Solvent deuterium isotope effect on hydrolysis of Pb(II)

The formation constants of the hydrolysis species of Pb(II) ion in D₂O and H₂OD₂O mixtures containing 3 mol dm⁻³ LiClO₄ were determined at 25°C by potentiometric titrations. The formation constants β_p,q are smaller in D₂O than in H₂O, while the formation constants expressed by K_p,q in D₂O have larger values than those in H₂O. These results are consistent with those previously reported, which indicates that there exist some isotope effects other than that ascribed to the difference between ionic products of H₂O and D₂O. The formation constant of the tetramer Pb₄(OL)₄⁴⁺ (L denotes H and D) decreased monotonously with the increase in the deuterium atom fraction. This variation was quantitatively interpreted in terms of the equilibrium theory of solvent deuterium isotope effects.     

Kinetic study of the isotope exchange reactions of malonic acid and its derivatives in various acidic D2O media using 1H NMR spectroscopy. Implication in the Belousov‐Zhabotinsky reaction

The kinetics of the isotope exchange reactions of RCH(COOH)₂ (RH, D, Me, Et, Bu, and Ph) in D₂O solution were studied by using ¹H NMR spectroscopy. It was observed that the rate of isotope exchange reaction was inhibited by the presence of 1 M of DNO₃, DCl, DBr or D₂SO₄ and catalyzed by the presence of 4 M of D₂SO₄. No inhibition effect was observed in the case of D₃PO₄. The effect of inorganic acids follows the order of D₃PO₄>D₂SO₄ ≫ (DNO₃, DCl, DBr). The conjugated base (RCH(COOD)(COO⁻)) of RCH(COOD)₂ plays an important role in the isotope exchange reaction. The presence of deuterium ion suppresses the generation of RCH(COOD)(COO⁻) ion from RCH(COOD)₂ and inhibits the rate of isotope exchange. In general, the order of reactivity of RCH(COOH)₂ toward isotope exchange with deuterium atom is RPh>(H, Br)>Me>(Et, Bu). © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 455–461, 1999     

Bimolecular radical scavenging processes for laser isotope separation: NH2D + O2

Infrared multiphoton photooxidation of NH₂D in NH₃ mixtures was observed to produce exclusively HDO, suggesting a single step deuterium separation efficiency of [D₂O]/([D₂0]+[H₂O]) ⩾ 50% which is significantly higher than that of the theoretical value, 33%. The results are explained by the large rate differences in the radical scavenging steps, i.e. k(D+O₂) = 2.2 × 10⁹M⁻¹ s⁻¹, k(NH₂+O₂) ⩽ 5 × 10⁶ M⁻¹ s⁻¹ and k(NH₂+NH₂)=1.6 × 10¹⁰ M⁻¹ s⁻¹. With Ti solid powder as a catalyst, we observed that the formation yields of HDO are at least three to four times higher than those without a catalyst.     

Kinetics of proton transfer in ice via the pH-jump method: Evaluation of the proton diffusion rate in polycrystalline doped ice

The value of the proton diffusion coefficient D_H⁺ in ice was extracted from the diffusion-controlled rate k_D of the proton recombination reaction RO⁻ + H₃O⁺ → k_D ROH + H₂O in polycrystalline doped ice. At −10°C, D_H⁺ was estimated to lie between 3.5×10⁻⁶ and 1.3×10⁻⁵ cm² s⁻¹, well below the corresponding value of (4.1 ± 0.1)×10⁻⁵ cm² s⁻¹ found in supercooled water.     

Weitere Evidenz für die mikroskopische Gleichzeitigkeit des Bruches zweier Bindungen bei einer E2-Reaktion: H-Isotopeneffekte und Substituentenwirkungen bei der Reaktion von 2,2-Diphenyläthyl-benzolsulfonat mit Methoxid-Ion

Second order rate constants are determined for the E2 reactions of 2,2-diphenyl-ethyl benzenesulfonates Ph₂C^xHCH₂O · O₂S–C₆H₄–X with CH₃ONa in methyl cellosolve solution (^xH = H or D, X = p-CH₃O, p-CH₃, H or p-NO₂). The HAMMETT ? values are of the same order of magnitude as those found in the first order solvolyses of methyl, ethyl or isopropyl benzenesulfonates. The primary deuterium isotope effects k_H/k_D are 5.27, 5.42 and 6.70 for X = p-CH₃O, H and p-NO₂. The ? values as well as the increase of k_H/k_D with introduction of p-NO₂ supply evidence for simultaneous C_αO and C_βH bond cleavages also in the E2 reactions of these compounds.     

