A laser flash photolysis kinetic study of reactions of the Cl2− radical anion with oxygenated hydrocarbons in aqueous solution

A laser photolysis–long path laser absorption (LP‐LPLA) experiment has been used to determine the rate constants for H‐atom abstraction reactions of the dichloride radical anion (Cl₂⁻) in aqueous solution. From direct measurements of the decay of Cl₂⁻ in the presence of different reactants at pH = 4 and I = 0.1 M the following rate constants at T = 298 K were derived: methanol, (5.1 ± 0.3)·10⁴ M⁻¹ s⁻¹; ethanol, (1.2 ± 0.2)·10⁵ M⁻¹ s⁻¹; 1‐propanol, (1.01 ± 0.07)·10⁵ M⁻¹ s⁻¹; 2‐propanol, (1.9 ± 0.3)·10⁵ M⁻¹ s⁻¹; tert.‐butanol, (2.6 ± 0.5)·10⁴ M⁻¹ s⁻¹; formaldehyde, (3.6 ± 0.5)·10⁴ M⁻¹ s⁻¹; diethylether, (4.0 ± 0.2)·10⁵ M⁻¹ s⁻¹; methyl‐tert.‐butylether, (7 ± 1)·10⁴ M⁻¹ s⁻¹; tetrahydrofuran, (4.8 ± 0.6)·10⁵ M⁻¹ s⁻¹; acetone, (1.41 ± 0.09)·10³ M⁻¹ s⁻¹. For the reactions of Cl₂⁻ with formic acid and acetic acid rate constants of (8.0 ± 1.4)·10⁴ M⁻¹ s⁻¹ (pH = 0, I = 1.1 M and T = 298 K) and (1.5 ± 0.8) · 10³ M⁻¹ s⁻¹ (pH = 0.42, I = 0.48 M and T = 298 K), respectively, were derived. A correlation between the rate constants at T = 298 K for all oxygenated hydrocarbons and the bond dissociation energy (BDE) of the weakest C‐H‐bond of log k_2nd = (32.9 ± 8.9) − (0.073 ± 0.022)·BDE/kJ mol⁻¹ is derived. From temperature‐dependent measurements the following Arrhenius expressions were derived: k (Cl₂⁻ + HCOOH) = (2.00 ± 0.05)·10¹⁰·exp(−(4500 ± 200) K/T) M⁻¹ s⁻¹, E_a = (37 ± 2) kJ mol⁻¹ k (Cl₂⁻ + CH₃COOH) = (2.7 ± 0.5)·10¹⁰·exp(−(4900 ± 1300) K/T) M⁻¹ s⁻¹, E_a = (41 ± 11) kJ mol⁻¹ k (Cl₂⁻ + CH₃OH) = (5.1 ± 0.9)·10¹²·exp(−(5500 ± 1500) K/T) M⁻¹ s⁻¹, E_a = (46 ± 13) kJ mol⁻¹ k (Cl₂⁻ + CH₂(OH)₂) = (7.9 ± 0.7)·10¹⁰·exp(−(4400 ± 700) K/T) M⁻¹ s⁻¹, E_a = (36 ± 5) kJ mol⁻¹ Finally, in measurements at different ionic strengths (I) a decrease of the rate constant with increasing I has been observed in the reactions of Cl₂⁻ with methanol and hydrated formaldehyde. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 169–181, 1999     

Absolute rate constants for the addition of hydroxymethyl radicals to alkenes in methanol solution

