The kinetics of the gas-phase thermal isomerization and decomposition of Trans- and Cis-1,2-Bis(trifluoromethyl)-1,2,3,3-tetrafluorocyclopropane

The kinetics of the gas-phase thermal isomerization between trans- and cis-1,2-bis(trifluoromethyl)-1,2,3,3-tetrafluorocyclopropane as well as their decomposition to trans- and cis-perfluoro-2-butene, respectively, and CF₂, was studied in the temperature range of 473–533°K, with an initial pressure of reactant of 1.5 to 7.0 Torr. Some runs were also made with the addition of SF₆ as an inert gas up to a total pressure of 100 Torr. The reactions are first order and homogeneous. The rate constants for the geometrical isomerization fit the following Arrhenius relations: and the corresponding equations for the decomposition of the trans and cis-cyclopropane are .     

Shock tube study of cyanogen oxidation kinetics

Mixtures of cyanogen and nitrous oxide diluted in argon were shock-heated to measure the rate constants of A broad-band mercury lamp was used to measure CN in absorption at 388 nm [B²Σ⁺(v = 0) ← X²Σ⁺(v = 0)], and the spectral coincidence of a CO infrared absorption line [v(2 ← 1), J(37 ← 38)] with a CO laser line [v(6 → 5), J(15 → 16)] was exploited to monitor CO in absorption. The CO measurement established that reaction (3) produces CO in excited vibrational states. A computer fit of the experiments near 2000 K led to An additional measurement of NO via infrared absorption led to an estimate of the ratio k₅/k₆: with k₅/k₆ ? 10^3.36±0.27 at 2150 K. Mixtures of cyanogen and oxygen diluted in argon were shock heated to measure the rate constant of and the ratio k₅/k₆ by monitoring CN in absorption. We found near 2400 K: and The combined measurements of k₅/k₆ lead to k₅/k₆ ? 10^?3.07 exp(+31,800/T) (±60%) for 2150 ≤ T ≤ 2400 K.     

Quenching of N2(A3Σu+) by O2, O,N, and H

Metastable N₂(A³Σ_u⁺), υ = 0, υ = 1, molecules are produced by a pulsed Tesla-type discharge of a dilute N₂/Ar gas mixture. Rate coefficients for quenching these metastable levels by O₂, O, N, and H were obtained by time-resolved emission measurements of the (0, 6) and (1, 5) Vegard–Kaplan bands. In units of cm³/mole · sec at 300°K and with an experimental uncertainty of ±20%, these rate coefficients for N₂(A³Σu⁺) are Within the limits of error these coefficients apply to quenching N₂(A³Σ_u⁺) υ′ = 1 as well.     

Studies on anionic polymerization of lactams. Part III. Copolymerization of pyrrolidone and caprolactam

On reacting acetylcaprolactam (AcCL) and pyrrolidonate MgBr (Py^?) in tetrahydrofuran solution, transacetylation takes place, giving acetylpyrrolidone (AcPy) and caprolactamate MgBr (CL^?). The rate constants for the transacetylation reactions were measured at 25°C. Their values in units of liters/mole-second were: The rate constants for the addition reactions measured were: As the transacetylation is much faster than the addition reaction the copolymer composition should be given by the equation: where K_trans, the transacetylation equilibrium constant, equals 0.3 while K_acidity reflects the relative acidities of the monomers and its value (from the literature) is about 0.4. Pyrrolidone is, therefore, more reactive than caprolactam in anionic copolymerization by a factor of about 8.     

Kinetic isotope effect in the protonation of anthracenide salts by MeOH and MeOD role of counterions and solvents

Kinetics of protonation of Li⁺, Na⁺, K⁺, and Cs⁺ salts of anthracene radical anions (A^?_·,Cat⁺) and dianions (A^2?, 2Cat⁺) by MeOH and MeOD in tetrahydrofuran (THF) and dimethoxyethane (DME) led to the determination of the isotope effect (k_H/k_D) in the following reactions: Studies of cation and solvent influence on the rate constants of these reactions and on the magnitude of the isotope effect permitted us to draw some conclusions about the structure of the pertinent transition states. It seems that only the tight A^?·,Na⁺ pairs participate in the protonation, and on this basis the fraction of tight ion paris of A^?·,Na⁺ in DME was estimated. Our results have been compared with data reported in the literature.     

