Ozone–olefin reactions in the gas phase 1. Rate constants and activation energies

Reactions of ozone with simple olefins have been studied between 6 and 800 mtorr total pressure in a 220-m³ reactor. Rate constants for the removal of ozone by an excess of olefin in the presence of 150 mtorr oxygen were determined over the temperature range 280 to 360° K by continuous optical absorption measurements at 2537 Å. The technique was tested by measuring the rate constants k₁ and k₂ of the reactions (1) NO + O₃ → NO₂ + O₂ and (2) NO₂ + O₃ rarr; NO₃ + O₂ which are known from the literature. The results for NO, NO₂, C₂H₄, C₃H₆, 2-butene (mixture of the isomers), 1,3→butadiene, isobutene, and 1,1 -difluoro-ethylene are 1.7 × 10^{?1 4} (290°K), 3.24 × 10^?17 (289°K), 1.2 × 10^{?1 4} exp (–4.95 ± 0.20/RT), 1.1 × 10^{?1 4} exp (–3.91 ± 0.20/RT), 0.94 × 10^{?1 4} exp ( –2.28 ± 0.15/RT), 5.45 ± 10^{?1 4} exp ( –5.33 ± 0.20/RT), 1.8 ×10^?17 (283°K), and 8 × 10^?20 cm³/molecule ·s(290°K). Productformation from the ozone–propylene reaction was studied by a mass spectrometric technique. The stoichiometry of the reaction is near unity in the presence of molecular oxygen.     

Spectrocoulometric study of the hydrolysis of the tris (1,10-phenanthroline)iron(III) complex ion

The spectrocoulometric technique reported earlier is applied to verify the mechanism and to evaluate the contributions k_Bi of the individual bases to the total rate constant k of the hydrolysis of the tris (1,10-phenanthroline) iron(III) complex, Fe (phen)³⁺₃. Both normal and “open-circuit” spectrocoulometric experiments are used. Partial rate constants for four bases in the acetate-buffered solutions are k_H2O=(3.4±1.2) × 10^?4s^?1 (k_H2O includes the H₂O concentration), k_OH=(1.20±0.06)×10⁷ mol^?1dm³s^?1, k_phen=(1.4±0.2) mol^?1dm³s^?1, k_Ac=(3.8±0.3)×10^?2 mol^?1dm³s^?1, at 25°C and ionic strength 0.5 mol dm^?3. The Fe(phen)³⁺³ hydrolysis, with (phen)₂ (H₂O) Fe-O-Fe (H₂O) (phen)⁴⁺² formation, is first order with respect to Fe (phen)³⁺³ and the bases present in the solution. The rate-determining step in the hydrolysis is the entry of a base to the coordinating sphere of the complex, as in the hydrolysis of the analogous 2,2′-bipyridyl complex.     

Base hydrolysis of (αβ S)-(o-methoxy benzoato) (tetraethylenepentamine) cobalt(III) ion: A comparative study of the role of ion pairs and micelles

The kinetics of base hydrolysis of (αβ S)-(o -methoxy benzoato) (tetraethylenepentamine)cobalt(III) obeyed the rate law: k_obs = k_OH[OH^?], in the range 0.05 ? [OH^?]_T, mol dm^?3 ? 1.0, I = 1.0 mol dm^?3, and 20.0–40.0°C. At 25°C, k_OH = 13.4 ± 0.4 dm³ mol^?1 s^?1, ΔH^≠ = 93 ± 2 kJ mol^?1 and ΔS^≠ = 90 ± 5 JK^?1 mol^?1. Several anions of varying charge and basicity, CH₃CO₂^?, SO₃^2?, SO₄^2?, CO₃^2?, C₂O₄^2?, CH₂(CO₂)₂^2?, PO₄^3?, and citrate^3? had no effect on the rate while phthalate^2?, NTA^3?, EDTA^4?, and DTPA^5? accelerated the process via formation of the reactive ion pairs. The anionic (SDS), cationic (CTAB), and neutral (Triton X-100) micelles, however, retarded the reaction, the effect being in the order SDS> CTAB > Triton X-100. The importance of electrostatic and hydrophobic effects of the micelles on the selective partitioning of the reactants between the micellar and bulk aqueous pseudo-phases which control the rate are discussed. © 1994 John Wiley & Sons, Inc.     

