An absolute measurement of the rate constant for ethyl radical combination

An absolute value of k_r of ethyl radicals at 860 ± 17°K of 4.5 × 10⁹ M^?1·sec^?1 was determined under VLPP conditions, where the value of k_r/k_r^∞ should be about 1/2. Thus k_r^∞(M^?1·sec^?1) ～ 10¹⁰ at 860°K. An error of as much as a factor of 2 in k_r would be surprising, but possible. The value of 10¹⁰M^?1·sec^?1 seems to be a factor of from 2 to 5 too high to be compatible with extensive data on the reverse reaction and the accepted thermochemistry. Changes in the heat of formation and entropy of the ethyl radical can change the situation somewhat, but even these changes when applied to the work of Hiatt and Benson [3] indicate that ethyl combination should be ～ 10^9.3 M^?1·sec^?1. More work is necessary if a better value is desired.     

Cationic polymerization of N-vinyl carbazole by trityl salts—I.: Reactivity of propagating species

The cationic polymerization of N-vinyl carbazole, initiated by Ph₃C⁺ AsF₆^? and Ph₃C⁺ PF₆^? in methylene dichloride at 20 and 0°, has been studied in some detail. Reactions were very fast and rates of monomer consumption were measured using an adiabatic calorimetric technique. Initiation was relatively “slow” but complete, and termination was deduced to be insignificant during kinetic lifetimes. Values for k_p were found to vary with the initial initiator concentration; this dependence is discussed in terms of current theories regarding equilibria between ion pairs and free ions in non-aqueous solvents. k_p⁺ values estimated from two methods of extrapolation are 9.5 · 10⁵ M^?1 sec^?1 at 20° and 4.8 · 10⁵ M^?1 sec^?1 at 0°. Finally, it has been found that ion pairs are much less reactive than free ions in this system.     

Study of thermal decomposition of poly(vinyl chloride) type polymers with the use of model substances—IV: Gas phase pyrolysis of 2-acetoxy-4-chloropentane

The kinetics of the gas phase pyrolysis were investigated for 2-acetoxy-4-chloropentane, the simplest model for the macromolecule of VC-VAc copolymer; both manometric and GLC method were used. It was concluded that the elimination of the first acid molecule from the model is a homogeneous unimolecular first order reaction with rate constants within the range 310–350° given by: log k₁ = (13·14 ± 0·17)—(44·9 ± 0·5)/2·303 RT for the iso and log k₁ = (13·23 + 0·15)—(44·9 ± 0·4)/2·303 RT for the syndio isomer. (Frequency factors in sec^?1 units, activation energies in kcal mol^?1.)Application of the results to the copolymer leads to the conclusion that the pronounced minimum observed by some authors in the plot of thermal stability against copolymer composition cannot be adequately explained solely in terms of the low thermal stability of an alternating unit.     

Study of thermal decomposition of poly-(vinyl chloride)-type polymers with the use of model substances-V: Pyrolysis of cis-5-chloro-3-heptene and cis- and trans-5-acetoxy-3-heptene in the phase

The gas phase pyrolyses of cis-5-chloro-3-heptene (in the range 267–337°) and cis- and trans-5-acetoxy-3-heptene (300–378°) are homogeneous unimolecular first-order reactions with rate constants given respectively by: log k = (12·03 = 0·13) - (36·2 ± 0·4)/2·303 RT and (12·80 ± 0·11) - (43·0 ± 0·3)/2·303 RT. (Frequency factors in sec^?1 units, activation energies in kcal mol^?1.) No significant differences were found between the rates of decomposition of cis and trans isomers of 5-acetoxy-3-heptene. From the decomposition of these models of poly(vinyl chloride) and poly(vinyl acetate), some conclusions about the role of internal unsaturated groups in the thermal decomposition of both polymers were drawn. The possibility that groups with cis internal double bonds are the most labile structures in a poly(vinyl) chloride macromolecule is discussed.     

Elektrometrische Untersuchungen über die Ag2S-Bildungsgeschwindigkeit in ammoniakalischen Lösungen von Ag+-Ionen mittels Thioacetamid, 5. Mitt.