Absolute rate constants and their temperature dependencies were determined for the addition of hydroxymethyl radicals (CH₂OH) to 20 mono- or 1,1-disubstituted alkenes (CH₂ = CXY) in methanol by time-resolved electron spin resonance spectroscopy. With the alkene substituents the rate constants at 298 K (k₂₉₈) vary from 180 M^?1s^?1 (ethyl vinylether) to 2.1 middot; 10⁶ M^?1s^?1 (acrolein). The frequency factors obey log A/M^?1s^?1 = 8.1 ± 0.1, whereas the activation energies (E_a) range from 11.6 kJ/mol (methacrylonitrile) to 35.7 kJ/mol (ethyl vinylether). As shown by good correlations with the alkene electron affinities (EA), log k₂₉₈/M^?1s^?1 = 5.57 + 1.53 · EA/eV (R² = 0.820) and E_a = 15.86 ? 7.38 · EA/eV (R² = 0.773), hydroxymethyl is a nucleophilic radical, and its addition rates are strongly influenced by polar effects. No apparent correlation was found between E_a or log k₂₉₈ with the overall reaction enthalpy. © 1995 John Wiley & Sons, Inc.     

A consistent model for the thermal decomposition of NCN3 and the singlet– triplet relaxation of NCN

The thermal decomposition of cyanogen azide (NCN₃) and the subsequent collision‐induced intersystem crossing (CIISC) process of cyanonitrene (NCN) have been investigated by monitoring excited electronic state ¹NCN and ground state ³NCN radicals. NCN was generated by the pyrolysis of NCN₃ behind shock waves and by the photolysis of NCN₃ at room temperature. Falloff rate constants of the thermal unimolecular decomposition of NCN₃ in argon have been extracted from ¹NCN concentration–time profiles in the temperature range 617 K <T< 927 K and at two different total densities: k(ρ ≈ 3 × 10^?6 mol/cm³)/s^?1=4.9 × 10⁹ × exp (?71±14 kJ mol^?1/RT) (± 30%); k(ρ ≈ 6 × 10^?6 mol/cm³)/s^?1=7.5 × 10⁹ × exp (‐71±14 kJ mol^?1/RT) (± 30%). In addition, high‐temperature ¹NCN absorption cross sections have been determined in the temperature range 618 K <T< 1231 K and can be expressed by σ /(cm²/mol)= 1.0 × 10⁸ ?6.3 × 10⁴ K^?1 × T (± 50%). Rate constants for the CIISC process have been measured by monitoring ³NCN in the temperature range 701 K <T< 1256 K resulting in k_CIISC (ρ ≈ 1.8 ×10^?6 mol/cm³)/ s^?1=2.6 × 10⁶× exp (‐36±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 3.5×10^?6 mol/cm³)/ s^?1 = 2.0 × 10⁶ × exp (?31±10 kJ mol^?1/RT) (± 20%), k_CIISC (ρ ≈ 7.0×10^?6 mol/cm³)/ s^?1=1.4 × 10⁶ × exp (?25±10 kJ mol^?1/RT) (± 20%). These values are in good agreement with CIISC rate constants extracted from corresponding ¹NCN measurements. The observed nonlinear pressure dependences reveal a pressure saturation effect of the CIISC process. © 2012 Wiley Periodicals, Inc. Int J Chem Kinet 45: 30–40, 2013     

Temperature dependence of the rate constants of the reactions of oxygen atoms with 1-pentene, 1-hexene,cis-2-pentene,and trans-2-pentene

The kinetics of the reactions of ground state oxygen atoms with 1-pentene, 1-hexene, cis-2-pentene, and trans-2-pentene was investigated in the temperature range 200 to 370 K. In this range the temperature dependences of the rate constants can be represented by k = A′ Tⁿ exp(− E′_a/RT) with A′ = (1.0 ± 0.6) · 10⁻¹⁴ cm³ s⁻¹, n = 1.13 ± 0.02, E′_a = 0.54 ± 0.05 kJ mol⁻¹ for 1-pentene: A′ = (1.3 ± 1.2) · 10⁻¹⁴ cm³ s⁻¹, n = 1.04 ± 0.08, E′_a = 0.2 ± 0.4 kJ mol⁻¹ for 1-hexene; A′ = (0.6 ± 0.6) · 10⁻¹⁴ cm³ s⁻¹, n = 1.12 ± 0.05, E′_a = − 3.8 ± 0.8 kJ mol⁻¹ for cis-2-pentene; and A′ = (0.6 ± 0.8) · 10⁻¹⁴ cm³ s⁻¹, n = 1.14 ± 0.06, E′_a = − 4.3 ± 0.5 kJ mol⁻¹ for trans-2-pentene. The atoms were generated by the H₂-laser photolysis of NO and detected by time resolved chemiluminescence in the presence of NO. The concentrations of the O(³P) atoms were kept so low that secondary reactions with products are unimportant. © 1997 John Wiley & Sons, Inc.     

