Syntheses and Characterizations of the Lanthanide Compounds with 4-(4-Pyridyl)benzoate and 2,6-Pyridinedicarboxylate as Ligands

Two new lanthanide coordination polymers, namely [Ln_2(μ_3-OH)(pydca)-(pyba)3(H_2O)]n(Ln = Pr, 1; Eu, 2; Hpyba = 4-(4-pyridyl)benzoic acid; H2 pydca = 2,6-pyridinedicarboxylic acid), have been hydrothermally synthesized and characterized by IR spectroscopy and X-ray single-crystal diffraction. The chains of 1 and 2 are constructed by tetrametallic units of [Ln_4(OH)_2(pyba)_2], which are further linked by μ_4-k_1N, k_1O, k_2O′, k_2O″-pydca and μ_2-k_1N, k_1O, k_1O′-pyba to form 2D frameworks. Luminescence measurement reveals that compound 2 exhibits strong reddish emission at room temperature.     

乙醇-苯乙烯体系的辐解及α-羟乙基自由基反应动力学

γ射线辐照乙醇, 通过苯乙烯抑制其辐解产物的研究, 证明在乙醇介质中α-羟乙基自由基只进行重合反应, 而无歧化反应; 苯乙烯可与α-羟乙基自由基反应, 其竞争反应为Sl+CH_3 CHOH→P 2CH_3CHOH→(CH_3CHOH)_2求得动力学方程为G'=G_0 k_6/2(k_7) 1/2 (G'/Dk')[Sl] G_0为纯乙醇γ射线辐照时2、3-丁二醇的产额, G_0=2.1, k_6/(k7)~(1/2)=0.53. 假定k_7为扩散反应速率常数, 则α-羟乙基自由基与丰乙烯加成反应的速率常数为k_6=4.0×10~4 L·mol~(-1)·s~(-1).     

乙醇-苯乙烯体系的辐解及α-羟乙基自由基反应动力学

γ射线辐照乙醇,通过苯乙烯抑制其辐解产物的研究,证明在乙醇介质中α-羟乙基自由基只进行重合反应,而无歧化反应;苯乙烯可与α-羟乙基自由基反应,其竞争反应为Sl+CH_3 CHOH→P 2CH_3CHOH→(CH_3CHOH)_2求得动力学方程为G'=G_0 k_6/2(k_7) 1/2 (G'/Dk')[Sl] G_0为纯乙醇γ射线辐照时2、3-丁二醇的产额,G_0=2.1,k_6/(k7)~(1/2)=0.53.假定k_7为扩散反应速率常数,则α-羟乙基自由基与丰乙烯加成反应的速率常数为k_6=4.0×10~4 L.mol~(-1).s~(-1).     

长链烷烃脱氢主反应及其失活过程表观动力学研究

本文提出了在绝热固定床上求取催化反应及其失活过程总表观动力学方程和参数的方法,并用此法处理长链烷烃催化脱氢的中试数据,得列在DH-140催化剂上脱氢主反应的表观动力学方程为:-r=k(p_P-p_(MO)·p_(H_2)/K_(P_I))~(1/2)主反应失活过程的表观动力学方程为:-(dk)/(dt)=k_dt 或k=k_0e~(-k)d~t主反应表观速度常数的总表达式为:k=e~8·~(53)R~(-26.7)/RT_(·e~(-te))~(0.64R-12.7/RT     

氟烯的结构-特性关系 7.取代基对a,β,β-三氟苯乙烯热环化二聚反应动力学参数的影响

在110～160℃范围内,测定了三氟苯乙烯(TFS)和六个取代三氟苯乙烯(p-OCH_3,p-CH_3,p-Cl,p-F,p-CF_3,m-CH_3)在正己烷溶液中热环化二聚反应的速率常数k_2,并计算其Arrhenius参数和在413K时的活化参数.讨论了取代基对反应速率常数k_2的影响,发现k_2与几乎所有取代基常数,如,σ,σ~+,σ~0,σ_R~0,σ_R~+和σ_R等均不能很好相关.说明除取代基的极性因素可影响k_2外,不可忽略取代基自旋离域能力的作用.     

