Laser-spectroscopic laboratory studies of atmospheric aqueous phase free radical chemistry

Nitrate radical (NO₃) reactions with benzene (R-1), toluene (R-2), p-xylene (R-3), p-cresol (R-4) and mesitylene (R-5) have been studied by laser photolysis/long path laser absorption (LP-LPLA) in aqueous solution. Rate constants of k₁=(4.0±0.6) 10⁸, k₂=(1.2±0.3)10⁹, k₃=(1.6±0.1)10⁹, k₄= (8.4±2.3)10⁸ and k₅=(1.3±0.3)10⁹ lmol^-1s^-1 were obtained at T=298 K. In addition, reaction rate coefficients for SO^-₅+Fe²⁺prod. (R-6) and SO^-₅+Mn²⁺prod. (R-7) of k₆=(4.3±2.4) 10⁷ lmol^-1s^-1 and k₇=(4.6±1.0)10⁶ lmol^-1s^-1 (T=298 K, I0) have been obtained by the application of laser photolysis/UV-VIS broadband diode array spectroscopy. A new laser photolysis/UV-long path laser absorption experiment has been applied to study the reaction of the Cl^-₂ radical anion with dissolved sulfur(IV). For the reactions Cl^-₂+HSO^-₃2Cl^-+H⁺+SO^-₃ (R-8) and Cl^-₂+SO^2-₃2Cl^-+SO^-₃ (R-9) rate coefficients of k₈=(1.7±0.2)10⁸ lmol^-1s^-1 (T=298 K, I0) and of k₉=(6.2±0.3)10⁷ lmol^-1s^-1 (T=279 K, I0) were obtained.     

Chemical algebra. II: Discriminating pairing products

The algebra of stereogenic pairing equlibria is presented in a very general context. Starting from the notions of fuzzy subgroup and conjugacy link, chemical pairing constants between molecular speciesu andv having a skeletal symmetry groupG are formulated as pairing products on aG-Hilbert space. Discriminating pairing productsK are defined by the conditions: K 1 and K = 1 the representative vectors of the paired species areG-equivalent. WhenG has only two elements, the pairing product is always discriminating. For several skeletal symmetries, if the vectors are enantiomorphic (v = u, ² =e, G), thenK is greater than 1 and reaches 1 only ifu is achiral: chirality indexes and general permutational indexes are then defined fromK(u u). The general model is illustrated by some examples.     

On the Interaction of Two Finite-Dimensional Quantum Systems

Interaction of quantum system S ^a described by the generalised × eigenvalue equation A| _s =E _s S ^a | _s (s=1,...,) with quantum system S ^b described by the generalised n×n eigenvalue equation B| _i = _i S ^b | _i (i=1,...,n) is considered. With the system S ^a is associated -dimensional space X ^a and with the system S ^b is associated an n-dimensional space X _n ^b that is orthogonal to X ^a . Combined system S is described by the generalised (+n)×(+n) eigenvalue equation [A+B+V]| _k = _k [S ^a +S ^b +P]| _k (k=1,...,n+) where operators V and P represent interaction between those two systems. All operators are Hermitian, while operators S ^a ,S ^b and S=S ^a +S ^b +P are, in addition, positive definite. It is shown that each eigenvalue _{k i} of the combined system is the eigenvalue of the × eigenvalue equation . Operator in this equation is expressed in terms of the eigenvalues _i of the system S ^b and in terms of matrix elements _s |V| _i and _s |P| _i where vectors | _s form a base in X ^a . Eigenstate | _k ^a of this equation is the projection of the eigenstate | _k of the combined system on the space X ^a . Projection | _k ^b of | _k on the space X _n ^b is given by | _k ^b =( _k S ^b –B)^–1(V– _k P})| _k ^a where ( _k S ^b –B)^–1 is inverse of ( _k S ^b –B) in X _n ^b . Hence, if the solution to the system S ^b is known, one can obtain all eigenvalues _{k i} } and all the corresponding eigenstates | _k of the combined system as a solution of the above × eigenvalue equation that refers to the system S ^a alone. Slightly more complicated expressions are obtained for the eigenvalues _{k i} } and the corresponding eigenstates, provided such eigenvalues and eigenstates exist.     

