Reactions of N2O4 with organic compounds

The previously described method for the one-step synthesis of aryltrinitromethanes from araldoximes may be utilized for the preparation of trinitromethyl derivatives of pyridine and thiophene. In the latter case, in addition to the conversion of the oxime group into the trinitromethyl group, nitration of the thiophene ring also occurs.For part VII, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 5, pp. 590–591, May, 1970.     

The reaction of N2O4 with organic compounds

The reaction of N₂O₄ with oximes of formylimidazoles is examined. It is shown that, in addition to the conversion of the oxime group to trinitromethyl, nitration of the imidazole ring occurs including nitration in the 2-position, which is not activated towards electrophilic substitution in acid media.For part VIII, see [1].Translated from Khimiya Geterotsiklicheskikh Soedinenii, Vol. 6, No. 5, pp. 669–673, May, 1970.     

Essential methodological improvements in the oxygen isotope ratio analysis of N‐containing organic compounds

The quantitative conversion of organically bound oxygen into CO, a prerequisite for the ¹⁸O/¹⁶O analysis of organic compounds, is generally performed by high‐temperature conversion in the presence of carbon at ～1450°C. Since this high‐temperature procedure demands complicated and expensive equipment, a lower temperature method that could be utilized on standard elemental analyzers was evaluated. By substituting glassy carbon with carbon black, the conversion temperature could be reduced to 1170°C. However, regardless of the temperature, N‐containing compounds yielded incorrect results, despite quantitative conversion of the bound oxygen into CO. We believe that the problems were partially caused by interfering gases produced by a secondary decomposition of N‐ and C‐containing polymers formed during the decomposition of the analyte. In order to overcome the interference, we replaced the gas chromatographic (GC) separation of CO and N₂ by reversible CO adsorption, yielding the possibility of collecting and purifying the CO more efficiently. After CO collection, the interfering gases were vented by means of a specific stream diverter, thus preventing them from entering the trap and the mass spectrometer. Simultaneously, a make‐up He flow was used to purge the gas‐specific trap before the desorption of the CO and its subsequent mass spectrometric analysis. Furthermore, the formation of interfering gases was reduced by the use of polyethylene as an additive for analytes with a N:O ratio greater than 1. These methodological modifications to the thermal conversion of N‐containing analytes, depending on their structure or O:N ratio, led to satisfactory results and showed that it was possible to optimize the conditions for their individual oxygen isotope ratio analysis, even at 1170°C. With these methodological modifications, correct and precise δ¹⁸O results were obtained on N‐containing analytes even at 1170°C. Differences from the expected standard values were below ±1‰ with standard deviations of the analysis <0.2‰. Copyright © 2010 John Wiley & Sons, Ltd.     

Noncatalytic high temperature extraction-nonaqueous titrimetric microdetermination of oxygen in organic compounds

Summary Oxygen in various organic compounds was directly converted to carbon monoxide by decomposing a sample in a graphite crucible at higher than 1800° C. The decomposition products containing the monoxide were purified with soda-asbestos and heated copper wire using argon as a carrier gas. Then the monoxide was oxidized with heated copper(II) oxide. Carbon dioxide produced was absorbed with dimethylformamide containing 2-aminoethanol, and was titrated with a standard solution of tetra-n-butylammonium hydroxide in benzene plus some methanol using thymolphthalein as an indicator.Various types of oxygen in many organic compounds were converted to carbon monoxide stoichiometrically by the above decomposition process. Down to 2g of oxygen was determined with 0.3g error (standard deviation) without any calibrations. Interferences of nitrogen, sulphur and halogene (including fluorine) were removed thoroughly. The method was also applicable to an organoiron compound.

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Unkatalysierte Hochtemperatur-Extraktion und Titration in nicht wäßriger Phase zur Mikrobestimmung von Sauerstoff in organischen Verbindungen

Zusammenfassung Der Sauerstoff verschiedener organischer Verbindungen läßt sich unmittelbar in Kohlenmonoxid umsetzen, indem man die Probe in einem Graphittiegel höher als 1800° C erhitzt. Die Zersetzungsprodukte mit dem Monoxid werden mit Natronasbest und erhitztem Kupferdraht gereinigt, wobei man Argon als Trägergas verwendet. Dann wird das Monoxid über Kupfer(II)oxid oxydiert. Das Kohlendioxid wird in einer Lösung von 2-Aminoethanol in Dimethylformamid absorbiert und mit einer Standardlösung von Tetra-n-butylammoniumhydroxid in Benzol und etwas Methanol titriert, wobei Thymolphthalein als Indikator dient. — Verschiedenartig gebundener Sauerstoff in vielerlei organischen Verbindungen läßt sich durch das angegebene Zersetzungsverfahren stöchiometrisch in Kohlenmonoxid umsetzen. Bis auf 2g Sauerstoff wurden mit einer Standardabweichung von 0,3g ohne vorhergehende Eichung bestimmt. Störungen durch Stickstoff, Schwefel und Halogene (einschließlich Fluor) lassen sich vollständig vermeiden. Das Verfahren eignet sich auch für organische Eisenverbindungen.