纤维素的高分子化学转化及其变性的研究——ⅩⅤ.纤维素在高铈盐溶液中的氧化动力学和氧化部位

从高铈盐水溶液分解动力学角度进一步确定了反应体系的光敏性质。 从水解纤维素、纤素二糖、二醛基纤维素、葡萄糖、葡萄糖甲甙等纤维素模型化合物在高铈盐溶液中的氧化动力学,确定了作为含有多种官能团的高聚物纤维素的氧化动力学方程式是: -(d[Ce~(4+)]/dt)=(k_Ⅰ[Ⅰ]_0+k_Ⅱ[Ⅱ]_0+k_Ⅲ[Ⅲ]_0+……)[Ce~(4+)]其中,[Ⅰ]_0、[Ⅱ]_0和[Ⅲ]_0分别为纤维素中第1、2和3官能团的初始浓度。k_Ⅰ、k_Ⅱ和k_Ⅲ分别为它们的反应速率常数。 不同模型化合物中相同官能团速率常数的对比,确定了速率常数的归属。k_Ⅰ、k_Ⅱ分别为巨分子端基环上的潜醛基和 5、6-乙二醇单元的反应速率常数。证明在纤维素巨分子中至少有三个氧化反应部位。 纤维素巨分子经高铈盐氧化时,每个潜醛基或5、6-乙二醇单元各消耗二个高铈离子,最后都转变为醛基。在消耗一个高铈离子时,可以生成中间络合物——巨分子自由基。自由基位于末端基环的第2位和第5位碳原子上。 第三反应部位位于中间基环上,其反应速率常数虽小,但由于含量很多,故其反应速率不容忽视。第三反应部位的精确位置现尚无法肯定。 用高铈引发所得共聚物主链没有明显的裂解,自由基的可能位置表明它可能是接枝-嵌段复合共聚物。     

过渡金属五卤苯基化合物的研究 Ⅸ. 双(二苯基甲基膦)合(五氯苯基)氯化镍(Ⅱ)与吡啶及取代吡啶亲核取代反应动力学和机理

前文报道了配合物trans-(Ph_2PR)_2Ni(C_8Cl_5)X(R=Me、Et、n-Pr;X=Cl、Br、I)与无机离子的亲核取代反应动力学和机理研究。反应遵循两项速率定律k_(obs)=k_1+k_2[Y],共中k_1、k_2分别为溶剂途径和试剂途径速率常数,[Y]为试剂浓度。然而,与吡啶或取代吡啶(am)进行反应时,表观速率常数     

葡萄糖水溶液中碳酸盐热力学研究 1.二氧化碳-碳酸氢钠-氯化钠-葡萄糖-水体系

在278.15～318.15K和一定离子强度范围内,测定了无液接电池Pt,(1-x)H_2+xCO_2|NaHCO_3(m_1),NaCl(m_2),CO_2(m_3),葡萄糖(m_4)|AgCl-Ag的电动势,利用改进的Harned外推法和我们提出的多项式拟合法确定了二氧化碳在15％葡萄糖水溶液中的一级酸常数K_1~0,两种方法所得pK_1~0值在实验误差范围内一致.pK_1~0随温度变化符合经验方程pK_1~0=A_1+A_2/T+A_3T,并计算了二氧化碳在葡萄糖水溶液中解离过程的各热力学量.     

顺-1,4-聚丁二烯的热氧化——Ⅳ.自催化过程中的有效支链反应动力学

1.根据烃类在自动催化氧化过程中的退化支链反应机理;并考虑到过氧化氢物的分解既可生成游离基,也可形成稳定产物;同时还考虑到高分子固体的反应特征,其中终止反应应包括单基终止这一步骤,因之本文作者重新推导在一定温度下聚合物吸氧动力学的方程式如下: lnV_t/V_∞/(1-V_t/V_∞)=(αk_3N_0-yk_5)_t+C其中α=xk_7/(xk_7+(1-x)k_8);x为支化分数,y为单基终止分数。 V_t——在时间为t时聚合物的吸氧量(毫升O_2/克聚合物); V_∞——聚合物在整个吸氧过程中的极限吸氧量(毫升O_2/克聚合物); k_7及k_8——过氧化氢物分解成游离基及生成稳定产物的速度常数; k_5及k_6-——链的单基及双基终止速度常数; k_3——链的增长速度常数。 2.上述方程式可用顺-1,4-聚丁二烯在不同实验温度和不同品种及浓度的添加剂存在时的吸氧数据来验证,因为这些可变因素可以直接影响α及y值的变化,而这些数值反映了自催化过程的有效支链反应程度。对于某一给定条件下所得的数据,若按上述方程式作lnV_t/V_∞/(1-V_t/V_∞)-t图便可得到两个不同的斜率,即反应的前期斜率较低,后期斜率较高,这假设为α及y值在反应前期及后期有所改变。因之,若以斜率较大者作基础,就可求得前后期不同斜率的比值γ_r,并可定义为有效支链反应程度的相对系数,     