Effect of substituents on ionization potentials of phosphorus compounds. Conjugation in radical cations

The first vertical ionization potentials (I) of phosphorus compounds P(X_i)₃, OP(X_i)₃, SP(X_i)₃, (4-XC₆H₄)₃P, and PCX are related to the inductive, resonance, and polarizability parameters of inorganic, organic, and organometallic substituents X by dependences of the type I = I _H + a_I + b_R ⁺ + c, where I _H is the I value for X = H. The I values are also affected by hyperconjugation. The ratio of the contributions of the resonance (b_R ⁺) and polarizability (c) effects to the I value is determined by the degree of delocalization of the unpaired electron and the positive charge in the radical cations formed upon ionization of neutral molecules. The _R ⁺ resonance parameters of organosilicon, organogermanium, and organotin substituents bound to the P ^·+ radical cation center were calculated for the first time.     

The quest for a stable silyne, RSi ≡ CR′. The effect of bulky substituents [1]

The two major fundamental obstacles which so far have prevented theisolation of stable silynes, RSiCR (1), are: (a)the existence of more stable isomers, e.g., RRC=Si: (2) and(b) their extremely facile (exothermic) dimerication. The steric andelectronic effects of various substituents R and R (R = alkoxy,alkyl, aryl and silyl; R = alkyl and aryl groups) on the stability ofRSiCR relative to the isomeric RRC=Si:(E(1-2)), and on the energy of dimerization tothe corresponding 1,3-disilacyclobutadienes (E(D)), werestudied computationally using density functional theory (DFT) and theONIOM method. The goal was to find a combination of substituents thatwill make RSiCR more stable than RRC=Si: and whichwill also prevent its dimerization. For R = R = H,E(1-2)) = 40.7 kcal/mol (i.e., 2 islower in energy than 1), and E(D) = –104.0kcal/mol. 1, R = OH, R = m-Tbt 2,6-bis[bis(silyl)methyl]phenyl, is by 11.1 kcal/mol morestable than the isomeric silylidene 2. However, thedimerization of 1, R = OH, R = m-Tbt remains highlyexothermic (by 101 kcal/mol). 1, R = R = m-Tbt and1, R = (t-Bu)₃Si, R = m-Tbt, are by 5.8 and 2.0kcal/mol, respectively, less stable than the corresponding 2.However, the dimerization of 1, R = (t-Bu)₃Si, = m-Tbt is exothermic by only 12 kcal/mol. For1, R = (t-Bu)₃Si, and R = Tbt 2,6-bis[bis(trimethylsilyl)methyl]phenyl, the corresponding1,3-disilacyclobutadiene dimer 3, dissociates spontaneously.Thus, (t-Bu₃Si)SiCTbt is predicted to be kineticallystable towards both, isomerization to (t-Bu₃Si)TbtC=Si: anddimerization to 3, making it a viable synthetic target. Thereported energies were calculated atB3LYP/6-31G^**//B3LYP/3-21G^*; good agreement is found betweenthe DFT and the ONIOM results.     

Thin-layer chromatography of tin on a cellulose support using fluorescent chloro-complexes

Summary A TLC method has been developed for direct quantitative estimation of Sn²⁺. The ion was converted to fluorescent chloro-complexes by HCl, in the presence of NaCl or KCl, on a cellulose support, and the complexes were estimated fluorometrically (excitation at 254 nm; measurement, in presence of KCl: 474 nm, in presence of NaCl: 445 nm). Reliable quantitative results were obtained with length concentrations of 0.8 g/cm with respect to Sn. Detection is possible with 0.5 g/cm.     

