Kinetic study of the reaction H2O2+H→H2O+OH by ab initio and density functional theory calculations

Theoretical investigations on the kinetics of the elementary reaction H₂O₂+H→H₂O+OH were performed using the transition state theory (TST). Ab initio (MP2//CASSCF) and density functional theory (B3LYP) methods were used with large basis set to predict the kinetic parameters; the classical barrier height and the pre-exponential factor. The ZPE and BSSE corrected value of the classical barrier height was predicted to be 4.1 kcal mol⁻¹ for MP2//CASSCF and 4.3 kcal mol⁻¹ for B3LYP calculations. The experimental value fitted from Arrhenius expressions ranges from 3.6 to 3.9 kcal mol⁻¹. Thermal rate constants of the title reaction, based on the ab initio and DFT calculations, was evaluated for temperature ranging from 200 to 2500 K assuming a direct reaction mechanism. The modeled ab initio-TST and DFT–TST rate constants calculated without tunneling were found to be in reasonable agreement with the observed ones indicating that the contribution of the tunneling effect to the reaction was predicted to be unimportant at ambient temperature.     

Direct dynamic study on the hydrogen abstraction reaction C2(Πu)+H2 → C2H+H

The ab initio direct dynamics method at the G2//UQCISD/6-311 + G(d,p) level is employed to study the hydrogen abstraction reaction C₂(³Π_u)+H₂ → C₂H+H over a wide temperature range 100–4650 K. The barrier heights obtained for the forward and reverse reactions are 7.78 and 17.53 kcal/mol, respectively. Comparing with one recent experiment, the calculated forward rate constants over the temperature range 2580–4650 K are about 4.4–13.5 times greater and show a steeper temperature-dependent effect. This indicates that further experimental investigation on this simple radical reaction may still be desired. Finally, G2//UQCISD/6-311 + G(2df,2p) calculations are performed to test the reliability of the G2//UQCISD/6-311 + G(d,p) results.     

Hydroformylation of propylene in supercritical CO2 + H2O and supercritical propylene + H2O

Hydroformylation of propylene has been carried out in supercritical CO₂ + H₂O and in supercritical propylene + H₂O mixtures using Rh(acac)(CO)₂ and triphenylphosphine trisulfonate trisodium salt (TPPTS), P(m-C₆H₄SO₃Na)₃, as catalyst. Visual observation of the reaction mixtures indicates that in both systems a single phase is present at supercritical temperatures and pressures so that the reaction occurs under homogeneous conditions. After reaction is complete, a biphasic system is formed when the pressure and temperature are reduced to ambient. This facilitates separation of the products in the organic phase and the rhodium catalyst in the aqueous phase. The rhodium concentration in the organic phase was found to be negligible (1.0 × 10⁻⁶ mg/ml). Furthermore, compared with traditional hydroformylation technology, the supercritical reactions also show better activity and selectivity.     

HNCO+OH->H2O+NCO的反应机理

采用从头算分子轨道法 (UHF/6 31G 水平 ,并用MP4加以相关能校正 )研究了HNCO OHH2 O NCO反应机理 .同时用Morokuma数值法获得了反应途径即内禀反应坐标 (IRC) .沿着IRC ,运用反应途径哈密顿理论 ,获得反应途径动态学信息 .在此基础上 ,根据过渡态理论和相应隧道效应校正 ,计算了在不同温度下的反应速率常数 ,得到了和实验相一致的结果 .计算结果表明 ,此反应是一步直接型的抽提H反应 .     

Theoretical study on the reaction pathways of HFCO + H2O

For the reaction of methanoyl fluoride with water, both optimized structures and vibrational wavenumbers of reaction intermediates, transition structures and product complexes were calculated and characterized with theory at the MP2/6-311++G(d,p) level. Including a catalytic path and concerted and stepwise hydrolysis paths, possible reaction mechanisms were also investigated. The catalytic reaction of HFCO yielding HF and CO has the smallest activation barrier, 29.6 kcal/mol, whereas for the concerted hydrolysis 33.0 kcal/mol is required to overcome the barrier to form transoid HCOOH + HF, which is less than for the stepwise counterpart, 42.0 kcal/mol.     

Theoretical study on the hydrogen abstraction reaction of CH3CH2F (HFC-161) with Cl atom

A direct dynamics method is employed to study the hydrogen abstraction reaction of CH₃CH₂F+Cl. Three distinct transition states are located, one for -H abstraction and two for β-H abstraction. The potential energy surface (PES) information is obtained at the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p), CCSD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) and G2//MP2/6-311G(d,p) level. Based on the QCISD(T)/6-311+G(3df,2p)//MP2/6-311G(d,p) results, the rate constants of the three reaction channels are evaluated by using the canonical variational transition state theory (CVT) with small-curvature tunneling (SCT) contributions over the temperature range of 220–2800 K. The calculated results indicate that -H abstraction dominates the total reaction almost over the whole temperature range.     

