Polarographic reduction of aqueous sulfur dioxide

Direct- and alternating-current polarograms of aqueous SO₂ · OH₂ solutions show four reduction waves, more than previously reported. Waves I and II probably result from the electroreduction of SO₂ · OH₂ and HSO⁻₃, respectively; these two waves completely overlap at pH 1 but are partially resolved at higher pH values due to different pH dependence. Reduction of SO₂ · OH₂ involves two electrons and two H⁺ ions and the initial product is probably sulfoxylic acid, H₂SO₂. This product can disproportionate to S⁰ and SO₂ · OH₂ in very acidic media (pH ≤ 1) and, in the limit, double the reduction current of SO₂ · OH₂. Reduction of HSO⁻₃ appears to occur via two paths: one is a two-electron three-H⁺ ion path and the other is a one-electron one-H⁺ ion path. The former dominates at pH ≤ 3 and probably produces H₂SO₂; the latter dominates at pH > 4 and may produce SO⁻₂. H₂SO₂ in less acidic media can react with HSO⁻₃ to yield dithionite species (such as H₂S₂O₄, HS₂O⁻₄ and S₂O²⁻₄) and HSO₂ and SO⁻₂ by dissociation of the dithionite species. Waves III and IV are believed to result from reduction of HSO₂ and SO⁻₂, respectively, to H₂SO₂ species.     

Assessing the Viability of the Methylsulfinyl Radical-Ozone Reaction

Although integral to remote marine atmospheric sulfur chemistry, the reaction between methylsulfinyl radical (CH₃SO) and ozone poses challenges to theoretical treatments. The lone theoretical study on this reaction reported an unphysically large barrier of 66 kcal mol⁻¹ for abstraction of an oxygen atom from O₃ by CH₃SO. Herein, we demonstrate that this result stems from improper use of MP2 with a single-reference, unrestricted Hartree-Fock (UHF) wavefunction. We characterized the potential energy surface using density functional theory (DFT), as well as multireference methodologies employing a complete active-space self-consistent field (CASSCF) reference. Our DFT PES shows, in contrast to previous work, that the reaction proceeds by forming an addition adduct [CH₃S(O₃)O] in a deep potential well of 37 kcal mol⁻¹. An O−O bond of this adduct dissociates via a flat, low barrier of 1 kcal mol⁻¹ to give CH₃SO₂+O₂. The multireference computations show that the initial addition of CH₃SO+O₃ is barrierless. These results provide a more physically intuitive and accurate picture of this reaction than the previous theoretical study. In addition, our results imply that the CH₃SO₂ formed in this reaction can readily decompose to give SO₂ as a major product, in alignment with the literature on CH₃SO reactions.     

A tr esr study of the reactions of excited organic triplet molecules with inorganic sulfur oxoanions

The reactions of excited triplet ketones including benzophenone, 4,4′-dihydroxybenzophenone, and acetone with inorganic sulfur oxoanions: sulfite (SO₃ ⁼), metabisulfite (S₂O₅ ⁼), and dithionite (S₂O₄ ⁼) in solution were studied by TRESR. Observation of radical anion intermediates polarized by the Triplet Mechanism demonstrated the reactions of electron transfer from the sulfur dianions to the organic triplet states. Thus, electron transfer from SO₃ ⁼ to the triplet organic carbonyl compounds gave rise to the SO₃ ^? radical; reactions with metabisulfite and dithionite were more complex and may be interpreted as occurring via electron transfer to the carbonyl system followed by dissociation of the S-S bond in the resulting sulfur oxoanion radical. The initial radical ion pairs thus formed consist of pairs of anion radicals, one organic and one inorganic.     

AB initio calculations and matrix ftir studies of the sulfur trioxide radical anion

The structures and vibrational frequencies of SO⁻₃ (C_3v) and SO⁻₂ (C_2v) have been calculated at the UHF SCF/3-21 + G¹ level. By cocondensation of Cs atoms and SO₃ in an Ar matrix the FTIR spectrum of Cs₄SO₃ has been measured. The molecule is proposed to have C_s symmetry with SO₃ binding to Cs in a bidentate fashion.     

