Oxidative degradation of nitrogen-containing organic compounds: vaccum-ultraviolet (VUV) photolysis of aqueous solutions of 3-amino 5-methylisoxazole

The oxidative degradation of 3-amino 5-methyl isoxazole initiated by the VUV photolysis of water at 172 nm has been studied. Mineralization of CO₂, H₂O, NO ₃ ^– and NH ₄ ⁺ is more efficient when reductive conditions (argon saturated solutions) are favoured. Formation of compounds which cannot be completely oxidised to CO₂ is observed. Experiments performed under strictly oxidative conditions show higher yields of these inert compounds and, hence, incomplete mineralization. Cyanide was formed in concentrations lower than 5×10^–5 mol/l. In alkaline aqueous solutions, cyanide is completely transformed into CO ₃ ^2– , NH ₄ ⁺ and NO ₃ ^– during the irradiation time needed to mineralize the isoxazole. Therefore, cyanide does not present a potential risk for the use of the VUV photolysis for isoxazole degradation. Similarly, organic nitrogen is converted into both, NO ₃ ^– and NH ₄ ⁺ . The relative concentrations of the two ions depend on total irradiation time, oxygen saturation and reactor geometry. A sequence of reactions is proposed and discussed.Dedicated to Professor Dr. Dieter Klockow on the occasion of his 60th birthday     

CNDO calculations: Electronic spectra and nitrogen-14 N.M.R. shielding constants for some small nitrogen ions

The ¹⁴N chemical shifts of the series NO ₂ ^– , NO ₃ ^– , NO ₂ ⁺ , CN^–, N ₃ ^– , and NH ₄ ⁺ have been calculated using CNDO molecular orbitals. The required average energies E were obtained by a simple virtual orbital method. The electronic spectra of the nitrite, nitrate and cyanide ions are discussed.

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Zusammenfassung Die chemischen Verschiebungen des ¹⁴N werden für die Reihe NO ₂ ^– , NO ₃ ^– , NO ₃ ^– , CN^–, N ₃ ^– und NH ₄ ⁺ mit CNDO-Molekülorbitalen berechnet. Die benötigten mittleren Energien E werden mit einer einfachen Virtual-Orbital-Methode erhalten. Die Elektronenspektren der Nitrit-, Nitrat- und Cyanidionen werden diskutiert.

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Résumé Les déplacements chimiques ¹⁴N dans la série: NO ₂ ^– , NO ₃ ^– , NO ₂ ⁺ , CN^–, N ₃ ^– et NH ₄ ⁺ ont été calculés en utilisant des orbitales moléculaires CNDO. Les énergies moyennes E nécessaires ont été obtenues par une simple méthode à orbitale virtuelle. Les spectres électroniques des ions nitrite, nitrate et cyanure sont discutés.

     

A direct hydrogen-1, carbon-13, and nitrogen-15 NMR study of lutetium(III)-isothiocyanate complexation in aqueous solvent mixtures

A direct, low-temperature hydrogen-1, carbon-13, and nitrogen-15 nuclear magnetic resonance study of lutetium(III)-isothiocyanate complex formation in aqueous solvent mixtures has been completed. At –100°C to –120°C in water-acetone-Freon mixtures, ligand exchange is slowed sufficiently to permit the observation of separate¹H,¹³C, and¹⁵N NMR signals for coordinated and free water and isothiocyanate ions. In the¹³C and¹⁵N spectra of NCS^–, resonance signals for five complexes are observed over the range of concentrations studied. The¹³C chemical shifts of complexed NCS^– varied from –0.5 ppm to –3 ppm from that of free anion. For the same complexes, the¹⁵N chemical shifts from free anion were about –11 ppm to –15 ppm. The magnitude and sign of the¹⁵N chemical shifts identified the nitrogen atom as the binding site in NCS^–. The concentration dependence of the¹³C and¹⁵N signal areas, and estimates of the fraction of anion bound at each NCS^–:Lu³⁺ mole ratio, were consistent with the formation of [(H₂O)₅Lu(NCS)]²⁺ through [(H₂O)Lu(NCS)₅]^2–. Although proton and/or ligand exchange and the resulting bulk-coordinated signal overlap prevented accurate hydration number measurements, a good qualitative correlation of the water¹H NMR spectral results with those of¹³C and¹⁵N was possible.     