支持电解质和离子强度对溶液中配合物稳定性的影响 Ⅲ.Pitzer理论在确定配合物热力学稳定常数中的应用

本文利用近十几年内发展起来的Pitzer方程表达配合平衡中各个电解质的活度系数,假设支持电解质的离子强度可近似地代表平衡体系的离子强度,并把Pitzer方程中的因子exp(-βμ~(1/2))展成级数,忽略高次项,从而使Pitzer参数B,B’皆与离子强度无关,于是得到: logK_μ+((0.39211△z~2)/(ln10))[((μ~(1/2))/(1+1.2μ~(1/2))+(5/3ln(1+1.2μ~(1/2))]=logK_0+A_1μ+A_2μ~2 (1)式中K_μ和K_0分别为配合物在一定离子强度μ下的逐级稳定常数和逐级热力学稳定常数,△z~2为配合反应中产物和反应物的电荷平方差,A_1,A_2为经验参数.根据方程式(1),利用曲线回归技术可以得logK_0.为了校正本公式推演过程中的两点假设,式(1)右边加上三次项,得到三次曲线方程式;考虑到计算和外推方便,舍去式(1)右边二次项,得到线性方程式.用本文的三种方法处理了前人的实验数据,与传统的方法相比,本文所提供的三种方法都可得到满意的结果.     

Temperature effects, arrhenius activation parameters and rate constants for the photochemical reactivity of cyano, boronato, trifluoromethyl and methoxy substituted toluenes in the excited singlet state

Total rate constants of decay (k(t)) as a function of temperature from -45 to +65 degrees C for the compounds 1 and 2 in AN and TFE and 3 and 4 in AN have been determined by fluorescence lifetime measurements. The data have been fit to an equation that assumes that the rate constants of fluorescence (k(f)) and intersystem crossing (k(isc)) are temperature independent, that k(ic) = 0 and that the rate constant of reaction (k(r)) is activated according to the Arrhenius expression. For compounds 1-3, values of k(f) and k(isc) were found to be independent of solvent for any given compound, but k(r) was consistently greater in TFE than AN. For the anisoles 4, the temperature effect was very small, indicating that k(r) did not compete with k(f) + k(isc) and suggesting that an activated intersystem crossing was the dominant temperature-dependent process. The k(r), A and E(a) values obtained for compounds 1-3 were rationalized in terms of their known photochemistry, phototransposition reactions in AN and photoadditions in TFE. The critical reactive intermediate in all cases is a bicycle[3.1.0]hexenyl biradical/zwitterion that is formed in an activated process from S1. This reactive intermediate returns to starting material faster than it rearranges, and therefore an activated internal conversion is a major pathway for deactivation of S1.     

Kinetics and mechanism of formation of the platinum-thallium bond: the [(CN)(5)Pt-Tl(CN)(3)](3)(-) complex

