Heterogeneous reactions of SO2 with HOCl and HOBr on ice surfaces

The heterogeneous reactions of SO2 + HOX (X = Cl or Br) --> products on ice surfaces at low temperature have been investigated in a flow reactor coupled with a differentially pumped quadrupole mass spectrometer. Pseudo-first-order loss of SO2 over the ice surfaces has been measured under the conditions of concurrent HOX flow. The initial uptake coefficient of SO2 reaction with HOX has been determined as a function of HOX surface coverage, theta(HOX), on the ice. The initial uptake coefficients increase as the HOX coverage increases. The uptake coefficient can be expressed as gamma(t) = k(h)theta(HOX), where k(h) is an overall rate constant of SO2 + HOCl, which was determined to be (2.3 +/- 0.6) x 10(-19) and (1.7 +/- 0.5) x 10(-19) molecules(-1) x cm2 at 190 and 210 K, and k(h) of SO2 + HOBr is (6.1 +/- 2.0) x 10(-18) molecules(-1) x cm2 at 190 K. theta( HOX) is in the range 8.1 x 10(13)-9.1 x 10(14) molecules x cm(-2). The kinetic results of the heterogeneous reaction of SO2 + HOX on ice surface are interpreted using the Eley-Rideal mechanism. The activation energy of the heterogeneous reaction of SO2 with HOCl on ice surface was determined to be about -37 +/- 10 kJ/mol in the 190-238 K range.     

Competitive hydrogen-bonding and halogen-bonding interactions in the dimerization of hypobromous acid (HOBr) molecules

Structural Chemistry - The dimerization of hypobromous acid molecules was investigated using MP2 method with aug-cc-pVTZ basis set. Six different configurations were found as the local minima,...     

DFT and ab initio dual-level direct dynamics studies on the reactions of fluorine atom with HOCl and HOBr

The multichannel reactions (1) HOCl + F --> products and (2) HOBr + F --> products have been investigated using the dual-level direct dynamics method. The minimum energy paths (MEPs) are calculated at both the MPW1K/6-311G(d,p) and QCISD/6-311G(d,p) levels, then the single-point energies are further corrected at the QCISD(T)/6-311++G(3df,3pd) level of theory. There are hydrogen-bonded complexes with the energies less than those of the reactants or products located at the entrance or exit channel of both hydrogen abstraction reactions; while for the halogen abstraction channels only one complex exists at the reactant side in the bromine abstraction channel. The rate constants are evaluated by the improved canonical variational transition-state theory (ICVT). The agreement of the rate constants with available experimental values for two reactions at room temperature is good. Theoretical results indicate that for the reaction HOCl + F, hydrogen abstraction channel leading to the formation of HF + ClO will predominate the reaction over the whole temperature range, and the reaction of HOBr + F may proceed mainly through the bromine abstraction channel at the lower temperature while the contribution of hydrogen abstraction channel will become significant as the temperature increases. Because of lack of the kinetic data of these reactions, the present theoretical results are expected to be useful and reasonable to estimate the dynamical properties of these reactions over a wide temperature range where no experimental value is available.     

A specific and sensitive method for detection of hypochlorous acid for the imaging of microbe-induced HOCl production

A specific and sensitive fluorescence-based method was developed for the imaging of microbe-induced HOCl production. Furthermore, we demonstrate dual oxidase (DUOX)-mediated HOCl generation in the mucosa of live animals providing a novel insight into mucosal innate immunity.     

The heterogeneous kinetics of HOBr and HOCl on acidified sea salt and model aerosol at 40-90% relative humidity and ambient temperature

The HOBr and HOCl uptake coefficient gamma on H(2)SO(4)-acidified submicron salt aerosol of known size distribution was measured in an atmospheric pressure laminar flow reactor. The interaction time of the trace gas with the aerosol was in the range 15 to 90 s and led to gamma values in the range 10(-4) to 10(-2). The acidity of the aerosol is essential in order to enable heterogeneous reactions of HOBr on NaCl, recrystallized sea salt (RSS) and natural sea salt (NSS) aerosols. Specifically, HOCl only reacts on acidified NSS aerosol with a gamma ranging from 0.4 x 10(-3) to 1.8 x 10(-3) at a relative humidity (rh) at 40 and 85%, respectively. Uptake experiments of HOBr on aqueous H(2)SO(4) as well as on H(2)SO(4)-acidified NaCl, RSS or NSS aerosol were performed for rh ranging from 40 to 93%. The gamma value of HOBr on acidified NSS reaches a maximum gamma = 1.9 x 10(-2) at rh = 76 +/- 1% and significantly decreases with increasing rh in contrast to acidified NaCl and RSS aerosols whose gamma values remain high at gamma = (1.0 +/- 0.2) x 10(-2) at rh >/= 80%. An explanation based on the formation of an organic coating on NSS aerosol with increasing rh is proposed.     