     

Removal of nitrite with sulfamic acid for nitrate N and O isotope analysis with the denitrifier method

In environmental water samples that contain both nitrate (NO) and nitrite (NO), isotopic analysis of nitrate alone by all currently available methods requires pretreatment to remove nitrite. Sulfamic acid addition, used previously for this purpose (Wu JP, Calvert SE, Wong CS. Deep‐Sea Research Part I – Oceanographic Research Papers 1997; 44: 287), is shown here to be compatible with the denitrifier method for both N and O isotope analysis of nitrate. Sulfamic acid at a pH of ～1.7 reduces nitrite to N₂. Samples are then neutralized with base prior to isotope analysis, to alleviate the buffering demands of the bacterial media and as a precaution to prevent modification of nitrate during storage with the residual sulfamic acid at low pH. Under appropriate reaction conditions, nitrite is completely removed within minutes. Sulfamic acid treatment does not compromise the completeness of the conversion of nitrate into N₂O or the precision and accuracy of N and O isotope measurements by the denitrifier method. Nitrite concentrations upwards of 7 times the ambient nitrate can be removed without affecting the isotope composition of nitrate. The method is applied to analyses of the coupled N and O isotopes of nitrate and nitrite in waters of the Mexican Margin, to illustrate its efficacy and utility when employed either in the field upon sample collection or in the lab after months of frozen sample storage. Copyright © 2009 John Wiley & Sons, Ltd.     

Position-specific 15N isotope analysis in organic molecules: A high-precision 15N NMR method to determine the intramolecular 15N isotope composition and fractionation at natural abundance

The position-specific ¹⁵N isotope content in organic molecules, at natural abundance, is for the first time determined by using a quantitative methodology based on ¹⁵N Nuclear Magnetic Resonance (NMR) spectrometry. ¹⁵N NMR spectra are obtained by using an adiabatic “Full-Spectrum” INEPT sequence in order to make possible ¹⁵N NMR experiments with a high signal-to-noise ratio (>500), to reach a precision with a standard deviation below 1‰ (0.1%). This level of precision is required for observing small changes in ¹⁵N content associated to ¹⁵N isotope effects. As an illustration, the measurement of an isotopic enrichment factor ε for each ¹⁵N isotopomer is presented for 1-methylimidazole induced during a separation process on a silica column. The precision expressed as the long-term repeatability of the methodology is good enough to evaluate small changes in the ¹⁵N isotope contents for a given isotopomer. As observed for ¹³C, inverse and normal ¹⁵N isotope effects occur concomitantly, giving access to new information on the origin of the ¹⁵N isotope effects, not detectable by other techniques such as isotope ratio measured by Mass Spectrometry for which bulk (average) values are obtained.     

Distinguishing sources of N2O in European grasslands by stable isotope analysis

Nitrifiers and denitrifiers are the main producers of the greenhouse gas nitrous oxide (N(2)O). Knowledge of the respective contributions of each of these microbial groups to N(2)O production is a prerequisite for the development of effective mitigation strategies for N(2)O. Often, the differentiation is made by the use of inhibitors. Measurements of the natural abundance of the stable isotopes of N and O in N(2)O have been suggested as an alternative for the often unreliable inhibition studies. Here, we tested the natural abundance incubation method developed by Tilsner et al.1 with soils from four European grasslands differing in long-term management practices. Emission rates of N(2)O and stable isotope natural abundance of N(2)O and mineral N were measured in four different soil incubations: a control with 60% water-filled pore space (WFPS), a treatment with 60% WFPS and added ammonium (NH(4) (+)) to support nitrifiers, a control with 80% WFPS and a treatment with 80% WFPS and added nitrate (NO(3) (-)) to support denitrifiers. Decreases in NH(4) (+) concentrations, linked with relative (15)N-enrichment of residual NH(4) (+) and production of (15)N-depleted NO(3) (-), showed that nitrification was the main process for mineral N conversions. The N(2)O production, however, was generally dominated by reduction processes, as indicated by the up to 20 times larger N(2)O production under conditions favouring denitrification than under conditions favouring nitrification. Interestingly, the N(2)O concentration in the incubation atmospheres often levelled off or even decreased, accompanied by increases in delta(15)N and delta(18)O values of N(2)O. This points to uptake and further reduction of N(2)O to N(2), even under conditions with small concentrations of N(2)O in the atmosphere. The measurements of the natural abundances of (15)N and (18)O proved to be a valuable integral part of the natural abundance incubation method. Without these measurements, nitrification would not have been identified as essential for mineral N conversions and N(2)O consumption could not have been detected.     