The cationic polymerization of fluoral—III. Thermodynamics of polymerization in solution

The equilibrium between fluoral in dichloromethane solution and live condensed liquid polyfluoral has been investigated between 22 and 43°C. Equilibrium monomer concentrations gave: ΔH_ac°(298 K) = -50-8 ± 2·3 kJ mol^?1 and ΔS_sc° (298 K) = -142·7 ± 7·4 J K^-1 mol^-1. With the aid of calibration and monomer vaporization data, thermodynamic values for the polymerization of liquid monomer to liquid polymer were also calculated: ΔH_tc° (298 K) = -47 ± 3 kJ mol^-1 and ΔS_1e° (298 K) = -97 ± 10 J K^-1 mol^-1.     

Kinetics and mechanism of the oxygenation of potassium nitronates. Evidence for a single electron transfer (SET) mechanism ??

Summary The oxygenation of the potassium salts of alkylnitronates in absolute DMSO leads to potassium nitrite (nitrate) and the corresponding aldehydes or ketones at 40°C. Kinetic measurements for potassium 1-propylnitronate (K-1-PN) resulted in the rate law -d[K-1-PN]/dt = k₂[K-1-PN][O₂]. The rate constant, activation enthalpy, and entropy at 313.16 K are as follows: k/M^-1 s^-1 = (1.43±0.04), DH^‡/kJ mol^-1 = 57±10 DS^‡/J mol^-1 K^-1 = -60±32. The presence of superoxide ion as a result of a SET from the nitronate to dioxygen was proved by NBT test.     

Preparation and Diels-Alder Reactivity of 2,3,5,6,7,8-Hexamethylidenebicyclo [2.2.2]octane (‘[2.2.2]Hericene’). Force-field calculations of exocyclic dienes as a moiety of bicyclic skeletons

