Chlorine atom migration in the fragmentation of α-mesyl sulfonyl chlorides

The mass spectra of alkanesulfonyl chlorides can be rationalized by loss of a chlorine atom from the molecular ion, followed by loss of SO₂ with concomitant alkyl cation formation. The mass spectra of two α-mesyl sulfonyl chlorides exhibit a new fragmentation process in which the chlorine atom initially attached to sulfur migrates to the α-carbon atom with loss of SO₂, thereby resulting in retention of chlorine in the alkyl cation.     

Direct study of the catalytic decomposition of chlorine and chloromethanes over carbon films

The decompositions of chlorine and chloromethanes over pyrolytic carbon surfaces have been studied by modulated beam mass spectrometry in a low-pressure flow reactor between 850–1280 K. Whereas CH₃Cl is thoroughly stable, molecular chlorine readily dissociates by a first-order process with an activation energy about a half of its bond energy. The decompositions of CH₂Cl₂ and CCl₄ over clean silica surfaces initially display marked autoacceleration associated with the formation of soot on reactor walls and reach limiting rates which are much faster than those predicted for their homogeneous pyrolysis under the same conditions.     

Preparation and characterization of Sb2O5-doped Ti/RuO2-ZrO2 for dye decolorization by means of active chlorine

Textile industry is one of the major generators of wastewaters containing recalcitrant compounds such as dyes that jeopardize public health and environment. Electro-oxidation is an alternative method for treating recalcitrant compounds, and the key element for efficient degradation is the adequate use of dimensionally stable anode (DSA) electrodes to efficiently generate active chlorine, which degrades dyes contained in effluents into more environment-friendly compounds. This work is thereby aimed at preparing a novel DSA electrode for efficient generation of active chlorine. Two different dimensionally stable anodes (Ti/RuO₂ and Sb₂O₅-doped Ti/RuO₂-ZrO₂) were prepared and then characterized by grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy, and scanning electron microscopy, which corroborated the presence of RuO₂, ZrO₂, and Sb₂O₅. The comparison of electroactive areas, assessed by chronoamperometry, showed that Zr helps increase the area of the ternary electrode facilitating the formation of active chlorine. Active chlorine formation was further studied by cyclic voltammetry that revealed a reduction peak attributed to chlorine (product of chloride oxidation). Additionally, decolorization of model solutions that simulate textile effluents containing indigo carmine and reactive black 5 in media with and without chlorides was performed. In the chloride-containing medium, decolorization occurred at a faster rate than in the presence of sulfates. Decolorization of carmine indigo and reactive black 5 in the chloride-containing medium took 40 min and 2 h, respectively. In conclusion, the DSA electrode made of Sb₂O₅-doped Ti/RuO₂-ZrO₂ can efficiently generate the active chlorine for degradation of recalcitrant compounds.     

Direct and mediated electrochemical oxidation of ammonia on boron-doped diamond electrode

Direct (non-mediated) electrochemical oxidation of ammonia on boron-doped diamond (BDD) electrode proceeds mainly at high pH (> 8) via free ammonia (NH₃) oxidation. To enhance ammonia oxidation on BDD at low pH (< 8), where mainly ammonium (NH₄⁺) is present, oxidation of ammonia was mediated by active free chlorine. In this process, electro-generated in situ active chlorine rapidly reacts with ammonia instead of being further electro-oxidized to chlorate at the electrode surface. Thus, active chlorine effectively removes ammonia from an acidic solution, while the formation of by-products such as chlorate and possibly perchlorate is minimized.     

Direct and initiated halogenation of carbon nanomaterials at low temperatures

Cryochemical reactions of the direct and initiated (by photolysis and radiolysis) halogenation of carbon nanomaterials (C₆₀ fullerene, nanotubes, and nanofibers) at 77–240 K were investigated by the ESR, IR spectroscopy, and elemental analysis techniques. A high reactivity of C₆₀ in reactions with fluorine and chlorine with the formation of corresponding derivatives was shown. High concentrations of radical intermediates indicating the radical chain halogenation of C₆₀ were detected (the kinetic chain length for the chlorination process reaches 10⁴–10⁶ units). The amount of chlorine attached to fullerene is ～35% and practically does not depend on the initiation mode (UV or γ-irradiation at doses up to 350 kGy). The mechanism of the cryochemical halogenation of C₆₀ is considered within the limits of the model of multicenter synchronous transitions in a molecular complex consisting of several reactant molecules including molecular fluorine or chlorine and ensuring a net exothermic effect. The amount of chlorine added to nanotubes and nanofibers did not exceed 2.5–8%, thereby indicating a low reactivity of these materials under cryogenic conditions.     