Inclusion complexation of N-substituted phenothiazines and their radical cations generated electrochemically with <Emphasis Type="Italic">β</Emphasis>-cyclodextrin

The interactions of -cyclodextrin (-CD) with N-phenylphenothiazine (1), N-benzylphenothiazine (2) and N-phenethylphenothiazine (3) were studied by cyclic voltammetry. In aqueous solutions, increasing the amount of -CD caused negative shifts in the anodic peaks and an increase in the current of the 1/1 ⁺ and 3/3 ⁺ couples owing to the fact that more 1 and 3 were included in the -CD cavities. However, compound 2 neither gave an anodic nor a cathodic wave in the presence of -CD because the oxidization reactions on the surface of electrode were controlled by the conformations of the N-substituted phenothiazines in the cavity of -CD. In 1:9 methanol/water binary solutions, 1 and 3 were investigated by fast scan cyclic voltammetry which showed that the irreversible waves became quasi-reversible waves in the presence of -CD, confirmed the stabilization of cation radical intermediates by -CD. The electrochemical and absorption spectral data indicated 1:1 inclusion complex formation of -CD with 1 and 3 cation radicals in methanol/water binary solutions and the binding constants of 1 ⁺ and 3 ⁺ were very large under this condition.     

Use of 2,4-dinitrophenylhydrazone of glyoxylic acid for the determination of glyoxylic acid by the chromatographic-spectrophotometric method and by differential pulse polarography

Two different methods (one based on chromatography and spectrophotometry and the other on polarography) have been developed for the determination of glyoxylic acid in the form of a derivative with 2,4-dinitrophenylhydrazine (DNPHGA). The TLC method allows the separation of two DNPHGA isomers (trans and cis). Spectrophotometric measurements of the eluents of the separated compounds (=360 nm) allow the determination of GA within the range from 4 to 30 g. Using differential pulse polarography, the conditions of DNPHGA formation were examined. The reduction peak of this derivative (E_P=–0.430 V), observed by dpp, was used to develop a polarographic determination of GA within the concentration range from 110^-4 to 710^–4 mol/l.     

Saure Hydrolyse von 2-(4-Chlorphenylazo)-2-(N-carbamidino-ureido)-propan

Zusammenfassung Die saure Hydrolyse der Arylazo-Verbindung1 wird beschrieben und interpretiert: Als Zwischenprodukte werden ungeladenes Aryldiazen (Ar–N=N–H) sowie zwitterionisches Aryldiazen (Ar–NH⁺=N:^–)und im weiteren Verlauf des Reaktionsgeschehens 1,4-Diaryltetrazenimionen postuliert.

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Acid hydrolysis of 2-(4-Chlorophenylazo)-2-(N-carbamidinoureido)-propane

Acid hydrolysis of the arylazo compound1 is described and discussed. As reaction intermediates uncharged aryldiazene (Ar–N=N–H) as well as zwitterionic aryldiazene (Ar–NH⁺=N:^–) and subsequently 1.4-diaryltetrazenium ions are postulated.

     

Determination of Total Selenium Content in Cereals and Bakery Products by Flow Injection Hydride Generation Graphite Furnace Atomic Absorption Spectrometry Applying in-situ Trapping on Iridium-Treated Graphite Platforms

A flow injection hydride generation graphite furnace atomic absorption spectrometric (FI-HG-GFAAS) method was applied to the determination of Se in Se-doped and undoped cereals and bakery products. For the purpose of doping, the soils used for the cultivation of the cereals were dosed with Se-doped foliar fertilizers. The samples were dissolved in a mixture of HNO₃ and H₂O₂ solutions using microwave-assisted digestion. The decomposition of H₂Se generated from the sample solutions and the trapping of elemental Se were performed at a temperature of 300°C on an Ir-pretreated integrated graphite platform of a transversally heated graphite atomizer (THGA). For release of the trapped Se within a fairly short atomization time (5s), an atomization temperature of 2200°C was observed to be optimal. The overall efficiency of hydride generation, transport and trapping was 86%.The upper limit of the linear dynamic range of calibration was 10µgL^–1, which corresponds to 0.5µgg^–1 for solid samples. Recovery of the samples spiked with Se^VI solutions was found to be 93±6% on average. The relative standard deviation of the determinations was less than 8%. The limit of detection was found to be 0.06µgL^–1, corresponding to 3ngg^–1 for solid samples. The accuracy of the method was verified with the use of IAEA-155 (whey powder) certified reference material. End-capped THGA tubes resulted in an extension of the linear calibration range compared to that of standard THGAs.The Se content in bakery products made of undoped cereals ranged from 7.7 to 68ngg^–1 (wet weight) in 18 samples, whereas the Se content of the corresponding cereals was found to be below 100ngg^–1 (wet weight). The Se level of cereals grown on soils treated with Se-doped fertilizers ranged from 128 to 1046ngg^–1 (wet weight), and it depended linearly on the Se concentration of the corresponding foliar fertilizer.     