The [2.2.2]hericene ( 6 ), a bicyclo[2.2.2]octane bearing three exocyclic s-cis-butadiene units has been prepared in eight steps from coumalic acid and maleic anhydride. The hexaene 6 adds successively three mol-equiv. of strong dienophiles such as ethylenetetracarbonitrile (TCE) and dimethyl acetylenedicarboxylate (DMAD) giving the corresponding monoadducts 17 and 20 (k₁), bis-adducts 18 and 21 (k₂) and tris-adducts 19 and 22 (k₃), respectively. The rate constant ratio k₁/k₂ is small as in the case of the cycloadditions of 2,3,5,6-tetramethylidene-bicyclo [2.2.2]octane ( 3 ) giving the corresponding monoadducts 23 and 27 (k₁) and bis-adducts 25 and 29 (k₂) with TCE and DMAD, respectively. Constrastingly, the rate constant ratio k₂/k₃ is relatively large as the rate constant ratio k₁/k₂ of the Diels-Alder additions for 5,6,7,8-tetramethylidenebicyclo [2.2.2]oct-2-ene ( 4 ) giving the corresponding monoadducts 24 and 28 (k₁) and bis-adducts 26 and 30 (k₂). The following second-order rate constants (toluene, 25°) and activation parameters were obtained for the TCE additions: 3 +TCE→ 23 : k₁ = 0.591±0.012 mol^?1·l·s^?1, ΔH^≠=10.6±0.4 kcal/mol, and ΔS^≠ = ?24.0±1.4 cal/mol·K (e.u.); 23 +TCE→ 25 : k₂=0.034±0.0010 mol^?1·l·s^?1, ΔH^≠ = 10.6±0.6 kcal/mol, and ΔS^≠ = ?29.7±2.0 e.u.; 4 +TCE→ 26 : k₁ = 0.172±0.035 mol^?1·l·s^?1, ΔH^≠ 11.3±0.8 kcal/mol, and ΔS^≠ = ?24.0±2.8 e.u.; 24 +TCE→ 26 : k₂ = (6.1±0.2)·10^?4 mol^?1·l·s^?1, ΔH^≠ = 13.0±0.3 kcal/mol, and ΔS^≠ = ?29.5±0.8 e.u.; 6 +TCE→ 17 : k₁ = 0.136±0.002 mol^?1·l·s^?1, ΔH^≠ = 11.3±0.2 kcal/mol, and ΔS^≠ = ?24.5±0.8 e.u.; 17 +TCE→ 18 : k₂ = 0.0156±0.0003 mol^?1·l·s^?1, ΔH^≠ = 10.9±0.5 kcal/mol, and ΔS^≠ = ?30.1 ± 1.5 e.u.; 18 +TCE→ 19 : k₃=(5±0.2) · 10^?5 mol^?1 mol^?1 ·l·s^?1, ΔH^≠ = 15±3 kcal/mol, and ΔS^≠ = ?28 ± 8 e.u. The following rate constants were evaluated for the DMAD additions (CD₂Cl₂, 30°): 6 +DMAD→ 20 : k₁ = (10±1)·10^?4 mol^?1 · l·s^?1; 20 +DMAD→ 21 : k₂ = (6.5±0.1) · 10^?4 mol^?1 ·l·^?1; 21 +DMAD→ 22 : k₃ = (1.0±0.1) · 10^?4 mol^?1 ·l·s^?1. The reactions giving the barrelene derivatives 19, 22, 26 and 30 are slower than those leading to adducts that are not barrelenes. The former are estimated less exothermic than the latter. It is proposed that the Diels-Alder reactivity of exocyclic s-cis-butadienes grafted onto bicycle [2.2.1]heptanes and bicyclo [2.2.2]octanes that are modified by remote substitution of the bicyclic skeletons can be affected by changes inthe exothermicity of the cycloadditions, in agreement with the Dimroth and Bell-Evans-Polanyi principle. Force-field calculations (MMPI 1) of 3, 4, 6 and related exocyclic s-cis-butadienes as a moiety of bicyclo [2.2.2]octane suggested single minimum energy hypersurfaces for these systems (eclipsed conformations, planar dienes). Their flexibility decreases with the degree of unsaturation of the bicyclic skeleton. The effect of an endocyclic double bond is larger than that of an exocyclic diene moiety.     

Kinetic study of the ligand substitution on the trimethylplatinum(iv) complexes with unidentate ligands