Hydrolyse acide du p-nitrophényl-diazométhane dans les mélanges H2O?D2O: analyse des effets isotopiques

The velocity of the hydrogen ion catalysed hydrolysis of p-nitrophenyl-diazo-methane (I) has been measured in H₂O? D₂O mixtures, giving an isotopic α_i = 0.49. The product isotope effect r = 5.1, determined from product analyses, combined with the (overall) solvent isotope effect k_H/k_D = 2.81, yields the primary kinetic isotope effect (k_H/k_D)^I = 3.8, and the secondary kinetic isotope effect (k_H/k_D)^II = 0.75. The CICH₂COOH-catalysed hydrolysis of I in H₂O? D₂O mixtures gave a straight-line plot of k_n/k_H versus the atomic fraction n of deuterium. With four carboxylic acids, as catalysts, values of about 4.3 for the kinetic (overall) isotope effects were observed.     

On the mechanism of reaction of tert-butoxyl radicals with dialkylphosphites

It has been shown by ESR spectroscopy that the title reaction involves abstraction of hydrogen from the phosphite, since at ?10°C the reaction has a kinetic deuterium isotope effect, k_H/k_D, or ～3. The rate constant for hydrogen abstraction is c. 2 × 10⁴ M^?1 s^?1. There is no significant addition of alkoxyl radicals to the phosphite.     

Reactivity of hydrogen atoms with liquid water

The reactivity of hydrogen atoms with liquid water was investigated by determination of the final products obtained by the photolysis (λ = 184.9 nm) of two systems in the range pH 10 – 13: (a) OH⁻/N₂O/H₂O and (b) OH⁻/H₂O (air free). Based on the product yields of the two systems, non-linear fitting computations were performed including all possible reactions; a value of k(H + H₂O) = 10 ± 2 dm³ mol⁻¹ s⁻¹ was determined. The share of each individual reaction leading to the formation of H₂ was also deduced.     

Participation of the ferrocenyl group in the solvolysis of ferrocenylmethyltrimethylammonium ion[1]

The α-deuterium kinetic isotope effect in the solvolysis of ferrocenyl-1,1-dideuteriomethyltrimethylammonium iodide in aqueous solution has been measured. The isotope effect, k_H/k_D, is 1.06 ± 0.04 at 80°C (about 3% per deuterium atom). This effect is only a small fraction of the limiting α-deuterium isotope effect for a nitrogen leaving group, which is estimated to be about 20% per deuterium atom at 80°C. The small isotope effect supports the transition state model involving participation of the electrons localized on the iron atom. The activation parameters for the solvolysis reaction in the temperature range 70–90°C are: ΔH^≠ = 132.6 ± 3.8 kJ mol⁻¹ and ΔS^≠ = 54.0 ± 20.1 JK⁻¹ mol⁻¹.     

Radiolysis in H2O/D2O mixtures. Hydrogen production under LOCA simulation

The hydrogen isotope radiolytic yields, G(H₂), G(HD) and G(D₂) were determined in H₂O/D₂O mixtures under chemical conditions close to a LOCA in a PHWR like Atucha I Nuclear Station, that is 2·10^–3 MH₃BO₃ and p(H+D)=8.5±0.2. The total hydrogen radiolytic yield G(H₂+HD+D₂) as a function of the deuterium atom fraction goes through a flat maximum at about 0.58. This result in dicates that the 4% flammability limit for hydrogen in the reactor's containment with be reached sooner than what is expected assuming a linear combination of pure H₂ and D₂ radiolytic yields. Hydrogen radiolytic production in 10^–3 M KBr in H₂O/D₂O mixtures gives the same results as in the boric solutions suggesting a bimolecular B(OH) ₄ ^– +OH reaction. Identical isotope concentration factors were calculated for both solutions.     

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.     

Kinetic isotope effect for hydrogen/deuterium abstraction by chlorine atoms from (CH3)2NNO2 and (CD3)2NNO2

The kinetic isotope effect for the abstraction of hydrogen/deuterium from dimethylnitramine and dimethylnitramine-d₆ by chlorine atoms has been studied in the temperature range 273–353 K. The rate constant ratio k_H0/k_D is given by the Arrhenius expression, k_H/k_D=(0.92 ± 0.07)exp(286 ± 250/RT), where R is expressed in cal mol^?1 K^?1. The absolute rate constant for the deuterium abstraction reaction is extrapolated as k_D=(1.50 ± 0.90) × 10^?10 exp(?1,486 ± 370/RT) cm³ molecule^?1 s^?1. The temperature dependence of the kinetic isotope effect was calculated using the conventional transition-state theory, and the obtained values for k_H/k_D and ΔE_{H, D} are in good agreement with the experimental value for a bent transition state geometry, with two new vibrational frequencies of 340 cm^?1 (272 cm^?1) corresponding to the in-plane and out-of-plane motions of hydrogen (deuterium) atoms in the Cl…H…C arrangement. © 1993 John Wiley & Sons, Inc.     