Transition metals in atmospheric aqueous samples, analytical determination and speciation

Summary Two rain water samples were analyzed with respect to the determination of the species which are present at the given conditions. The parameters determined were: pH, E_h, electrolytical conductivity, concentration of anions (SO ₄ ^2– , NO ₃ ^– , Cl^–, NO ₂ ^– , HCOO^–, CH₃COO^–), of main cations (Na⁺, K⁺, NH ₄ ⁺ , Mg²⁺, Ca²⁺), and of transition metals (V, Cr, Mn, Fe, Co, Cu, Zn). The methods used were filtration and ultrafiltration, voltammetry, sorption on various sorbents and ion chromatography. Furthermore, E_h-pH-diagrams were taken into account and the partition of the species was calculated by means of stability constants. The transition elements species in the atmospheric aqueous solutions are discussed.     

14N NMR studies of thallium nitrate solutions in liquid ammonia

¹⁴N chemical shifts and linewidths were determined for NO ₃ ^– and NH₃ in liquid ammonia solutions of thallium nitrate at concentrations between 0.07 and 10 M. The concentration dependences of the¹⁴NO ₃ ^– shift and linewidth are consistent with the presence of C_2v ion pairs at a 2:1 mole ratio of NH₃ to TINO₃ and C_3v ion pairs at mole ratios of 3:1 or higher. Previous studies had indicated the formation of ion pairs at low concentrations. The small value of the¹⁴NO ₃ ^– linewidth below 1 M suggests that these are contact ion pairs. Studies of the¹⁴NH₃ linewidth as a function of thallium salt concentration indicate slow solvent exchange at very high concentrations.¹⁴NH₃ exhibits a downfield shift upon incorporation into the solvation sphere of the Tl⁺NO ₃ ^– ion pair, in constrast to upfield shifts reported for complexation with transition metal cations.     

On the chemistry of Baltic amber inclusion droplets

Summary Baltic amber inclusion droplets were analyzed by means of gas chromatography, mass spectroscopy, FTIR spectroscopy, and capillary electrophoresis. It turned out that they were constituted of water in which a variety of inorganic cations (Na⁺, K⁺, Ca²⁺, Mg²⁺) and anions (Cl^–, Br^–, NO ₃ ^– , SO ₄ ^2– ) were dissolved. Moreover, NH ₄ ⁺ , acetate, and succinate ions were detected with the latter strongly predominating. However, no terpenes could be traced. From these results it was concluded that the inclusion droplets stem from splash water of a saline environment into which amber genuine succinic acid was extracted. Ammonium and acetate ions could originate from either tree sap contents or biogenic contents of the splash water.

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Zur Chemie von Inklusionströpfchen des baltischen Bernsteins

Zusammenfassung Inklusionströpfchen des baltischen Bernsteins wurden mit Hilfe von GC-MS, FTIR Spektroskopie und Kapillarelektrophorese analysiert. Es stellte sich heraus, daß es sich dabei um Wasser handelt, in dem eine Reihe von anorganischen Kationen (Na⁺, K⁺, Ca²⁺, Mg²⁺) und Anionen (Cl^–, Br^–, NO ₃ ^– , SO ₄ ^2– ) gelöst sind. Darüber hinaus enthalten sie auch NH ₄ ⁺ , Acetat- und Succinationen, wobei letztere in großem Überschuß vorhanden sind. Terpene waren jedoch nicht nachzuweisen. Aus diesen Ergebnissen wurde abgeleitet, daß die Inklusionströpfchen von salinem Spritzwasser stammen, in welches aus dem Bernstein stammende genuine Bernsteinsäure extrahiert worden war. Ammonium- und Acetationen könnten entweder aus den Inhaltsstoffen des Baumsaftes oder aus biogenen Materialien des Spritzwassers herrühren.

     

Reaction of13N atoms formed in propionic acid-d6 irradiated in a nuclear reactor

The chemical behaviour of¹³N formed by the¹²C/d,n/¹³N reaction by recoil deuterons was studied in propionic acid-d₆ irradiated at 195 to 295 K for 10 min in a reactor. The yields of¹³NH₃ and H¹³NO_x showed remarkable change with the phase change of the media from solid to liquid, i.e., the yield of¹³NH₃ increased from 49.1±2.6 to 57.3±1.5% and that of H¹³NO_x decreased from 28.9±1.8 to 20.4±1.9%. Based on the results, reaction mechanisms involved were argued as: /A/ formation of primary radicals, NH and HNO or NO, and /B/ subsequent reactions converting primary products to the final forms.     

The synthesis of13N-labelled nitrite of high specific activity and purity

An improvement in a method for the synthesis of¹³NO ₂ ⁻ from¹³NO ₃ ⁻ with specific activity>30 mCi/mL and radiochemical purity>99% is described.¹³NO ₃ ⁻ is produced by the¹⁶O(p, α)¹³N reaction using a recirculating water target and 20 MeV protons.¹³NO ₂ ⁻ is synthesized by reduction of¹³NO ₃ ⁻ in a cadmium-copper column. Contaminating¹³NH ₄ ⁺ is removed by rotatory evaporation at pH>11.0. The synthetic procedure takes less than 20 minutes from collection of irradiated target water to sterilization of the radiopharmaceutical.     

