅N(O)R³⁻ where RH = tert-butyl alcohol, tert-butyl amine, N,N-dimethylacetamide, α-aminoisobutyric acid, pivalic acid, and α-hydroxyisobutyric acid. The products form from the rapid combination of the β-carbon radical derived from the reaction of the organic compound with OH radicals (OH + RH → R· + H₂O) and the one-electron reduced metal complex formed by interaction with e_aq⁻: Ru(NH₃)₅NO³⁺ + e_aq⁻ → Ru(NH₃)₅NO²⁺; Fe(CN)₅NO²⁻ + e_aq⁻ → Fe(CN)₅NO³⁻. The alkylnitroso complexes are moderately O₂-insensitive but display varying degrees of thermal stability. Stability permitting, these complexes have been characterized by ion-exchange chromatography and UV-vis-IR spectroscopy. The green ruthenium complexes exhibit λ_max 740 and 342 nm (ϵ 22 and 4.5 × 10³ M⁻¹ cm⁻¹, respectively) and ν_NO in the 1365–1405 cm⁻¹ region. The less stable red iron analogues absorb at 475 and ∼ 250 nm (ϵ 5.0 × 10³ and ∼ 9 × 10³ M⁻¹ cm⁻¹, respectively).     

Substitution reactions of H2GeFBeF with RH (R = F,OH, NH2): A theoretical study

A combined density functional and ab initio quantum chemical study of the substitution reactions of the germylenoid H₂GeFBeF with RH (R = F, OH, NH₂) compounds was carried out. The geometries of all the stationary points of the reactions were optimized using the DFT B3LYP method and then the QCISD method was used to calculate the single-point energies. The theoretical calculations indicated that along the potential energy surface, there were one transition state (TS) and one intermediate (IM) which connected the reactants and the products. The three substitution reactions of H₂GeFBeF with RH are compared with the addition reactions of H₂Ge with RH. And based on the calculated results we concluded that the substitution reactions of H₂GeFBeF + RH involve two steps. One is dissociation onto H₂Ge + BeF₂, and the other is the addition reaction of H₂Ge with RH.     

Sorption of strontium and lanthanum on polyantimonic acid and two phosphatoantimonic acids

The sorption of strontium and lanthanum on antimonic acid (HAP) and on two phosphatoantimonic acids, H₃Sb₃O₆(PO₄)₂ (RH3) and H₅Sb₅O₁₂(PO₄)₂ (RH5) were studied by three types of measurements: kinetics of fixation, distribution coefficients at trace level and sorption capacity. A 2H⁺/Sr²⁺ or 3H⁺/La³⁺ exchange stoichiometry and an affinity order of HAP>RH5>RH3 for Sr and RH3>HAP>RH5 for La were observed. The fixation kinetics is very fast for RH3. For HAP and RH5, there is a fast step followed by a slow diffusion-controlled step. The results are interpreted by comparing the chemical compositions and crystal structures of the three sorbents. Applications to radioactive waste treatment are discussed.     

MIDA- and TIDA-Boronates Stabilize α-Radicals Through B−N Hyperconjugation

Multifunctional organoboron compounds increasingly enable the simple generation of complex, Csp³-rich small molecules. The ability of boron-containing functional groups to modify the reactivity of α-radicals has also enabled a myriad of chemical reactions. Boronic esters with vacant p-orbitals have a significant stabilizing effect on α-radicals due to delocalization of spin density into the empty orbital. The effect of coordinatively saturated derivatives, such as N-methyliminodiacetic acid (MIDA) boronates and counterparts, remains less clear. Herein, we demonstrate that coordinatively saturated MIDA and TIDA boronates stabilize secondary alkyl α-radicals via σ_B-N hyperconjugation in a manner that allows site-selective C−H bromination. DFT calculated radical stabilization energies and spin density maps as well as LED NMR kinetic analysis of photochemical bromination rates of different boronic esters further these findings. This work clarifies that the α-radical stabilizing effect of boronic esters does not only proceed via delocalization of radical character into vacant boron p-orbitals, but that hyperconjugation of tetrahedral boron-containing functional groups and their ligand electron delocalizing ability also play a critical role. These findings establish boron ligands as a useful dial for tuning reactivity at the α-carbon.     