Rapid Determination of Trifluoromethanesulfonate and p-Toluenesulfonate by Ion-Pair Chromatography Using a Reversed-Phase Silica-Based Monolithic Column: Application to the Analysis of Ionic Liquids

A method of ion-pair chromatography was developed on a reversed-phase silica-based monolithic column for the fast and simultaneous determination of trifluoromethanesulfonate (CF₃SO₃ ⁻) and p-toluenesulfonate (C₇H₇SO₃ ⁻). The analysis was performed using a mobile phase of tetrabutylammonium hydroxide + citric acid + acetonitrile on the Chromolith Speed ROD RP-18e column with direct conductivity detection. The effects of the eluent, column temperature and flow rate on the retention of the anions were investigated. The experimental phenomenon was discussed according to hydrophobic interaction and ion-exchange mechanism in the separation. The optimized chromatographic conditions were selected. The optimized eluent for the separation consisted of 0.2 mmol L⁻¹ tetrabutylammonium hydroxide + 0.10 mmol L⁻¹ citric acid + 9% acetonitrile (pH 5.5). The flow rate was set at 6.0 mL min⁻¹. The column temperature was 25 °C. Under the optimal conditions, the better separation of CF₃SO₃ ⁻ and C₇H₇SO₃ ⁻ was achieved without any interference by other anions (Cl⁻, Br⁻, I⁻, NO₃ ⁻, SO₄ ²⁻, ClO₃ ⁻, BF₄ ⁻ and PF₆ ⁻). The detection limit (S/N = 3) was 0.28 and 0.71 mg L⁻¹ for CF₃SO₃ ⁻ and C₇H₇SO₃ ⁻, respectively. The method has been applied to the determination of CF₃SO₃ ⁻ and C₇H₇SO₃ ⁻ in ionic liquids. The spiked recoveries of CF₃SO₃ ⁻ and C₇H₇SO₃ ⁻ were 101.1 and 100.2%, respectively.

     

Efficient activation of sulfite for reductive-oxidative degradation of chloramphenicol by carbon-supported cobalt ferrite catalysts

Activation of (bi)sulfite (S(IV)) by metal oxides is strongly limited by low electrons utilization.In this study,two carbon-supported cobalt ferrites spinels (Co Fe₂O₄QDs-GO and CoFe₂O₄MOFs-CNTs) have been successfully synthesized by one-step solvothermal method.It was found that both catalysts could efficiently activate S(IV),with rapid reductive dechlorination and then oxidative degradation of a recalcitrant antibiotic chloramphenicol (CAP).Character...     

Darstellung und Kristallstruktur von Tetramethylammoniumbromid‐Brom‐SO2‐Addukt, [(CH3)4N]+Br‐�Br2�2SO2

Preparation and Crystal Structure of Tetramethylammoniumbromide‐Bromine‐Sulfur Dioxide Adduct, [(CH₃)₄N]⁺Br^‐�Br₂�2SO₂ Tetramethylammoniumtribromide forms with sulfur dioxide a salt which is characterized by vibrational spectroscopy and crystal structure analysis. [(CH₃)₄N]⁺Br^‐�Br₂�2SO₂ crystallizes monoclinic in the space group P2₁/m with a = 657.4(5) pm, b = 2933.0(5) pm, c = 1462.2(5) pm, β = 91.241(5)° and four formula units in the unit cell. The crystal structure possesses bent infinite chains which consist of alternately arranged bromine and bromide ions. The bromide ions are connected to the molecules of bromine and sulfur dioxide by strong interactions forming a three dimensional network.     

Reduction of Sulfur Dioxide to Sulfur Monoxide by Ferrous Porphyrin**

The reduction of SO₂ to fixed forms of sulfur can address the growing concerns regarding its detrimental effect on health and the environment as well as enable its valorization into valuable chemicals. The naturally occurring heme enzyme sulfite reductase (SiR) is known to reduce SO₂ to H₂S and is an integral part of the global sulfur cycle. However, its action has not yet been mimicked in artificial systems outside of the protein matrix even after several decades of structural elucidation of the enzyme. While the coordination of SO₂ to transition metals is documented, its reduction using molecular catalysts has remained elusive. Herein reduction of SO₂ by iron(II) tetraphenylporphyrin is demonstrated. A combination of spectroscopic data backed up by theoretical calculations indicate that Fe^IITPP reduces SO₂ by 2e⁻/2H⁺ to form an intermediate [Fe^III−SO]⁺ species, also proposed for SiR, which releases SO. The SO obtained from the chemical reduction of SO₂ could be evidenced in the form of a cheletropic adduct of butadiene resulting in an organic sulfoxide.     