205Tl NMR studies: Ion pairing of Tl+ and (CH3)2Tl+ with NO 3 − and ClO 4 − in various solvents

The concentration dependence of the²⁰⁵Tl chemical shifts of Tl⁺ and of (CH₃)₂Tl⁺ ions was determined in several solvents with NO ₃ ^– and ClO ₄ ^– counterions. In general, increased ion pairing caused a low-frequency shift of the²⁰⁵Tl resonance, with the exceptions of (CH₃)₂TlNO₃ inn-butylamine and TlNO₃ in N,N-dimethylformamide (DMF) and in hexamethylphosphorotriamide (HMPA). In HMPA,²⁰⁵Tl linewidths of both Tl⁺ and (CH₃)₂Tl⁺ increased dramatically with dilution below 0.1M. Analysis of the data allowed ion-pair formation constants and²⁰⁵Tl chemical shifts for the ion-paired cation and for the free (solvated) cation to be estimated for some of the solvents.     

Deuteron activation analysis of ultra-trace carbon in boron-doped Si single crystals

The charged particle activation analysis of ultra-trace carbon in boron-doped silicon with the¹²C(d,n)¹³N reaction has been developed. In order to apply¹³N substoichiometric separation to determine carbon in silicon, we studied the rapid dissolution of silicon using nitric acid as the¹³N carrier. Its amounts were as small and definite as possible and the nitrogen oxide gas produced during the dissolution was collected. Silicon was dissolved for 6 min in a mixture of hydrofluoric acid, acetic acid and phosphoric acid, which contained potassium nitrate as the¹³N carrier and nitrogen oxide was collected in the sodium hydroxide solution. In order to combine the dissolution method with¹³N substoichiometric separation, the conditions for steam distillation as pre-separation were also refined in relation to increases in the amount of carrier. Nitrogen-13 was separated substoichiometrically after silicon dissolution and steam distillation. This analytical procedure was used to determine carbon in boron-doped CZ–Si. Carbon at 0.7–12.7·10¹⁵ atoms/cm³ was determined with good reproducibility. It took less than 30 min to start the radioactivity measurement after the end of iradiation. The detection limit was 2·10¹³ atoms/cm³ (0.2 ppb).     

Determination of sulphate in natural water by flow-injection analysis

Summary Sulphate was determined in natural water samples by flow-injection analysis using dimethylsulphonazo-III as reagent. The interference by Ca was eliminated by a cation-exchanger column inserted directly after the sample injection valve. In order to ensure high sensitivity and reproducibility it was necessary to saturate the carrier solution with barium sulphate and to fill the reaction coil with ethanol-water (11) when not in use. Standard deviations were 0.94–1.2% for 6–10mg/l sulphate. The limit of detection was about 0.2mg/l. The calibration graph was linear up to 14mg/l Mg²⁺, NH ₄ ⁺ , Na⁺, K⁺, Cl^–, NO ₃ ^– , PO ₄ ^3– , HCO ₃ ^– and SiO ₃ ^2– did not interfere in the normally occurring concentrations.

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Sulfatbestimmung in natürlichem Wasser durch Flow-Injection-Analyse

Zusammenfassung Als Reagens dient Dimethylsulfonazo-III. Die Störung durch Calcium bei dieser Bestimmung wird durch eine Kationenaustauschersäule eliminiert, die direkt nach dem Probeinjektions-Ventil angeordnet ist. Zur Erhöhung der Empfindlichkeit und Reproduzierbarkeit ist es notwendig, die Trägerlösung mit Bariumsulfat zu sättigen sowie bei Nichtbenutzung des Systems den Reaktionsteil mit Ethanol-Wasser (11) zu füllen. Mit dem so modifizierten Verfahren ergaben sich Standardabweichungen von 0,94–1,2% für 6–10 mg/l Sulfat, die Nachweisgrenze liegt bei 0,2 mg/l. Die Eichkurve ist bis 14 mg/l linear. Mg²⁺, NH ₄ ⁺ , Na⁺, K⁺, Cl^–, NO ₃ ^– , PO ₄ ^3– , HCO ₃ ^– und SiO ₃ ^2– stören in den normalerweise vorkommenden Konzentrationen nicht.

