Supercooling phenomena in the binary systems: Acetamide-electrolytes

This paper presents a final discussion on studies of solutions of electrolytes in molten acetamide. These studies deal with cryoscopic and ultrasonic (by shear waves) techniques and reveal the complexity of the behaviour of these systems due to strong ion-solvent interactions.

---

Zusammenfassung Die über Lösungen von Elektrolyten in geschmolzenem Acetamid ausgeführten Untersuchungen werden diskutiert. Diese Untersuchungen erstrecken sich auf kryoskopische und Ultraschall-Methoden und vermitteln ein Bild von der durch starke Ionen-Lösungsmittel-Wechselwirkungen bedingten Komplexität des Verhaltens dieser Systeme.

---

. , - - .

---

---

Thanks are due to CNR and MPI (Rome) for financial support, and to R. Borgarucci for technical assistance.     

Acidity modification by thermal and steam treatment in silica-alumina and its relation with methanol to hydrocarbons reaction

The physical properties as well as the acidity of an amorphous silica-alumina were modified by steam and thermal treatments and a general correlation (including samples modified by other methods) between hydrocarbon formation and surface acidity was obtained.

---

, . ( , ) .

     

Comparison of DSC and optical transmission measurements of polymorphic transitions

Using optical measurements on single crystals, the speed of first order transitions (K₂Cr207, KNO₃, AgNO₃) was determined and compared with the strongly smeared DSC signals. Such optical measurements are proposed to select materials which are suitable for the determination of the DSC apparatus function.

---

Zusammenfassung Mit Hilfe von optischen Messungen wird die Geschwindigkeit von polymorphen Phasenumwandlungen 1. Ordnung (K₂Cr₂O₇, KNO₃, AgNO₃) bestimmt und mit entsprechenden stark verschmierten DSC-Signalen verglichen. Derartige optische Messungen erscheinen geeignet, um Substanzen zu suchen, welche für die Bestimmung der DSC-Apparatefunktion geeignet sind.

---

K₂Cr₂O₇, KNO₃ AgNO₃ $ , $ . , $ .

     

A rapid method for catalyst activity measurements by combination of pulse reactor, mass spectrometer and process computer

The combination of a pulse reactor attached directly (without a separation column) to a mass spectrometer/process computer system is described. To obtain a conversion/temperature diagram for the dehydration and dehydrogenation of 2-butanol less than one hour is required. Therefore, the method can be used for rapid characterization or comparison of the activities of various samples.

---

, ( ) - . / 2- . .

     

Structural changes of NaX zeolite during the H2S+O2 reaction

Infrared spectra in the 600, 700, and 1000 cm^–1 regions and X-ray investigations indicate that during H₂S+O₂ reaction in the temperature region of 293–473 K partial dealumination of the NaX zeolite crystal structure occurs. The dealumination increases with reaction temperature.

---

- 600, 700 7000 ^–1 , H₂S+O₂ 293–473 NaX. .

     

Mixed Micelles in the Presence of Macrocyclic Additives: A Host–Guest Conductometric Study

The conductances of sodium dodecylsulphate (SDS) + sodium decylsulfate (SDeS) and decyltrimethylammonium bromide (DeTAB) + tetradecyltrimethylammonium bromide (TTAB) over the entire mole fraction range of SDS (_SDS) or DeTAB (_DeTAB) were measured in water, 18-crown-6 ether + water (CR + W) and -cyclodextrin + water (CYC + W) mixtures at fixed 4 mM and 8 mM of CR or CYC in their respective binary mixtures at 30 °C. The conductivity plots for SDS + SDeS mixtures show a single break whereas two breaks are observed at most of the _DeTAB for DeTAB + TTAB mixtures. From the break in the conductivity data, the mixed critical micellar concentration (cmc) and degree of counter-ion association () were computed. The first break corresponds to the classical cmc of TTAB is termed as the first cmc (C₁) and the second break which is observed at concentrations about 4 times the first one, corresponding to the classical cmc of DeTAB and is considered to be the second cmc (C₂). The non-ideality in SDS + SDeS mixtures has been evaluated by using the regular solution theory and it has been observed that the mixture is close to ideal in the absence and presence of additives. The variation in C₁, C₂ and ₁, ₂ for DeTAB + TTAB has been discussed in terms of the mixed micelle formation which are predominantly rich in the TTAB and DeTAB monomers respectively.     

On the dioximine complexes of transition metals

Twelve new complexes NH₄[Co(DH)₂(SO₃)(amine)]·t H₂O (DH ₂=dimethylglyoxime) have been synthesized and characterized. Their i.r. spectra show the SO₃ to be co-ordinated to the Co atom through the S atom. The thermal decompositions of a series of derivatives of this type have been investigated with a derivatograph. The first process is an endothermic dehydration reaction, occurring in a single stage or in two successive ones. The loss of the crystallization water is followed by another endothermic reaction, without a clear stoichiometry, which is referred to as deamination. At higher temperatures, exothermic pyrolysis processes occur. From the TG curves, kinetic parameters have been derived for the dehydration and deamination reactions.