Visible Light Excitable SCN− Selective Fluorescence Probe Derived from Thiophene

An efficient fluorescence probe, 4‐methyl‐2,6‐bis((thiophen‐2‐ylmethylimino)methyl)phenol (DFPTMA) and its SCN^? adduct has been synthesized and characterized by different spectroscopic techniques like ¹H NMR,¹³C NMR, QTOF‐MS ES⁺, UV‐Vis and FTIR spectroscopy. Single crystal X‐ray structure of DFPTMA is reported. In presence of SCN^?, DFPTMA exhibits significant fluorescence enhancement (λ_Ex, 455 nm, λ_Em, 504 nm) in aqueous methanol (water‐methanol, 1:4, V/V, 0.1 mol/L HEPES buffer, pH 7.4). Common bio‐relevant anions viz. CH₃COO^?, NO₂^?, NO₃^?, Cl^?, Br^?, I^?, SO₄^2?, HSO₄^?, N₃^?, HAsO₄^2?, Cr₂O₇^2?, H₂PO₄^?, ClO₄^?, NCO^?, CN^?, CO₃^2?, F^?, PO₄^3?, S^2?, HS^? do not interfere in the recognition of SCN^?. Lowest detection limit for SCN^? is 0.88 µmol/L with response time <5 min. The SCN^? assisted enhancement in emission intensity may be attributed to the formation of H‐bond which enhances the rigidity of the molecular assembly.     

Effect of added salts on the rates of dissociation and racemization of tris(1,10-phenanthroline)iron(II) ion in aqueous methanol solutions

The kinetics of dissociation and racemization of [Fe(phen)₃]²⁺ have been studied in aqueous methanol solutions containing perchlorate, chloride, and thiocyanate ions. The racemization rate was decreased by ClO^?₄ and increased by SCN^?, while the dissociation rate was decreased by ClO^?₄ and increased slightly by Cl^? and remarkably by SCN^?. The effect of anions on the reaction rates became remarkable with the increase in methanol content of the solutions. The results were reasonably explained in terms of ion association. The dissociation rate of the complex ion in the ion-pair increased in the order, ClO^?₄ < Cl^? < SCN^?, of associated anions, suggesting the ion-pair interchange mechanism for the dissociation. The ion-association constants were determined to be 11 ± 4, 18 ± 4, and 25 ± 15 (I = 0.1, 25°C) for ClO^?₄, Cl^?, and SCN^?, respectively, in 0.64 mole-fraction (0.8 volume-fraction) aqueous methanol.     

Kinetic Study of the Bromine-Catalyzed Isomerization of Maleic Acid in Aqueous Ce(IV)-Br−-H2SO4 Medium

The presence of ceric and bromide ions catalyzes the isomerization of maleic acid (MA) to fumaric acid (FA) in aqueous sulfuric acid. A kinetic study of this bromine-catalyzed reaction was carried out. The reaction between ceric ion and maleic acid is first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [H₂SO₄]₀=1.2 M, μ=2.0 M (adjusted by NaClO₄), and [MA]₀=(0.5–1.0)M, the observed pseudo-first-order rate constant (k₀₃) at 25° is k₀₃=7.622×10^?5 [MA]₀/(1+0.205[MA]₀). The reaction between ceric and bromide ions is first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [Br^?]₀=(0.025–0.150)M, the pseudo-first-order rate constant (k₀₂) at 25° is k₀₂= (4.313±0.095)x10^?2[Br^?]²+(2.060±0.119)x10^?3[Br^?]. The reaction of Ce(IV) with maleic acid and bromide ion is also first order with respect to Ce(IV). For [Ce(IV)]₀=5.0×10^?4 M, [MA]₀=0.75 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [Br^?]₀= (0.025–0.150)M, the pseudo-first-order rate constant (k₀₃) at 25° is k₀₃= (5.286±0.045)x10^?2[Br^?]²+(3.568±0.056)x10^?3[Br^?]. For [Ce(IV)]₀=5.0 × 10^?4 M, [Br^?]₀=0.050 M, [H₂SO₄]₀=1.2 M, μ=2.0 M, and [MA]₀=(0.15–1.0)M at 25°, k₀₃=(2.108×10^?4+2.127×10^?4[MA]₀)/(1+0.205[MA]₀). A mechanism is proposed to rationalize the results. The effect of temperature on the reaction rate was also studied. The energy barrier of Ce(IV)—Br^? reaction is much less than that of Ce(IV)—MA reaction. Maleic and fumaric acids have very different mass spectra. The mass spectrum of fumaric acid exhibits a strong metastable peak at m/e 66.5.     