The kinetics and mechanism of the oxidation of formic acid by bromine in acid aqueous media

The reaction between formic acid and bromine in strongly acid aqueous media at 298 K was studied by absorption spectrophotometry (λ = 447 nm). Reaction rates, expressed as R = -d[Br₂]/dt, depend on the concentrations of HCOOH (0.3–2.4M), Br₂[(2.7–13.6) × 10^?3M], H⁺ (0.03–2.0M), and Br^? (up to 0.6M). The mechanism with k₁ = 20.2 ± 1.2 M^?1 sec^?1, pK₂ = 3.76, pK₃ = ?1.20, accounts for all experimental observations. Br₃^? and HCOOH can be considered unreactive within experimental error. Apparent deviations from the basic mechanism at higher acidities can be quantitatively ascribed to the nonideality of ionic species.     

Kinetics of the reactions of cyclopropane derivatives. III. Gas-phase unimolecular isomerization of cyclopropyl cyanide to the cyanopropenes

Cyclopropyl cyanide isomerizes in the gas phase at 660°–760°K and 2–89 torr to give mainly cis- and trans-crotonitrile and allyl cyanide, with traces of methacrylonitrile. The reactions are first order, homogeneous, and unaffected by the presence of radical-chain inhibitors. The rate constants are given by Overall: cis-Crotonitrile: trans-Crotonitrile: Allyl cyanide: where the error limits are standard deviations. On the basis of a biradical mechanism, it is deduced that the ? CH? CN radical center is resonance stabilized by ca. 30 kJ mole^?1. Approximate equilibrium data are given for interconversion of the 1- and 3-cyanopropenes.     

Mechanism of the hydroxyiodination of 2-butenoic acid

Aqueous iodination of trans-2-butenoic acid proceeds via hydrolysis of I₂ to form HOI and I^?, then rapid addition of HOI across the double bond to form the iodohydrin product. In the presence of iodate to keep iodide concentration low, the reaction proceeds at a conveniently measurable rate. The rate for the addition reaction is ?d[C₄H₆O₂]/dt = 5900 [H⁺][C₄H₆O₂][HOI]M/s at 25.0°C when [IO] = 0.025M and ionic strength = 0.3. The overall rate law in the presence of iodate is where [H⁺] and [IO] are total concentrations used to prepare the solution.     

Kinetics of the oxidation of cyclohexene by thallium(III) acetate

The kinetics of the reaction by which thallium(III) acetate oxidizes cyclohexene in glacial acetic acid medium, has been studied by UV spectrophotometric observation at 30°C. The consumption of thallium(III) acetate follows a second-order rate law exhibiting first-order dependence on each of thallium(III) acetate and cyclohexene; however, the first-order dependence on cyclohexene disappears at high cyclohexene concentrations as pseudo-first-order conditions prevail above 0.2 M cyclohexene. A steady-state model of the following form is proposed: where Tl, Cy, and Com are units of Thallium(III) acetate, cyclohexene, and a reaction complex. The value of k₂ has been evaluated as 0.00027 and (k_?1 + k₂) as 0.0385k₁. For low thallium(III) acetate concentrations the reaction kinetics follow the rate law: where α = the excess concentration of cyclohexene over thallium(III) triacetate. For thallium(III) acetate concentrations above 0.02 M, double salt formation of thallium(III) acetate with product thallium(I) acetate removes thallium(III) acetate from the reaction and a modified rate law is observed. Runge–Kutta numerical solutions to the differential equations provide confirmation that the rate expressions are valid in predicting the observed concentrations of thallium(III) acetate.     