New variants in the total synthesis of 14β-hydroxy-17α,R-8α,9β-estradiol derivatives

Two procedures were developed for the synthesis of 17-alkyl-8,9-estra-1,3,5(10)-triene-3,14,17-triols from 3-methoxy-estra-1,3,5(10),8(9),14(15)-pentaene-17-one (1) using photosensitized oxidation by atmospheric oxygen or ionic hydrogenation in the presence of oxygen. It was shown that 17-hexynyl-8,9-estra-1,3,5(10)-triene-3,14,17-triol (23) and its 3-methoxy derivative (26) inhibit K⁺,Na⁺-ATPase, with inhibition degree increasing on introduction of an oxygen-containing substituent into position 17. For the first time steroids were found with ₂-adrenoblocking action.Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 207–212, January, 1993.     

Competitive uptake of Cs+, Ba2+, and Zn2+ ions from binary aqueous mixtures by zeolite-13X

The preferential exchange uptake of the cations Cs⁺, Ba²⁺ and Zn²⁺ from pure solutions by zeolite-13X follows the order Q [Cs⁺]>Q [Ba²⁺]>Q [Zn²⁺], while in case of binary mixtures the order is Q [Ba²⁺(Zn²⁺)]>Q [Ba²⁺(Cs⁺)]>Q [Cs⁺(Zn²⁺)]>Q [Cs⁺(Ba²⁺)]>Q [Zn²⁺(Cs⁺)]>Q [Zn²⁺(Ba²⁺)]. Ba²⁺ uptake from mixtures shows the least suppression effect.

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Cs⁺, Ba⁺² Zn⁺² -13 Q[Cs⁺]>Q[Ba⁺²]>Q[Zn⁺²] Q[Ba⁺²(mix Zn⁺²)]>Q[Ba⁺²(mix Cs⁺)]>Q[Cs⁺(mix Zn⁺²)]>Q[Cs⁺(mix Ba⁺²)]>Q[Zn⁺²(mix Cs⁺)]>Q[Zn⁺²(mix Ba⁺²)]. Ba⁺² .

     

Enthalpimetric determinations with sodium hypobromit

The applicability of sodium hypobromite as a reagent in enthalpimetric determinations of various organic and inorganic compounds is reviewed. Using this method it is possible to determine various oxidizable nitrogen and sulphur compounds, e.g. ammonium salts, urea, -amino acids, sulphides, sulphites, thiosulphates, organic compounds with sulphidic sulphur, aromatic amines, mono- and polyphenols, and other compounds. Determinations are sufficiently precise and sensitive. The enthalpy changes of these reactions are approximately 10² to 10³ kJ mole^–1. Suggested determinations are advantageous due to their simplicity, quickness and possible automatization of measurements.

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Zusammenfassung Die Autoren geben einen Überblick zur Anwendung von Natriumhypobromit als Reagenz bei den enthalpimetrischen Bestimmungen verschiedener organischer und anorganischer Verbindungen. Der Einsatz dieser Methode ermöglicht die Bestimmung verschiedener oxidierbarer Stickstoff- und Schwefelverbindungen, wie z.B. Ammoniumsalze, Karbamid, -Aminosäuren, Sulfide, Sulfite, Thiosulfate, organische Verbindungen mit Sulfidschwefel, aromatische Amine, ein- und mehrwertige Phenole und andere Verbindungen. Die Bestimmungen sind genügend genau und empfindlich. Die Enthalpie-Änderungen dieser Reaktionen liegen in der Größenordnung von 10² is 10³ kJ Mol^–1. Die vorgeschlagenen Bestimmungen sind wegen ihrer Einfachheit, Schnelligkeit und der Möglichkeit der Automatisierung der Messungen vorteilhaft.