---

Zusammenfassung Zwölf neue Komplexe der allgemeinen Formel NH₄[Co(DH)₂(SO₃)(amin)]·t H₂O (DH=Dimethylglyoxim) wurden synthetisiert und charakterisiert. Die IR-Spektren zeigen, daß SO₃ über das S-Atom koordinativ an das Co-Atom gebunden ist. Die thermische Zersetzung einer Reihe von Derivaten dieses Typs wurde mittels eines Derivatographen untersucht. Der erste Prozeß ist die in einem einzigen oder in zwei aufeinander folgenden Schritten verlaufende endotherme Dehydratisierung. Auf die Abgabe des Kristallwassers folgt eine andere endotherme Reaktion unklarer Stöchiometrie, die als Deaminierung bezeichnet wird. Bei höheren Temperaturen verlaufen exotherme Pyrolyseprozesse. Aus den TG-Kurven wurden kinetische Parameter für die Dehydratisierung und die Deaminierung bestimmt.

---

NH₄Co(DH)₂(SO₃)(a)]·tH₂O, DH ₂ — . , . . , . «». . .

     

Chlorination of V2O5 by CCl4. The proposed reaction mechanism

Initial stage of the reaction of CCl₄ with V₂O₅ has been studied by MS and XPS techniques. According to the proposed mechanism dissociatively chemisorbed CCl₄ transforms to CO₂ via adsorbed COCl₂, while surface vanadium atoms involved are gaining step by step two chlorine atoms before the formation of the volatile end-product VOCl₃.

---

CCl₄ V₂O₅ . - CCl₄ CO₂ COCl₂, VOCl₃.

     

The investigation of thermally treated glasses of controlled porosity by means of differential thermal analysis

Some of the materials used as chromatography packings, adsorbents or catalyst supports are glasses of controlled porosity (CPGs). The chemical structure of these materials can easily be changed by heating the porous glass. Such thermal modification leads to the enrichment of the CPG surface in boron atoms. The long exposure of CPGs to thermal treatment can even cause the formation of borate crystals in the pores of the glasses. This paper considers the application of thermal analysis to the investigation of porous glasses heated for different periods of time.

---

Zusammenfassung Einige der als chromatographische Säulenpackungen, Adsorbenten oder Katalysatorträger verwendeten Materialien sind Gläser mit definierter Porosität (CPGs). Die chemische Struktur dieser Materialien kann leicht durch Erhitzen verändert werden. Eine solche thermische Modifizierung führt zu einer Anreicherung von Bor in der Oberflächenschicht. Eine langdauernde Erhitzung der CPGs kann sogar zur Bildung von Boratkristallen in den Poren der Gläser führen. Im vorliegenden Artikel wird die Anwendung der thermischen Analyse zur Untersuchung von porösen Gläsern in Abhängigkeit von der Erhitzungsdauer behandelt.

---

, , , . . . . , .

     

Interaction of propylene with a V2O5/Al2O3 catalyst

IR-spectroscopic studies indicate that on the oxidized surface of V₂O₅/Al₂O₃ catalysts propylene interacts mainly with Brönsted acid centers to form an alcoholate type complex transforming into acetone. On the reduced surface propylene is stabilized as a -complex of V³⁺ and V⁴⁺ ions.

---

- , V₂O₅/Al₂O₃ , . - V³⁺ V⁴⁺.

     

Eichinvariante Berechnung des Diamagnetismus und der chemischen Verschiebung, 2. Mitt.: Berechnung magnetischer Daten von zweiatomigen Molekülen auf der Grundlage lokalisierter Orbitale

Expressions are derived for the decomposition of tensorial properties into additive increments.In the second part of the paper calculations of _H andC _H for LiH and of the susceptibilities for Li₂, BH, HF, CO, F₂, and LiF are presented. The contributions of the various LMO's to , ^P andg-values are discussed. The results are compared to those obtained from coupledHF-perturbation theory and to experimental values where available. The values for are in good agreement with the experiment and—except for BH—with theHF-perturbation theory, however deviations are found in some molecules for andg-values and traced back to specific electronic features.     

Kinetics of reaction between 1,3-butadiene and p-benzoquinone

Kinetics of Diels-Alder reaction between 1,3-butadiene and p-benzoquinone in benzene and glacial acetic acid as a catalyst has been studied. Influence of reactant and catalyst concentrations on the rate has been established. Kinetic equation has been derived to describe experimental data.

---

- 1,3- 1,4- - . , .

     

Third-Order Nonlinear Optical Response of a New PVA Composite with PbS Nanocrystals

High third-order nonlinear optical susceptibility (⁽³⁾(;, –,)=3.4·10 ^–16 m²/V²) in the visible spectral range may be achieved in PVA composites with narrow-gap PbS semiconductor nanocrystals with a large exciton diameter.     

