Kinetics and mechanism in the decomposition of CCl4 in a radio-frequency pulse discharge

In the decomposition of CCl₄ in an r.f. pulse discharge the observation of time-resolved absorption spectra of the CCl radical allowed concentration measurements and a kinetic and mechanistic investigation of the system. Kinetic spectroscopy and end product analysis, with computer simulation of proposed mechanisms, indicates that the major decomposition reaction is CCl₄»CCl+3Cl (Cl₂+Cl), with a minor contribution from CCl₄»CCl₂+2Cl. Radical concentrations were of the order of 10^–7 mol dm^–3 (10¹⁴ molec. cm^–3). CCl removal was kinetically second order with a rate coefficient value of (3.7±8)×10¹⁰ mol^–1 dm^–3 s^–1 at 295±3 K at gas pressure 0.1 torr.     

Structural characteristics of chlorine-substituted diazadienes in the solid state from35NQR data

The quadrupole resonance spectra and the quadrupole spin-lattice relaxation times of the³⁵Cl nuclei are correlated with the molecular structures of the two chlorine-containing diazadienes CCl₃CCl=NCCl=NC₆H₅ and CCl₃CCl=NCCl=NCCl₂CCl₃. The monotropic polymorphism found in the case of the second crystal is discussed.Perm State University. Translated from Zhurnal Strukturnoi Khimii, Vol. 34, No. 2, pp. 84–87, March–April, 1993.     

Effect of the physical state on the scavenging of quasi-free electrons by a solute

The reactivity of carbon tetrachloride toward quasi-free electrons generated during the decay of ⁵⁷Co atoms in its alcohol solutions frozen at 80 K has been studied by Mössbauer emission spectroscopy. It has been found that an increase in CCl₄ concentration to 10 mol/L slightly affects the yield of ⁵⁷Fe²⁺ and ⁵⁷Fe³⁺ ions as ⁵⁷Co decay products. The inertness of CCl₄ has been interpreted as a consequence of a change of the energy state of quasi-free track electrons results from freezing the alcohol solution. This effect inhibits the dissociative attachment reaction of scavenging of track electrons and increases the ground-state energy of quasi-free electrons (on passing to the frozen matrix), thereby fundamentally altering the energy balance of the electron scavenging reaction in comparison with the liquid medium and, hence, decreasing the rate constant of electron scavenging by CCl₄.     

On the mechanism of the Kharash reaction catalyzed by Fe(CO)5

Fe(CO)₅ is sufficiently stable at 80 °C in benzene solution and its thermal decomposition is not accelerated in the presence of phenyl cinnamate or/and DMF. The decomposition is accelerated by CCl₃Br (drastically) and by CCl₄ (to a lesser extent). DMF accelerates the reaction of Fe(CO)₅ with CCl₄. The (FeCl(DMF)₅]²⁺[Cl₃FeOFeCl₃]^2– complex has been isolated as a product; its composition and structure have been determined by X-ray analysis. The obtained data indicate the absence of coordination of DMF or/and an olefin with Fe⁰ species at the stage preceding oxidation. The mechanisms of the generation of CCl₃ radicals in thermal and photochemical Kharash reactions in the presence of Fe(CO)₅ are basically different. The probable pathways of the effect of DMF on the rate of the oxidative decomposition of Fe(CO)₅ are discussed.For Part 2, see Ref. 1.Translated from IzvestiyaAkademii Nauk. Seriya Khimicheskaya, No. 4, pp. 916–919, April, 1996.     