Thermochemistry of the complexes of chromium nitrate with l-a-amino acids

The solid complexes of Cr(NO₃)₃ with L-α-amino acids (AA=Val, Leu, Thr, Arg, Phe and Try) have been prepared in 95% alcoholic, the compositions of which were identified as the general formula Cr(AA)₂(NO₃)₃·2H₂O by elemental and chemical analyses. The bonding characteristics of the title complexes were characterized by IR, indicating that nitrogen and oxygen atoms in the ligands coordinated to Cr³⁺ in a bidentate fashion. With the aid of TG-DTG and IR techniques, the complexes were subjected to thermal decomposition in an atmosphere of oxygen, presuming that the decompositions of the complexes consist of two steps and the complexes were decomposed into chromium hemitrioxide after undergoing dehydration and skeleton splitting of the complexes. The constant volume energies of combustion of the complexes were determined by a RBC-P type rotating-bomb calorimeter. According to Hess's law, the standard enthalpies of formation of the complexes were calculated as (-1831.40±4.40), (-2542.03±6.13), (-1723.81±3.99), (-2224.31±3.02), (-2911.61±6.53) and (-659.32±7.42) kJ mol^-1, respectively. This revised version was published online in August 2006 with corrections to the Cover Date.     

Thermochemistry of 2- and 3-thiopheneacetic acids: calorimetric and computational study

The enthalpies of formation in the condensed and gas states, Delta f H m degrees (cd) and Delta f H m degrees (g), of 2- and 3-thiopheneacetic acids were derived from their respective enthalpies of combustion in oxygen, measured by a rotating bomb calorimeter, and the variation of vapor pressure with temperature determined by the Knudsen effusion technique. Theoretical calculations at the G3 level were performed, and a study on molecular and electronic structure of the compounds has been carried out. Calculated Delta f H m degrees (g) values using atomization and isodesmic reactions are compared with the experimental data. Experimental and theoretical results show that the 3-thiopheneacetic acid is thermodynamically more stable than the 2-isomer.     

Thermochemistry of biphenylcarboxylic and dicarboxylic acids. A combined experimental and theoretical study

The standard molar enthalpies of combustion and sublimation of 2- and 4-biphenylcarboxylic acid, 2,2'- and 4,4'-biphenyldicarboxylic acid were measured and the gas-phase enthalpies of formation, at T= 298.15 K, were determined. Ab initio calculations were performed and a theoretical study on molecular structure of all the biphenyl acid isomers has been carried out. Calculated enthalpies of formation using appropriate isodesmic reactions are compared with experimental values, and a good agreement is observed. Estimates of enthalpies of formation for the isomers, which were not studied experimentally, are presented. All the acids containing at least one ortho COOH are comparatively less stable than their isomers having just meta or para COOH group(s).     

水合烟酸钡的合成、结构表征和热化学性质

选择烟酸和氢氧化钡作为反应物,利用室温固相合成方法,借助于球磨技术,合成了一种新的化合物-水合烟酸钡.利用化学分析、元素分析、FTIR和X射线粉末衍射等方法确定了它的组成和结构为Ba(Nic)2·3H2O(s).利用精密自动绝热热量计直接测定了此化合物在78-400 K温区的摩尔热容.在热容曲线上出现了一个明显的吸热峰,通过对热容曲线的解析,得到了相变过程的峰温、相变焓和相变熵分别为(327.097±1.082)K、(16.793±0.084)kJ·mol-1和(51.340±0.164)J·K-1·mol-1将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp,m)对温度(T)的多项式方程,并且在此基础上计算出了它的舒平热容值和各种热力学函数值.另外,依据Hess定律,通过设计合理的热化学循环,选择体积为100mL、浓度为0.5mol·L-1的盐酸作为量热溶剂,利用等温环境溶解-反应热量计分别测量固相反应的反应物和产物在所选溶剂中的溶解焓,利用溶解焓确定固相反应的反应焓为△rH0m=-(84.12±0.38)kJ·mol-1.最后,利用固相反应的反应焓和其它反应物和产物已知的热力学数据计算出水合烟酸钡的标准摩尔生成焓为△rH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90)kJ·mol-1.     