Using n-mode potentials for reactive scattering: Application to the 6D H2 + Pt(1 1 1) problem

The accuracy of n-mode representations of potential energy surfaces (PESs) is investigated, for a reaction involving six degrees of freedom. Probabilities computed with the time-dependent wave packet (TDWP) method for reaction of (v = 0,1; j = 0) H₂ on Pt(1 1 1) employing a 5-mode (4-mode) PES show quantitative (semi-quantitative) agreement with results for the full PES. The ratio of the v = 1 and v = 0 reaction probabilities obtained with the 5-mode PES is in quantitative agreement with full PES results for most of the energy range considered. The results suggest that n-mode representations can be employed successfully to study reactions of polyatomic molecules with surfaces.     

Site-specific rate coefficients for reaction of OH with ethanol from 298 to 900 K

The rate coefficients for reactions of OH with ethanol and partially deuterated ethanols have been measured by laser flash photolysis/laser-induced fluorescence over the temperature range 298-523 K and 5-100 Torr of helium bath gas. The rate coefficient, k(1.1), for reaction of OH with C(2)H(5)OH is given by the expression k(1.1) = 1.06 × 10(-22)T(3.58)?exp(1126/T) cm(3) molecule(-1) s(-1), and the values are in good agreement with previous literature. Site-specific rate coefficients were determined from the measured kinetic isotope effects. Over the temperature region 298-523 K abstraction from the hydroxyl site is a minor channel. The reaction is dominated by abstraction of the α hydrogens (92 ± 8)% at 298 K decreasing to (76 ± 9)% with the balance being abstraction at the β position where the errors are 2σ. At higher temperatures decomposition of the CH(2)CH(2)OH product from β abstraction complicates the kinetics. From 575 to 650 K, biexponential decays were observed, allowing estimates to be made for k(1.1) and the fractional production of CH(2)CH(2)OH. Above 650 K, decomposition of the CH(2)CH(2)OH product was fast on the time scale of the measured kinetics and removal of OH corresponds to reaction at the α and OH sites. The kinetics agree (within ±20%) with previous measurements. Evidence suggests that reaction at the OH site is significant at our higher temperatures: 47-53% at 865 K.     

Theoretical studies and rate constant calculations of the reactions C2F5CHO with OH radicals and Cl atoms

The hydrogen abstraction reactions of C₂F₅CHO with OH radicals and Cl atoms have been investigated theoretically by a dual-level direct dynamics method. In this study, the optimized geometries and frequencies of the stationary points are calculated at the MP2/cc-pVDZ level of theory. The energies of the stationery points and the selected points along the minimum energy paths are further refined at the MC-QCISD level using the MP2 geometries. Complexes with energies less than those of the reactants or products are located at the entrance or the exit channels of the two reactions. This result indicates that both of reactions proceed via indirect reaction mechanisms. The enthalpies of formation for the reactant C₂F₅CHO and the product radical C₂F₅CO are estimated by isodesmic reactions at the MC-QCISD//MP2/cc-pVDZ level. At the same level, the rate constants are calculated by canonical variational transition state theory (CVT) incorporating with the small-curvature tunneling correction (SCT) in the temperature range 200–1000 K. Good agreement between the calculated and experimental rate constants is obtained at the room temperature. Due to the lack of the kinetic data of these reactions, the fitted three-parameter expressions based on the CVT/SCT rate constants within 200–1000 K are k₁ = 1.64 × 10⁻²⁴ T^4.33 exp (−566.1/T) and k₂ = 6.33 × 10⁻¹⁵ T^1.35 exp (550.3/T) cm³ molecule⁻¹ s⁻¹, respectively.     

Liquid–liquid equilibria of ternary mixture (propargyl alcohol + diisopropyl ether + water)

The liquid–liquid equilibria (LLE) of ternary mixture (propargyl alcohol + diisopropyl ether + water) were measured under atmospheric pressure and at different temperatures of 297.25, 304.35, 313.15, and 323.25 K. It was found that the end points of tie-lines at the four temperatures were located almost on a common solubility curve but the tie-lines possessed different slopes that described different equilibrium relations. A comparison of the predicted values through use of UNIFAC method with the measured LLE data was carried out but the predicted values showed remarkable deviations from the experimental data.     

Reaction path dynamics and theoretical rate constants for the SiH3Cl+H→SiH2Cl+H2 reaction by ab initio direct dynamics method

Ab initio direct dynamics method has been used to study the title reaction. Electronic structure information including geometries, gradients and force constants (Hessians) are calculated at the UQCISD/6-311+G^** level. Energies along the minimum energy path are improved by a series of single-point G2//QCISD calculations. The changes of the geometries, vibratioanal frequencies, potential energies and total curvature along the reaction path are discussed. The rate constants in the temperature range 200–3000 K are calculated by canonical variational transition state theory with small-curvature tunneling correction (CVT/SCT) method. The results show that the variational effect is small and in the lower temperature range, the small curvature tunneling effect is important for the reaction.     

