Etude par rmn de31p de la reaction de l'hexamethylphosphotriamide avec le trichlorure de phosphoryle

The reaction of HMPT with POCl₃ was studied by ³¹P NMR at various temperatures and stoechiometries. Progressive substitution of chlorine atoms of phosphoryl chloride by HMPT molecules was observed. Six new species were involved in the system. The main produce was the $\text{1}\text{1}$ adduct, (Me₂N)₃P⁺Cl, O₂PCl₂^?, analogous to Vilsmeier complex.     

Some aspects of the chlorine evolution reaction at ruthenium dioxide anodes

Cyclic voltammograms for ruthenium dioxide-coated titanium electrodes in acid solutionwere unaffected, below 1.2 V, by the addition of large quantities of chloride ions. Chlorine discharge at such surfaces was assumed to involve participation of surface oxygen species such as O_ads, rather than specific adsorption of Cl^? ions, at the oxide surface. In contrast to the oxygen evolution reaction, the rate of chlorine evolution was independent of both the roughness factor and the oxide loading of these anodes, the discharge apparently occurring at the external surface of these microporous electrodes. In view of the reversibility of the chlorine/chloride electrode system, especially as compared with oxygen, the main factor influencing the rate of chlorine evolution was assumed to be transfer of chlorine gas away from the electrode surface. Deviations from simple Tafel behaviour were also attributed to mass transfer of the product. Cyclic voltammograms recorded at various temperatures indicated that reduction of the oxide layer at potentials below about 0.3 V was considerably enhanced by an increase in temperature.     

Über den Mechanismus der Bildung von Chrom(IV)-oxid aus Chromylchlorid

On the Mechanism of the Formations of Chromium(IV)oxide from Chromyl Chloride The decomposition of chromyl chloride in the temperature range from 380 to 400°C leads with increasing oxygen pressure to chromium oxides containing up to nearly 90% of CrO₂. The interaction with the chlorine prevents a quantitative formation of CrO₂. Up to 315°C during the decomposition of chromyl chloride chromium oxides of higher valencies are formed separating chlorine and taking up oxygen simultaneously. By working in flowing oxygen it could be proved that the decomposition goes at lower temperatures via the nondetectable CrO₃. By heating gradually and by removing the chlorine as far as possible stoichiometric CrO₂ at oxygen pressures above 60 atm could be obtained.     

EPR evidence of off-centred nickel at room temperature in NH4Cl

Electron paramagnetic resonance of γ-irradiated ammonium chloride single crystals doped with Ni²⁺ show the formation of Ni⁺ at orthorhombic sites at room temperature. The chlorine hyperfine structure clearly shows that nickel is at an off-centred interstitial position, lending support to the “off-centred impurity ion” model for the recently discovered spontaneous polarization in ammonium chloride.     

Surface reactions of chlorine molecules and atoms with water and sulfuric acid at low temperatures

Reactions of chlorine-containing species are of great current interest, particularly in reference to possible stratospheric ozone depletion. We have been investigating the potential role of heterogeneous reactions of these species with stratospheric aerosols. Here we wish to report on the results of a study of the interactions of Cl atoms and Cl₂ with H₂SO₄ and H₂O, the dominant components of stratospheric aerosols, at low temperature using X-ray photoelectron spectroscopy (XPS). It appears that chlorine atoms and molecules form chloride ion and higher oxidation states of chlorine upon reacting with cooled surfuric acid surfaces while only chloride ion forms with ice. To test the validity of the chlorine oxidation assignment, an XPS study was also made of chlorine in its various oxidation states as found in the chlorides, hypochlorites, chlorites, chlorates, and perchlorates of sodium, potassium, and calcium. Possible mechanisms by which chlorine changes its oxidation state on contact with H₂SO₄ glasses are discussed.     

