共查询到20条相似文献,搜索用时 359 毫秒
1.
LAILA H. ABDEL‐RAHMAN RAFAT M. EL‐KHATIB LOBNA A. E. NASSR AHMED M. ABU‐DIEF 《国际化学动力学杂志》2014,46(9):543-553
The reactivity of few novel high‐spin Fe(II) complexes of Schiff base ligands derived from 2‐hydroxynaphthaldehyde and some variety of amino acids with the OH? ion has been examined in an aqueous mixture at the temperature range from 10 to 40°C. Based on the kinetic investigations, the rate law and a plausible mechanism were proposed and discussed. The general rate equation was suggested as follows: rate = kobs[complex], where kobs. = k1 + k2[OH?]. Base‐catalyzed hydrolysis kinetic measurements imply pseudo–first‐order doubly stage rates due the presence of mer‐ and fac‐isomers. The observed rate constants kobs are correlated with the effect of substituent R in the structure of the ligands. From the effect of temperature on the rate base hydrolysis reaction, various thermodynamic parameters were evaluated. The evaluated rate constants and activation parameters are in a good agreement with the stability constants of the investigated complexes. Moreover, the reactivity of the investigated complexes toward DNA was examined and found to be in a good agreement with the reported binding constants. 相似文献
2.
The first-order kinetics of the decomposition of ferrocenium ion (Fc+) and its substitution derivatives have been studied in aqueous sulfuric acid and in the presence of excess Ce(IV) ion. The observed first-order rate constant (kobs) is expressed as kobs = kd for the acyl-substituted ferrocenium ions and kobs = kd+ kox[Ce(IV)]o for the unsubstituted and alkyl-substituted ferrocenium ions. Electron-donating alkyl substituents stabilize the ferrocenium ion whereas electron-withdrawing acyl substituents make it less stable. The order of relative stability toward decomposition is 1,1′-dimethyl Fc+ ≥ butyl Fc+ > 1,1-dimethylpropyl Fc+ > Fc+ > > formyl Fc+ > acetyl Fc+ > > benzoyl Fc+. A mechanism to interpret the kinetics is also given. 相似文献
3.
Electrochemical oxidation of some catecholamines such as dopamine ( 1 ), L ‐dopa ( 2 ), and methyldopa ( 3 ) has been studied in various pH values, using cyclic voltammetry. The results indicate participation of catecholamines ( 1–3 ) in intramolecular cyclization reaction to form the corresponding o‐quinone derivatives ( 1d–3d ). In various pHs, based on ECE mechanism, the observed homogeneous rate constants (kobs) of cyclization reaction were estimated by comparing the experimental cyclic voltammetric responses with the digital‐simulated results. Also, the cyclization rate constants (kcyc) were calculated using microscopic acidic dissociation constant of ammonium groups. The significant differences in electrochemical behavior, kobs and kcyc, of L ‐dopa ( 2 ) and methyldopa ( 3 ) with dopamine ( 1 ) are due to the effects of the side chain carboxyl group. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 37: 17–24, 2005 相似文献
4.
The catalytic effect of MnII ions on the pseudo-first-order rate constants (k
obs) for chromic acid oxidations of malic and oxaloethanoic acids (an oxidation product of malic acid) has been studied spectrophotometrically at 25 °C. The rates show a first-order dependence on the CrVI concentration for each reductant. The order with respect to [malic acid] was found to lie between 1 and 2, and 1 for [oxaloethanoic acid]. The rate increased markedly with increasing [MnII] in both the cases. The catalytic effects of MnII have been ascribed to a one-step three-electron process in which a termolecular complex is formed between the reductant, MnII and HCrO–
4. The intermediate CrIV is ruled out; details of such a process are discussed. Mechanisms in accordance with the experimental data are proposed for the reactions. 相似文献
5.
We have carried out relative rate experiments (T = 294 ± 2 K, atmospheric pressure) to investigate the OH‐oxidation of o‐, m‐, and p‐ethyltoluene and n‐nonane (k1, k2, k3, and k4 respectively). The experiments were performed in a 2‐m3 smog chamber with Teflon coated walls. The rate constants obtained are (in cm3 molecule?1 s?1 with two sigma uncertainties): k1 = (1.36 ± 0.07) × 10?11; k2 = (2.12 ± 0.26) × 10?11; k3 = (1.47 ± 0.04) × 10?11, and k4 = (0.95 ± 0.02) × 10?11. The measured rate constants are in accordance with previously published data, so that a coherent group of values for the compounds studied can be established. Atmospheric implications, ozone, and particle production are discussed. In addition, we have determined the amount of o‐, m‐, and p‐ethyltoluenes in different types of gasoline. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 367–378 2004 相似文献
6.