Sensing the ortho Positions in C6Cl6 and C6H4Cl2 from Cl2− Formation upon Molecular Reduction

The geometrical effect of chlorine atom positions in polyatomic molecules after capturing a low-energy electron is shown to be a prevalent mechanism yielding Cl₂⁻. In this work, we investigated hexachlorobenzene reduction in electron transfer experiments to determine the role of chlorine atom positions around the aromatic ring, and compared our results with those using ortho-, meta- and para-dichlorobenzene molecules. This was achieved by combining gas-phase experiments to determine the reaction threshold by means of mass spectrometry together with quantum chemical calculations. We also observed that Cl₂⁻ formation can only occur in 1,2-C₆H₄Cl₂, where the two closest C–Cl bonds are cleaved while the chlorine atoms are brought together within the ring framework due to excess energy dissipation. These results show that a strong coupling between electronic and C–Cl bending motion is responsible for a positional isomeric effect, where molecular recognition is a determining factor in chlorine anion formation.     

Ionization-recombination equilibrium in cold cluster plasma under conditions of retardation by high energy barrier

The kinetics of charge separation in a cold plasma was studied with the degradation reaction in molecular clusters HCl(H₂O) _n + m(H₂O) ? H₃O⁺(H₂O) _{n + m ?1}Cl^?, taken as an example, which precedes chlorine adsorption on the ice surface in the stratosphere. The formation of a vast population of H⁺, Cl^? ion pairs stabilized in water clusters ensures the intense binding of chlorine in ice microcrystals that occur in stratospheric clouds. The accumulation of chlorine in the stratosphere is recognized as the main cause of the destruction of the protective ozone layer. The ion buildup effect is a result of the balance between opposite ionization and recombination processes in the presence of a high energy barrier that retards ion recombination in water clusters. A kinetic equation for the process was obtained and its solution was analyzed. The parameters of the barrier were calculated by computer simulation.     

Electrocatalytic activity of sol-gel-prepared RuO2/Ti anode in chlorine and oxygen evolution reactions

Electrocatalytic properties of RuO₂/Ti anode with different coating masses, which are prepared by the alkoxide sol-gel procedure, are investigated in chlorine and oxygen evolution reactions by polarization measurements and electrochemical impedance spectroscopy in H₂SO₄ and NaCl electrolytes. According to polarization measurements, the activity of anodes at overpotentials below 100 mV is independent of coating mass. However, impedance measurements above 100 mV reveal changes in the activity of anodes in chlorine evolution reaction for different coating masses. The diffusion limitations related to the evolved chlorine are registered in low-frequency domain at 1.10 V (SCE), diminishing with the increase in potential to the 1.15 V (SCE). The observed impedance behavior is discussed with respect to the activity model for activated titanium anodes in chlorine evolution reaction involving formation of gas channels within porous coating structure. Gas channels enhance the mass transfer rate similarly to the forced convection, which also increases the activity of anode. This is more pronounced for the anode of greater coating mass due to its more compact surface structure. The more compact structure appears to be beneficial for gas channels formation. Published in Russian in Elektrokhimiya, 2006, Vol. 42, No. 10, pp. 1173–1179. The text was submitted by the authors in English.     

Investigation of the mechanism of formation of chlorine atoms in chlorine-hydrogen plasmas

To explain the trend of an experimental dependence for concentration of chlorine atoms in a discharge, the principal processes of the formation and decay in the plasma of a chlorine mixture with hydrogen were considered. The rate coefficients and rates of processes involving electrons were calculated by mathematical modeling in order to reveal the contribution of each process to the observed concentration of chlorine atoms. The greatest contribution is made by direct electron-impact dissociation. The experimental concentration of chlorine atoms at a high percentage of hydrogen is explained by an increase in electron concentration and, hence, in the rate of the direct dissociation process. It is suggested that chain reactions can make a substantial contribution to the formation of atoms at low hydrogen concentrations.     

Rearrangements in the electron impact induced fragmentations of sulfonyl chlorides

The major fragmentation pattern obsrved in the mass spectra of simple alkane- and arylsulfonyl chlorides may be rationalized by loss of a chlorine atom from the molecular ion, followed by loss of SO₂ with concomitant carbocation formation. The mass spectra of α-mesyl sulfonyl chlorides and napthalenesulfonyl chlorides exhibit ions resulting from chlorine atom migration to the α-carbon atom with concomitant loss of SO₂. The mass spectra of α-mesyl sulfonyl chlorides also show ions which involve chlorine atom migration to the β-sulfonyl group.     