Etude vibrationnelle de la phase II des hydrogénodisulfates de triammonium, (NH4)3H(SO4)2 et (ND4)3D(SO4)2

The i.r. and Raman spectra of room temperature phase (phase II) of (NH₄)₃H(SO₄)₂ and (ND₄)₃D(SO₄)₂ as polycrystalline samples and single crystals have been investigated between 4000 and 30 cm⁻¹. An assignment of internal and external modes is given in terms of group frequencies and symmetry types. This crystal contains non-centrosymmetric dimers (SO₄HSO₄)³⁻ where sulphate ions are associated by strong asymmetric OH … O hydrogen bonds; they are characterized by two strong Raman bands at 1078 and 966 cm⁻¹, and a νOH frequency at about 1250 cm⁻¹. The acidic proton is statistically disordered around the crystallographic symmetry centre while all of the NH⁺₄ ions show an important dynamical orientational disorder.     

ESR characterisation of SO−3 and SO−4 radicals in X-irradiated kainite (KMgClSO4.3H2O)

The ESR spectra of the kainite (KMgClSO₄.3H₂O) crystal revealed an intense isotropic (g = 2.004) peak C attributed to the SO⁻₃ radical and two pairs of lines (A₁, A₂) and (B₁, B₂) bearing intensity ratio 5:3. The intensity and linewidth variation of peak C suggested that the signal contains an unresolved shf structure. The power saturation studies on SO⁻₃ indicate that its ESR line is homogeneously broadened and its line shape is Lorentzian. The spin—lattice and spin—spin relaxation times (T₁ and T₂) of SO⁻₃ have been estimated to be 0.44 s and 656 μs, respectively. The analysis of the anisotropic pairs of lines show that they constitute two sets A and B and are due to two chemically inequivalent SO⁻₄ radical species in the lattice. The ESR spectra of the polycrystalline samples recorded at 300 and 77 K confirm the isotropic behaviour of SO⁻₃ and chemical inequivalence of two types of SO⁻₄ radicals. The principal g-values of the SO⁻₄ radical were evaluated to be: g₁ = 2.007, g₂ = 2.011, g₃ = 2.014 for species A and g₁ = 2.008, g₂ = 2.012, g₃ = 2.015 for species B. The low microsymmetry of the SO²⁻₄ ion in the lattice seems to promote the radiation damage.     

Utilization of Solid Acid SO42−/TiO2 as Catalyst to the Three‐Component Mannich Reaction at Ambient Temperature

The three‐component Mannich reaction of among dimethyl malonate, aromatic primary amine, and aromatic aldehyde was made successfully in the presence of solid acidic catalyst SO₄²⁻/TiO₂, with excellent catalytic activity, as compared to SO₄²⁻/γ‐Al₂O₃ and SO₄²⁻/ZnO. To the best of our knowledge, SO₄²⁻/TiO₂ prepared at varied calcination temperatures can perform different intensities of Lewis and Brønsted acidities. Because of this point, under the optimum conditions, the effect of SO₄²⁻/TiO₂ (prepared at 200°C) was much more than that of SO₄²⁻/TiO₂ (prepared at 300°C or 400°C) in the three‐component Mannich reaction. In observing ionization activation mode of the three‐component Mannich reaction, it disclosed that the plausible mechanism possibly undergoes formation of aldimines and transformation of aldimines into β‐amino esters by applying solid acidic catalyst SO₄²⁻/M_xO_y.     

ESR studies on the reactions of the sulphite radical anion,SO−3, with olefinic compounds in aqueous solutions

The reactions of the sulphite radical anion, SO⁻₃, which was generated either from a Ce⁴⁺-NaHSO₃ system at pH 2.5 or from a Ti³⁺ (ethylenediaminetetraacetic acid)-H₂O₂-Na₂SO₃ system at pH 9 in aqueous solutions, with some olefinic compounds were investigated by use of a rapid-mixing flow technique coupled with ESR which can detect the radicals having a lifetime of 5-100 ms. The SO⁻₃ radical could add to the CO double bond in the olefinic compounds in both acidic and alkaline aqueous solutions, although the SO⁻₃ radical is more active in acidic conditions than in alkaline conditions. From the observed hyperfine splitting constants of the SO⁻₃ adducts of the olefinic compounds, the preferred conformation of the adducts was discussed.     