Determination of the equilibrium constant of hydrogen bonding between substituted h-[d]-phenols and vinyl acetate in CCl4 by i.r. measurements

Equilibrium constants are reported for 26 light and 7 heavy phenols in terms of the usual equilibrium model of 1 : 1 complex formation. A solvation model sensitive to steric hindrance is also described. Linear correlations between log K_H and ΔνOH as well as log K_D and ΔνOH have been found for the interval: 30≤ΔνOH≤200 cm⁻¹. These allow estimates on the equilibrium isotope effect.     

Analysis of the molecular bands of D2H and H2D at 5600 Å

Spectral simulation was used to analyze the molecular rovibrational bands of D₂H and H₂D at 5600 Å. These bands were previously measured by the ion beam neutralization method. They were assigned to the electronic 3p²B₁ ? 2s²A₁ and vibrational (ν - ν″) = (0, 0, 0,-0, 0, 0) transitions. Least squares fits to the experimental line-positions were made to determine the asymmetric rotator constants A, B and C for the 2s²A₁ and 3p²B₁ ν = 0 states of D₂H and H₂D, hitherto unknown. Lorentz line-profiles were assumed for the D₂H and H₂D rotational lines, whose widths are mainly governed by the lifetimes of the lower states. The bands at 5600 Å were simulated and the 2s²A₁ state lifetimes were estimated to be σ ≥ 0.5 ± 0.2 ps for D₂H and σ ≥ 0.4 ± 0.2 ps for H₂D. Vibrational constants of D₃ and D₂H in the 2s²A₁ states are determined from the positions of the 0-0 and 0-1 vibrational bands given in respective experimental spectra previously measured. For the first time the vibrational constants ω₁ and ω₂ of the 2s²A₁ state of H₂D were estimated from the positions of the 0-0 and 0-1 band maxima. These vibrational constants are compared with the corresponding vibrational constants of their ions.     

Hydrolysis and Photolysis of Tris(tetraethylammonium) Pentacyanoperoxynitritocobaltate(III): Evidence for a Novel Complex,Pentacyanonitratocobaltate(III)

At pH 2, the rate constant of hydrolysis of tris(tetraethylammonium) pentacyanoperoxynitritocobaltate(III) in H₂O is 9.6×10⁻⁶ s⁻¹. In the absence of any light, ONOO⁻ is not replaced by H₂O and isomerizes within the coordination sphere to NO₃⁻. The novel complex [Co(CN)₅NO₃]³⁻ released NO₃⁻ slowly, as detected by ion chromatography. At pH 6, no hydrolysis is observed. Direct photolysis, both at pH 2 and pH 6, of tris(tetraethylammonium) pentacyanoperoxynitritocobaltate(III) by irradiation (YAG laser) at 355 nm destroys the coordinated ONOO⁻ and releases NO₂^., which hydrolyzes to NO₃⁻ and NO₂⁻. We also measured the ⁵⁹Co‐NMR spectra of [Co(CN)₅OONO]³⁻ and [Co(CN)₅H₂O]²⁻; the chemical shifts correspond very well to those predicted and are in agreement with the expected contribution to the ligand field by H₂O and ONOO⁻.     

Highly Selective Benzylic C?H Bond Activation of Toluene 1 by ‘Bare’ FeO+ in the Gas Phase. Short communication

The reaction of FeO⁺ with toluene in the gas phase occurs at collision rate (k_r = 1.36 × 10⁻⁹ cm³ molecule⁻¹ s⁻¹), and labeling experiments demonstrate that the total products due to C H bond activation involve to > 92% the benzylic position. In the ‘hydride’ abstraction process (formation of FeOH and C₇H), the H-atom originates elusively from the benzylic position to generate a benzyl cation, and an intramolecular kinetic isotope effect k_H/k_D = 1.75 has been obtained. There is no evidence for the existence of isotopically sensitive branching (‘metabolic switching’) in the system studied.     

Tautomerization of Phenols,Part III,The Anthrone−Anthrol Equilibrium in Aqueous Solution

The equilibrium between 10H‐anthr‐9‐one and 9‐anthrol favors the ketone, which ionizes as a carbon acid in aqueous base. Rates of equilibration were measured over the pH range 1 – 13 in aqueous solution (25°, ionic strength I=0. M ). Five independent thermodynamic and kinetic parameters were determined by analysis of the pH‐rate profile: the equilibrium constant of enolization, pK_E=2.17, the ionization quotient of anthrol, pQ=7.84, and the rate constants of enolization catalyzed by acid, k=2.2⋅10⁻⁴ M ⁻¹ s⁻¹, base, k=51.0 M ⁻¹ s⁻¹, and water, k=1.21⋅10⁻⁵ s⁻¹. Structure‐reactivity relationships strongly support the view that pH‐independent enolization of anthrone in water proceeds by rate‐determining ionization of the C‐acid.     