A Novel Thermooptical Detection Method for Enzyme Reaction Based on the Optical Beam Deflection Induced by Reaction Heat

A novel thermooptical detection method for enzyme reaction based on the optical beam deflection induced by reaction heat is proposed. A probe beam passes through a CCl₄ phase above which a model enzyme reaction occurs. The enzyme reaction medium is arranged to be either interfaced directly with the CCl₄ phase or separated from the CCl₄ phase by a thin gold film. The decomposition reaction of hydrogen peroxide catalyzed by catalase is used as a model enzyme reaction. In the arrangement that the reaction medium is interfaced directly with the CCl₄ phase, both the reaction heat and the reaction product O₂ diffuse into the CCl₄ phase, and thus generate temperature and concentration gradients, respectively. Since both the temperature and concentration gradients induce the deflections of the probe beam, two peaks are observed in the deflection signal. On the other hand, in the arrangement that the reaction medium is separated from the CCl₄ phase by the gold film, only the deflection signal generated by the temperature gradient is detected. The quantitative relations between the deflection signals induced by the reaction heat and the concentrations of catalase and H₂O₂ are investigated. Under the present batch experimental conditions, deflection signals are linear in the concentration ranges of 4 × 10⁻³-4 × 10⁻² mol/liter for H₂O₂, and 11-550 μg/ml (activity, 11-550 unit/ml) for catalase solution, respectively. The detection limits for H₂O₂ and catalase solution are 4 × 10⁻³ mol/liter and 11 μg/ml (activity, 11 unit/ml), respectively. In addition, the possibilities of development as a new thermooptical biosensor and application to the determination of activity distribution of this method are also discussed.     

Thermal decomposition rate of tetraphenylhydrazine in inert solvents

Conclusions The decomposition of tetraphenylhydrazine in inert media at 348°K proceeds not as an induced, but instead as a pseudomonomolecular process, with decomposition rate constants of 6.3 · 10^–5 and 8.6 · 10^–5 sec^–1 in CCl₄ and n-heptadecane, respectively.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1629–1631, July, 1982.     

Absolute partial and total electron ionization cross sections for CCl4 from threshold up to 180 eV

Electron impact ionization of carbon tetrachloride was studied as a function of electron energy from threshold up to 180 eV. A double-focusing mass spectrometer system in combination with an improved electron impact ion source was used, alleviating the problems of ion extraction from the source and the transmission of the extracted ions through the mass spectrometer system. Absolute partial ionization cross sections for the occurrence of CCl ₃ ⁺ , CCl ₂ ⁺ , CCl⁺, Cl ₂ ⁺ , Cl⁺, C⁺, CCl ₃ ²⁺ , and CCl ₂ ²⁺ have been determined. In addition, the total ionization cross-section function of CCl₄ is reported and compared with theoretical predictions based on a classical binary encounter approximation. Using nth root extrapolation the following ionization energies of the doubly ionized fragment ions have been derived: AE(CCl ₃ ²⁺ )=30.4±0.3 eV; and AE (CCl ₂ ²⁺ )=31.8±0.3 eV. In accordance with theoretical predictions and previous results, no stable CCl ₄ ⁺ has been detected, however, metastable dissociation processes CCl ₄ ⁺ CCl ₃ ⁺ have been observed.     

Quantum chemical estimation of the possibility of the formation of chloro- and bromomethane radical anions and their fragmentation paths in the gas phase and in solution by MNDO and AM1 techniques

By semiempirical MNDO and AM1 methods it was shown that electron transfer on the chloro-and bromomethane molecules of the general formula CH_nHal_4–n (n=1–3) results either in a kinetically independent particle, i.e., a radical anion, or in C-Hal-bond cleavage with the formation of Hal^– and the respective radical. The enthalpy, activation energy of the reactions, and data on the geometry of the radical anion obtained show that the increasing the number of halogen atoms in the initial molecule and decreasing the solvent polarity favor radical anion stabilization. It was established that the cleavage of the C-H-bond in the radical anion is not favored energetically. Fragmentation at the C-H-bond can proceed according to the mechanism of dissociative electron capture by halomethane molecule only with additional factors favoring this reaction.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 1886–1892, November, 1993.     

Redox reactions between organic halo-compounds and ferrous cations in isopropanol

Summary Halo-compounds of which the half-wave reduction potential is equal to or less negative than that of carbon tetrachloride, are reduced by tetrachloroferrate(II) anions. The bimolecular rate constants measured at 250 in isopropanol are 2 × 10^–5 M^–1 s^–1 and 1 × 10^–4 M^–1 s^–1 respectively for CCl₄ and CCl₃CO₂Me.     