Phosphate oxygen isotope analysis on microsamples of bioapatite: removal of organic contamination and minimization of sample size

Modern and fossil teeth record seasonal information on climate, diet, and migration through stable isotope compositions in enamel and dentine. Climatic signals such as seasonal variation in meteoric water isotopic composition can be recovered through a microscale histology-based sampling and isotopic analysis of enamel phosphate oxygen. The phosphate moiety in bioapatite is particularly resistant to post mortem diagenesis. In order to determine the phosphate oxygen isotope composition of enamel, phosphate must be chemically purified from other oxygen sources in the enamel lattice and matrix, mainly hydroxyl and carbonate ions, and trace quantities of organics.We present a wet chemical technique for purifying phosphate from microsampled enamel and dentine. This technique uses a sodium hypochlorite oxidation step to remove interferences from residual organic constituents of the enamel and/or dentine scaffold, isolates phosphate as relatively large and easily manipulated Ag(3)PO(4) crystals by using a strongly buffered, moderate-temperature microprecipitation, and preserves the oxygen isotope composition of the initial tooth phosphate. The reproducibility of phosphate oxygen isotope compositions thus determined (measured as delta(18)O, V-SMOW scale) is typically 0.2-0.3 per thousand (1 s.d.) on samples as small as 300 microg of enamel or dentine, a considerable improvement over available techniques for analyses of bioapatite phosphate oxygen.     

固相微萃取-气相色谱/同位素质谱法测定水中挥发性有机物单体碳同位素

建立了采用75μm碳分子筛/聚二甲基硅氧烷(CAR-PDMS)纤维的固相微萃取-气相色谱/同位素质谱联用方法测定水中挥发性有机污染物碳同位素。使用浸入式固相微萃取和顶空固相微萃取方法进行实验确定在低浓度条件下最佳δ13C测试方法。通过使用顶空固相微萃取前处理技术进行单体同位素分析分析灵敏度更高,应用CSIA技术对1,2-二氯乙烯,三氯乙烯,四氯化碳进行单体同位素分析,方法的检出限为70μg/L,与样本的标准偏差小于0.3‰。该法适用于水体中微量挥发性有机污染物的同位素组成测定。     

Direct micro determination of oxygen in organic compounds

Summary A simple procedure for the determination of oxygen has been tried with compounds containing carbon, hydrogen, and oxygen. It has the advantage that a temperature of 700° C is sufficient.

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Zusammenfassung Eine einfache Verbrennungsmethode zur Bestimmung von Sauerstoff, für die eine Temperatur von 700° C ausreicht, wurde an Verbindungen, die nur Kohlenstoff, Wasserstoff und Sauerstoff enthalten, erprobt.

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Résumé On a essayé une méthode simple pour doser l'oxygène dans des composés contenant du carbone, de l'hydrogène et de l'oxygène. Elle a l'avantage de ne pas nécessiter une température supérieure à 700° C.

     

The determination of oxygen in sulphur-containing organic compounds

Summary The reactions of anhydroiodic acid with CS₂, H₂S, and COS have been quantitatively investigated at 120° C and 170° C. The iodine formed was titrated and the gaseous reaction products determined by gas chromatography. At 170° C, CS₂ and COS are quantitatively oxidized to CO₂ and SO₂, and H₂S is oxidized to water and partially to SO₂ while a stoicheiometric fraction of the sulphur is obtained as elemental S. At 120° C the reactions are the same although in no case is the oxidation completely quantitative at this temperature.