On basis of polarographic method of continuous registration at constant potential, the quantitative investigation of the rate of Ag₂S formation by thioacetamide (TAA) was performed and, the following equation for the reaction rate between Ag⁺-ions andTAA in ammoniacal solutions has been derived: 1 $$ - \frac{{d[Ag^I ]}}{{d t}} = k \cdot \frac{{[Ag^I ] \cdot [CH_3 CSNH_2 ]^{1/4} }}{{[H^ + ]^{1/10} }} \cdot \frac{{fAg}}{{f_H^{1/10} }}$$ The value, at 25.0^o, of the rate constantk is (6.8±0.4)· ·10^?2 mole^?3/20·litre^3/20·sec^?1. The validity of equation (1) has been proved over the pH range 8.3–10.8 and the ammonia concentration of 5.6·10^?2–1.0 mole per litre, by only a small excess ofTAA and moderate reaction rates.     

Kinetik der Diazotierung des Anilins in methanolischer Bromwasserstoff- und Chlorwasserstofflösung

The kinetics of the diazotization of aniline in methanolic HBr- and HCl-solution from 0.003 um to 0.4n at 0°C were investigated. It was found that the nitrosation reaction $$C_6 H_5 NH_2 + NOX \mathop \rightleftarrows \limits^{k_v } C_6 H_5 NH_2 NO^ + (I) + X^ - (X... halogen)$$ is a preceeding advance-back-reaction (velocity coefficient of the nitrosation: 0.88·10⁸ for bromide and 2.43·10⁸l·Mol^?1·sec^?1 for chloride). The decomposition ofI by splitting off a proton is the rate determining reaction. The free enthalpy of activation for the nitrosation reaction (given above) equals 6.00 kcal/mol for bromide and 5.46 for chloride.     

Decomposition of diacyl peroxide—VII : Oxygen scrambling in 1-apocamphoryl peroxide and related diacyl peroxides-general remarks on the relationship between the stability of acyloxy radical and amounts of cage recombinations and ester formation in the decomposition of diacyl peroxide

Thermal decomposition of 1-apocamphoryl peroxide has been investigated in CCl₄ using the ¹⁸O-labelled peroxide. 1-Apocamphoryl peroxide is the first example which undergoes radical decomposition, carboxy-inversion and oxygen scrambling reaction between carbonyl and peroxidic O atoms in the peroxide in comparable rates. The major product of the decomposition was the inversion product, 1-apocamphoryl 1-apocamphyl carbonate (52·5%), and only a minute amount of 1-apocamphyl 1-apocamphorate (2·2%) was formed. The rates of oxygen scrambling were found to be 2·70±0·21 × 10^?6 (55°), 1·85±0·12 × 10^?1 sec^?1 (70°) and 9·33±0·18 × 10^?5 sec^?1 (84·3°) (E_a, 27·5 Kcal/mol, ΔS3, ?2·3 e.u.). The cage recombination mechanism was suggested for the oxygen scrambling and the amounts of cage recombination of 1-apocamphoryloxy radical pair were calculated as 65% (55°), 60% (70°) and 52% (84·3°). The yield of the ester and the amount of cage recombination of geminate acyloxy radical pair were rationalized in terms of the stability of acyloxy radicals formed in the cage.     

Chlorine nuclear quadrupole resonance study on 1,3-dichloroacetone: dimorphism and temperature dependence of the 35Cl-NQR

Solid 1,3-dichloroacetone, CH₂ClCOCH₂Cl, is dimorphic. The ³⁵Cl-NQR spectra and the X-ray powder patterns are given for both modifications. Phase I shows a single chlorine resonance, whereas phase II (considered to be metastable) gives a four line spectrum. The implications from the NQR spectra with respect to the crystal structures of the two modifications are discussed. The temperature dependence of the ³⁵Cl-NQR frequencies is described by the relationships v^I = 35.9989 ? 16.02 · 10^?1 · T ? 7.350 · 10^?6 · T² + 8.57 · T^?1 (v in MHz, T in K) (Phase I in the range 77 K ? T ? 318 K), and by v₁^II = 36.2968 + 8.19 · 10^?4 · T ? 11.409 · 10^?6 · T² + 13.39 · T^?1, v₂^II = 36.1459 + 5.93 · 10^?4 · T ? 10.447 · 10^?6 · T² + 12.27 · T^?1, v₃^II = 36.0691 + 1.55 · 10^?4 · T ? 9.537 · 10^?6 · T² + 11.72 · T^?1, v₄^II = 35.8244 + 4.42 · 10^?4 · T ? 13.502 · 10^?6 · T² + 17.22 · T^?1, (Phase II in the range 77 K ? T ? 308 K).     