Investigation of radical reactions in C2Cl4 and C2Cl4/O2 discharges by EPR,mass, and emission spectroscopy

The reaction of tetrachloroethylene, C₂Cl₄, with O(³P) atoms as well as the plasma decomposition of C₂Cl₄ and C₂Cl₄/O₂ mixtures have been investigated by combined application of electron paramagnetic resonance (EPR) and emission and mass spectroscopies. C₂Cl₄ plasma decomposition is shown to proceed primarily to the formation of CCl₃ radicals and chlorine-deficient products, which are ultimately involved in the formation of carbonaceous layers. A simple reaction model accounts for all the detected stable and radical species, encountered during the plasma decomposition. The model also enables order-of-magnitude estimates of decomposition rate constants to be made. The suppression of the formation of both carbonaceous layers and products C_mCl_n (m3) in C₂Cl₄/O₂ discharges is explained using results of an investigation of elementary reactions in the system C₂Cl₄/O(³P)/O₂. The stable products of C₂Cl₄/O₂ discharges, i.e., COCl₂, CCl₄, and C₂Cl₆, respectively, are shown to originate from recombination of the peroxy radicals CCl₃OO and C₂Cl₅OO.     

Kinetic study of the reaction betweentrans-tetracyanodioxomolybdate(IV) and fluoride ions

Summary The kinetics of the reaction between [MoO₂(CN)₄]^4– and F^– have been studied in the pH range 8 to 11. The results indicated that the diprotonated form, [MoO(OH₂)(CN)₄]^2–, is the only reactive species and that the aqua-ligand is substituted by the F^– ion according to the following reaction. The k₁ and k_–1 values are 8.8(2) M^–1 s^–1 and 0.6(1)s^–1, respectively, at 15°C. A dissociative substitution process is proposed.     

Radical telomerization of 3,3,3-trifluoro-1-propene with carbon tetrachloride

Telomerization of 3,3,3-trifluoropropene with CCl₄ was carried out in the presence of Fe(CO)₅ in combination with dimethylformamide (DMF) or hexamethylphoshoric triamide (HMPA) with formation of the telomers CCl₃(CH₂CHCF₃)_nCl, n=1–3, as the main products. Chromatography-mass spectrometry showed the presence of CCl₃CH₂CH(CCL₃)CF₃, a product of recombination of the adduct radical and CCl₃, in the reaction mixture, which confirms the radical nature of the process. The structure of all the reaction products was confirmed by¹³C NMR and (or) mass spectrometry.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1807–1811, August, 1990.     

Spectroscopic study of vinylidene chloride—Vinyl chloride copolymers

Summary Deuteration technique was applied to study the micro structures of copolymer series VDC/VC by infrared spectroscopy and high resolution NMR. The CH₂ bending modes of chlorine atom containing polymers assigned as follows; –CCl₂CH₂CCl₂– 1405 cm^–1 (cryst.) and 1410 cm^–1 (amorph.), –CHClCH₂CCl₂– 1422 cm^–1, –CHClCH₂CHCl– 1428 cm^–1 (cryst.) and 1432 cm^–1 (amorph.) –CHClCH₂CH₂CHCl– 1445 cm^–1 and –CCl₂CH₂CH₂CCl₂– 1448 cm^–1. This infrared interpretation shows that only the head to tail addition occurs in the copolymerisation. Nine peaks of the methylene protons were observed clearly in the NMR spectra of the copolymers. The study of the deuterated copolymers revealed that the effects of the chemical groups until the third at both sides from the marked methylene and the stereo configuration of long VC part should be considered to assign the NMR spectra. The CCl₂ group made the chemical shift of the methylene proton to appear at lower magnetic field and the CHCl group gave the opposite behavior.