Pulse radiolysis study of the reaction of OH radicals with C2H4 over the temperature range 343–1173 K

The reaction of OH and OD radicals with ethylene in the presence of 1 atm argon and 6 Torr water vapor was studied in the temperature range 343–1173 K. The results reveal three kinetically separate temperature regions: (1) 343–563 K, where the disappearance of OH radical is dominated by the addition of OH to the double bond of ethylene; (2) 563–748 K, where concurrent reactions of addition, the reverse reaction of addition and H-atom abstraction is dominant; and (3) 748–1173 K, where H-atom abstraction is likely the main reaction. The rate for hydrogen abstraction is 2.4 × 10^?11 exp[(?2104 ± 125)/T] cm³/molec-s (for OD 2.1 × 10^?11 exp[(?2130 ± 172)/T] cm³/molec-s). There was no obvious pyrolysis of ethylene below 1073 K. The study of OD radical with ethylene shows a small isotope effect.     

Mechanistic and kinetic study of the O + CH2OH reaction

The mechanism for the O + CH2OH reaction was investigated by various ab initio quantum chemistry methods. For the chemical activation mechanism, that is, the addition/elimination path, the couple-cluster methods including CCSD and CCSD(T) were employed with the cc-pVXZ (X = D, T, Q, 5) basis sets. For the abstraction channels, multireference methods including CASSCF, CASPT2, and MRCISD were used with the cc-pVDZ and cc-pVTZ basis sets. It has been shown that the production of H + HCOOH is the major channel in the chemical activation mechanism. The minor channels include HCO + H2O and OH + CH2O. The hydrogen abstraction by an O atom from the CH2OH radical produces either OH + CH2O or OH + HCOH. Moreover, the two abstraction reactions are essentially barrierless processes. The rate constants for the association of O with CH2OH have been calculated using the flexible transition state theory. A weak negative temperature dependence of the rate constants is found in the range 250-1000 K. Furthermore, it is estimated that the abstraction processes also play an important role in the O + CH2OH reaction. Additionally, the falloff behavior for the OCH2OH --> H + HCOOH reaction has been investigated. The present theoretical results are compared to the experimental measurements to understand the mechanism and kinetic behavior of the O + CH2OH reaction and the unimolecular reaction of the OCH2OH radical.     

Thermal decomposition of ethanol. 4. Ab initio chemical kinetics for reactions of H atoms with CH3CH2O and CH3CHOH radicals

The potential energy surfaces of H-atom reactions with CH(3)CH(2)O and CH(3)CHOH, two major radicals in the decomposition and oxidation of ethanol, have been studied at the CCSD(T)/6-311+G(3df,2p) level of theory with geometric optimization carried out at the BH&HLYP/6-311+G(3df,2p) level. The direct hydrogen abstraction channels and the indirect association/decomposition channels from the chemically activated ethanol molecule have been considered for both reactions. The rate constants for both reactions have been calculated at 100-3000 K and 10(-4) Torr to 10(3) atm Ar pressure by microcanonical VTST/RRKM theory with master equation solution for all accessible product channels. The results show that the major product channel of the CH(3)CH(2)O + H reaction is CH(3) + CH(2)OH under atmospheric pressure conditions. Only at high pressure and low temperature, the rate constant for CH(3)CH(2)OH formation by collisonal deactivation becomes dominant. For CH(3)CHOH + H, there are three major product channels; at high temperatures, CH(3)+CH(2)OH production predominates at low pressures (P < 100 Torr), while the formation of CH(3)CH(2)OH by collisional deactivation becomes competitive at high pressures and low temperatures (T < 500 K). At high temperatures, the direct hydrogen abstraction reaction producing CH(2)CHOH + H(2) becomes dominant. Rate constants for all accessible product channels in both systems have been predicted and tabulated for modeling applications. The predicted value for CH(3)CHOH + H at 295 K and 1 Torr pressure agrees closely with available experimental data. For practical modeling applications, the rate constants for the thermal unimolecular decomposition of ethanol giving key accessible products have been predicted; those for the two major product channels taking place by dehydration and C-C breaking agree closely with available literature data.     