Rate constants for the termination of benzyl radicals in solution

The rate constant for the bimolecular combination of benzyl radicals in cyclohexane and toluene is determined as a function of temperature. Further, it is studied in cyclohexane–toluene mixtures of different compositions. In the entire range covered, 9.8 × 10⁸ ? 2k_t ? 9.0 × 10⁹M^?1·sec^?1, the data are very well described by the Smoluchowski equation for a diffusion-controlled reaction to ground-state products using a spin statistical factor of 1/4, a temperature- and solvent-independent reaction distance, and the known diffusion coefficient of toluene.     

The ultraviolet absorption by alkylperoxy radicals and their mutual reactions

Methylperoxy radicals, CH₃O₂ · have been detected by UV light absorption in the photolysis of azomethane, oxygen and nitrogen mixtures using the technique of molecular modulation spectrometry. The radical concentration is shown to be governed by second-order kinetics. The results give the extinction coefficient, o (exponential), at the peak (λ = 240 nm) = 4.4 × 10^?18 molecule^?1 cm² and a value for the rate constant of mutual recombination, k, which lies between 2.2 × 10^?13 and 4.4 × 10^?13 molecule^?1 cm³ sec^?1. Similar results have been obtained when the azomethane was replaced by azoethane, suggesting the formation of C₂H₅O₂.     

Electrocyclic reactions : Stereochemistry of the triene electrocyclization

Four trienes of known stereochemistry have been prepared and their thermal cyclization studied to ascertain the general stereochemistry of thermal triene electrocyclic reactions. A mixture containing (Z)-1,2-dicyclohexenylethylene was obtained by semihydrogenation. Spectra evidence for thermal cyclization of the triene was obtained, but inability to isolate pure materials canceled plans for stereochemical study.A stereoselective synthesis for (E,Z,E)-2,4,6-octatriene was devised and a pure sample was cyclized thermally to give a 5,6-dimethylcyclohexadiene. Oxidative cleavage of this diene gave meso-2,3-dimethylsuccinic acid. Pure samples of (Z,Z,E)- and (Z,Z,Z)-2,4,6-octatrienes were prepared and found to interconvert thermally at 110°. Cyclization of the equilibrium mixture occurred at 178° to give a 5,6-dimethylcyclohexadiene which gave rac-2,3-dimethylsuccinic acid upon oxidative cleavage. Evidence is presented to suggest that the (E,Z,Z) isomer is the actual reactant undergoing cyclization. Both cyclohexadienes were shown to undergo a 1,5-hydrogen shift to form 1,6-dimethyl-1,3-cyclohexadiene.Rates of the electrocyclic reactions were measured in pentane solution, and thermodynamic activation parameters were ascertained. The results are: (E,Z,E) k(132°) = 4·45 × 10^?5 sec^?1, ΔH

= 28·6 kcal/mole and ΔS

= ?7 eu; (E,Z,Z)+(Z,Z,Z) k(178°)= 1·53 × 10^?5 sec^?1 or (E,Z,Z) k(178°) = 2·13 × 10^?5 sec^?1, ΔH

= 32 kcal/mole, ΔS

= ?9 eu; cis-5,6-dimethyl-1,3-cyclohexadiene (1,5-H shift), k(178°) = 1·77 × 10^?5 sec^?1, ΔH

= 33 kcal/mole, ΔS

= ?7 eu; trans-5,6-dimethyl-1,3-cyclohexadiene (1,5-H shift), k(178°) = 7·7 × 10^?6 sec^?1, ΔH

= 36 kcal/mole, ΔS

= ?3 eu.     

On the photolysis of homo- and copolymers of phenylisopropenylketone

Poly(phenylisopropenylketone (PPIK) and copolymers of PIK and methylmethacrylate (MMA) or styrene (St) were irradiated in benzene solution at 30° with 313 nm light (stationary irradiations) or with 347 nm light (flash photolysis experiments). Homo PPIK undergoes main chain degradation (β-scission) with ø(S) ≈ 0.05. The quantum yield for α-scission is ø(α) = 0.3. For copolymers of MMA and PIK (1 to 15 mol%), ø(S) is 0.04 independent of the copolymer composition. With copolymers of St and PIK, ø(S) was found to increase with decreasing PIK content and to approach 0.15 for very small PIK contents. The flash photolysis experiments showed: (a) the carbonyl triplet decay rate constant k_T(6 × 10⁶ sec^?1) for CP-MMA-PIK samples is independent of copolymer composition but is lower than for homo PPIK (1 × 10⁷ sec^?1). In CP-St-PIK samples k_T decreases with decreasing PIK content [from 8 × 10⁶ sec^?1 (12 mol% PIK) to 3 × 10⁶ sec^?1 (1 mol% PIK)]; (b) the transient spectra of triplet decay products indicate the formation of benzoyl radicals in the cases of PPIK and CP-MMA-PIK, and the formation of various different species in the case of CP-St-PIK.The results are consistent with the following concept. In homo PPIK and CP-MMA-PIK, α-scission (Norrish type I) is the dominant chemical route of triplet deactivation. In CP-St-PIK, however, type II processes become more and more important as the PIK content decreases.     