Trägerfixierte Organometallkomplexe. VI. Charakterisierung und Reaktivität Polysiloxan-gebundener (Ether-phosphan)ruthenium(II)-Komplexe

Supported Organometallic Complexes. VI. Characterization und Reactivity of Polysiloxane-Bound (Ether-phosphane)ruthenium(II) Complexes The ligands PhP(R)CH₂D [R = (CH₃O)₃Si(CH₂)₃; D = CH₂OCH₃ ( 1b ); D = tetrahydrofuryl ( 1c ); D = 1,4-dioxanyl ( 1d )] have been used to synthesize (ether-phosphane)ruthenium(II) complexes, which have been copolymerized with Si(OEt)₄ to yield polysiloxane-bound complexes. The monomers cis,cis,trans-Cl₂Ru(CO)₂(P ～ O)₂ ( 3b ) and HRuCl(CO)(P ～ O)₃ ( 5b ) were treated with NaBH₄ to form cis,cis,trans-H₂Ru(CO)₂(P ～ O)₂ ( 4b ) and H₂Ru(CO)(P ～ O)₃ ( 6b ), respectively (P ～ O = η¹-P coordinated; = η²- coordinated). Addition of Si(OEt)₄ and water leads to a base catalyzed hydrolysis of the silicon alkoxy-functions and a precipitation of the immobilized counterparts 4b ′, 6b ′. The polysiloxane matrix resulting by this new sol gel route has been described under quantitative aspects by ²⁹Si CP-MAS NMR spectroscopy. 4b ′ reacts with carbon monoxide to form Ru(CO)₃(P ～ O)₂ ( 7b ′). Chelated polysiloxane-bound complexes Cl₂Ru( )₂ ( 9c ′, d ′) and Cl₂Ru( )(P ～ O)₂ ( 10b ′, c ′) have been synthesized by the reaction of 1b–c with Cl₂Ru(PPh₃)₃ ( 8 ) followed by a copolymerization with Si(OEt)₄. The polysiloxane-bound complexes 9c ′, d ′ and 10b ′, c ′ react with one equivalent of CO to give Cl₂Ru(CO)( )(P ～ O) ( 12b ′– d ′). Excess CO leads to the all-trans-complexes Cl₂Ru(CO)₂(P ～ O)₂ ( 14b ′– d ′), which are thermally isomerized to cis,cis,trans- 3b ′– d ′. The chemical shift anisotropy of ³¹P in crystalline Cl₂Ru( )₂ ( 9a , R = Ph, D = CH₂OCH₃) has been compared with polysiloxane-bound 9d ′ indicating a non-rigid behavior of the complexes in the matrix.     

Mechanism of catalytic ascorbic acid oxidation system Cu2+–ascorbic acid–O2

Analysis is made of reported results on the kinetics and mechanism of ascorbic acid oxidation with oxygen in the presence of cupric ions. The diversities due to methodological reasons are cleared up. A kinetic study of the mechanism of Cu²⁺ anaerobic reaction with ascorbic acid (DH₂) is carried out. The true kinetic regularities of catalytic ascorbic acid oxidation with oxygen are established at 2.7 ≤ pH < 4, 5 × 10^?4 ≤ [DH₂] ≤ 10^?2M, 10^?4 ≤ [Cu²⁺] ≤ 10^?3M, and 10^?4 ≤ [O₂] ≤ 10^?3M: where??₁ (25°C) = 0.13 ± 0.01 M^?0.5˙sec^?1. The activation energy for this reaction is E₁ = 22 ± 1 kcal/mol. It is found by means of adding Cu⁺ acceptors (acetonitrile and allyl alcohol) that the catalytic process is of a chain nature. The Cu⁺ ion generation at the interaction of the Cu²⁺ ion with ascorbic acid is the initiation step. The rate of the chain initiation at [Cu²⁺] ± 10^?4M, [DH₂] ± 10^?2M, 2.5 < pH < 4, is where??_i,1 (25°C) = (1.8 ± 0.3)M^?1˙sec^?1, E_i,1 = 31 ± 2 kcal/mol. The reaction of the Cu⁺ ion with O₂ is involved in a chain propagation, so that the rate of catalytic ascorbic acid oxidation for the system Cu²⁺? DH₂? O₂ is where??₁ (25°C) = (5 ± 0.5) × 10⁴ M^?1˙sec^?1. The Cu⁺ ion and a species interacting with ascorbate are involved to quadratic chain termination. By means of photochemical and flow electron spin resonance methods we obtained data characteristic of the reactivities of ascorbic acid radicals and ruled out their importance for the catalytic chain process. A new type of chain mechanism of catalytic ascorbic acid oxidation with oxygen is proposed: .     