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Zusammenfassung Mit deuterierten Monomeren wurde die Mikrostruktur der Copolymerenserie Vinyliden-Chlorid/Vinyl-Chlorid im Infraroten und mit hochauflösender Kernresonanz untersucht. Für die Biegeschwingung der Chloratome enthaltenden Polymeren der Methylengruppe ergeben sich folgende Werte: –CCl₂CH₂CCl₂– 1405 cm^–1 (krist.) und 1410 cm^–1 (amorph.), –CHClCH₂CCl₂– 1422 cm^–1, –CHClCH₂CHCl– 1428 cm^–1 (krist.) und 1432 cm^–1 (amorph.), –CHClCH₂CH₂CHCl– 1445 cm^–1 und –CCl₂CH₂CH₂CCl₂– 1448 cm^–1.Diese Interpretation des Infraroten zeigt, daß nur die Kopf-Schwanz-Addition bei der Copolymerisation stattfindet. Neun Maxima des Methylenprotons wurden deutlich in den NMR-Spektren der Copolymeren beobachtet. Die Untersuchungen an den deuterierten Copolymeren zeigen, daß die Effekte der chemischen Gruppen bis zur dritten nach beiden Seiten vom markierten Methylen und die Stereokonfiguration von langen Vinyl-Chlorid-Anteilen betrachtet werden müssen, um die NMR-Spektren zu beschreiben. Die CCl₂-Gruppe läßt die chemische Verschiebung des Methylen-protons bei geringeren magnetischen Feldern und die CHCl-Gruppe bei höheren erscheinen.

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With 5 figures in 13 details and 4 tables     

Metallocomplex catalyst of the addition reaction of CCl4 to ethylene

The catalyst Fe^IIFe₂ ^IIICl₈ (DMA)₆-iron(2+)diiron(3+)octachlorohexakis(dimethylacetamide), was isolated from the media of the catalytic synthesis of 1,1,1,3-tetrachloropropane (C₃), and characterized by physicochemical methods. A counter synthesis of the catalyst was carried out. The telomerization of ethylene with CCl₄ proceeds with a 98% selectivity with respect to C₃ in its presence, while the conversion of CCl₄, reaches 55–60% after 4 h. A coordination-ionic mechanism of the reaction of CCl₄ with C₂H₄ was proposed, which followed the concept of the donor-accpetor electron-transporting systems (the DAET systems), thus accounting for its high selectivity.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2794–2798. December, 1990.     

Complex compounds of ferrocene in a biacceptor system

Summary Three-component systems of ferrocene (FcH): carbon tetrachloride: tetranitromethane have been investigated spectrally in the 290–800 nm range. Quantitative relationships were investigated between electron-donor acceptor (EDA) complexes of ferrocene and CCl₄ (FcH · CCl₄) and C(NO₂)₄ [FcH · C(NO₂)₄] and the ferricenium cation (FcH⁺) which is formed as a result of dissociation of complexes and which depends upon the initial concentration of C(NO₂)₄ and duration the reaction. The results prove the destabilizing influence of C(NO₂)₄ on the EDA complex of ferrocene and CCl₄.     

Structure of the CCl3CCl=NCH2C6H5 molecule and reorientations of its CCl3 group, according to ab initio calculations

The optimal geometry of the isolated CCl₃CCl=NCH₂C₆H₅ molecule and the intramolecular barrier to reorientations of its trichloromethyl group are calculated by the RHF/6-31G* and B3LYP/6-31G* methods. The barrier found (14.1 kJ mol^?1) is compared to that determined previously by ³⁵Cl NQR for a crystal of this compound, which allows estimation of the contribution of intermolecular interactions to braking of this motion of the CCl₃ group. The structural features of the molecule of this compound are consistently manifested in quantum-chemical calculations and NQR spectra.     