Thermal decomposition kinetics of bisthiourea cadmuim(II) tetrathiocyanato diammine chromate(III)

Cadmium thiourea reinickate undergoes two-stage thermal decomposition on heating. The DTG peak temperatures are 291 and 469°C and the corresponding DTA temperatures are 255 and 490°C. The kinetic parameters for the first stage decomposition are E* ≈ 120kJ mole^?1; Z ≈ 1.2 × 10⁸ cm³ mole^?1 sec^?1 and ΔS* ≈ ?95 J mole^?1 K^?1. For the second stage, E* ≈ 133 kJ mole^?1; Z ≈ 6.1 × 10⁵ cm^?1 mole^?1 sec^?1 and ΔS* ≈ ?142 J mole^?1 K^?1.     

KINETICS OF THE CHROMIUM(II) REDUCTIONS OF CHELATED AMINO ACIDO-BIS(ETHYLENE-DIAMINE)COBALT(III) COMPLEXES

Abstract

The kinetics of Cr²⁺(aq) reductions of glycinato-, D,L-alanato, D,L-phenylalanato-, and D,L-leucinatobis-(ethylenediamine)cobalt(III) ions have been investigated. The rate law is of the form d(ln[Co(III)]/dt = k[Cr²⁺], where the rate constant k(M^?1sec^?1) and associated activation parameters δH^δ(kcal mol^?1 and δS^δ (cal deg ^?1mol^?1) in parentheses, are respectively 1.65 · 0.06 (9.7 · 0.1, -25 · 1), 0.367 · 0.008 (10.9 · 04,-24 ·1), 0.529 · 0.021 (11.2 · 0.4, -22 · 1); and 0.358 · 0.019 (11.5 · 0.3, -22 · 1) at 298^·K and ·[CIO·] = 1.0 M. The reactions are all inner-sphere.     

SINGLET-TRIPLET SPIN TRANSITION IN AN IRON(II) COMPLEX OF 1,10-PHENANTHROLINE-2-CARBOTHIOAMIDE

Abstract

The ⁵⁷Fe Mössbauer effect for the solid complex FeLCl₂·H₂O (L=10-phenanthroline-2-carbothioamide) has been studied between 4.2°K and 298°K. Two overlapping doublets (I and II) are observed, their relative intensity being strongly temperature dependent. The doublets are characterized by δE_Q(I)=0.53 mm sec^?1, δ^IS(I)=+ 0.22 mm sec^?1 and δE_Q(II)=1.33 mm sec^?1, δ^IS(II)=+0.23 mm sec^?1 at 4.2°K. In conjunction with magnetic data, the Mössbauer spectra are interpreted in terms of a singlet-triplet spin transition of the central iron(II) ion. In an applied magnetic field at 4.2°K, H_int=0, V_ZZ(I)>0, and V_ZZ(II)>0. The results are consistent with optical electronic and infrared vibrational spectra.     

The free-radical reaction of tri-n-butyltin hydride with peroxides

Rate constants for the tri-n-butyltin radical ( Sn · ) induced decomposition of a number of peroxides have been measured in benzene at 10°C. The values range from ～100 M^?1 sec^?1 for di-t-butyl peroxide to 2.6 × 10⁷ M^?1 sec^?1 for di-t-butyl diperoxyisophthalate. The majority of the peroxides, including diethyl peroxide, diacetyl peroxide, and t-butyl peracetate, have rate constants of ～10⁵ M^?1 sec^?1. It is shown that di-n-alkyl disulfides are ten times as reactive toward Sn · as di-n-alkyl peroxides, although the exothermicities of these reactions are ～15 and ～39 kcal/mole, respectively. The enhanced reactivity of the disulfides is attributed to the easier formation of an intermediate or transition state with 9 electrons around sulfur, compared with an analogous species with 9 electrons around oxygen. The following bond strengths (kcal/mole) have been estimated: D[ Sn ? OR] = 77; D[ Sn ? H] = 82; D[ Sn ? SR] = 83; and D[ Sn ? OC(O)R] = 86, where R = alkyl. Rate constants for reaction of Sn · with some benzyl esters have also been measured. It has been found that t-butoxy radicals can add to benzene and abstract hydrogen from benzene at ambient temperatures.     