     

Nitrosonium nitrate: A simple cryogenic preparation and phase transitions

A simple method is suggested for the preparation of pure nitrosonium nitrate (NO⁺ NO ₃ ^– ) thin films, by deposition of nitrogen dioxide from the gas phase onto a cold tip under specified conditions and subsequent warming up of the layer. Fourier-transform infrared spectra were used for its characterization and to determine its purity. The NO⁺ NO ₃ ^– solid thus formed was found to be stable up to 230 K. Raman examination of temperature cycling effects on thev(NO⁺) band and on the phonon region of the thin films indicates one amorphous and two crystalline phases. Amorphous-crystalline and crystalline-crystalline transition temperatures are reported.     

Does the ion–molecule reaction between HCCH and HCN lead to CH2CH–CN? A computational and experimental study of the reverse process

The title ion–molecule reaction has been proposed to play an important role in interstellar chemistry if it yields acrylonitrile ions CH₂CH–CN⁺. This question was probed by examining the formation of HCCH⁺ and HCN from low-energy ions CH₂CH–CN⁺ and related isomers, using tandem mass spectrometry based experiments (D and ¹³C labelling) in conjunction with model chemistry calculations (CBS-QB3/APNO). We conclude that the title reaction is a barrierless multistep rearrangement that may not effectively compete with the straightforward formation of stable distonic ions HCCH–NCH⁺ from HCCH⁺(ion)–HCN(dipole) encounter complexes.     

Photocatalytic Reduction of Nitrate in Water on Meso-Porous Hollandite Catalyst: A New Pathway on Removal of Nitrate in Water

Photocatalysis of a hollandite compound K _x Ga _x Sn_8–x O₁₆ (x = ca. 1.8) was examined for the reduction of nitrate to N₂ with a reducing agent of methanol in water under UV irradiation. Hollandites have a characteristic one-dimensional tunnel structure. The meso-porous hollandite was prepared by sol-gel method. This hollandite was used as the photocatalyst and its reaction process was quantitatively analyzed by using ion chromatograph and on-line mass spectrometry. The hollandite photocatalyst showed a significant activity for the formation of N₂ from NO ₃ ^– . Two factors, an increase in UV intensity and a lowering in pH of the solution, contributed to improvement in the selectivity for N₂. The selectivity for N₂ was improved to reach the perfect level by adjusting the factors. Although, in the previous report, the nitrate was mainly reduced to NH ₄ ⁺ or NO ₂ ^– , the present photocatalytic conditions converted it to N₂. The observed photocatalytic reduction of NO ₃ ^– to N₂ with reducing agent CH₃OH was conjugated to the partial oxidation of CH₃OH to HCOOH. This high selective photocatalytic decomposition of NO ₃ ^– to N₂ may be a new pathway among the others reported so far, and it would be useful for environmental protection of water.     

Ag Clusters as Active Species for HC-SCR Over Ag-Zeolites

The addition of hydrogen in the reaction atmosphere is effective in promoting the activity of Ag/alumina and Ag-zeolites on the selective reduction of NO by hydrocarbons (HC-SCR) at low temperatures. The increment of NO conversion over Ag-MFI corresponds to the periodic addition of hydrogen into C₃H₈-SCR conditions. The UV–VIS spectra of Ag-MFI have revealed that the addition of hydrogen results in the formation of Ag_n^δ+ clusters due to partial reduction and agglomeration of Ag species. The coincidence of the formation of the Ag_n^δ+ clusters and the increment of NO conversion suggests that Ag_n^δ+ clusters are the highly active species for HC-SCR. From analysis by H₂-TPR, UV–VIS, and EXAFS, the structure of Ag_n^δ+ clusters on Ag-MFI is identified as being Ag₄²⁺ on average. The formation of Ag clusters was strongly affected by the type of zeolites: The major Ag species are Ag⁺ ions for MOR, Ag_n^δ+ clusters for MFI and BEA, and relatively large metallic Ag_mparticles for Y. The sequence of Ag agglomeration (MOR < MFI < BEA < Y) is in accordance with the strength of the acid sites of zeolites. It can be expected that the interaction between the positive charge of Ag_n^δ+ clusters and acid sites, i.e., the ion-exchange site of zeolites, stabilizes Ag_n^δ+ clusters. The type of Ag species under HC-SCR conditions depends on the concentration of gas-phase oxidants (NO, O₂) and reductants (H₂, HC), and also on the number and strength of the zeolite acid sites.     