Measurement and correlation of the solubility of MnSO4·H2O in ethanol + water + MgSO4·7H2O solutions

Data on the solubility of manganese sulphate monohydrate in water, and in aqueous alcohols is essential for salting-out crystallisation studies. The solubilities of the quaternary system MnSO₄·H₂O + MgSO₄·7H₂O + H₂O + EtOH were determined in the temperature range 293.2–323.2 K over the ethanol mole fraction range of 0.00–0.12. The solubility data were used for modelling with the modified extended electrolyte non-random two-liquid (NRTL) equation. The present extension uses ion-specific parameters instead of the electrolyte-specific NRTL binary interaction parameters. This approach has feasibility for many electrolytes and mixed aqueous solution systems in principle. The model was found to correlate the solubility data satisfactorily.     

Quasiclassical trajectory scattering calculations for the OH + O → H + O2 reaction: Cross sections and rate constants

We report quasiclassical trajectory studies of the OH + O → H + O₂ reaction using a recently developed ab initio potential energy surface for the ground electronic state of HO₂. The total reaction probability is in good agreement with the quantum result. Integral cross sections show no energy threshold and decrease as the collision energy increases. Rate constants have been calculated in the (1–500 K) temperature range. They exhibit a negative temperature dependence for temperatures above 50 K, and the thermal rate constant is in quantitative agreement with the most recent experimental data. The reactivity is slightly enhanced by rotational excitation of OH.     

Kinetics study of the gas-phase reactions of C2F5OC(O)H and n-C3F7OC(O)H with OH radicals at 253–328 K

The rate constants, k₁ and k₂ for the reactions of C₂F₅OC(O)H and n-C₃F₇OC(O)H with OH radicals were measured using an FT-IR technique at 253–328 K. k₁ and k₂ were determined as (9.24 ± 1.33) × 10⁻¹³ exp[−(1230 ± 40)/T] and (1.41 ± 0.26) × 10⁻¹² exp[−(1260 ± 50)/T] cm³ molecule⁻¹ s⁻¹. The random errors reported are ±2 σ, and potential systematic errors of 10% could add to the k₁ and k₂. The atmospheric lifetimes of C₂F₅OC(O)H and n-C₃F₇OC(O)H with respect to reaction with OH radicals were estimated at 3.6 and 2.6 years, respectively.     

Absolute rate coefficient of the OH + CH(3)C(O)OH reaction at T = 287-802 K. The two faces of pre-reactive H-bonding

The rate constants for the reaction OH + CH3C(O)OH --> products (1) were determined over the temperature range 287-802 K at 50 and 100 Torr of Ar or N2 bath gas using pulsed laser photolysis generation of OH by CH3C(O)OH photolysis at 193 nm coupled with OH detection by pulsed laser-induced fluorescence. The rate coefficient displays a complex temperature dependence with a sharp minimum at 530 K, indicating the competition between a reaction proceeding through a pre-reactive H-bonded complex to form CH3C(O)O + H2O, expected to prevail at low temperatures, and a direct methyl-H abstraction channel leading to CH2C(O)OH + H2O, which should dominate at high temperatures. The temperature dependence of the rate constant can be described adequately by k1(287-802 K) = 2.9 x 10(-9) exp{-6030 K/T} + 1.50 x 10(-13) exp{515 K/T} cm3 molecule(-1)(s-1), with a value of (8.5 +/- 0.9) x 10-13 cm3 molecule(-1)(s-1) at 298 K. The steep increase in rate constant in the range 550-800 K, which is reported for the first time, implies that direct abstraction of a methyl-H becomes the dominant pathway at temperatures greater than 550 K. However, the data indicates that up to about 800 K direct methyl-H abstraction remains adversely affected by the long-range H-bonding attraction between the approaching OH radical and the carboxyl -C(O)OH functionality.     

First Experimental and Theoretical Kinetic Study of the Reaction of 4‐Hydroxy‐4‐methyl 2‐pentanone as a Function of Temperature

In this work, experimental and theoretical rate coefficients were determined for the first time for the gas‐phase reaction of 4‐hydroxy‐4‐methyl‐2‐pentanone (4H4M2P) with OH radicals as a function of temperature. Experimental studies were carried out over the pressure range of 5–80 Torr and the temperature range of 280–365 K, by using a cryogenically cooled cell coupled to the pulsed laser photolysis‐laser induced fluorescence (PLP–LIF) technique. A detailed oxidation mechanism of 4H4M2P with OH radicals was discussed theoretically under three hydrogen abstraction pathways by using density functional theory calculations and wave function based MP2 method. Single‐point energy calculations were performed at CCSD(T) level of theory with 6–311++G(d,p) basis set. The H‐atom abstraction from the ‐CH₂ group was found to be the dominant channel. The reaction force analysis predicts that the abstraction process is mainly dominated by structural rearrangement. Linear kinetic behavior for all the pathways was found in the range of 278–365 K. An atmospheric lifetime less than 3 days was evaluated for 4H4M2P with respect to its reaction with OH, indicating that the reaction with OH of 4H4M2P may be competitive with losses via photolysis.