The very-low-pressure pyrolysis (VLPP) of n-propyl nitrate,tert-butyl nitrite,and methyl nitrite. Rate constants for some alkoxy radical reactions

The pyrolysis of n-propyl nitrate and tert-butyl nitrite at very low pressures (VLPP technique) is reported. For the reaction the high-pressure rate expression at 300°K, log k₁ (sec^?1) = 16.5 ? 40.0 kcal/mole/2.3 RT, is derived. The reaction was studied and the high-pressure parameters at 300°K are log k₂(sec^?1) = 15.8 ? 39.3 kcal/mole/2.3 RT. From ΔS_1,?1⁰ and ΔS_2,?2⁰ and the assumption E_?1 and E_?2 ? 0, we derive log k_?1(M^?1·sec^?1) (300°K) = 9.5 and log k_?2 (M^?1·sec^?1) (300°K) = 9.8. In contrast, the pyrolysis of methyl nitrite and methyl d₃ nitrite afford NO and HNO and DNO, respectively, in what appears to be a heterogeneous process. The values of k_?1 and k_?2 in conjunction with independent measurements imply a value at 300°K for of 3.5 × 10⁵ M^?1·sec^?1, which is two orders of magnitude greater than currently accepted values. In the high-pressure static pyrolysis of dimethyl peroxide in the presence of NO₂, the yield of methyl nitrate indicates that the combination of methoxy radicals with NO₂ is in the high-pressure limit at atmospheric pressure.     

Voltammetric behavior of neptunium(vi) in glutamic acid media at the rotating glassy carbon electrode

The voltammetry of neptunium(VI) glutamate was investigated over the pH range 3.8–10.0. A reversible, one-electron wave was obtained for glutamate concentrations above 0.1 M in the pH range 3.8–6.1, or above 0.3 M in the pH range 6.1–10.0. At pH 3.8–6.1, the half-wave potential was independent of pH, but at pH 6.1–10.0, it was a function of pH. The metal-ligand ratio was found to be 1:2 by conductometric titration. The limiting current was proportional to the concentration of the neptunium(VI) from 7.83·10^-5 to 1.96·10^-3M. The diffusion coefficient was 0.35·10^-5 cm² sec^-1 at pH 4.5 and 0.30·10^-5 cm² sec^-1 at pH 9.4.     

HFS and isotope shift in the atomic spectrum of205Pb

The hfs of²⁰⁵Pb in the 283.3-nm resonance line and its isotope shift (IS) have been measured in absorption with the use of dispersive spectroscopy. A new method for calibration and analysis, when internal standards are not available is described. The results are: hfs interaction constantsA=70.3(5)×10^?3 cm^?1,B=?0.6(1.1)×10^?3 cm^?1,²⁰⁵Pb-²⁰⁸Pb IS=?123.9(2.0)×10^?3 cm^?1. The derived nuclear magnetic dipole moment,μ=0.704(5)μ _N is in good agreement with values calculated with a nuclear configuration mixing model.     

Polymer reactions—Part VII: Thermal pyrolysis of polypropylene

Polypropylene has been pyrolysed in a carrier stream of helium from 388° to 900°C in both the programmed heating and flash pyrolysis modes. The products were on-line identified and quantitatively analysed by an interfaced GC peak identification system. The first order rate constants for pyrolysis are 3·7 × 10^?4 sec^?1 and 4·0 × 10^?4 sec^?1, respectively, for atactic and isotactic polypropylene at 388°C; the corresponding overall activation energies are 56 ± 6 and 51 ± 5 kcal mole^?1. The main products in decreasing yields are 2,4-dimethyl-1-heptene, 2-pentene, propylene, 2 methyl-1-pentene and 2,4,6-trimethyl-1-nonene. Also isolated, but in much smaller quantities, are: ethane, isobutylene, 4,6-dimethyl-2-nonene, 2,4,6-trimethyl-1-heptene, 3-methyl-3,5-hexadiene and methane. Propylene is the product of an unzipping reaction. Most of the other products can be accounted for by a mechanism involving first, random scission of carbon-carbon bonds to produce methyl, primary and secondary alkyl radicals, followed by intramolecular hydrogen transfer processes. Methane and ethane are formed from the methyl radicals. All the products found in high yields are derived from the secondary alkyl radicals.