Formation kinetics of the metal-metal bonded [(CN)(5)PtTl(CN)(3)](3)(-) complex from Pt(CN)(4)(2)(-) and Tl(CN)(4)(-) has been studied in the pH range of 5-10, using standard mix-and-measure spectrophotometric technique at pH 5-8 and stopped-flow method at pH > 8. The overall order of the reaction, Pt(CN)(4)(2)(-) + Tl(CN)(4)(-) right harpoon over left harpoon [(CN)(5)PtTl(CN)(3)](3)(-), is 2 in the slightly acidic region and 3 in the alkaline region, which means first order for the two reactants in both cases and also for CN(-) at high pH. The two-term rate law corresponds to two different pathways via the Tl(CN)(3) and Tl(CN)(4)(-) complexes in acidic and alkaline solution, respectively. The two complexes are in fast equilibrium, and their actual concentration ratio is controlled by the concentration of free cyanide ion. The following expression was derived for the pseudo-first-order rate constant of the overall reaction: k(obs) = (k(1)(a)[Tl(CN)(4)(-) + (k(1)(a)/K(f)))(1/(1 + K(p)[H(+)]))[CN(-)](free) + k(1)(b)[Tl(CN)(4)(-)] + (k(1)(b)/K(f)), where k(1)(a) and k(1)(b) are the forward rate constants for the alkaline and slightly acidic paths, K(f) is the stability constant of [(CN)(5)PtTl(CN)(3)](3)(-), and K(p) is the protonation constant of cyanide ion. k(1)(a) = 143 +/- 13 M(-)(2) s(-)(1), k(1)(b) = 0.056 +/- 0.004 M(-)(1) s(-)(1), K(f) = 250 +/- 54 M(-)(1), and log K(p) = 9.15 +/- 0.05 (I = 1 M NaClO(4), T = 298 K). Two possible mechanisms were postulated for the overall reaction in both pH regions, which include a metal-metal bond formation step and the coordination of the axial cyanide ion to the platinum center. The alternative mechanisms are different in the sequence of these steps.     

Room temperature and shock tube study of the reaction HCO+O2 using the photolysis of glyoxal as an efficient HCO source

The rate of the reaction 1, HCO+O2-->HO2+CO, has been determined (i) at room temperature using a slow flow reactor setup (20 mbarH2+HCO+CO, into additional HCO radicals. The rate constants of reaction 4 were determined from unperturbed photolysis experiments to be k4(295 K)=(3.6+/-0.3)x10(10) cm3 mol-1 s-1 and k4(769-1107 K)=5.4x10(13)exp(-18 kJ mol-1/RT) cm3 mol-1 s-1(Delta log k4=+/-0.12).     

Thermodynamics, kinetics, and mechanism of the reversible formation of oxorhenium(VII) catecholate complexes

Mononuclear Re(V) compounds MeReO(mtp)NC(5)H(4)X, 3, where mtpH(2) is 2-(mercaptomethyl)thiophenol have been prepared from the monomerization of [MeReO(mtp)](2) by pyridines with electron-donating substituents in the para or meta position; X = 4-Me, 4-Bu(t), 3-Me, 4-Ph, and H. Analogous compounds, MeReO(edt)N(5)H(4)X, 4, edtH(2) = 1,2-ethanedithiol, were prepared similarly. The equilibrium constants for the reaction, dimer + 2Py = 2M-Py, are in the range (2.5-31.6) x 10(2) L mol(-1). Both groups of monomeric compounds react with quinones (phenanthrenequinone, PQ, and 3,5-tert-butyl-1,2-benzoquinone, DBQ), displacing the pyridine ligand and forming Re(VII) catecholate complexes MeReO(dithiolate)PCat and MeReO(dithiolate)DBCat. With PQ, the reaction MeReO(dithiolate)Py + PQ = MeReO(dithiolate)PCat + Py is an equilibrium; values of K(Q) for different Py ligands lie in the ranges 9.2-42.7 (mtp) and 3.2-11.2 (edt) at 298 K. These second-order rate constants (L mol(-1) s(-1)) at 25 degrees C in benzene were obtained for the PQ reactions: k(f) = (5.3-15.5) x 10(-2) (mtp), (6.6-16.4) x 10(-2) (edt); k(r) = (3.63-5.71) x 10(-3) (mtp), (14.7-22.0) x 10(-3) (edt). The ranges in each case refer to the series of pyridine ligands, the forward rate constant being the largest for C(5)H(5)N, with the lowest Lewis basicity. The reactions of MeReO(dithiolate)Py with DBQ proceed to completion. Values of k(f)/L mol(-1) s(-1) fall in a narrow range, 4.02 (X = Bu(t)) to 8.4 (X = H) with the dithiolate being mtp.     