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Résumé Les auteurs examinent l'emploi de l'hypobromite de sodium comme réactif pour le dosage enthalpimétrique de divers composés organiques et inorganiques. Par cette méthode il est possible de doser différents composés azotés et sulfurés, par ex. les sels d'ammonium, l'urée, les -amino-acides, les sulfures, les sulfites, les thiosulfates, les composés organiques sulfurés, les amines aromatiques, les phénols mono et polyvalents et d'autres composés. Les dosages sont suffisamment précis et sensibles. Les variations d'enthalpie de ces réactions sont de l'ordre de 10²-10³ kJ · mol^–1. Les dosages proposés ont l'avantage d'être simples, rapides et susceptibles d'être automatisés

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, , . - , : , , -, , , , , , . . 10² 10³ /. , .

     

Determination of Attogram Quantities of Silver via Quenching of the Solid Substrate Room-Temperature Phosphorescence of Rhodamine B Based on the Catalysis of its Oxidation by Potassium Persulfate

A new method of SS-RTP for the determination of trace silver has been established. This method is based on the fact that Ag⁺, when activated by ,-bipyridyl (bipy) in a media of HAc–NaAc (pH=4.9), can catalyze the reaction of Rhodamine B (RhoB) oxidized by K₂S₂O₈, thus causing the Solid Substrate Room-Temperature Phosphorescence (SS-RTP) of RhoB to be quenched. The activating efficiency of bipy is 6.7 times higher than that of o-phenanthroline (phen). The reduction of the phosphorescence intensity (I_p) of RhoB is directly proportional to the concentration of Ag⁺ ions in the range of 1.6016.0agspot^–1 (0.40µLspot^–1). The regression equation of the working curve can be expressed as I_p=18.78+5.100m_Ag+ (agspot^–1) (r=0.9994, n=6), the detection limit is 0.28agspot^–1. This rapid, accurate and sensitive method has been successfully applied to the determination of trace silver in tea and human hair samples, and the results agree well with the Atomic Absorption Spectroscopy (AAS) method. The mechanism of the catalyzing reaction is also discussed.     

Spectral properties and structures of supramolecular complexes of naphthylpyridine with β-cyclodextrin

The electronic absorption and fluorescence spectra of 4-(2-naphthyl)pyridine (1) and N-methyl-4-(2-naphthyl)pyridinium perchlorate (2 ⁺·ClO₄ ^–) were studied in aqueous solutions in the absence and presence of -cyclodextrin (-CD). In aqueous solutions and organic solvents in the presence of water or H⁺ ions, compound 1 exhibits intense fluorescence with a maximum at 21 270 cm^–1, and its quantum yield in an aqueous solution is 0.9±0.09. The same fluorescence spectrum was detected for an aqueous solution of 2 ⁺·ClO₄ ^–. In an aqueous solution, compound 1 and -CD form stable fluorescing supramolecular 2:2 complexes, whose structure was calculated by the quantum-chemical MNDO/PM3 method. The formation of these complexes induces a hypsochromic shift of the fluorescence maximum of 1 by 5000 cm^–1. The stability constant of the complex is 2·10³ L mol^–1. A decrease in the pH results in the formation of a protonated form of 1(1·H⁺) and destruction of the complex, thus favoring the escape of the substrate from the -CD cavity. The quantum-chemical calculations showed that the insertion of 1 into the -CD cavity is thermodynamically more favorable than hydration; on the contrary, the formation of 1·H⁺ increases dramatically the hydration energy, which promotes the escape of 1·H⁺ from the -CD cavity; cation 2 ⁺ does not form a complex with -CD; in the thermodynamically most favorable 2:2 complex, the naphthalene fragments of two molecules 1 are parallel to each other in a broad section of the -CD dimer constructed according to the head-to-head type.__________Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2420–2425, November, 2004.     