Komplexone XLVI. EDTA-Komplexe des Pt(II)-Ions mit und ohne einzähnige Fremdliganden

The formation of complexes between Pt(II)EDTA^2? and H⁺, OH^?, Cl^?, Br^?, SCN^?, CN^? and NH₃ was investigated using pH and UV.-spectrophotometric measurements at ionic strength 1.0 and 25°. The existence of the following species could be proved (charges are omitted): H_pPt(EDTA) (0 ≤ p ≤ 3), Pt(EDTA)X (X = OH, NH₃, Cl, Br, I, SCN), H_pPt(EDTA)X (1 ≤ p ≤ 3; X = Cl, Br) and H₄Pt(EDTA)Cl₂. They have been characterised by spectral data as well as with equilibrium constants. The different modes of attachment of EDTA are discussed.     

Equilibrium,kinetics, and mechanism of the malonic acid–iodine reaction

The equilibrium constant for the reaction CH₂(COOH)₂ + I₃^? ? CHI(COOH)₂ + 2I^? + H⁺, measured spectrophotometrically at 25°C and ionic strength 1.00M (NaClO₄), is (2.79 ± 0.48) × 10^?4M². Stopped-flow kinetic measurements at 25°C and ionic strength 1.00M with [H⁺] = (2.09-95.0) × 10^?3M and [I^?] = (1.23-26.1) × 10^?3M indicate that the rate of the forward reaction is given by (k₁[I₂] + k₃[I₃^?]) [HOOCCH₂COO^?] + (k₂[I₂] + k₄[I₃^?]) [CH(COOH)₂] + k₅[H⁺] [I₃^?] [CH₂(COOH)₂]. The values of the rate constants k₁-k₅ are (1.21 ± 0.31) × 10², (2.41 ± 0.15) × 10¹, (1.16 ± 0.33) × 10¹, (8.7 ± 4.5) × 10^?1M^?1·sec^?1, and (3.20 ± 0.56) × 10¹M^?2·sec^?1, respectively. The rate of enolization of malonic acid, measured by the bromine scavenging technique, is given by k_en[CH₂(COOH)₂], with k_en = 2.0 × 10^?3 + 1.0 × 10^?2 [CH₂(COOH)₂]. An intramolecular mechanism, featuring a six-member cyclic transition state, is postulated to account for the results on the enolization of malonic acid. The reactions of the enol, enolate ion, and protonated enol with iodine and/or triodide ion are proposed to account for the various rate terms.     