Kinetics of Chlorohydrination of Allyl Chloride

The chlorohydrination of allyl chloride with chlorine in water was studied at 20–80°C. The effect of the concentration of chloride ions within the range 0–3.6 mol/l on the selectivity of formation of glycerol dichlorohydrins was studied. An equation that relates the selectivity and the concentration of Cl^–was derived, which adequately describes experimental data. The schemes of parallel and consecutive reactions occurring in the system were suggested. The ratios between the rate constants of the following reactions were found: the reactions of chlorine with water and allyl chloride dissolved in water (k ₁/k ₄= 4.1 × 10^–4), the reaction of allyl chloride with hypochlorous acid and the decomposition of hypochlorous acid (k ₂/k ₃= 1.7 × 10³), and the reactions of the allyl chloride–chlorine complex with a water molecule and Cl^–(k ₅/k ₆= 2.9 × 10^–2).     

Conversion of phosphogypsum to potassium sulfate

Summary Solubility of calcium sulfate in concentrated aqueous chloride solutions is of particular significance in chloride hydrometallurgy and various crystallization processes, such as the production of potassium sulfate from phosphogypsum and potassium chloride. This paper examines an example of the second type of application in which gypsum and potassium chloride are reacted to form K₂SO₄. The solubility of phosphogypsum in aqueous solutions of KCl, HCl, and mixtures of both has first been measured at various temperatures and concentrations. The parameters investigated are HCl concentration up to 6M, KCl concentration up to 180 g L^-1 and temperature from 25 to 80°C. In addition, the influence of co-existing chloride salts, such as (HCl+KCl), on the solubility of calcium sulfate is estimated from 25 to 80°C. The solubility increases obviously with the temperature increment as it does initially with acid concentration, reaching a maximum of about 3M HCl, 130 g L^-1 KCl and then drops. At the same time, the solubility of CaSO₄·2H₂O decreases with increasing KCl concentration.     

Determination of total chlorine in waste oil

Summary A simple method has been developed to determine the concentration of organic chlorine in waste oil. The determination is based on the conversion of organic chlorine to inorganic chloride by reaction with sodium biphenyl followed by extraction with nitric acid and a mixture of nitric acid and water. The concentration of chloride is determined by direct potentiometry with an ion-selective electrode. The limit of determination amounts to 3·10^–5 mol·l^–1 chloride ions with a standard deviation of 3.5%. Different samples of waste oil have been analyzed and the results have been compared to those obtained by combustion in a H₂/O₂ flame followed by potentiometric titration with silver nitrate.     

Kinetics of reaction of chlorine atoms with some biogenic organics

The reaction kinetics of atomic chlorine with a series of biogenic hydrocarbons, including the two enantiomers of α‐pinene, were studied at 298 K and 1 atm pressure using a relative rate technique. The simultaneous losses of the biogenic of interest and a reference compound, either n‐nonane or n‐butane, were followed using gas chromatography with flame ionization detection as a function of the extent of photolysis of a chlorine atom precursor. Thionyl chloride, trichloroacetyl chloride or in a few trials, acetyl chloride, were photolyzed at 254 nm to generate chlorine atoms, since molecular chlorine reacted in the dark with these organics. The relative rate constants for ethane and isoprene determined relative to n‐butane using SOCl₂ and CCl₃COCl were compared to those determined using Cl₂ to check for possible artifacts. The average relative rate constants for ethane and isoprene (both relative to n‐butane) using these new sources are (0.281 ± 0.021) and (2.49 ± 0.39) (±2 σ) respectively, within experimental error of those measured using Cl₂ as the chlorine atom source. The relative rate constants averaged over all sources including Cl₂ are (0.277 ± 0.025) for ethane and (2.42 ± 0.45) for isoprene. The ratios of rate constants for the chlorine atom reactions with the biogenics with formula C₁₀H₁₆ relative to n‐nonane were as follows: (R)‐α‐pinene (0.991 ± 0.264); (S)‐α‐pinene (0.946 ± 0.240); β‐pinene (1.09 ± 0.30); (R)‐limonene (1.33 ± 0.15); myrcene (1.36 ± 0.31); 3‐carene (1.16 ± 0.23). That for p‐cymene, C₁₀H₁₄, is (0.433 ± 0.072). Taking k(Cl + n‐nonane) = (4.82 ± 0.14) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹, the absolute rate constants (in units of 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹) are: (R)‐α‐pinene (4.8 ± 1.3); (S)‐α‐pinene (4.6 ± 1.2); β‐pinene (5.3 ± 1.5); limonene (6.4 ± 0.8); myrcene (6.6 ± 1.5); 3‐carene (5.6 ± 1.3); p‐cymene (2.1 ± 0.4). (All errors are ± 2 σ). Although abstraction was not measured directly in this study, it is likely a significant contributor to the overall reactions of the C₁₀H₁₆ biogenics. The rate constant for the reaction of the aromatic compound p‐cymene is within experimental error of that predicted from the sum of reaction with toluene plus the isopropyl substituent. A limited number of experiments for methyl vinyl ketone in N₂ using CCl₃COCl as the chlorine atom source and nonane as the reference compound gave a relative rate constant of (0.422 ± 0.034), corresponding to an absolute rate constant of (2.0 ± 0.2) × 10⁻¹⁰ cm³ molecule⁻¹ s⁻¹. Based on these rate constants, the lifetimes of these biogenics at dawn with respect to reaction with chlorine atoms are expected to be comparable to reaction with OH. Thus, loss of these biogenics by reaction with atomic chlorine must be taken into account in coastal regions in addition to their reactions with OH, O₃ and at night, NO₃. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 491–499, 1999     