Free radical additions to the C=O bond of formaldehyde

The reactions between formaldehyde and n-propyl radicals were studied at 333 and 363 K. Addition to the C=O bond was found to be several times faster than abstraction of the formyl hydrogen atom. With a TST estimate of log(A/dm³ mol^–1 s^–1)=7.9±0.5, 28.0±2.1 kJ mol^–1 was obtained for the activation energy of the addition reaction.

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- 333 363 . C=O . 28.0±2.1 ^–1 , lg(A/ ^{–1 –1})=7.9±0.5 .

     

Applications of thermoelectrometry to metal-ion modified polyimide films

As part of a research program to decrease the electrical resistivity of polyimide films with ionic additives a variable temperature three probe electrical resistivity measurement system has been designed and constructed. Sample temperature, electrification time, atmosphere, and measurement mode are computer controlled. As a data interpretation aid, temperature cycled analysis can be routinely performed. Surface resistivities in the range 10³–10¹⁵ ohm and volume resistivities in the range 10⁵–10¹⁸ ohm-cm are theoretically measurable under well controlled experimental conditions from room temperature to 250°. The electrical resistivity measurement system is useful for the evaluation of polymer films or films in general. Application of the system for analysis of cobalt, lithium and tin ion-modified polyimide films and some experimental considerations are presented. Correlation of the electrical measurements with differential scanning calorimetry, thermomechanical analysis, and thermogravimetric analysis is demonstrated.

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Zusammenfassung Als Teil eines Forschungsprogramms zur Herabsetzung des elektrischen Widerstandes von Polyimidfilmen mit ionischen Additiven wurde ein 3-Proben-Meßsystem zur Ermittlung des elektrischen Widerstandes in Abhängigkeit von der Temperatur entworfen und konstruiert. Probentemperatur, Elektrisierungszeit, Atmosphäre und Meßmethoden waren computergesteuert. Als Dateninterpretationshilfe kann eine hinsichtlich der Temperatur zyklische Analyse routinemäßig ausgeführt werden. Die Oberflächenwiderstände sind im Bereich von 10³–10¹⁵ Ohm und die Volumenwiderstände im Bereich von 10⁵–10¹⁸ Ohm-cm unter gut kontrollierten experimentellen Bedingungen von Raumtemperatur bis 250° theoretisch meßbar. Das elektrische Widerstandmeßsystem ist nützlich für die Bewertung von Polymerfilmen oder Filmen im allgemeinen. Die Anwendung des Systems zur Analyse von mit Co-, Li- und Sn-Ionen modifizierten Polyimidfilmen und einige experimentelle Hinweise werden angegeben. Es wird gezeigt, daß die mit dem beschriebenen System erhaltenen Resultate mit durch DSC, thermomechanische Analyse und TG erhaltenen Werten korrelieren.

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, , . , , . . 10³–10¹⁵ , 10⁵–10¹⁸ 250°. , . , , , . , .

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The financial support of the National Aeronautics and Space Administration is gratefully appreciated. The assistance of John Swartzentruber in performing many of the measurements is recognized.     

Phase transformation of ammonium nitrate by thermal factors and inoculation

The reason for the special thermal behaviour of ammonium nitrate (AN) has been examined. Under certain experimental conditions more transition temperatures were obtained than hitherto found (37–42°, 50° and 86°). With Du Pont DSC curves several exothermic peaks or exothermic oscillations were shown after the endothermic peak at 51°, indicating that phase IV had been transformed to metastable phase III, as a consequence of which the IIIII transformation at 86° also became possible. On repeated cycling the exothermic peak decreased or disappeared if the IIIII transformation had developed to a greater extent. A successful IVIII transformation was induced by inoculation of AN with phase III, an unusual procedure in investigating the phase transformation of AN. The use of the method is obvious with regard to the fact that all transformations are controlled by the rate of nucleation.