Ligand substitution kinetics for the reaction [Pt^IVMe₃(X)(NN)]+NaY=[Pt^IVMe₃(Y)(NN)]+NaX, where NN=bipy or phen, X=MeO⁻, CH₃COO⁻, or HCOO⁻, and Y=SCN⁻ or N₃⁻, has been studied in methanol at various temperatures. The kinetic parameters for the reaction are as follows. The reaction of [PtMe₃(OMe)(phen)] with NaSCN: k₁=36.1±10.0 s⁻¹; ΔH₁^≠=65.9±14.2 kJ mol⁻¹; ΔS₁^≠=6±47 J mol⁻¹ K⁻¹; k₋₂=0.0355±0.0034 s⁻¹; ΔH₋₂^≠=63.8±1.1 kJ mol⁻¹; ΔS₋₂^≠=−58.8±3.6 J mol⁻¹ K⁻¹; and k₋₁/k₂=148±19. The reaction of [PtMe₃(OAc)(bipy)] with NaN₃: k₁=26.2±0.1 s⁻¹; ΔH₁^≠=60.5±6.6 kJ mol⁻¹; ΔS₁^≠=−14±22 J mol⁻¹K⁻¹; k₋₂=0.134±0.081 s⁻¹; ΔH₋₂^≠=74.1±24.3 kJ mol⁻¹; ΔS₋₂^≠=−10±82 J mol⁻¹K⁻¹; and k₋₁/k₂=0.479±0.012. The reaction of [PtMe₃(OAc)(bipy)] with NaSCN: k₁=26.4±0.3 s⁻¹; ΔH₁^≠=59.6±6.7 kJ mol⁻¹; ΔS₁^≠=−17±23 J mol⁻¹K⁻¹; k₋₂=0.174±0.200 s⁻¹; ΔH₋₂^≠=62.7±10.3 kJ mol⁻¹; ΔS₋₂^≠=−48±35 J mol⁻¹K⁻¹; and k₋₁/k₂=1.01±0.08. The reaction of [PtMe₃(OOCH)(bipy)] with NaN₃: k₁=36.8±0.3 s⁻¹; ΔH₁^≠=66.4±4.7 kJ mol⁻¹; ΔS₁^≠=7±16 J mol⁻¹K⁻¹; k₋₂=0.164±0.076 s⁻¹; ΔH₋₂^≠=47.0±18.1 kJ mol⁻¹; ΔS₋₂^≠=−101±61 J mol⁻¹ K⁻¹; and k₋₁/k₂=5.90±0.18. The reaction of [PtMe₃(OOCH)(bipy)] with NaSCN: k₁ =33.5±0.2 s⁻¹; ΔH₁^≠=58.0±0.4 kJ mol⁻¹; ΔS₁^≠=−20.5±1.6 J mol⁻¹ K⁻¹; k₋₂=0.222±0.083 s⁻¹; ΔH₋₂^≠=54.9±6.3 kJ mol⁻¹; ΔS₋₂^≠=−73.0±21.3 J mol⁻¹ K⁻¹; and k₋₁/k₂=12.0±0.3. Conditional pseudo-first-order rate constant k₀ increased linearly with the concentration of NaY, while it decreased drastically with the concentration of NaX. Some plausible mechanisms were examined, and the following mechanism was proposed. [Note to reader: Please see article pdf to view this scheme.] © 1998 John Wiley & Sons, Inc. Int J Chem Kinet 30: 523–532, 1998     

Rate constant for the reaction of OH radicals with CH3C(O)Cl determined by direct kinetic method

Summary The fast flow technique with OH resonance fluorescence detection has been applied at T = 298 ± 2 K to study the kinetics of the overall reaction: H + CH₃C(O)Cl → products (1) A rate constant value of k₁ = (1.02 ± 0.12) x 10¹⁰ cm³ mol^-1 s^-1 has been determined which is the first direct kinetic parameter reported for reaction (1) in the literature (the error given refers to 2σ accuracy).     

Kinetics and mechanism of the reduction of monochloramine by hydroxylamine and hydroxylammonium ion

The kinetics and mechanism by which monochloramine is reduced by hydroxylamine in aqueous solution over the pH range of 5–8 are reported. The reaction proceeds via two different mechanisms depending upon whether the hydroxylamine is protonated or unprotonated. When the hydroxylamine is protonated, the reaction stoichiometry is 1:1. The reaction stoichiometry becomes 3:1 (hydroxylamine:monochloramine) when the hydroxylamine is unprotonated. The principle products under both conditions are Cl^–, NH⁺₄, and N₂O. The rate law is given by ?[d[NH₂Cl]/dt] = k₊[NH₃OH⁺][NH₂Cl] + k₀[NH₂OH][NH₂Cl]. At an ionic strength of 1.2 M, at 25°C, and under pseudo‐first‐order conditions, k₊= (1.03 ± 0.06) ×10³ L · mol^?1 · s^?1 and k₀=91 ± 15 L · mol^?1 · s^?1. Isotopic studies demonstrate that both nitrogen atoms in the N₂O come from the NH₂OH/NH₃OH⁺. Activation parameters for the reaction determined at pH 5.1 and 8.0 at an ionic strength of 1.2 M were found to be ΔH? = 36 ± 3 kJ · mol^–1 and Δ S? = ?66 ± 9 J · K^?1 · mol^?1, and Δ H? = 12 ± 2 kJ · mol^?1 and Δ S? = ?168 ± 6 J · K^?1 · mol^?1, respectively, and confirm that the transition states are significantly different for the two reaction pathways. © 2005 Wiley Periodicals, Inc. Int J Chem Kinet 38: 124–135, 2006     