Pseudo‐first‐order rate constants (kobs) for hydrolysis of a sulfonylurea herbicide, azimsulfuron, AZIM®, {N‐[[(4,6‐dimethoxy‐2‐pyrimidinyl)amino]carbony]‐1‐methyl‐4‐(2‐methyl‐2H‐tetrazol‐5‐yl)‐1H‐pyrazole‐5‐sulfonamide} (AZS) follow an empirical relationship: kobs =α1 + α2[−OH] + α3[−OH]2 within the [NaOH] range of 0.1–2.0 M at different temperatures ranging from 40 to 55°C. The contribution of α3[−OH]2 term is small compared with α2[−OH] term and this turns out to be zero at 60°C. Pseudo‐first‐order rate constants (kobs) for hydrolysis of AZS within the [H+] range from 2.5 × 10−6 to 1.4 M follow the relationship: kobs = (α1K a + B1[H+] + B2[H+]2)/([H+] + Ka) where pKa = 4.37 at 50°C. The value of B1 is nearly 25 times larger than that of α1. The rate of alkaline hydrolysis of AZIM is weakly sensitive to ionic strength. © 1999 John Wiley & Sons, Inc., Int J Chem Kinet 31: 253–260, 1999 相似文献
7.
Lida Fotouhi Esmail Tammari Samaneh Asadi Majid M. Heravi Davood Nematollahi 《国际化学动力学杂志》2009,41(6):426-431
The reaction of o‐benzoquinone derived by the oxidation of catechols ( 1a–c ) with some nucleophiles containing thiol group ( 2a–f ) has been studied in various conditions, such as pH, nucleophile concentration, and scan rate, using cyclic voltammetry. In various conditions, based on an EC electrochemical mechanism (“E” represents an electron transfer at the electrode surface and “C” represents a homogeneous chemical reaction), the observed homogeneous rate constants (kobs) were estimated by comparison of the experimental cyclic voltammetric responses with the digital simulated results for each of the nucleophile. The results show that the magnitude of kobs is dependent on the nature of the substituted group on the catechol ring and nucleophilicity of nucleophile. © 2009 Wiley Periodicals, Inc. Int J Chem Kinet 41: 426–431, 2009 相似文献
8.
The reaction rate studies on the hydrolytic cleavage of acetyl salicylate ion (AS-) within the [-OH] range 0.010-0.025 M reveal AS- and -OH as the reactants. The effects of micelles of sodium dodecyl sulfate (SDS) on observed pseudo-first-order rate constants (kobs) for the hydrolytic cleavage of AS- have been studied at different [OH-]. At a constant [OH-], the rate constants (kobs) follow an empirical relationship: kobs = C + F [SDS]T where [SDS]T represents total SDS concentration. The magnitudes of C and F increase with an increase in [OH-]. These data are explained in terms of the pseudophase model of the micelle. 相似文献
9.
M. Niyaz Khan 《国际化学动力学杂志》1997,29(9):647-654
Pseudo-first-order rate constants (k1 obs) for the reaction of MeNHOH with NCPH obey the relationship: k1 obs=k′b[MeNHOH]T2 where [MeNHOH]T represents total concentration of N-methylhydroxylamine buffer. The rate constants, k1 obs obtained at different total concentration of acetate buffer ([Buf]T) in the presence of 0.004 mol dm−3 MeNHOH follow the relationship: k1 obs=kb[Buf]T. The values of acetate buffer-catalyzed rate constant (kb) at different pH reveal the occurrence of both general base- and general acid- or general base-specific acid-catalysis in the reaction of MeNHOH with NCPH. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 647–654, 1997. 相似文献
10.