Kinetics and mechanism of the reaction between N-and N,N′-methyl ethylenediamines and palladium(II) chloro complexes in aqueous acid medium

The substitution of N-alkyl substituted ethylenediamines for chloride ions in the rapidly equilibrating system has been investigated in aqueous acid medium. The kinetic data can be accommodated by the general rate law where n = 0, 1, or 2 and m = 0, 1, or 2, depending on whether none, one, or two methyl groups are attached to the two nitrogen atoms of ethylenediamine. Reaction with the most heavily substituted ethylenediamine, namely, N₂N₂en discloses a change of the mentioned rate law to on going from a lower to a higher chloride ion concentration range. This change in the mathematical form of the rate law can be explained in terms of an ion-pair association of N₂N₂enH⁺ and free chloride ions.     

The oxidation of cis- and trans-CHClCHCl

When Cl atoms react with CHClCHCl in the presence of O₂ at 31°C, a long-chain oxidation occurs. The products are the geometrical isomer of the starting olefin and CHClO, HCl, CO, and CCl₂O. The quantum yields of the oxygen-containing products are the same with both isomers and are Φ{CHClO} = 30, Φ{CO} = 11.7, and Φ{CCl₂O} = 1.29. The chlorine atom adds to the olefin and is followed by O₂ addition. The reaction then proceeds with k_6a/k_6b = 19 and k_7a/k₇ ～ 0.5, where k₇ ≡ k_7a + k_7b. The CCl₂H radical oxidizes to regenerate the chain carrier. O(³P) reacts with CHClCHCl at 25°C with a rate coefficient of 6.6 × 10⁸ M^?1 sec^?1 for trans-CHClCHCl and 2.8 × 10⁸ M^?1 sec^?1 for cis-CHClCHCl. The reaction channels are with k_1a/k₁ = 0.23 and 0.28, respectively, for the cis and trans compounds. Reaction (1b) occurs < 4% of the time. Reaction (1c) leads to polymer production and presumably, via redissociation, to the geometrical isomer of the starting olefin. In the presence of O₂ the same long-chain oxidation is observed as in the chlorine-atom initiated oxidation. The chain-initiating step is      

Zur Thermodynamik der Metallcarbonate 3. Mitteilung [1]. Löslichkeitskonstanten und Freie Bildungsenthalpien von ZnCO3 und Zn5(OH)6(CO3)2 bei 25°

The solubilities of ZnCO₃ and Zn₅(OH)₆(CO₃)₂ have been investigated at 25°C in solutions of the constant ionic strength 0,2 M consisting primarily of sodium perchlorate. From experimental data the following values for equilibrium constants and GIBBS free energies of formation are deduced: A predominance area diagram for the ternary system Zn²⁺–H₂O–CO_2(g) including ZnO, ZnCO₃, Zn₅(OH)₆(CO₃₎₂, and Zn²⁺ is given.     

Chain ion molecular mechanism of ascorbic acid oxidation with hydrogen peroxide. Cu3+ ion as a chain carrier

The kinetics and mechanism of ascorbic acid (DH₂) oxidation have been studied under anaerobic conditions in the presence of Cu²⁺ ions. At 10^?4 ≤ [Cu²⁺]₀ < 10^?3M, 10^?3 ≤ [DH₂]₀ < 10^?2M, 10^?2 ≤ [H₂O₂] ≤ 0.1M, 3 ≤ pH < 4, the following expression for the initial rate of ascorbic acid oxidation was obtained: where χ₂ (25°C) = (6.5 ± 0.6) × 10^?3 sec^?1. The effective activation energy is E₂ = 25 ± 1 kcal/mol. The chain mechanism of the reaction was established by addition of Cu⁺ acceptors (allyl alcohol and acetonitrile). The rate of the catalytic reaction is related to the rate of Cu⁺ initiation in the Cu²⁺ reaction with ascorbic acid by the expression where C is a function of pH and of H₂O₂ concentration. The rate equation where k₁(25°C) = (5.3 ± 1) × 10³M^?1 sec^?1 is true for the steady-state catalytic reaction. The Cu⁺ ion and a species, which undergoes acid–base and unimolecular conversions at the chain propagation step, are involved in quadratic chain termination. Ethanol and terbutanol do not affect the rate of the chain reaction at concentrations up to ≈0.3M. When the Cu²⁺–DH₂–H₂O₂ system is irradiated with UV light (λ = 313 nm), the rate of ascorbic acid oxidation increases by the value of the rate of the photochemical reaction in the absence of the catalyst. Hydroxyl radicals are not formed during the interaction of Cu⁺ with H₂O₂, and the chain mechanism of catalytic oxidation of ascorbic acid is quantitatively described by the following scheme. Initiation: Propagation: Termination:      