水合烟酸钡的合成、±结构表征和热化学性质

选择烟酸和氢氧化钡作为反应物, 利用室温固相合成方法, 借助于球磨技术, 合成了一种新的化合物——水合烟酸钡. 利用化学分析、元素分析、FTIR和X射线粉末衍射等方法确定了它的组成和结构为Ba(Nic)2·3H2O(s). 利用精密自动绝热热量计直接测定了此化合物在78-400 K温区的摩尔热容. 在热容曲线上出现了一个明显的吸热峰, 通过对热容曲线的解析, 得到了相变过程的峰温、相变焓和相变熵分别为(327.097±1.082) K、(16.793±0.084) kJ·mol-1和(51.340±0.164) J·K-1·mol-1. 将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp,m)对温度(T)的多项式方程, 并且在此基础上计算出了它的舒平热容值和各种热力学函数值. 另外, 依据Hess定律, 通过设计合理的热化学循环, 选择体积为100 mL、浓度为0.5 mol·L-1的盐酸作为量热溶剂, 利用等温环境溶解-反应热量计分别测量固相反应的反应物和产物在所选溶剂中的溶解焓, 利用溶解焓确定固相反应的反应焓为⊿rH0m=-(84.12±0.38) kJ·mol-1. 最后, 利用固相反应的反应焓和其它反应物和产物已知的热力学数据计算出水合烟酸钡的标准摩尔生成焓为⊿fH0m[Ba(Nic)2·3H2O(s)]=-(2115.13±1.90) kJ·mol-1.     

无水烟酸锂的合成、结构表征及热化学性质

选择分析纯烟酸和一水氢氧化锂为反应物, 利用水热合成方法合成了无水烟酸锂. 利用FTIR和X射线粉末衍射等方法表征了它的结构. 用精密自动绝热热量计测定了它在78～400 K温区的低温热容, 将该温区的摩尔热容实验值用最小二乘法拟合, 得到热容随温度变化的多项式方程. 用此方程进行数值积分, 得到温区内每隔5 K的舒平热容值和相对于298.15 K时的各种热力学函数值. 在此基础上, 通过设计合理的热化学循环, 利用等温环境溶解-反应热量计分别测定该反应的反应物和生成物在所选溶剂中的溶解焓, 从而得到此反应的反应焓为: ＝－(20.21±0.41) kJ• mol－1. 最后, 依据Hess定律计算出无水烟酸锂的标准摩尔生成焓为: [Li(C6H4NO2), s]＝－(278.29±1.01) kJ•mol－1.     

水合邻苯二甲酸钠的合成、结构表征及热化学性质

选择邻苯二甲酸和氢氧化钠作为反应物,利用液相合成方法合成了水合邻苯二甲酸钠.利用X射线粉末衍射、化学与元素分析等方法表征了它的组成和结构.利用精密自动绝热热量计测定了该化合物在78～366K温区的摩尔热容.将该温区的摩尔热容实验值用最小二乘法拟合得到摩尔热容(Cp,m)对温度(T)的多项式方程,用此方程进行数值积分得到此温度区间内每隔5K的舒平热容值和相对于298.15K时的热力学函数值.另外,依据Hess定律,通过设计合理的热化学循环,利用等温环境溶解-反应热量计分别测量了固相量热反应的反应物和产物在所选溶剂中的溶解焓,从而确定反应的反应焓为:ΔrHm=29.073±1.05kJ·mol-1.最后,利用反应的反应焓和其它反应物和产物已知的热力学数据计算出水合邻苯二甲酸钠的标准摩尔生成焓为:-1493.637±1.11kJ·mol-1.     

无水烟酸钾的合成、表征及热化学

选择分析纯烟酸和无水醋酸钾为反应物, 利用室温固相合成方法, 合成了无水烟酸钾. 利用FTIR和X射线粉末衍射等方法表征了它的结构. 用精密自动绝热热量计测定了它在77～400 K温区的低温热容, 将该温区的摩尔热容实验值用最小二乘法拟合, 得到热容随温度变化的多项式方程. 用此方程进行数值积分, 得到此温区内每隔5 K的舒平热容值和相对于298.15 K时的各种热力学函数值. 在此基础上, 通过设计合理的热化学循环, 利用等温环境溶解-反应热量计分别测定固相反应的反应物和生成物在所选溶剂中的溶解焓, 从而得到该固相反应的反应焓为 (25.87±0.47) kJ•mol^－1. 最后, 依据Hess定律计算出烟酸钾的标准摩尔生成焓为 ＝－(560.57±1.09) kJ•mol^－1.     