The kinetic study of the decarboxylation of aspartic acid has been carried out at various [ninhydrin], [H+] and at different temperature ranging from 60–95°C. The reaction follows an irreversible first-order reaction path under pseudo first-order kinetic conditions. The variation of pseudo first-order rate constant (kobs) with ninhydrin concentration was found to be in agreement with equation 1/kobs = B1 + B2/[Ninhydrin]. One mol of carbondioxide evolved from decarboxylation of α-COOH and second mol of carbondioxide comes from the decarboxylation of β-keto acid which is an intermediate and formed during the course of ninhydrin and aspartic acid reaction. On the basis of the observed data, a possible mechanism has been proposed. 相似文献
11.
Prof. Dr. Begoña García Dr. Francisco J. Hoyuelos Dr. Saturnino Ibeas Dr. María S. Muñoz Dr. Ana M. Navarro Dr. Indalecio A. Peñacoba Prof. Dr. José M. Leal 《化学:亚洲杂志》2010,5(12):2530-2540
The mechanisms for the hydrolysis of organopalladium complexes [Pd(CNN)R]BF4 (R=P(OPh)3, PPh3, and SC4H8) were investigated at 25 °C by using UV/Vis absorbance measurements in 10 % v/v ethanol/water mixtures containing different sulphuric acid concentrations in the 1.3–11.7 M range. In all cases, a biphasic behavior was observed with rate constants k1obs, which corresponds to the initial step of the hydrolysis reaction, and k2obs, where k1obs>k2obs. The plots of k1obs and k2obs versus sulfuric acid concentration suggest a change in the reaction mechanism. The change with respect to the k1obs value corresponds to 35 %, 2 %, and 99 % of the protonated complexes for R=PPh3, P(OPh)3, and SC4H8, respectively. Regarding k2obs, the change occurred in all cases at about 6.5 M H2SO4 and matched up with the results reported for the hydrolysis of the 2‐acetylpyridinephenylhydrazone (CNN) ligand. By using the excess acidity method, the mechanisms were elucidated by carefully looking at the variation of ki,obs (i=1,2) versus ${c_{{\rm{H}}^ + } }$ . The rate‐determining constants, k0,A‐1, k0,A‐2, and k0,A‐SE2 were evaluated in all cases. The R=P(OPh)3 complex was most reactive due to its π‐acid character, which favors the rupture of the trans nitrogen–palladium bond in the A‐2 mechanism and also that of the pyridine nitrogen–palladium bond in the A‐1 mechanism. The organometallic bond exerts no effect on the relative basicity of the complexes, which are strongly reliant on the substituent. 相似文献
12.
Pseudo‐first‐order rate constants (kobs) for alkaline hydrolysis of 4‐nitrophthalimide (NPTH) decreased by nearly 8‐ and 6‐fold with the increase in the total concentration of cetyltrimethyl‐ammonium bromide ([CTABr]T) from 0 to 0.02 M at 0.01 and 0.05 M NaOH, respectively. These observations are explained in terms of the pseudophase model and pseudophase ion‐exchange model of micelle. The increase in the contents of CH3CN from 1 to 70% v/v and CH3OH from 0 to 80% v/v in mixed aqueous solvents decreases kobs by nearly 12‐ and 11‐fold, respectively. The values of kobs increase by nearly 27% with the increase in the ionic strength from 0.03 to 3.0 M. The mechanism of alkaline hydrolysis of NPTH involves the reactions between HO? and nonionized NPTH as well as between HO? and ionized NPTH. The micellar inhibition of the rate of alkaline hydrolysis of NPTH is attributed to medium polarity effect. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 33: 407–414, 2001 相似文献
13.
The chromium(III) complexes with a new potential chromium transporting ligand—2,5-pyridinedicarboxylic acid (isocinchomeronic
acid, icaH2):[Cr(icaH)3]0, [Cr(icaH)2 (H2O)2]+ and [Cr(icaH)(H2O)4]2+ (where icaH = N,O-bonded isocinchomeronic acid anion), have been obtained and characterized in solution. The [Cr(icaH)3]0 complex undergoes aquation in acidic media to the diaqua-product. Kinetics of this process was studied spectrophotometrically
in the 0.1–1.0 M HClO4 range, at I = 1.0 M. The first aquation stage, the chelate-ring opening at the Cr–N bond, is a much faster than the second one. The rate
laws are of the form: k
obs = k
1 + k
−1/Q
1[H+] and k
obs = k
2
Q
2[H+]/(1 + Q
2[H+]), where k
1 and k
2 are the rate constants for the chelate-ring opening and the ligand liberation, respectively, k
−1 is the rate constant of the chelate-ring closure, Q
1 and Q
2 are the protonation constants of the pyridine nitrogen and 5-carboxylate group in the one-end bonded intermediate, respectively.