Study of the reactions of OH with HCl,HBr, and HI between 298 K and 460 K

The reactions between OH radicals and hydrogen halides (HCl, HBr, HI) have been studied between 298 and 460 K by using a discharge flow-electron paramagnetic resonance technique. The rate constants were found to be k_HCl(298 K) = (7.9 ± 1.3) × 10⁻¹³ cm³ molecule⁻¹ s⁻¹ with a weak positive temperature dependence, k_HBr (298-460 K) = (1.04 ± 0.2) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, and k_HI(298 K) = (3.0 ± 0.3) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹, respectively. The homogeneous nature of these reactions has been experimentally tested.     

Rate constants for the addition of the 2-hydroxy-2-propyl radical to alkenes in solution

Absolute rate constants for the addition of the 2-hydroxy-2-propyl radical to 18 substituted alkenes (CH₂ = CXY) were determined at (296 ± 1) K in 2-propanol by time-resolved electronspin-resonance spectroscopy. With alkene substitution the rate constants vary by more than 6 orders of magnitude. For 3,3-dimethyl-but-1-ene the temperature dependence is given by log k/M^?1 · s^?1 = 6.4 minus;; 19.1/Θ where Θ = 2.303 RT in kJ/mol^?1. As shown by a good correlation with the alkene electron affinities, log k₂₉₆/M^?1 · s^?1 = 6.46 + 1.71 · EA/eV (r = 0.930), 2-hydroxy-2-propyl is a very nucleophilic radical, and its addition rates are highly governed by polar effects. © 1993 John Wiley & Sons, Inc.     

Experimental study of the kinetics of reaction of chlorine atoms with tetrahydrofuran and fully deuterated tetrahydrofuran

The overall rate constants for H-abstraction (k_H) from tetrahydrofuran and D-abstraction (k_D) from fully deuterated tetrahydrofuran by chlorine atoms in the temperature range of 298-547 K were determined. In both cases, very weak negative temperature dependences of the overall rate constants were observed, described by the expressions: k_H = (1.55 ± 0.13) × 10⁻¹⁰ exp(52 ± 28/T) cm³ molecule⁻¹ s⁻¹ and k_D = (1.27 ± 0.25) × 10⁻¹⁰exp(55 ± 62/T) cm³ molecule⁻¹ s⁻¹. The experimental results show that the value of the kinetic isotope effect (k_H/k_D), amounting to 1.21 ± 0.10, is temperature independent at 298-547 K.     

Rate constant for the reaction CH3CO?+ HBr and the enthalpy of formation of the CH3CO?radical

Summary Pulsed laser photolysis coupled with time-resolved UV-absorption monitoring of CH₃CO^•radicals was applied to obtain the rate constant, k₁, for the reaction CH₃CO^•+ HBr → CH₃C(O)H + Br (1); k₁(298 K) = (3.59 ± 0.23 (2σ))x10^-12cm³molecule^-1s^-1. Utilization of k₁in a third law procedure has provided the standard enthalpy of formation value ofD_fH°₂₉₈(CH₃CO^•) = -10.04 ± 1.10 (2σ) kJ mol^-1in excellent agreement with a very recent IUPAC recommendation.     