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Zusammenfassung Die Ursachen des besonderen thermischen Verhaltens von Ammoniumnitrat (AN) wurden untersucht. Unter gewissen Versuchsbedingungen wurden mehrere Übergangstemperaturen erhalten als bisher gefunden wurden (37°–42°, 51° und 86 °C). An Du Pont DSC Thermogrammen wurden mehrere exotherme Peaks oder exotherme Oszillationen nach dem endothermen Peak bei 51 °C nachgewiesen, welche zeigen, daß die Phase IV in die metastabile Phase III umgewandelt wurde. Infolgedessen wurde die Umwandlung IIIII bei 86 °C ebenfalls möglich. Bei wiederholtem Meßzyklus nahm der exotherme Peak ab oder verschwand, wenn die Umwandlung IIIII sich in größerem Maße entwickelte. Eine erfolgreiche IV III Umwandlung wurde durch Inokulierung mit der Phase III von AN induziert, was ein ungewöhnliches Verfahren bei der Untersuchung der Phasenumwandlung von AN ist. Die Vorteile dieser Methode sind offensichtlich, da sämtliche Umwandlungen durch die Geschwindigkeit der Nuklierung geregelt werden.

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Résumé On a étudié les causes du comportement thermique spécial du nitrate d'ammonium. Dans certaines conditions d'expériences, on a obtenu des températures de transition en plus grand nombre qu'il n'avait été trouvé auparavant (37–42 °C, 51 °C et 86 °C). On a mis en évidence sur des enregistrements obtenus à l'aide d'un appareil d'analyse calorimétrique différentielle DSC Dupont, plusieurs pics exothermiques ou oscillations exothermiques après le pic endothermique à 51°C, ce qui indique que la phase IV a été transformée en phase métastable III. Par conséquent, la transformation IIIII à 86 °C devient également possible. Lors du cyclage répété, le pic exothermique diminue ou disparaît si la transformation IIIII s'est développée dans une plus grande mesure. On induit avec certitude une transformation IVIII en inoculant le nitrate d'ammonium avec la phase III, procédure insolite dans l'étude des transformations de phases du nitrate d'ammonium. L'avantage de la méthode est évident, puisque toutes les transformations sont contrôlées par la vitesse de nucléation.

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. , (37–42°, 51° 86 °C). , , 51°C, , IV - III, 86 ° IIIII. , IIIII . IVIII , III, . , .

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The author is grateful to Prof. Z. G. Szabó for helpful criticism and for valuable discussions.     

Energy Transfer Electrogenerated Chemiluminescence for the Determination of Sulfite

A simple and novel electrogenerated chemiluminescence (ECL) method for the determination of sulfite has been developed based on the energy transfer ECL process. It was found that a weak ECL signal of sulfite was electrochemically generated on a platinum electrode in neutral aqueous solution. The signal was strongly enhanced by rhodamine B as an energy receptor and further enhanced by the neutral surfactant Tween 80. In 0.10M phosphate buffer solution (pH=7.5) containing 2.0×10^–6gmL^–1 rhodamine B and 0.4% (v/v) Tween 80, the ECL response to the concentration of sulfite at a potential of 0.82V was linear over a range of 1.0×10^–7gmL^–1 to 8.0×10^–6gmL^–1, and the detection limit was 5×10^–8gmL^–1. The relative standard deviation (n=11, 1.0×10^–6gmL^–1) was 3.8%. The proposed method has been successfully applied to the determination of sulfite in pharmaceutical injections and white sugar samples.     

Leitfähigkeitsmessungen in Phosphoroxychlorid, 3. Mitt. Triäthylamin

Zusammenfassung Am Beispiel des Triäthylamins wird das Leitfähigkeitsverhalten eines gekoppelten Dissoziationsgleichgewichtes mit nichtleitender Zwischenstufe (ABC⁺+D^–) untersucht.Mit 3 AbbildungenZugleich 14. Mitteilung der Reihe: Das Solvosystem Phosphoroxychlorid.2. Mitt:M. Baaz undV. Gutmann, Mh. Chem.90, 256 (1959).