Phase and dose effects of13N in pile-irradiated propionic-d2 acid

A sharp phase effect on the yields of¹³NH₄ ⁺ and¹³NO₂ ^– has been observed in propionic-d₂ acid irradiated in a reactor similarly to the other carboxylic acids previously reported. In the formation of¹³NH₄ ⁺,¹³NO₂ ^– and [¹³N]amide, there is no (H/D)-isotope effect between CH₃CD₂COOH and C₂D₅COOD systems unlike for protiated and deuterated benzene and cyclohexane. With a rise in irradiation dose from 100 to 400 MGy, the yield of¹³NH₄ ⁺ increased, but that of¹³NO₂ ^– decreased in proportion to the dose. The dose effect was clear more in liquid phase than in frozen one. The results are in harmony with the reaction mechanism proposed in our previous works.     

The preparation and characterisation of chromium(III) complexes of C-meso-5, 12-dimethyl-1, 4, 8, 11-tetraazacyclotetradecane (LM). Aquation and base hydrolysis kinetics ofcis- andtrans-[CrLMCl2]+

Summary The reaction of [CrCl₃(DMF)₃] with C-meso-5, 12-dimethyl-1, 4, 8, 11-tetra-azacyclotetradecane(L_M) in DMF gives a mixture ofcis-[CrL_MCl₂]Cl (ca. 90%) andtrans-[CrL_MCl₂]Cl (ca. 10%). These complexes are readily separated, as thecis-isomer is insoluble in warm methanol while thetrans-isomer is soluble. Using the dichlorocomplexes as precursors it has been possible to prepare a range ofcis-[CrL_MX₂]⁺ complexes (X=Br^–, NO ₃ ^– , N ₃ ^– , NCS^– and X₂=bidentate oxalate) and alsotrans-[CrL_MX₂]⁺ complexes (X=Br^–, H₂O or NCS^–). The spectroscopic properties and detailed stereochemistry of the complexes are discussed.The aquation and base hydrolysis kinetics ofcis- andtrans-[CrL_MCl₂]⁺ have been studied at 25° C. Base hydrolysis of thecis-complex is extremely rapid with K_OH =1.46×10⁵ dm³ mol^–1 at 25° C. This unusual reactivity appears to be associated with thetrans II stereochemistry of thesec-NH centres of the macrocycle. Base hydrolysis of thetrans complex with thetrans III chiral nitrogen stereochemistry is quite normal with k_OH =1.1 dm³ mol^–1 s^–1 at 25° C.     

An open-shell INDO study of models for the stabilized O− ion in γ-irradiated alkaline ices

Structural models for stabilized O^– in -irradiated alkaline ices are evaluated. INDO calculations on hydrated O^– indicate octahedral coordination and hydrogen bond orientations for the water molecules are preferred. INDO results for hydrated OH^– are compared with crystallographic data for NaOH hydrates: a scaling factor for calculated hydrogen bond lengths is developed and applied to hydrogen bonded O^– models. The hydrated O^– model is closely similar to the hydrated anions in KF · 4H₂O, NaOH · 4H₂O, and NaOH · 7H₂O. A second model is developed, involving H₃O⁺ along with H₂O, in the O^– stabilization shell. Both models are discussed in terms of alkaline ice radiation chemistry.     

Ab initio studies of peroxynitrite anion-water complexes

Quantum mechanical methods have been applied to thecis-ONOO^–-H₂O,cis-ONOO^–-(H₂O)₂ andtrans- ONOO^–-H₂O complexes. Equilibrium geometries, binding energies, net atomic charges and vibrational frequencies are presented for several different arrangements. The MØller-Plessett second-order perturbation (MP2) method predicted shorter hydrogen bonds than the SCF method, but the computed Hartree-Fock (HF) binding energies are similar to counterpoise corrected MP2 values. The geometry changes of ONOO^– and water after solvation are examined. The ONOO^– and H₂O bond length changes follow typical hydrogen bond structural trends, whereas bond angles in ONOO^– are unaffected when the hydrogen bond is formed, similar to the conclusions from NO ₂ ^– -(H₂O) _n HF/6-31G studies and Monte Carlo simulations. Thecis-ONOO^–-(H₂O) _n frequencies are compared with the solution Raman spectrum and with calculations on isolated ONOO^–.     

Interlaboratory exercises to compare analytical method performances

Three intercomparison exercises on simulated rainwater were held in the period 1991–93 involving 72 to 99 laboratories in Europe and South America. The exercises required the analysis of pH, conductivity, main anions (Cl^–, NO ₃ ^– and SO ₄ ^2– ) and main cations (Ca²⁺, K⁺, Mg²⁺, Na⁺ and NH ₄ ⁺ ). The concentrations of the single ions ranged between 5 and 150 moll^–1. Results were used to evaluate and compare the precision of the analytical methods. A general improvement in precision was observed in the course of the exercises.