The interaction of radiation-generated radicals with myoglobin in aqueous solution—VI: The reduction of ferrimyoglobin by α-hydroxyalkyl radicals

G-values of the formation of ferromyoglobin (Mb^II) have been determined for the continuous γ-radiolysis of N₂O-saturated neutral aqueous solutions containing ferrimyoglobin (Mb^III) and a series of aliphatic alcohols (RH) under conditions such that the competition for the primary ^.OH radicals favors RH. A comparison of the efficiencies of reduction of Mb^III by the secondary organic radicals formed via H-abstraction reactions with estimates from the literature of the fraction of ^.OH attack at the C-atom α to the —OH group indicates that α-hydroxyalkyl radicals are primarily responsible for the observed reduction. Significantly lower reduction yields are observed when RH = 1,2-diol, compared with the expected yields of strongly reducing 1,2-dihydroxyalkyl radicals; the initial reducing radicals convert into inactive β-alkanonyl analogues so that the reduction of Mb^III is not kinetically competitive with the β-elimination process. Mb^III is useful as a probe of the occurence of slow conversion processes involving radiolytically-generated radicals.     

Heterogeneous reaction of NO2 with sea salt particles

To understand how NO₂ reacts with sea salt particles in the atmosphere of Mega-cities in coastal zones, the heterogeneous reaction of NO₂ on the surface of wet sea salt was investigated with diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and ion chromatography (IC). Kinetic measurements indicated that nitrate formation on sea salt was second order in NO₂ concentration and reactive uptake coefficients were (5.51 ± 0.19) × 10^?7 and 1.26 ± 10^?6 respectively under 0% and 20% relative humidity (RH) at NO₂ molecular concentration of 1.96 × 10¹⁵ mol/cm³. The results showed that liquid water was formed at the site of MgCl₂·6H₂O, CaCl₂·2H₂O on the surface of sea salt and made the reaction more sustainable by releasing hydrated water and absorbing water from air even under a low RH (? 30%). Therefore, pure NaCl particles should not be used to represent sea salt in studies of the heterogeneous reaction with NO₂.     

Capillary electrophoretic separation of serum proteins of workers occupationally exposed to heavy metals

Metallurgy processes are associated with many hazardous and toxic factors, including heavy metals. Exposure to heavy metals can cause damage to different organs, which can be observed through variation in the concentration of proteins in serum. The aim of this study was to evaluate the changes in a serum protein profile of copper smelters exposed to As, Cd and Pb ions, and xenobiotics present in tobacco smoke. A 2.3-fold higher Pb concentration in the blood and a 2.8-fold greater As concentration have been observed in the urine of non-smoking smelters compared to a control group. In the blood of smoking smelters, Cd concentration was 2-fold higher than in non-smoking ones. Serum proteins were separated by capillary electrophoresis, and in the group of non-smoking smelters, a higher amount of α₁-globulins was observed. In the group of smoking smelters, fewer α₁-globulins were noted. Furthermore, a greater amount of α₂-globulins in the serum of smoking and non-smoking workers in relation to the control group was revealed. A positive correlation between the concentration of Cd in the blood and the content of a fraction containing α₁- and α₂-globulins was revealed. Urine Cd concentration was found to be negatively associated with the α₁- and α₂-globulins fraction. Observed abnormalities in the proteins profiles of smelters can be important markers when assessing exposure to heavy metals and in the early diagnosis of diseases caused by them.     

Optical CO(2) sensor of the combination of colorimetric change of alpha-naphtholphthalein in poly(isobutyl methacrylate) and fluorescent porphyrin in polystyrene

An optical CO₂ sensor based on the overlay of the CO₂ induced absorbance change of pH indicator dye α-naphtholphthalein in poly(isobutyl methacrylate) (polyIBM) layer with the fluorescence of tetraphenylporphyrin (TPP) in polystyrene layer is developed. The observed luminescence intensity from TPP at 655 nm increased with increasing the CO₂ concentration. The ratio I₁₀₀/I₀ value of the sensing film consisting of α-naphtholphthalein in polyIBM and TPP in polystyrene layer, where I₀ and I₁₀₀ represent the detected luminescence intensities from a layer exposed to argon and CO₂ saturated conditions, respectively, that the sensitivity of the sensor, is estimated to be 192. The response and recovery times of the sensing film are less than 6.0 s for switching from argon to CO₂, and for switching from CO₂ to argon. The signal changes are fully reversible and no hysterisis is observed during the measurements. The highly sensitive optical CO₂ sensor based on fluorescence intensity changes of TPP due to the absorption change of α-naphtholphthalein in polyIBM layer with CO₂ is achieved.