Kinetic studies on the metal(II) tartarate–peroxomonosulfate reaction

The kinetics of oxidation of tartaric acid (TAR) by peroxomonosulfate (PMS) in the presence of Cu(II) and Ni(II) ions was studied in the pH range 4.05–5.20 and also in alkaline medium (pH ～12.7). The rate was calculated by measuring the [PMS] at various time intervals. The metal ions concentration range used in the kinetic studies was 2.50 × 10^?5 to 1.00 × 10^?4 M [Cu(II)], 2.50 × 10^?4 to 2.00 × 10^?3M [Ni(II)], 0.05 to 0.10 M [TAR], and µ = 0.15 M. The metal(II) tartarates, not TAR/tartarate, are oxidized by PMS. The oxidation of copper(II) tartarate at the acidic pH shows an appreciable induction period, usually 30–60 min, as in classical autocatalysis reaction. The induction period in nickel(II) tartarate is small. Analysis of the [PMS]–time profile shows that the reactions proceed through autocatalysis. In alkaline medium, the Cu(II) tartarate–PMS reaction involves autocatalysis whereas Ni(II) tartarate obeys simple first‐order kinetics with respect to [PMS]. The calculated rate constants for the initial oxidation (k₁) and catalyzed oxidation (k₂) at [TAR] = 0.05 M, pH 4.05, and 31°C are Cu(II) (1.00 × 10^?4 M): k₁ = 4.12 × 10^?6 s^?1, k₂ = 7.76 × 10^?1 M^?1s^?1 and Ni(II) (1.00 × 10^?3 M): k₁ = 5.80 × 10^?5 s^?1, k₂ = 8.11 × 10^?2 M^?1 s^?1. The results suggest that the initial reaction is the oxidative decarboxylation of the tartarate to an aldehyde. The aldehyde intermediate may react with the alpha hydroxyl group of the tartarate to give a hemi acetal, which may be responsible for the autocatalysis. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 620–630, 2011     

A new copper(I) thiocyanato thiocyanogen complex

The reaction between Cu²⁺ and SCN^?, in glacial acetic acid at a Cu/SCN ratio, of 1:4, gave a dark red solution that exhibited an absorption band at 496 nm. The colour of the freshly prepared solution was bleached by water with concomitant production of SO₄^2? ion. On standing, the stability of the colour towards water is increased and the position of the absorption band shifts to a higher wavelength. It is inferred that the thiocyanogen produced on oxidation of SCN^? by Cu²⁺ is stable in the non-aqueous medium and is coordinated together with SCN^? in a Cu(I) complex. The bleaching action of water is attributed to the hydrolysis of thiocyanogen, mainly to SO₄^2?. The presence of thiocyanogen enhanced polymerization and subsequent deposition of an orange-brown solid complex. On the basis of chemical, spectral, and thermal analyses the formula K[Cu(SCN)₂(NCS—SCN)], is assigned to the new compound.     

Rate constants for some reactions of inorganic radicals with inorganic ions. Temperature and solvent dependence

Rate constants for several reactions of inorganic radicals with inorganic anions in aqueous and aqueous/acetonitrile solutions have been measured as a function of temperature by laser flash photolysis. The reactions studied were (1) Cl₂^? + N₃^?, (2) Br₂^? + N₃^?, (3) Cl₂^? + SCN^?, (4) Br₂^? + SCN^?, (5) SO₄^? + Cl^?, (6) SO₄^? + CO₃^2?, and (7) N₃? + I^?. The rate constants were corrected for ionic strength and ranged from 10⁶ to 10⁹ L mol^?1 s^?1. The Arrhenius activation energies varied from 2 to 12 kJ mol^?1 for the first 4 reactions, were higher for reaction 6, and negative for reaction 5. The pre-exponential factors also varied considerably with log A ranging from 5 to 14. The values of k₂₉₈ decreased in most cases by more than an order of magnitude upon increasing the acetonitrile (ACN) fraction from 0 to 70%. For most reactions, this decrease in k₂₉₈ was due to changes in log A with little regularity in the small changes observed in E_a. For reaction 7, k₂₉₈ was practically unchanged due to compensating effects of the changes in E_a and log A with ACN mol fraction, giving an isokinetic relationship. An isokinetic relationship was also observed in the case of reaction 6; E_a and log A change in parallel while changing ACN mol fraction. Reaction 3 (Cl₂^? + SCN^?) was also studied in water/t-butanol and water/acetic acid mixtures. Linear correlation was found between log k and the dielectric constant of the medium for water/ACN and water/t-BuOH but the lines for the two solvent mixtures had different slopes, suggesting specific solvation effects in addition to the primary solvent polarity effects. With water/acetic acid, k decreased and then increased upon addition of acetic acid. © 1993 John Wiley & Sons, Inc.     