Ab initio chemical kinetics for the OH+HNCN reaction

The kinetics and mechanism of the reaction of the cyanomidyl radical (HNCN) with the hydroxyl radical (OH) have been investigated by ab initio calculations with rate constants prediction. The single and triplet potential energy surfaces of this reaction have been calculated by single-point calculations at the CCSD(T)/6-311+G(3df,2p) level based on geometries optimized at the B3LYP/6-311+G(3df,2p) and CCSD/6-311++G(d,p) levels. The rate constants for various product channels in the temperature range of 300-3000 K are predicted by variational transition-state and Rice-Ramsperger-Kassel-Marcus (RRKM) theories. The predicted total rate constants can be represented by the expressions ktotal=2.66 x 10(+2)xT-4.50 exp(-239/T) in which T=300-1000 K and 1.38x10(-20)xT2.78 exp(1578/T) cm3 molecule(-1) s(-1) where T=1000-3000 K. The branching ratios of primary channels are predicted: k1 for forming singlet HON(H)CN accounts for 0.32-0.28, and k4 for forming singlet HONCNH accounts for 0.68-0.17 in the temperature range of 300-800 K. k2+k7 for producing H2O+NCN accounts for 0.55-0.99 in the high-temperature range of 800-3000 K. The branching ratios of k3 for producing HCN+HNO, k6 for producing H2N+NCO, k8 for forming 3HN(OH)CN, k9 for producing CNOH+3NH, and k5+k10 for producing NH2+NCO are negligible. The rate constants for key individual product channels are provided in a table for different temperature and pressure conditions.     

Kinetics and mechanism of bromate-bromide reaction catalyzed by acetate

The initial rate of the bromate-bromide reaction, BrO3- + 5Br- + 6H+ --> 3Br2 + 3H2O, has been measured at constant ionic strength, I = 3.0 mol L(-1), and at several initial concentrations of acetate, bromate, bromide, and perchloric acid. The reaction was followed at the Br2/Br3- isosbestic point (lambda = 446 nm) by the stopped-flow technique. A very complex behavior was found such that the results could be fitted only by a six term rate law, nu = k1[BrO3-][Br-][H+]2 + k2[BrO3-][Br-]2[H+]2 + k3[BrO3-][H+]2[acetate]2 + k4[BrO3-][Br-]2[H+]2[acetate] + k5[BrO3-][Br-][H+]3[acetate]2 + k6[BrO3-][Br-][H+]2[acetate], where k1 = 4.12 L3 mol(-3) s(-1), k2 = 0.810 L4 mol(-4) s(-1), k3 = 2.80 x 10(3) L4 mol(-4) s(-1), k4 = 278 L5 mol(-5) s(-1), k5 = 5.45 x 10(7) L6 mol(-6) s(-1), and k6 = 850 L4 mol(-4) s(-1). A mechanism, based on elementary steps, is proposed to explain each term of the rate law. This mechanism considers that when acetate binds to bromate it facilitates its second protonation.     

CH(A2Delta) Formation in hydrocarbon combustion: the temperature dependence of the rate constant of the reaction C2H + O2--> CH(A2Delta) + CO2

The temperature dependence of the rate constant of the chemiluminescence reaction C2H + O2 --> CH(A) + CO2, k1e, has been experimentally determined over the temperature range 316-837 K using pulsed laser photolysis techniques. The rate constant was found to have a pronounced positive temperature dependence given by k1e(T) = AT(4.4) exp(1150 +/- 150/T), where A = 1 x 10(-27) cm(3) s(-1). The preexponential factor for k1e, A, which is known only to within an order of magnitude, is based on a revised expression for the rate constant for the C2H + O(3P) --> CH(A) + CO reaction, k2b, of (1.0 +/- 0.5) x 10(-11) exp(-230 K/T) cm3 s(-1) [Devriendt, K.; Van Look, H.; Ceursters, B.; Peeters, J. Chem. Phys. Lett. 1996, 261, 450] and a k2b/k1e determination of this work of 1200 +/- 500 at 295 K. Using the temperature dependence of the rate constant k1e(T)/k1e(300 K), which is much more accurately and precisely determined than is A, we predict an increase in k(1e) of a factor 60 +/- 16 between 300 and 1500 K. The ratio of rate constants k2b/k1e is predicted to change from 1200 +/- 500 at 295 K to 40 +/- 25 at 1500 K. These results suggest that the reaction C2H + O2 --> CH(A) + CO2 contributes significantly to CH(A-->X) chemiluminescence in hot flames and especially under fuel-lean conditions where it probably dominates the reaction C2H + O(3P) --> CH(A) + CO.     