Polymorphism of paracetamol

The thermodynamic relationship between crystal modifications of paracetamol was studied by alternative methods. Temperature dependence of saturated vapor pressure for polymorphic modifications of the drug paracetamol (acetaminophen) was mea sured and thermodynamic functions of the sublimation process calculated. Solution calorimetry was carried out for the two modifications in the same solvent. Thermodynamic parameters for sublimation for form I (monoclinic) were found: ΔG _sub²⁹⁸=60.0 kJ mol⁻¹; ΔH _sub²⁹⁸=117.9±0.7 kJ mol⁻¹; ΔS _sub²⁹⁸=190±2 J mol⁻¹ K⁻¹. For the orthorhombic modification (form II), the saturated vapor pressure could only be studied at 391 K. Phase transition enthalpy at 298 K, ΔH _tr²⁹⁸(I→II)=2.0±0.4 kJ mol⁻¹, was derived as the difference between the solution enthalpies of the noted polymorphs in the same solution (methanol). Based on ΔH _tr²⁹⁸ (I→II), differences between temperature dependencies of heat capacities of both modifications and the vapor pressure value of form II at 391 K, the temperature dependence of saturated vapor pressure and thermodynamic sublimation parameters for modification II were also estimated (ΔG _sub²⁹⁸=56.1 kJ mol⁻¹; ΔH _sub²⁹⁸=115.9±0.9 kJ mol⁻¹; ΔS _sub²⁹⁸=200±3 J mol⁻¹ K⁻¹). The results indicate that the modifications are monotropically related, which is in contrast to findings recently reported found by classical thermochemical methods.     

The recombination of iodine atoms in the presence of nitric oxide

The recombination of iodine atoms following the flash photolysis of iodine in the presence of nitric oxide is interpreted through the mechanism with k₁ = 3.5 × 10⁹ l.²/mol²·sec; k₂ ≈ 1 × 10¹¹ l./mol·sec; k₃ = 2.1 × 10⁷ l./mol·sec at 298°K; E₃ = 11 kJ/ mol; and ΔH°₁ = 76 ± 6 kJ/mol. Lower and upper limits for the equilibrium constant are also established. The absorption spectrum of INO has been extended down to 223 nm and extinction coefficients for the region of 223–310 nm and 360–460 nm have been measured.     

Rate constant and activation energy for the gaseous reaction between hydroxyl and formaldehyde

The rate constant k₄ has been measured at 268°, 298°, and 334° K for the reaction CH₂O + 2OH → CO + 2H₂O relative to that for OH + OH (k₂) by competition experiments in a discharge flow tube using mass-spectrometric analysis. Based on k₂ = 2.24 × 10^?12cm³/molec·sec at 298°K and E₂ = 4 kJ/mol, k₄ = (6.5 ± 1.5) × 10^?12cm³/molec·sec at 298°K and E₄ = (6 ± 2)kJ/mol.     

THE MECHANISM OF THE 9,10-DIBROMOANTHRACENE MEDIATED TRIPLET-SINGLET ENERGY TRANSFER IN THE TETRAMETHYL-1,2-DIOXETANE ENERGIZED RUBRENE LUMINESCENCE*

Abstract— The ternary chemiluminescent system consisting of tetramethyl-dioxetane (TMD), 9 ,10-dibromoanthracene (DBA) and rubrene (Ru) has been investigated in benzene solution and in polystyrene matrices. DBA has been found to mediate the energy transfer between excited triplet acetone (³K), generated from TMD, and rubrene resulting in the enhancement of the Ru emission and reduction in the DBA emission. A detailed kinetic analysis confirms that ca. 50% of the enhanced chemilumines-cence involves triplet-singlet (TS) energy transfer from ³K to DBA, followed by singlet-singlet (SS) energy transfer from DBA to Ru, the remainder ca. 50% being due to reabsorption of DBA fluorescence by rubrene. It is concluded that the TS energy transfer is of the resonance type, occurring with a rate of k^TS_K.DBA= (1.4 ± 0.4) ± 10⁹M^-1s^-1 and an efficiency of ø^TS_K.DBA= 0.3 ± 0.1. As expected, the SS energy transfer is also of the resonance type, taking place at comparable rates in benzene solution and in polystyrene matrices, is. k^SS_DBARU= 1.5 ± 10¹⁰ M^-1 and (2.2 ± 0.2) ± 10¹⁰M^-1s^-1, respectively.     