Stable associates of polyether oligomers with chlorine anion as revealed by the data of electrospray mass spectrometry and molecular dynamics

Stable complexes of oligomers of polyether (oxyethylated glycerol derivatives) with a chlorine anion have first been registered in negative-ion electrospray ionization mass spectra. The results of molecular dynamics simulation demonstrate that the stabilization of such complexes in the gas phase can be due to the formation of a quasicyclic structure of the polymer chain around the chlorine anion and its coordination by CH₂- and OH- groups of the oligomer. This structure is inverted towards the known quasicyclic structure of polyethers, in which metal cations are coordinated by oxygen atoms of ether groups.     

Selective Production of Carbon Monoxide via Methane Oxychlorination over Vanadyl Pyrophosphate

A catalytic process is demonstrated for the selective conversion of methane into carbon monoxide via oxychlorination chemistry. The process involves addition of HCl to a CH₄–O₂ feed to facilitate C?H bond activation under mild conditions, leading to the formation of chloromethanes, CH₃Cl and CH₂Cl₂. The latter are oxidized in situ over the same catalyst, yielding CO and recycling HCl. A material exhibiting chlorine evolution by HCl oxidation, high activity to oxidize chloromethanes into CO, and no ability to oxidize CO, is therefore essential to accomplish this target. Following these design criteria, vanadyl pyrophosphate (VPO) was identified as an outstanding catalyst, exhibiting a CO yield up to approximately 35 % at 96 % selectivity and stable behavior. These findings constitute a basis for the development of a process enabling the on‐site valorization of stranded natural‐gas reserves using CO as a highly versatile platform molecule.     

Recoil chlorine reactions with ethylene

The reactions of recoil³⁸Cl atoms produced through the³⁷Cl(n,)³⁸Cl process in the CF₃Cl–C₂H₄ gas phase are described in this work. The CF₃Cl is a chlorine source as well as moderator. Scavengers, such as O₂ and H₂S, were added to the system to discriminate the reactions induced by energetic and/or thermal chlorine atoms. The radioactive³⁸Cl-labeled products were separated using gas-chromatogarphic technique followed by an external proportional counter for quantitative determination of the product yeids. The mechanisms of the chemical reactions are predicted to account for the formation of these organic compounds.     

Stoichiometry and products of ozone reaction with chloride ion in an acidic medium

It is shown by means of direct spectrophotometry in the UV and visible ranges that the only product of the O₃ reaction with Cl⁻(aq) in an acidic medium is molecular chlorine Cl₂; in solutions, it is in equilibrium with the complex ion Cl₃⁻. It is found that the consumption of one ozone molecule corresponds to the formation of one chlorine molecule. The stoichiometric equation for the reaction is obtained.     

Ammonia oxidation to nitrogen mediated by electrogenerated active chlorine on Ti/PtOx-IrO2

The electrochemical oxidation of ammonia (NH₃ and/or NH₄⁺) in the presence of chloride was investigated on a Ti/PtO_x–IrO₂ electrode. It was shown that ammonia is effectively removed from solution via electrogenerated active chlorine. Based on mass balances, nitrogen is postulated to be the main product of ammonia electrolysis. In the bulk, the concentration of chloramines was low. This could be explained by the fact that the oxidation of ammonia takes place close to the electrode surface where an excess of chlorine relative to ammonia is ensured during the process. This results in the oxidation of ammonia to N₂ and in a local pH decrease. As a result, chloramines were decomposed in the proximity of the electrode prior to diffusing into the bulk.     

Branched-Chain Reaction of Dichlorosilane Chlorination in the Presence of Inhibiting and Deactivating Additives

Dichlorosilylene (SiCl₂) was identified along with SiHCl radicals in the chlorination reaction of dichlorosilane at low pressures and 293 K. The inhibiting effect of propylene additives (>4 vol %) on the self-ignition of dichlorosilane mixtures with molecular chlorine was found. In the presence of a chemically inert additive of SF₆ (>45%), the inhibiting effect was dramatically increased; this fact is an indication that energy factors play an important role. The absence of a isothermal flame propagation regime under experimental conditions suggests that chain branching occurs in a reaction whose rate is a linear function of the concentration of active centers. A kinetic mechanism was proposed, which includes the participation of silylenes in the branching process with the formation of excited states. This mechanism qualitatively describes the experimentally observed behavior.     