Thermochemistry, bond energies, and internal rotor potentials of dimethyl tetraoxide

Thermochemical properties of dimethyl tetraoxide (CH(3)OOOOCH(3)), the dimer of the methylperoxy radical, are studied using ab initio and density functional theory methods. Methylperoxy radicals are known to be important intermediates in the tropospheric ozone cycle, and the self-reaction of methylperoxy radicals, which is thought to proceed via dimethyl tetraoxide, leads to significant chain radical termination in this process. Dimethyl tetraoxide has five internal rotors, three of them unique; the potential energy profiles are calculated for these rotors, as well as for those in the CH(3)OO, CH(3)OOO, and CH(3)OOOO radicals. The dimethyl tetraoxide internal rotor profiles show barriers to rotation of 2-8 kcal mol(-1). Using B3LYP/6-31(d) geometries, frequencies, internal rotor potentials, and moments of inertia, we determine entropy and heat capacity values for dimethyl tetraoxide and its radicals. Isodesmic work reactions with the G3B3 and CBS-APNO methods are used; we calculate this enthalpy as -9.8 kcal mol(-1). Bond dissociation energies (BDEs) are calculated for all C-O and O-O bonds in dimethyl tetraoxide, again with the G3B3 and CBS-APNO theoretical methods, and we suggest the following BDEs: 46.0 kcal mol(-1) for CH(3)-OOOOCH(3), 20.0 kcal mol(-1) for CH(3)O-OOOCH(3), and 13.9 kcal mol(-1) for CH(3)OO-OOCH(3). From the BDE calculations and the isodesmic enthalpy of formation for dimethyl tetraoxide, we suggest enthalpies of 2.1, 5.8, and 1.4 kcal mol(-1) for the CH(3)OO, CH(3)OOO, and CH(3)OOOO radicals, respectively. We evaluate the suitability of 10 different density functional theory (DFT) methods for calculating thermochemical properties of dimethyl tetraoxide and its radicals with the 6-31G(d) and 6-311++G(3df,3pd) basis sets, using a variety of work reaction schemes. Overall, the best-performed DFT methods of those tested were TPSSh, BMK, and B1B95. Significant improvements in accuracy were made by moving from atomization to isodesmic work reactions, with most DFT methods yielding errors of less than 2 kcal mol(-1) with the 6-311++G(3df,3pd) basis set for isodesmic calculations on the dimethyl tetraoxide enthalpy. These isodesmic calculations were basis set consistent, with a considerable reduction in error found by using the 6-311++G(3df,3pd) basis set over the 6-31G(d) basis set. This was not the case, however, for atomization and bond dissociation work reactions, where the two basis sets returned similar results. Improved group additivity terms for the O-O-O moiety (O/O2 central atom group) are also determined.     

Thermochemistry of the Binary System Nitrocellulose-s-Diethyldiphenylurea

A method of gelation enthalpy determination of nitrocellulose (NC)+s-diethyldiphenylurea (Centralite 1, C1) binary system was elaborated using the change of Centralite 1 melting enthalpy in the mixture. The heats of C1 melting together with gelation and dissolution of NC fibres were determined by DSC calorimetric methods. A sharp maximum of the gelation enthalpy for C1 mole fraction x _C1 ^max =0.555 suggests that the complex is very stable and one partly nitrated anhydroglucose ring is interacting with about 1.25 C1 molecules. The gelatinization enthalpy maximum equals =−4.59 kJ mol⁻¹. This revised version was published online in August 2006 with corrections to the Cover Date.     

无水苯甲酸锂的合成、结构表征及热化学研究

用分析纯苯甲酸和一水氢氧化锂作为反应物, 采用水热合成法制得苯甲酸锂. 利用X射线粉末衍射、FTIR、元素分析及化学分析等方法对样品进行组成和结构表征. 采用精密自动绝热热量计测量了其在80~400 K范围内的摩尔热容, 利用最小二乘法将此温区热容实验值对折合温度进行拟合, 得到热容随温度变化的多项式方程. 通过设计合理的热化学循环, 选用0.1 mol/L HCl溶液作为量热溶剂, 利用等温环境溶解-反应热量计分别测定合成反应的反应物和产物在所选溶剂中的溶解焓, 得到反应焓Δ_rH_m⁰=-(9.75±0.27) kJ/mol. 利用Hess定律计算出苯甲酸锂的标准摩尔生成焓Δ_fH_m⁰(C₆H₅COOLi, s)=-(307.82±0.57) kJ/mol.