The phenomenon of conglomerate crystallization in coordination compounds. XXIII: The crystallization behavior of [cis-Co(en)2(N3)(SO3)] · 2H2O (I) and of [cis-Co(en)2(NO2)(SO3)] · H2O (II)

A room temperature water solution of (I) crystallizes as a racemate, space groupP2 ₁/n with lattice constantsa=7.737(6),b=10.694(5),c=15.097(6) Å, and=102.83(5)°;V=1218.05 ų andd (calc; M.W.=337.24, Z=4) = 1.642 g cm^–3. A total of 2381 data were collected over the range 4° 2 < 50°; of these, 1452 (independent and withI 3(I)) were used in the structural analysis. Data were corrected for absorption ( = 15.76 cm^–1), and the relative transmission coefficients ranged from 0.8976 to 0.9984. Refinement led to the finalR(F) andR _w(F) residuals of 0.0858 and 0.1116. A room temperature water solution of (II) crystallizes as a racemate in space group P2₁/c with lattice constantsa=6.638(3),b=11.425(8),c=15.147(16) Å, and=93.27(6)°; F=1146.8 Å andd (calc; M.W.=323.2,Z=4) = 1.872 g cm^–3. A total of 2200 data were collected over the range 4° 2 < 50°; of these, 1918 (independent and withI 3(I)) were used in the structural analysis. Data were corrected for absorption (=16.94 cm^–1), and the relative transmission coefficients ranged from 0.9049 to 0.9967. Refinement led to the finalR(F) andR _w(F) residuals of 0.0231 and 0.0279. The chirality symbol for the particular enantiomer of (I) refined here is (), while for (II) the chirality symbol is (), which means that in the latter compound one of the en rings is in a higher energy conformation. We attribute this result to competitive intramolecular hydrogen-bonded interactions between the — NH₂ hydrogens of the en ligands and the oxygens of the -NO₂ and -SO₃ ligands, strengths which are enhanced by coercing a change in sign of the torsional angle of one en ringa motion which permits both oxo ligands to form stronger hydrogen bonds while retaining proper O O contacts. This phenomenon is not observed in (I) since the azide ligand does not compete with -SO₃ for such hydrogen-bonded interactions, and nonbonded pair repulsions can be minimized without affecting the ability of — SO₃ oxygens to form strong intramolecular hydrogen bonds.     

Liquid-phase hydrogenation of cyclohexene by dihydrogen in the presence of dimolybdenum tetraacetate

Catalytic liquid-phase hydrogenation of cyclohexene in DMF by dihydrogen in the presence of dinuclear bridged complex Mo₂(OAc)₄ has been studied. A kinetic equation for the steady-state rate of cyclohexene hydrogenation and the activation parameters are suggested.

---

Mo₂(OAc)₄. .

     

Upper limits of magnetic anisotropy of molecule with closed electron shell

Two simple upper limits have been established for the anisotropy of magnetic susceptibility of linear molecules with closed electron shells; these can be used to estimate the top limit on magnetic anisotropy of a molecule = – if its mean magnetic susceptibility is known, without any information whatever on the electronic wave function. The first of these limits is valid for the magnetic anisotropy of the ground electronic state X¹, and the second is valid for any ¹ state, including the excited state. The application of these limits to the evaluation of magnetic anisotropy is illustrated in the examples of the molecules of CO₂, FCCF, HCCF, FCN, LiH, and the excited state of the H₂ molecule. It is shown that these limits are useful for revealing cases of internal contradictions (or error) in individual values of magnetic anisotropy, including very rough values obtained in calculations of the magnetic properties of molecules in a limited basis set.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 2, pp. 143–149, March–April, 1988.     

Properties of χ-alumina as related to catalysis

-Alumina was synthesized by thermal decomposition of aluminium(III) isopropoxide, and its properties were investigated. The change in its surface area with increasing calcination temperature resembled that of -alumina. Both aluminas had the same acid strength, and their activities in isomerization of 1-butene were the same. -Alumina as a support for molybdenum catalyst in the epoxidation of allyl alcohol also behavedin the same manner as -alumina. Thus -alumina has almost the same catalytic properties as -alumina.     

Kinetics of catalytic hydrolysis of tetraethoxysilane by polycomponent solutions of neutral salts

The effect of salt concentrations on the hydrolysis kinetics in three-component systems containing tetraethoxysilane and aqueous solutions of sodium, neodymium and lead nitrates has been shown. A generalized model for the synthesis of polycomponent hydrolytes is suggested, which permits to predict the conditions to prepare compositions with specified characteristics.

---

, , . , .

     

Study of selective dissociation in C6F5H?C6F5D mixtures induced by intense CO2 laser pulses

Irradiation of a C₆F₅H–C₆F₅D mixture at 1 Torr by a tunable CO₂ pulse laser brings about chiefly dissociation of one component depending on the frequency of emission absorbed by the proper molecules. The addition of radical acceptors increases the selectivity by suppressing secondary reactions.

---

C₆F₅H C₆F₅D 1 CO₂-, , . .

     

51V-NMR spectra of vanadates and oxosulfato-vanadates of alkali metals

A relation between the type of vanadium environment and the chemical shift anisotropy in the⁵¹V-NMR spectra has been established. The results obtained are compared with spectra of real catalysts.

---

⁵¹V , .