Paramagnetic complexes of nickel(I) stabilized by norbornadiene

Nickel(I) compounds whose concentration was 10^–4–10^–6 of the total concentration of nickel added to the system were identified by EPR in the reaction of 2,5-norbornadiene with nickel homoligand allyl complexes Niall₂ (all is C₃H₅, 1-CH₃C₃H₄, or 2-CH₃C₃H₄). The Ni(I) complexes were stable at room temperature under oxygen-free conditions. It was shown that the paramagnetic complexes were in equilibrium with diamagnetic forms. The temperature dependence of the concentration of the paramagnetic species was determined. The structure of the paramagnetic nickel(I) complexes and the possible routes of their formation are discussed on the basis of the obtained data.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 26, No. 4, pp. 490–493, July–August, 1990.     

Thermoanalytical investigations of niobium(V) chloride aryloxides

Niobium(V) chloride aryloxides [NbCl₃(OAr)₂] and [NbCl₂(OAr)₃] (Oar = —OC₆H₄Bu ^t -4 and —OC₆H₄OMe-4) have been prepared by reacting NbCl₅ with two and three equivalents of the respective phenol in CCl₄. The complexes have been characterized by elemental analysis, molecular weight determination, i.r., ¹H-n.m.r., u.v.–vis. and MS techniques. Thermal behaviour (t.g.–d.t.) of the complexes has also been studied and decomposition schemes proposed. The kinetic and thermodynamic parameters namely, the activation energy 'E ^*', the frequency factor 'A', entropy of activation 'S' and specific rate constant 'kr' etc. have been calculated employing the Coats–Redfern equation. The non-isothermal t.g. data has also been utilized to determine the most probable mechanism and corresponding activation energy for the decomposition of niobium(V) complexes by testing seven different theoretically possible decomposition mechanisms.     

Pharmacokinetic detection of penicillin excreted in urine using a totally internally reflected resonance light scattering technique with cetyltrimethylammonium bromide

A quantitative analysis method for penicillins including ampicillin (AmP), benzyl penicillin (BP), oxacillin (OA) and amoxycillin (AmO) is proposed that makes use of the totally internally reflected resonance light scattering (TIR-RLS) signal from the penicillin at the H₂O/CCl₄ interface in the presence of cetyltrimethylammonium bromide (CTMAB), and enables the pharmacokinetics of penicillin taken orally and excreted through urine to be monitored. Penicillin is coadsorbed with CTMAB at the H₂O/CCl₄ interface in neutral solution, resulting in the formation of ion associates that display greatly enhanced TIR-RLS signals (maximum at 368–372 nm). This enhanced TIR-RLS intensity was found to be proportional to the penicillin concentration over the range 0.2×10^–6 to 2.2×10^–6 mol L^–1, with limits of determination (3) of 5.0×10^–8 to 7.0×10^–8 mol L^–1. Pharmacokinetics studies performed using the present method show that the excretion of orally-taken ampicillin through urine has a half-time of 1.05 h and an excremental quantum over 8 h of 49.3%, respectively.     

The limiting dissociative mechanism for substitution at thed 6 centres molybdenum(O), iron(II), and cobalt(III): Kinetics of substitution at the pentacyano-4-Cyanopyridineferrate(II) anion and at 4-cyanopyridinemolybdenum(I) pentacarbonyl

Summary Rate constants are reported for reaction of the 4-cyanopyridine complexes [Fe(CN)₅(4CNpy)]^3– and [Mo(CO)₅(4CNpy)] with a variety of incoming ligands, in aqueous methanol (40 vol % MeOH) and in toluene respectively, at 298.2 K (ambient pressure). The dependence of rate constants on the nature and concentration of the incoming ligand is discussed in terms of the operation of the limiting dissociative,D, mechanism for substitution; the operation of this mechanism here, and in analogous pentacyanoferrate(II), pentacarbonylmolybdenum(I), and penta- and tetra-cyanocobaltate(III) complexes is reviewed. The effect of pressure on rate constants for replacement of 4-cyanopyridine in [Mo(CO)₅(4CNpy)], in toluene solution at 298.2 K, indicates an activation volume of +3 cm³ mol^–1.