13C, 18O, and D fractionation effects in the reactions of CH3OH isotopologues with Cl and OH radicals

A relative rate experiment is carried out for six isotopologues of methanol and their reactions with OH and Cl radicals. The reaction rates of CH2DOH, CHD2OH, CD3OH, (13)CH3OH, and CH3(18)OH with Cl and OH radicals are measured by long-path FTIR spectroscopy relative to CH3OH at 298 +/- 2 K and 1013 +/- 10 mbar. The OH source in the reaction chamber is photolysis of ozone to produce O((1)D) in the presence of a large excess of molecular hydrogen: O((1)D) + H2 --> OH + H. Cl is produced by the photolysis of Cl2. The FTIR spectra are fitted using a nonlinear least-squares spectral fitting method with measured high-resolution infrared spectra as references. The relative reaction rates defined as alpha = k(light)/k(heavy) are determined to be: k(OH + CH3OH)/k(OH + (13)CH3OH) = 1.031 +/- 0.020, k(OH + CH3OH)/k(OH + CH3(18)OH) = 1.017 +/- 0.012, k(OH + CH3OH)/k(OH + CH2DOH) = 1.119 +/- 0.045, k(OH + CH3OH)/k(OH + CHD2OH) = 1.326 +/- 0.021 and k(OH + CH3OH)/k(OH + CD3OH) = 2.566 +/- 0.042, k(Cl + CH3OH)/k(Cl + (13)CH3OH) = 1.055 +/- 0.016, k(Cl + CH3OH)/k(Cl + CH3(18)OH) = 1.025 +/- 0.022, k(Cl + CH3OH)/k(Cl + CH2DOH) = 1.162 +/- 0.022 and k(Cl + CH3OH)/k(Cl + CHD2OH) = 1.536 +/- 0.060, and k(Cl + CH3OH)/k(Cl + CD3OH) = 3.011 +/- 0.059. The errors represent 2sigma from the statistical analyses and do not include possible systematic errors. Ground-state potential energy hypersurfaces of the reactions were investigated in quantum chemistry calculations at the CCSD(T) level of theory with an extrapolated basis set. The (2)H, (13)C, and (18)O kinetic isotope effects of the OH and Cl reactions with CH3OH were further investigated using canonical variational transition state theory with small curvature tunneling and compared to experimental measurements as well as to those observed in CH4 and several other substituted methane species.     

Serine protease mechanism-based mimics. Direct evidence for a transition state bridge proton in stable potentials

We have synthesized 1-(2-hydroxyacetyl)piperidine-2-one (2) and 1-(2-hydroxyacetyl)azepan-2-one (3). Equilibrium (K(f)) between the free alcohol (open form) and the tetrahedral intermediate (cyclol) is readily established, and both forms are observed in the D(2)O (1)H NMR spectra of 2 and 3. Therefore, their interconversion can be considered as an almost thermoneutral non-identical one. Pseudo-first-order rate constants (k(obs)) were obtained by simulating the AB (1)H NMR system observed for the cyclol. By best fitting the experimental points of a k(obs) versus pD profile to the equation k(obs) = 0.5k(0r) + 0.5k(r) K(ac)/(K(ac) + [D(+)]) + 0.5k(f)K(ao)/(K(ao)+ [D(+)]), the parameters involved were obtained: rate constants of rupture and formation (k(0r) and k(0f) = K(f)k(0r)) catalyzed by water, rate constants of rupture (k(r)) and formation (k(f)) from the conjugated bases of the cyclol form and the open form, and their acidity equilibrium constants K(ac) and K(ao). The system studied mimics the serine alcohol attack on the peptide bond and its reverse reaction in serine protease enzymes. In fact, the reaction rates are similar or perhaps even faster than the ones obtained for enzymatic reactions. The results also show the participation of water molecules forming catalytic proton bridges in stable potentials with the two interconverted forms. The position change of the bridged proton is sensitive to lactam ring size, and it is manifested by considerable change in the pKa values of both cyclol and open forms. Other evidence such as kinetics, DeltaS degrees , DeltaS, and proton inventory experiments and semiempirical molecular calculations support this proposal.