An alternative approach to selective sea water oxidation for hydrogen production

Sea water electrolysis is one of the promising ways to produce hydrogen since it is available in plentiful supply on the earth. However, in sea water electrolysis toxic chlorine evolution is the preferred reaction over oxygen evolution at the anode. In this work, research has been focused on the development of electrode materials with a high selectivity for oxygen evolution over chlorine evolution. Selective oxidation in sea water electrolysis has been demonstrated by using a cation-selective polymer. We have used a perm-selective membrane (Nafion^®), which electrostatically repels chloride ions (Cl⁻) to the electrode surface and thereby enhances oxygen evolution at the anode. The efficiency and behaviour of the electrode have been characterized by means of anode current efficiency and polarization studies. The surface morphology of the electrode has been characterized by using a scanning electron microscope (SEM). The results suggest that nearly 100% oxygen evolution efficiency could be achieved when using an IrO₂/Ti electrode surface-modified by a perm-selective polymer.     

Investigation of ion pair formation in the triphenylmethyl chloride–trimethyl aluminium system,as a model for the activation of olefin polymerization catalyst

Triphenylmethyl chloride (“trityl chloride”, Ph₃CCl) will transfer chloride ions to aluminium alkyls and methylaluminoxane and it is thereby converted into 1,1,1-triphenylethane (“trityl methyl” Ph₃CMe) and the triphenylcarbonium ion (“trityl ion”, Ph₃C⁺). IR spectra of these trityl species have been recorded. Assignments are supported by quantum chemical calculations, leading to significant revisions for some of the modes that are most influenced by reactions. A bright yellow colour shown to be due to the trityl cation, makes trityl chloride a useful indicator for ion pair formation. Trimethyl aluminium (TMA) is chlorinated by trityl chloride and forms dimethyl aluminium chloride (DMAC). DMAC will form a stable ion pair with trityl chloride, probably by forming the anion Al₂Cl₃Me₄⁻. Large excess of trityl chloride causes the formation of AlCl₄⁻, and probably AlCl₃Me⁻ and AlCl₂Me₂⁻ anions. It appears that methyl aluminium chloride anions are formed if, and only if, the anions have at least three chlorine atoms, possibly because of the need to dissipate the negative charge enough to keep the anion dissolved in the hydrocarbon solvent. Methylaluminoxane (MAO) also forms ion pair with trityl chloride, although to lesser extent and less persistent.     

Catalytic generation of chlorine with slight overpotential by micellar ferrocene

Ferrocene solubilized with poly(vinylpyrrolidone) in aqueous KCl solution exhibited a well-defined voltammetric peak at 1.33 V vs. Ag∣AgCl at a platinum electrode. The wave was attributed to the oxidation of chloride to chlorine, demonstrated by smell of chlorine, by a view of formation of gas bubbles, by coloration through the reaction with diethyl-p-phenylene diamine, and by the increase in the anodic current with the concentration of chloride. Since no wave was observed in the ferrocene-free solution or KCl-free solution in this potential domain, the reaction mechanism was suggested to be the oxidation of chloride into chlorine catalyzed by micellar ferrocene. The potential at the foot of the wave (1.08 V) was less positive that the standard potential of Cl₂/Cl⁻, and hence the reaction may be useful for enhancing the energetic efficiency at chlor-alkali industry. The value of the peak current was one-sixth the theoretical diffusion-controlled current, and was proportional to the square-root of the potential scan rate.     