Studies on the oxidation mechanism of H2S based on direct examination of the key reactions

By conducting an excimer laser photolysis (193 and 248 nm) behind shock waves, three elementary reactions important in the oxidation of H₂S have been examined, where, H, O, and S atoms have been monitored by the atomic resonance absorption spectrometry. For HS + O₂ → products (1), the rate constants evaluated by numerical simulations are summarized as: k₁ = 3.1 × 10⁻¹¹exp|-75 kJ mol⁻¹/RT| cm³molecule⁻¹s⁻¹ (T = 1400-1850 K) with an uncertainty factor of about 2. Direct measurements of the rate constants for S + O2 → SO + O (2), and SO + O₂ → SO₂ + O (3) yield k₂ = (2.5 ± 0.6) × 10⁻¹¹ exp|-(15.3 ± 2.5) kJ mol⁻¹/RT| cm³molecule⁻¹s⁻¹ (T = 980-1610 K) and, k₃ = (1.7 ± 0.9) × 10⁻¹² exp|-(34 ± 11) kJ mol⁻¹/RT| cm³molecule⁻¹s⁻¹ (T = 1130-1640 K), respectively. By summarizing these data together with the recent experimental results on the H(SINGLE BOND)S(SINGLE BOND)O reaction systems, a new kinetic model for the H₂S oxidation process is constructed. It is found that this simple reaction scheme is consistent with the experimental result on the induction time of SO₂ formation obtained by Bradley and Dobson. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 57–66, 1997.     

Theoretical Study on the Gas‐Phase SN2 Reaction of Microhydrated Fluoride with Methyl Fluoride

The rate constants for the gas‐phase S_N2 reaction of F^?(H₂O) with CH₃F have been calculated using the dual‐level variational transition state theory including multidimensional tunneling from 50 to 500 K. Tunneling was found to dominate the reaction below 200 K. The deuterium, ¹³C, and ¹⁴C kinetic isotope effects (KIEs) and solvent (D₂O) isotope effects (SKIEs) were also calculated in the same temperature range. The results indicated that the deuterium and heavy water substitutions resulted in inverse KIEs (0.6～0.8 ) while the ¹³C and ¹⁴C substitutions resulted in normal KIEs (1.0～1.2) at room temperature. The calculated carbon KIEs increased significantly below 80 K due to the differences in the magnitude of the tunneling effects for different isotopic substitutions.     

Kinetics and mechanism of base hydrolysis of cisα-oxalato(amine)(trien)cobalt(III) and salicylato(amine)(trien)cobalt(III)cations

Oxalato(amine)(trien)cobalt(III) and salicylato(amine)(trien)cobalt(III) perchlorates have been synthesized and tentatively assigned a cis α configuration. The dissociation constants of the complexes have been determined. The base hydrolysis of the complexes have been investigated at 30, 35, 38.6°C and I = 1.0 mol dm⁻³. The rate laws for the oxalato and salicylato complexes are −dln[Complex]_T/dt = k₂[OH⁻] and −dln[Complex]_T = k₁ + k₂[OH⁻] respectively. For the oxalato complex, k₂(30°C) = (2.95 ± 0.05) × 10⁻² dm³ mol⁻¹ s⁻¹, ΔH¹ = (109 ± 4) KJ mol⁻¹, ΔS¹ = (85 ± 13) JK⁻¹ mol⁻¹ and for the salicylato complex, k₁(30°C) = (1.58 ± 0.28) × 10⁻⁴ s⁻¹, ΔH¹ = (166 ± 7) KJ mol⁻¹, ΔS¹ = (229 ± 21) JK⁻¹ mol⁻¹ and k₂(30°C) = (3.56 ± 0.10) × 10⁻³ dm³ mol⁻¹ s⁻¹, ΔH¹ = (101 ± 6) KJ mol⁻¹, ΔS¹ = (42 ± 20) JK⁻¹ mol⁻¹. The base hydrolysis reactions of the complexes were followed in presence of imidazole and ethanolamine, in the presence of added anions and also in D₂O medium. The results are discussed in terms of δ SN₁CB mechanism involving rate limiting CoO bond fission for both k₁ and k₂ paths. However, the possibility of CO bond cleavage in the base hydrolysis of the oxalato complex is not ruled out.