Kinetic Studies on the Reaction of Sodium Hexacyanoferrate（ll） Complex with Peroxydisulfate Anion

The oxidation of Na₄Fe(CN)₆ complex by S₂O anion was found to follow an outer‐sphere electron transfer mechanism. We firstly carried out the reaction at pH=1. The specific rate constants of the reaction, k_ox, are (8.1±0.07)×10^?2 and (4.3±0.1)×10^?2 mol^?1·L·s^?1 at μ=1.0 mol·L^?1 NaClO₄, T=298 K for pH=1 (0.1 mol·L^?1 HCl0₄) and 8, respectively. The activation parameters, obtained by measuring the rate constants of oxidation 283–303 K, were ΔH^≠=(69.0±5.6) kJ·mol^?1, ΔS^≠=(?0.34±0.041)×10² J·mol^?1·K^?1 at pH=l and ΔH^≠=(41.3±5.5) kJ·mol^?1, ΔS^≠=(?1.27±0.33)×10² J·mol^?1·K^?1 at pH=8, respectively. The cyclic voltammetry of Fe(CN) shows that the oxidation is a one‐electron reversible redox process with E_1/2 values of 0.55 and 0.46 V vs. normal hydrogen electrode at μ=1.0 mol·L^?1 LiClO₄, for pH=1 and pH=8 (Tris). respectively. The kinetic results were discussed on the basis of Marcus theory.     

Synthesis and Diels-Alder Reactivity of 2,3,5,6-Tetramethylidenenorbornane

Pd-catalyzed double carbomethoxylation of the Diels-Alder adduct of cyclo-pentadiene and maleic anhydride yielded the methyl norbornane-2,3-endo-5, 6-exo-tetracarboxylate ( 4 ) which was transformed in three steps into 2,3,5,6-tetramethyl-idenenorbornane ( 1 ). The cycloaddition of tetracyanoethylene (TCNE) to 1 giving the corresponding monoadduct 7 was 364 times faster (toluene, 25°) than the addition of TCNE to 7 yielding the bis-adduct 9 . Similar reactivity trends were observed for the additions of TCNE to the less reactive 2,3,5,6-tetramethylidene-7-oxanorbornane ( 2 ). The following second order rate constants (toluene, 25°) and activation parameters were obtained for: 1 + TCNE → 7 : k₁ = (255 + 5) 10^?4 mol^?1 · s^?1, ΔH≠ = (12.2 ± 0.5) kcal/mol, ΔS≠ = (?24.8 ± 1.6) eu.; 7 + TCNE → 9 , k₂ = (0.7 ± 0.02) 10^?4 mol^?1 · s^?1, ΔH≠ = (14.1 ± 1.0) kcal/mol, ΔS≠ = ( ?30 ± 3.5) eu.; 2 + TCNE → 8 : k₁ = (1.5 ± 0.03) 10^?4 mol^?1 · s^?1, ΔH≠ = (14.8 ± 0.7) kcal/mol, ΔS≠ = (?26.4 ± 2.3) eu.; 8 + TCNE → 10 ; k₂ = (0.004 ± 0.0002) 10^?4 mol^?1 · s^?1, ΔH≠ = (17 ± 1.5) kcal/mol, ΔS≠ = (?30 ± 4) eu. The possible origins of the relatively large rate ratios k₁/k₂ are discussed briefly.