ESR and structure of SO2Cl−√2

A single crystal ESR study is reported on the radial anion of sulphury chloride. In addition to the main spectrum which can be ananyzed in terms of anisotropic hyperfine coupling to two equivalent chlorines, the satellite spectrum of ³³SO₂Cl^?√₂ has been observed in natural abundance. The isotropic value of ca. 200 G for the ³³S hyperfine splitting corresponds to a spin population of 0.21–0.24 in the 3s orbital of sulphur. From the anisotropic chlorine coupling, a spin population of 0.31 in the 3p orbital on each chlorine atom has been derived. These results are consistent with a C_2v trigonal-bipyramid structure, the unpaired electron occupying a molecular orbital of a₁ representation which is localized to a considerable extent in the σ orbitals of the chlorine ligands in the apical positions. A similar structure is indicated by other results for certain isoelectronic phosphorus-centered radicals.     

Photo-oxidation of poly(vinyl chloride)

The photo-oxidation of PVC has been studied over the temperature range 30–150°C. Initiation with ultraviolet (2537A) radiation has been correlated with the presence of minute amounts of ozone. The contribution of atomic oxygen and singlet oxygen (¹Δ_g) molecules to the initiation mechanism is discussed. The β-chloroketones probably formed in the photo-oxidation of PVC, decomposed according to a Norrish type I reaction without loss of chlorine atoms. The gaseous products of the photo-oxidation of PVC at 30°C were carbon dioxide, carbon monoxide, hydrogen, and methane. Hydrogen chloride was obtained only when PVC was heated at high temperatures. When PVC was photo-oxidized and then heated at high temperature, benzene was obtained in addition to hydrogen chloride. The gaseous products from the photo-oxidations of model compounds, such as 4-chloro-2-butanone and 2,4-dichloropentane, were also compared with those from PVC. Hydrogen chloride was detected only after photo-oxidation at temperatures of 25°C or higher. Therefore, it was concluded that hydrogen chloride is mainly a product of thermal decomposition. Since unsaturation was not observed in photo-oxidized PVC films, the cause of discoloration is unclear. When PVC was modified by stabilizers or additives, the oxidative degradation was further complicated by side reactions with the additives.     

Linear-sweep polarographic determination of active chlorine in aqueous solutions containing phenylthiourea

The linear-sweep polarographic determination of active chlorine is based on its reaction with phenylthiourea in acidic phosphate buffer (pH 2.5) containing potassium chloride. The product, C,C-diphenyldithiodiformamidine, is strongly adsorbed and then reduced at a mercury electrode with two peaks at about ?0.35 V and ?0.87 V (vs. SCE). In the presence of 0.05 M potassium chloride, the potential of the first peak shifts positively to ?0.31 V. This peak provides high sensitivity and selectivity for the determination of traces of active chlorine. The linear range is 1×10^?7?2.5×10^?5 M and the detection limit is 5×10^?8 M (3.6 μg l^?1). The method is used for the direct determination of active chlorine in tap water. The mechanism of the reaction was studied by cyclic voltammetry, electrolysis and potentiometric titration. The first peak (?0.35 V) is ascribed to the reduction of a mercury (II) sulfide film produced by reaction of the adsorbed dithio product with mercury. In the presence of 0.05 M chloride, the formation of a mixed HgS·xHg₂Cl2 film shifts the peak to ?0.31 V.     