The FTIR image comparison of zirconium sulfate synthesis products from the pathways of Na2ZrO3 and zirconium oxychloride compounds

PSTA BATAN has synthesized zirconium sulfate (ZS) through two methods. Synthesis pathway (I) from Na₂ZrO₃ (CDZ) and (II) through zirconium oxychloride (ZOC). This research aimed to compare both pathways by utilizing FTIR. Path (I) was done using concentrations of H₂SO₄ 65%, contact time of 30, 60, 90, and 150 min, and temperatures of 125, 150, 175, and 225 °C. While path II has been carried out in previous studies [1]. The FTIR image comparison was finished by tracing sulfate derivative functional groups from a wavenumber of 4000–400 cm⁻¹. The O–H stretching at 3441.01 cm⁻¹ as the Zr(OH)Zr group and OH vibration in 3425.68 cm⁻¹ were found at each pathway. However, at pathway (II), we observed another vibration at 3132.40 cm⁻¹ as the NH₃ compound group. Furthermore, the track records of S–O and SO stretching on both pathways were checked at 1635.64, 1095.57, and 956.69 cm⁻¹, respectively, as H₃O⁺, SO₄²⁻, and SO₃²⁻ species. The real difference in pathway (I) was revealed by the presence of H₂SO₄ residue at 802.39 cm⁻¹. At the same time, the Zr–O–Zr and O–Zr–O stretching could be detected in both pathways at the wavenumber of 594.09 and 470.63 cm⁻¹ consecutively. The form of synthesis pathway (I) product was predicted as Zr(SO₄)₂, while the product of path (II) forecasted as Zr(NH₃)(SO₄)₂ compound.     

Cyclic potential sweep electropolymerization of aniline: The role of anions in the polymerization mechanism

The cyclic potential sweep (CPS) method was applied to aniline electropolymerization in several strong acids (H₂SO₄, HNO₃, HCl, HBF₄, HClO₄ and CF₃COOH). It is mainly the type of anion that determines the morphology of polyaniline (PANI) deposits, promoting either a compact (BF⁻₄, ClO₄⁻ and CF₃COO⁻, class 1 anions) or an open structure (SO₄²⁻, NO₃⁻ and Cl⁻, class 2 anions), as suggested by the linear (class 1) or quadratic (class 2) dependence of deposition charges on number of cycles, scan rate and concentration of anilinium and anion, as well as by SEM analysis. From the potential dependence of deposition currents, PANI growth onto PANI is suggested to occur via adsorption of anilinium-anion ionic couples onto fully oxidized (pernigraniline) sites of PANI.     

Self-Assembled,Highly Positively Charged,Allyl–Pd Crowns: Cavity-Pocket-Driven Interactions of Fluoroanions

A series of dodecanuclear highly positively charged homo- and heterometallamacrocycles [{Pd(η³-2-Me-C₃H₄)}₆(4-PPh₂py)₁₂{M₂(tpbz)}₃]¹⁸⁺ (M=Pd, Pt; tpbz=1,2,4,5-tetrakis(diphenylphosphanyl)benzene were synthesized by the quantitative self-assembly of {Pd(η³-2-Me-C₃H₄)}⁺, {M₂(tpbz)}⁴⁺ and 4-PPh₂py moieties in 2:1:4 molar ratio. The cationic assemblies were obtained as salts of different fluorinated anions with diverse sizes and electronic properties, namely BF₄⁻, PF₆⁻, SbF₆⁻ and CF₃SO₃⁻. The new crown-like metallamacrocycles showed remarkable differences in their NMR spectra due to the presence of the different counteranions. On the basis of the observed variations, the metallacycles have been tested as catalytic precursors in allylic alkylation reactions. The anion-dependent activity and selectivity has been analysed and compared with that of the corresponding monometallic allylic corners [Pd(η³-2-Me-C₃H₄)(4-PPh₂py)₂]X (X=BF₄⁻, PF₆⁻, SbF₆⁻, CF₃SO₃⁻). DFT calculations have been employed in order to help to the interpretation of the experimental data and to model the anion–crown interactions.     

The complexing of Np(V) by some inorganic ligands

The complexing of Np(V) with Cl⁻, F⁻, NO₃⁻, NO₂⁻, SO₄⁻², SCN⁻ and IO₃⁻ has been studied by the solvent extraction method using Dinonylnaphthalene sulphonic acid (DNNS) as the extractant. An attempt is made to establish existence of the complexes by solvent extraction and spectrophotometric studies.     