Kinetic studies of the reactions of pentacyanoferrate(III) complexes with L‐ascorbic acid

The reduction of Fe(CN)₅L^2? (L = pyridine, isonicotinamide, 4,4′‐bipyridine) complexes by ascorbic acid has been subjected to a detailed kinetic study in the range of pH 1–7.5. The rate law of the reaction is interpreted as a rate determining reaction between Fe(III) complexes and the ascorbic acid in the form of H₂A(k₀), HA^?(k₁), and A^2? (k₂), depending on the pH of the solution, followed by a rapid scavenge of the ascorbic acid radicals by Fe(III) complex. With given Ka₁ and Ka₂, the rate constants are k₀ = 1.8, 7.0, and 4.4 M^?1 s^?1; k₁ = 2.4 × 10³, 5.8 × 10³, and 5.3 × 10³ M^?1 s^?1; k₂ = 6.5 × 10⁸, 8.8 × 10⁸, and 7.9 × 10⁸ M^?1 s^?1 for L = py, isn, and bpy, respectively, at μ = 0.10 M HClO₄/LiClO₄, T = 25°C. The kinetic results are compatible with the Marcus prediction. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 37: 126–133, 2005     

La matrice eau de mer et le signal du cuivre en spectrometrie d'adsorption atomique sans flamme : Partie 1: Etude de l'influence des principaux composants

(Copper signals from seawater matrices in electrothermal atomic absorption spectrometry. Part 1: study of the effects of principal inorganic ions.)The effects of the main inorganic ions of seawater (Na⁺, Mg²⁺, Ca²⁺, Cl^?, SO^2?₄), and of nitrate as modifier, on the electrothermal atomic absorption spectrometric signal of copper are studied. Sodium chloride, sulfate or nitrate, magnesium chloride or nitrate, and calcium chloride can cause serious interferences. Thermal treatment at about 700°C prevents the interference of MgCl₂ by its hydrolysis. Ashing can be done without loss of copper at higher temperatures in the presence of sulfate salts (1300°C) and nitrate salts (1200°C) than in the presence of chloride salts (1100°C). This is ascribed to the stabilising effect of oxides and sulfides. A study of the influence of two-component matrices, MCl-MNO₃ or MCl-MSO₄, on the atomization signal of copper confirms this stabilizing effect which adds to the decrease in interference connected with removal of chloride in acidic medium.     

Laser-induced kinetics: Arrhenius parameters for t-C4H9 + XI → i-C4H9X + I (X = H,D) and the Heat of Formation of the t-butyl radical

The metathesis reaction of DI with t-C₄H₉ generated by 351-nm photolysis of 2,2′-azoisopropane was studied in a low-pressure reactor (VLP? Knudsen cell) in the temperature range of 302–411 K. The data obeyed the following Arrhenius relation when combined with recent data by Rossi and Golden gathered by the same technique (t-C₄H₉ by thermal decomposition of 2,2′-azoisobutane): log k₂^D(M^?1s^?1) = 9.60 – 1.90/θ, where θ = 2.303RT kcal/mol for 302 K < T > 722 K. The metathesis reaction of HI with t-C₄H₉ was studied at 301 K and resulted in k₂^H(M^?1·s^?1) = (3.20 ± 0.62) × 10⁸. An analogous Arrhenius relation was calculated for the protiated system if the small primary isotope effect k₂^H/k₂^D was assumed to be √2 at 700 K. It was of the following form: log k₂^H(M^?1·s^?1) = 9.73 – 1.68/θ. Preliminary data of Bracey and Walsh indicate that earlier Arrhenius parameters determined for the reverse reaction are somewhat in error. Their value of log k₁(M^?1·s^?1) = 11.5 – 23.8/θ yields 7delta;H_f,300⁰(t-butyl) = 9.2 kcal/mol and S₃₀₀⁰(t-butyl) = 74.2 cal/mol7°K when taken in conjuction with this study.     