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Zusammenfassung Die Reaktionen der Anhydrojodsäure mit CS₂, H₂S und COS wurden bei 120 und 170° C quantitativ untersucht. Das freigesetzte Jod wurde titriert und die gasförmigen Reaktionsprodukte gaschromatographisch bestimmt. Bei 170° C werden CS₂ und COS quantitativ zu CO₂ und SO₂ oxydiert, H₂S zu Wasser und teilweise zu SO₂, während ein stöhiometrischer Anteil des Schwefels in elementare Form übergeht. Bei 120° C laufen die gleichen Reaktionen ab, aber keinesfalls quantitativ.

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Résumé On a fait l'étude quantitative des réactions de l'acide anhydroiodique avec CS₂, H₃S et COS à 120° C et 170° C. On a titré l'iode formé et réalisé le dosage des produits gazeux de la réaction par Chromatographie en phase gazeuse. A 170° C, CS₂ et COS sont oxydés quantitativement en CO₂ et SO₂; H₂S est oxydé en eau et partiellement en SO₂ et il se forme une fraction stoechiométrique de soufre à l'état élémentaire. A 120° C, les réactions sont les mêmes bien que l'oxydation ne soit jamais quantitative à cette température.

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This work was supported by grants from the Statens Tekniska Forskningsrad (Swedish Technical Research Council).     

Trace analysis of organic compounds

The trace analysis of organic compounds presents a number of additional difficulties in comparison with the trace analysis of inorganic compounds. Thus special problems arise in sampling and in the storage of samples (e. g. because of the instability of many organic compounds). It is also difficult to choose suitable mild separation methods and to find highly sensitive, molecule-specific determination methods.     

A new approach to determine method detection limits for compound-specific isotope analysis of volatile organic compounds

Compound-specific isotope analysis (CSIA) has been established as a useful tool in the field of environmental science, in particular in the assessment of contaminated sites. What limits the use of gas chromatography/isotope ratio mass spectrometry (GC/IRMS) is the low sensitivity of the method compared with GC/MS analysis; however, the development of suitable extraction and enrichment techniques for important groundwater contaminants will extend the fields of application for GC/IRMS. So far, purge and trap (P&T) is the most effective, known preconcentration technique for on-line CSIA with the lowest reported method detection limits (MDLs in the low microg/L range). With the goal of improving the sensitivity of a fully automated GC/IRMS analysis method, a commercially available P&T system was modified. The method was evaluated for ten monoaromatic compounds (benzene, toluene, para-xylene, ethylbenzene, propylbenzene, isopropylbenzene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, fluorobenzene) and ten halogenated volatile organic compounds (VOCs) (dichloromethane, cis-1,2-dichloroethene, trans-1,2-dichloroethene, carbon tetrachloride, chloroform, 1,2-dichloroethane, trichloroethene, tetrachlorethene, 1,2-dibromoethane, bromoform). The influence of method parameters, including purge gas flow rates and purge times, on delta13C values of target compounds was evaluated. The P&T method showed good reproducibility, high linearity and small isotopic fractionation. MDLs were determined by consecutive calculation of the delta13C mean values. The last concentration for which the delta13C value was within this iterative interval and for which the standard deviation was lower than +/-0.5 per thousand for triplicate measurements was defined as the MDL. MDLs for monoaromatic compounds between 0.07 and 0.35 microg/L are the lowest values reported so far for continuous-flow isotope ratio measurements using an automated system. MDLs for halogenated hydrocarbons were between 0.76 and 27 microg/L. The environmental applicability of the P&T-GC/IRMS method in the low-microg/L range was demonstrated in a case study on groundwater samples from a former military air field contaminated with VOCs.     

Micro determination of oxygen in organic compounds with an automatic elemental analyzer

Zusammenfassung Die Sauerstoffmikrobestimmung nach dem Prinzip von Schütze,Zimmermann, Unterzaucher bzw.Oita undConway wurde der Verwendung eines automatischen Elementaranalysengerätes angepaßt. Dessen Elektronik braucht nicht verändert zu werden, nur der Verbrennungsteil. Die Einwaage wird bei 950° in Heliumatmosphäre pyrolysiert; platinierte Kohle dient zur Konversion des Sauerstoffes in Kohlenmonoxid. Die gasförmigen Reaktionsprodukte werden bei 900° über reduziertes Kupfer geleitet, wo schwefelhältige Verbindungen zurückgehalten werden, dann über Ascarite, womit saure Gase entfernt werden. Kohlenmonoxid wird dann bei 610° über Kupferoxid oxydiert und CO₂ in einer Wärmeleitfähigkeitszelle gemessen. Testsubstanzen dienen zu deren Eichung für Sauerstoff.