PEO-b-PS Block Copolymer Templated Mesoporous Carbons: A Comparative Study of Nitrogen and Sulfur Doping in the Oxygen Reduction Reaction to Hydrogen Peroxide

Carbon materials slightly doped with heteroatoms such as nitrogen (N-RFC) or sulfur (S-RFC) are investigated as active catalysts for the electrochemical bielectronic oxygen reduction reaction (ORR) to H₂O₂. Mesoporous carbons with wide, accessible pores were prepared by pyrolysis of a resorcinol-formaldehyde resin using a PEO-b-PS block copolymer as a sacrificial templating agent and the nitrogen and sulfur doping were accomplished in a second thermal treatment employing 1,10-phenanthroline and dibenzothiophene as nitrogen and sulfur precursors, respectively. The synthetic strategy allowed to obtain carbon materials with very high surface area and mesopore volume without any further physicochemical post treatment. Voltammetric rotating ring-disk measurements in combination with potentiostatic and galvanostatic bulk electrolysis measurements in 0.5 m H₂SO₄ demonstrated a pronounced effect of heteroatom doping and mesopores volume on the catalytic activity and selectivity for H₂O₂. N-RFC electrode was employed as electrode material in a 45 h electrolysis showing a constant H₂O₂ production of 298 mmol g⁻¹ h⁻¹ (millimoles of H₂O₂ divided by mass of catalyst and electrolysis time), with a faradic efficiency (FE) up to 61 % and without any clear evidence of degradation. The undoped carbon RFC showed a lower production rate (218 mmol g⁻¹ h⁻¹) but a higher FE of 76 %, while the performances drastically dropped when S-RFC (production rate 11 mmol g⁻¹ h⁻¹ and FE=39 %) was used.     

Synergistic Effects between Atomically Dispersed Fe−N−C and C−S−C for the Oxygen Reduction Reaction in Acidic Media

Various advanced catalysts based on sulfur‐doped Fe/N/C materials have recently been designed for the oxygen reduction reaction (ORR); however, the enhanced activity is still controversial and usually attributed to differences in the surface area, improved conductivity, or uncertain synergistic effects. Herein, a sulfur‐doped Fe/N/C catalyst (denoted as Fe/SNC) was obtained by a template‐sacrificing method. The incorporated sulfur gives a thiophene‐like structure (C−S−C), reduces the electron localization around the Fe centers, improves the interaction with oxygenated species, and therefore facilitates the complete 4 e⁻ ORR in acidic solution. Owing to these synergistic effects, the Fe/SNC catalyst exhibits much better ORR activity than the sulfur‐free variant (Fe/NC) in 0.5 m H₂SO₄.     

Kinetic studies on the reactions of Ru(II) tetraammines with CS2N−3

The kinetics of the reactions of Ru(II) complexes with CS₂N⁻₃ ions were studied spectrophotometrically. The formation rate constants data for trans-[Ru(NH₃)₄L(CS₂N₃)] are 2.2 × 10², 1.8 × 10 and 1.3 × 10² M⁻¹ s⁻¹ for L = SO^2-₃, HSO⁻₃ and P(OEt)₃), respectively [μ = 1.0 M (NaCF₃COO), 25°C]. Under the same experimental conditions, the values of k⁻¹ (specific rate for the aquation reaction) are 1.5 × 10⁻², 5.0 × 10⁻² and 4.5 × 10 s⁻¹ for L = SO²⁻₃, HSO⁻₃ and P(OEt)₃, respectively. The free-energy change (ΔG^≠) for the systems where L = P(OEt)₃ and SO²⁻₃ are in agreement within the experimental error. It was observed that the affinity of the CS₂N⁻₃ ion decreases with the increasing π-acidity of the auxiliary ligand L. The order of affinity of the CS₂N⁻₃ ion for the Ru(II) center studies is SO²⁻₃ > HSO⁻₃ > P(OEt)₃ >SO₂.     

Boron–π interactions in two 3-(dihydroxyboryl)anilinium salts analyzed by crystallographic studies and supported by the noncovalent interactions (NCI) index theoretical approach

In the title compounds, 3-(dihydroxyboryl)anilinium bisulfate monohydrate, C₆H₉BNO₂⁺·HSO₄⁻·H₂O ( I ), and 3-(dihydroxyboryl)anilinium methyl sulfate, C₆H₉BNO₂⁺·CH₃SO₄⁻ ( II ), the almost planar boronic acid molecules are linked by pairs of O—H…O hydrogen bonds, forming centrosymmetric motifs that can be described by the graph-set R₂²(8) motif. In both crystals, the B(OH)₂ group acquires a syn–anti conformation (with respect to the H atoms). The presence of the hydrogen-bonding functional groups B(OH)₂, NH₃⁺, HSO₄⁻, CH₃SO₄⁻ and H₂O generates three-dimensional hydrogen-bonded networks, in which the bisulfate (HSO₄⁻) and methyl sulfate (CH₃SO₄⁻) counter-ions act as the central building blocks within the crystal structures. Furthermore, in both structures, the packing is stabilized by weak boron–π interactions, as shown by noncovalent interactions (NCI) index calculations.