Primary steps in the photolysis of cis-1,2-dichloroethylene

The photolysis of cis-1,2-dichloroethylene has been investigated in the presence of I₂ as a function of incident wavelength and as a function of initial cis pressure. The results indicate that at ± > 2200Å the following primary processes occur: The lifetime of the excited state yielding the above products is estimated at about 2.4×10^?9 sec. At shorter wavelengths additional C₂H₂ is produced by decomposition of a vibrationally excited C₂H₂Cl radical. Scavenging of the CHClCH radical by I₂ produced trans and cis-CHClCHl in a ratio of 4 to 1, respectively.     

Kinetic investigation of the bromate–ascorbic acid–malonic acid system

According to our experiments the bromide ion concentration exhibits in the bromate–ascorbic acid–malonic acid–perchloric acid system three extrema as a function of time. To describe this peculiar phenomenon, the kinetics of four component reactions have been studied separately. The following rate equations were obtained: Bromate–ascorbic acid reaction: Bromate–bromide ion reaction: Bromide–ascorbic acid reaction: Bromine–malonic acid reaction: k₄ = 6 × 10^?3 s^?1, k_-4 ≥ 1.7 × 10³ s^?1, k₅ ≥ 1 × 10⁷M^?1 · s^?1 Taking into account the stoichiometry of the component reactions and using these rate equations, the concentration versus time curves of the composite system were calculated. Although the agreement is not as good as in the case of the component reactions, it is remarkable that this kinetic structure exhibits the three extrema found.     

The reaction of OH with NO2 and the deactivation of O(1D) by CO

NO₂ was photolyzed with 2288 Å radiation at 300° and 423°K in the presence of H₂O, CO, and in some cases excess He. The photolysis produces O(¹D) atoms which react with H₂O to give HO radicals or are deactivated by CO to O(³P) atoms The ratio k₅/k₃ is temperature dependent, being 0.33 at 300°K and 0.60 at 423°K. From these two points, the Arrhenius expression is estimated to be k₅/k₃ = 2.6 exp(?1200/RT) where R is in cal/mole – °K. The OH radical is either removed by NO₂ or reacts with CO The ratio k₂/k^α is 0.019 at 300°K and 0.027 at 423°K, and the ratio k₂/k⁰ is 1.65 × 10^?5M at 300°K and 2.84 × 10^?5M at 423°K, with H₂O as the chaperone gas, where k^α = k₁ in the high-pressure limit and k⁰[M] = k₁ in the low-pressure limit. When combined with the value of k₂ = 4.2 × 10⁸ exp(?1100/RT) M^?1sec^?1, k^α = 6.3 × 10⁹ exp (?340/RT)M^?1sec^?1 and k⁰ = 4.0 × 10¹²M^?2sec^?1, independent of temperature for H₂O as the chaperone gas. He is about 1/8 as efficient as H₂O.     

Reaction of O(1D) with N2O

O(¹D), produced from the photolysis of N₂O at 2139 Å, reacts with N₂O in accord with: We have used the method of chemical difference to obtain an accurate measure of k₂/k₃ = 0.59 ± 0.01. Furthermore, the quantum yield of production of O(³P), either on direct photolysis or on deactivation of O(¹D) by N₂O, is less than 0.02 and probably zero.     

Thermal stability of alcohols

3,3-Dimethylbutanol-2 (3,3-DMB-ol-2) and 2,3-dimethylbutanol-2 (2,3-DMB-ol-2) have been decomposed in comparative-rate single-pulse shock-tube experiments. The mechanisms of the decompositions are The rate expressions are They lead to D(iC₃H₇? H) – D((CH₃)₂(OH) C? H) = 8.3 kJ and D(C₂H₅? H) – D(CH₃(OH) CH? H) = 24.2 kJ. These data, in conjunction with reasonable assumptions, give and The rate expressions for the decomposition of 2,3-DMB-1 and 3,3-DMB-1 are and