Kinetics of the acid-catalyzed hydrolysis of tetraethoxysilane (TEOS) by <Superscript>29</Superscript>Si NMR spectroscopy and mathematical modeling

Tetraethoxysilane (TEOS) is widely used to synthesize siliceous material by the sol–gel process. However, there is still some disagreement about the nature of the limiting step in the hydrolysis and condensation reactions. The goal of this research was to measure the variation in the concentration of intermediates formed in the acid-catalyzed hydrolysis by ²⁹Si NMR spectroscopy, to model the reactions, and to obtain the rate constants and the activation energy for the hydrolysis and early condensation steps. We studied the kinetics of TEOS between pH 3.8 and 4.4, and four temperature values in the range of 277.2–313.2?K, with a TEOS:ethanol:water molar ratio of 1:30:20. Both hydrolysis and the condensation rate speeded up with the temperature and the concentration of oxonium ions. The kinetic constants for hydrolysis reactions increased in each step k_h1?<?k_h2?<?k_h3?<?k_h4, but the condensation rate was lower for dimer formation than for the formation of the fully hydrolyzed Si(OH)₄. The system was described according to 13 parameters: six of them for the kinetic constants estimated at 298.2?K, six to the activation energies, and one to the equilibrium constant for the fourth hydrolysis. The mathematical model shows a steady increase in the activation energy from 34.5?kJ?mol^?1 for the first hydrolysis to 39.2?kJ?mol^?1 in the last step. The activation energy for the condensation reaction from Si(OH)₄ was ca. 10?kJ?mol^?1 higher than the largest activation energy in the hydrolytic reactions. The decrease in the net positive charge on the Si atom contributes to the protonation of the ethoxy group and makes it a better leaving group.

Open image in new window

     

Kinetics and mechanism of hydrolysis of N‐(2′‐hydroxyphenyl)phthalamic acid (1) and N‐(2′‐methoxyphenyl)phthalamic Acid (2) in a highly alkaline medium

A kinetic study on hydrolysis of N‐(2′‐hydroxyphenyl)phthalamic acid ( 1 ), N‐(2′‐methoxyphenyl)phthalamic acid ( 2 ), and N‐(2′‐methoxyphenyl)benzamide ( 3 ) under a highly alkaline medium gives second‐order rate constants, k_OH, for the reactions of HO^? with 1, 2 , and 3 as (4.73 ± 0.36) × 10^?8 at 35°C, (2.42 ± 0.28) × 10^?6 and (5.94 ± 0.23) × 10^?5 M^?1 s^?1 at 65°C, respectively. Similar values of k_OH for 3 , N‐methylbenzanilide, N‐methylbenzamide, and N,N‐dimethylbenzamide despite the difference between pK_a values of aniline and ammonia of ～10 pK units are qualitatively explained. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 1–11, 2009     

Reactions of mer(exo)‐ and mer(endo)‐[Co(dien)(dapo)X]2+ Isomers (X=OH,Cl, ONO2, N3)

Properties indirectly determined, or alluded to, in previous publications on the titled isomers have been measured, and the results generally support the earlier conclusions. Thus, the common five‐coordinate intermediate generated in the OH^?‐catalyzed hydrolysis of exo‐ and endo‐[Co(dien)(dapo)X]²⁺ (X=Cl, ONO₂) has the same properties as that generated in the rapid spontaneous loss of OH^? from exo‐ and endo‐[Co(dien)(dapo)OH]²⁺ (40±2% endo‐OH, 60±2% exo‐OH) and an unusually large capacity for capturing (R=[CoN₃]/[CoOH][]=1.3; exo‐[CoN₃]/endo‐[CoN₃]=2.1±0.1). Solvent exchange for spontaneous loss of OH^? from exo‐[Co(dien)(dapo)OH]²⁺ has been measured at 0.04 s^?1 (k₁, 0.50M NaClO₄, 25°) from which similar loss from the endo‐OH isomer may be calculated as 0.24 s^?1 (k₂). The OH^?‐catalyzed reactions of exo‐ and endo‐[Co(dien)(dapo)N₃]²⁺ result in both hydrolysis of coordinated via an OH^?‐limiting process =153 M ^?1 s^?1; =295 M ^?1 s^?1; K_H=1.3±0.1 M ^?1; 0.50M NaClO₄, 25.0°) and direct epimerization between the two reactants =33 M ^?1 s^?1; =110 M ^?1 s^?1; 1.0M NaClO₄, 25.0°). Comparisons are made with other rapidly reacting Co^III‐acido systems.     