The Effect of Gadolinium Doping in [13C6,2H7]Glucose Formulations on 13C Dynamic Nuclear Polarization at 3.35 T

The promise of hyperpolarized glucose as a non-radioactive imaging agent capable of reporting on multiple metabolic routes has led to recent advances in its dissolution-DNP (dDNP) driven polarization using UV-light induced radicals and trityl radicals at high field (6.7 T) and 1.1 K. However, most preclinical dDNP polarizers operate at the field of 3.35 T and 1.4–1.5 K. Minute amounts of Gd³⁺ complexes have shown large improvements in solid-state polarization, which can be translated to improved hyperpolarization in solution. However, this Gd³⁺ effect seems to depend on magnetic field strength, metal ion concentration, and sample formulation. The effect of varying Gd³⁺ concentrations at 3.35 T has been described for ¹³C-labeled pyruvic acid and acetate. However, it has not been studied for other compounds at this field. The results presented here suggest that Gd³⁺ doping can lead to various concentration and temperature dependent effects on the polarization of [¹³C₆,²H₇]glucose, not necessarily similar to the effects observed in pyruvic acid or acetate in size or direction. The maximal polarization for [¹³C₆,²H₇]glucose appears to be at a Gd³⁺ concentration of 2 mM, when irradiating for more than 2 h at the negative maximum of the DNP intensity profile. Surprisingly, for shorter irradiation times, higher polarization levels were determined at 1.50 K compared to 1.45 K, at a [Gd³⁺]=1.3 mM. This was explained by the build-up time constant and maximum at these temperatures.     

Effect of porosity on the kinetics of the two-route chlorine reaction: The chlorine evolution—ionization kinetics on iridium dioxide

The porosity effect on the kinetics of the chlorine reaction proceeding via two parallel paths is analyzed theoretically. An equation for the steady-state polarization curve is derived for these conditions. The chlorine evolution-ionization kinetics is studied by steady-state polarization measurements at a rotating disk electrode with an active iridium dioxide coating. A comparison of experimental and theoretical polarization curves shows the chlorine reaction to proceed via two parallel paths not only on DSA and RuO₂, but on IrO₂ as well     

The structure of chlorinated poly(vinyl chloride). VI. Comparison of the chlorination of poly(vinyl chloride) and β,β-d2-poly(vinyl chloride) with 1H-NMR and 13C-NMR spectroscopy

Samples of chlorinated poly(vinyl chloride) (CPVC) and chlorinated β,β-dideuterated poly(vinyl chloride) (β,β-d₂-CPVC) were prepared under identical reaction conditions. The microstructure of CPVC and β,β-d₂-(CPVC) was characterized by a combination of ¹H-NMR, ¹³C-NMR spectroscopy, and analytically determined chlorine content. A difference was observed in the reaction rates of chlorination of PVC and β,β-d₂-PVC, and, in their thermal chlorination in solution, also in the structure of the chlorinated products. It was proved that in the chlorination of β,β-d₂-PVC a new chlorine atom can also enter the original? CHCl? group. The results are discussed from the standpoint of the chlorination mechanism.     

Preparation and structure of chlorinated poly(vinyl flouride)

The low-temperature chlorination of poly(vinyl fluoride) (PVF) proceeds readily in CCl₄ suspension. The rate of chlorination is high initially, but the reaction slows down considerably when the chlorine content of the polymer reaches 40–50%. At long reaction times, polymers containing 62% chlorine (1.88 chlorine atoms per monomer unit) can be obtained. As the degree of chlorination increases, the solubility of PVF in organic solvents increases. Polymer crystallinity and polymer softening point decrease with chlorination. Polymers containing 40% chlorine appear to be completely amorphous by x-ray analysis. In this respect, PVF differs from poly(vinyl chloride) (PVC), where chlorination increases the softening point, and it resembles polyethylene where both crystallinity and softening point decrease with chlorination. ¹⁹F NMR analysis of the polymers indicates that up to a degree of chlorination of 1 chlorine atom per monomer unit, 50% of the substitution occurs on the α-carbon of the PVF molecule. This result is very different from the predominant β-chlorination of PVC reported by several workers. The chemical selectivity observed in the chlorination of PVF is in quantitative agreement with the results of free-radical chlorination of organic compounds and can be rationalized by considering the size and the electronic properties of the fluorine atom. The results of ¹H NMR analysis are also in support of a polymer structure where the chlorine atoms are distributed between α- and β-carbons. Based on a comparison of the ¹⁹F and ¹H NMR data, the average composition of chlorinated PVF at the 1 chlorine atom per monomer unit level can be represented as: C₂₀₀H₂₀₀F₁₀₀Cl₁₀₀ = (CH₂)₆₃(CHF)₅₀(CHCl)₂₄(CClF)₅₀-(CCl₂)₁₃.     

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.