Hydroalumination of a Chlorotrialkynylsilane: Spontaneous Stepwise 1,3‐Dyotropic Rearrangement via an Intermediate Silyl Cation

A new functionalised alkynylsilane, Cl‐Si(C?C‐CMe₃)₃ ( 3 ), was obtained by a facile multistep synthesis. Treatment of 3 with equimolar quantities of the hydrides H‐M(CMe₃)₂ (M=Al, Ga) gave the mixed alkenyl‐di(alkynyl)silanes, in which the chlorine atom adopts a bridging position between the aluminium and silicon atoms. Dual hydrogallation of 3 resulted in the formation of a di(alkenyl)‐alkynylsilane containing two gallium atoms, one of which is coordinated to the chlorine atom, and the second is bonded to the α‐carbon atom of the remaining alkynyl group. A tert‐butylsilane was unexpectedly formed by a unique 1,3‐dyotropic chlorine–tert‐butyl exchange for the corresponding dialuminium compound. One aluminium atom is bonded to a tert‐butyl group, a terminal chlorine atom and the α‐carbon atom of the ethynyl moiety; the second is coordinatively unsaturated, with two terminal tert‐butyl substituents. High‐level quantum‐chemical calculations favour a stepwise dyotropic rearrangement with an intermediate cationic silicon species over a simultaneous tert‐butyl–chlorine migration via a five‐coordinate silicon atom in the transition state.     

Kinetics of the gas-phase chlorination of activated carbon with carbon tetrachloride

The chlorination of activated charcoals KAU and SCN with CCl₄ vapor in the temperature range 300–600 °C and also the thermal stability of the added chlorine has been studied. It is shown that chlorination with CCl₄ vapor led to the addition of up to 22 mass % (6.2 mmol/g) of chlorine to the surface layer of the carbon. The added chlorine is desorbed from the surface with formation of HCl, while at temperatures above 500 °C desorption of chlorine goes practically to completion. The effective rate constants and the energies of activation of the processes of chlorination and desorption have been found.     

Polymeric p-benzoquinone-tin derivatives as thermal stabilizers for rigid poly(vinyl chloride). I. Preparation of the stabilizers

The reaction of p-benzoquinone with tin tetrachloride in the absence of solvents was investigated by isolation and identification of the reaction products. This reaction leads to the formation of polymeric quinone-tin derivatives free from combined chlorine, chlorinated quinones, quinhydrone, and minute amounts of CI₂ and HCI gases. The tin content varies accroding to the molar ratios of the reactants and reaches its maximum (72%) at the smallest SnCI₄ ratio. The existence of the Sn-Sn bond in the polymeric derivatives was confirmed chemically and spectroscopically. A mechanism based on the formation of radical intermediates which can account for the reaction products was developed. In view of their quinonoid nature, high thermal stability, and the presence of Sn-Sn bonds, the polytin derivatives are to be investigated as radical traps in the stabilization of polymeric arcticles against radical degradation process.     

Titanium Anodes with an Active Coating Based on Iridium Oxides: The Effect of the Coating's Thickness,Porosity, and Morphology on Its Stability,Selectivity, and Catalytic Activity

The corrosion resistance and the electrochemical behavior of oxide iridium-ruthenium titanium anode (OIRTA) containing 4 mol % RuO₂ + 26 mol % IrO₂ + 70 mol % TiO₂, with a relatively thick active coating (iridium load 15 g m^?2) are studied in conditions of chlorine electrolysis. It is established that polarization curves for the chlorine evolution at low currents exhibit an extended “Tafel” segment with a “Nernstian” slope equal to 0.036 V and that the process rate is limited by the chlorine diffusion away from the electrode surface. In the region of high currents, which is precisely where the chlorine evolution reaction is realized in the industry, polarization curves start displaying an extended, practically horizontal, segment of low polarizability (SOLP) and the chlorine evolution occurs out of the entire depth of the coating. It is shown that the rate of iridium dissolution out of these anodes is in excess of the rate of its dissolution out of OIRTA with a thin coating and the larger the iridium load in the coating, the larger the excess. This phenomenon is attributed to a higher porosity of OIRTA with a thick coating and to the occurrence of the process of iridium dissolution out of the coating throughout the entire depth of the coating. As a result, such an increase in the coating's thickness is likely to lead to a decrease in the lifetime of the anodes. It is discovered that a prolonged polarization of OIRTA in the region of the SOLP leads to an increase in the overvoltage and to a practically complete disappearance of the SOLP from the polarization curves. All this served as the grounds for our drawing the conclusion that it would make no sense to enlarge the thickness and increase the porosity of the active coating of the OIRTA anodes in order to enhance their catalytic activity. It proved manageable to produce substantially more efficient anodes by depositing a thin active coating onto rough titanium out of a diluted covering solution. In so doing, the OIRTA anodes possessed a higher corrosion resistance and a better selectivity at a small iridium load in the coating.