Effects of alkyltrimethylammonium bromide surfactants on the kinetics of the oxidation of tris(1,10-phenanthroline)iron(II) by azido-pentacyanocobaltate(III) complex

The redox reaction between tris(1,10-phenanthroline)iron(II), [Fe(phen)₃]²⁺, and azido-pentacyanocobaltate(III), [Co(CN)₅N₃]^3? was investigated in three cationic surfactants: dodecyltrimethylammonium bromide (DTAB), tetradecyltrimethylammonium bromide (TTAB) and cetyltrimethylammonium bromide (CTAB) in the presence of 0.1?M NaCl at 35°C. Second-order rate constant in the absence and presence of surfactant, k_w and k_ψ, respectively, were obtained in the concentration ranges DTAB?=?0???4.667?×?10^?4?mol?dm^?3, TTAB?=?0–9.364?×?10^?5?mol?dm^?3, CTAB?=?0???6.220?×?10^?5?mol?dm^?3. Electron transfer rate was inhibited by the surfactants with premicelllar activity. Inhibition factors, k_w/k_ψ followed the trend CTAB?>?TTAB?>?DTAB with respect to the surfactant concentrations used. The magnitudes of the binding constants obtained suggest significant electrostatic and hydrophobic interactions. Activation parameters ΔH^≠, ΔS^≠, and E_a have larger positive values in the presence of surfactants than in surfactant-free medium. The electron transfer is proposed to proceed via outer-sphere mechanism in the presence of the surfactants.     

The carbon–hydrogen bond strength in dimethyl ether and some properties of iodomethyl methyl ether

The kinetics and mechanism of the reaction between iodine and dimethyl ether (DME) have been studied spectrophotometrically from 515–630°K over the pressure ranges, I₂ 3.8–18.9 torr and DME 39.6–592 torr in a static system. The rate-determining step is, where k₁ is given by log (k₁/M^?1 sec^?1) = 11.5 ± 0.3 – 23.2 ± 0.7/θ, with θ = 2.303RT in kcal/mole. The ratio k₂/k_?1, is given by log (k₂/k_?1) = ?0.05 ± 0.19 + (0.9 ± 0.45)/θ, whence the carbon-hydrogen bond dissociation energy, DH° (H? CH₂OCH₃) = 93.3 ± 1 kcal/mole. From this, ΔH°_f(CH₂OCH₃) = ?2.8 kcal and DH°(CH₃? OCH₂) = 9.1 kcal/mole. Some nmr and uv spectral features of iodomethyl ether are reported.     

Kinetic study of the reactions of atomic chlorine with several volatile organic compounds at 240–340 K

The rate constant for the reactions of atomic chlorine with 1,4‐dioxane (k₁), cyclohexane (k₂), cyclohexane‐d₁₂(k₃), and n‐octane (k₄) has been determined at 240–340 K using the relative rate/discharge fast flow/mass spectrometer (RR/DF/MS) technique developed in our laboratory. Essentially, no temperature dependence for these reactions was observed over this temperature range, with an average of k₁ = (1.91 ± 0.20) × 10^?10 cm³ molecule^?1 s^?1, k₂ = (2.91 ± 0.31) × 10^?10 cm³ molecule^?1 s^?1, k₃ = (2.73 ± 0.30) × 10^?10 cm³ molecule^?1 s^?1, and k₄ = (3.22 ± 0.36) × 10^?10 cm³ molecule^?1 s^?1, respectively. The kinetic isotope effect of the reaction of cyclohexane with atomic chlorine has also been determined to be 1.14 by directly monitoring the decay of both cyclohexane and cyclohexane‐d₁₂ in the presence of chlorine atoms, which is consistent with the literature value of 1.20. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 38: 386–398, 2006