The results are discussed in terms of potential pharmaceutical application of the complex. 相似文献
14.
Pseudo‐first‐order rate constants (kobs) for tertiary amine (DABCO and Me3N) buffer‐catalyzed cyclization of N′‐morpholino‐N‐(2′‐methoxyphenyl)phthalamide ( 1 ) to N‐(2′‐methoxyphenyl)phthalimide ( 2 ) reveal saturation (nonlinear) plots of kobs versus [Buf]T (total tertiary amine buffer concentration) at a constant pH. Such plots at different pH have been attributed to the presence of a reactive intermediate (T?) formed by tertiary amine buffer‐catalyzed intramolecular nucleophilic addition of the secondary amide nitrogen to the carbonyl carbon of the tertiary amide group of 1 . © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 263–272, 2010 相似文献
15.
M. Niyaz Khan 《国际化学动力学杂志》2001,33(1):29-40
Pseudo‐first‐order rate constants (kobs) for the cleavage of phthalimide in the presence of piperidine (Pip) vary linearly with the total concentration of Pip ([Pip]T) at a constant content of methanol in mixed aqueous solvents containing 2% v/v acetonitrile. Such linear variation of kobs against [Pip]T exists within the methanol content range 10%–∼80% v/v. The change in kobs with the change in [Pip]T at 98% v/v CH3OH in mixed methanol‐acetonitrile solvent shows the relationship: kobs = k[Pip]T + k[Pip], where respective k and k represent apparent second‐order and third‐order rate constants for nucleophilic and general base‐catalyzed piperidinolysis of phthalimide. The values of kobs, obtained within [Pip]T range 0.02–0.40 M at 0.03 M NaOH and 20 as well as 50% v/v CH3OH reveal the relationship: kobs = k0/(1 + {kn[Pip]/kOX[−OX]T}), where k0 is the pseudo‐first‐order rate constant for hydrolysis of phthalimide, kn and kOX represent nucleophilic second‐order rate constants for the reaction of Pip with phthalimide and for the XO−‐catalyzed cyclization of N‐piperidinylphthalamide to phthalimide, respectively, and [−OX]T = [NaOH] + [−OXre], where [−OXre] = [−OHre] + [CH3Ore−]. The reversible reactions of Pip with H2O and CH3OH produce −OHre and CH3Ore− ions. The effects of mixed methanol‐water solvents on the rates of piperidinolysis of PTH reveal a nonlinear decrease in k with the increase in the content of methanol. © 2000 John Wiley & Sons, Inc. Int J Chem Kinet 33: 29–40, 2001 相似文献
16.
Hisham J. Y. El‐Aila 《Journal of Dispersion Science and Technology》2013,34(6):927-931
The kinetic complex formation of 0.001 M 2‐nitroso‐1‐naphthol (NAPH)with 0.01 M cobalt (II) ion (Co2+) in aqueous in presence of 0.02 M NaOH at 30°C in aqueous and/or in and 0.002 M cetyltrimethylammonium bromide (CTAB) have been studied using spectrophotometer at 430 nm. The present data showed that the reaction is first‐order with respect to [Co2+]T and NAPH. Also, k obs have constant values within concentration 0.015–0.05 M of NaOH and decreases with increase of concentration of CTAB to 0.002 M, then, k obs have constant values up to 0.005 M. The rate of the reaction in the presence of micelles has been explained with the pseudo‐phase model of the kinetics. Association constants of Co2+ and NAPH to CTAB micelle have been calculated. The activation parameters ΔH* and ΔS* have been obtained. The increase of reaction rate with sodium benzoate (C7H5O2Na) also has been discussed. 相似文献
17.
Davood Nematollahi Leila Mohammadi‐Behzad Saied Saeed Hossainy Davarani 《Electroanalysis》2009,21(9):1099-1106
The electrochemical oxidation of catechols ( 1 ) have been studied in the presence of diaza‐18‐crown‐6 (DA18C6) ( 3a ), diaza‐15‐crown‐5 (DA15C5) ( 3b ), and aza‐15‐crown‐5 (A15C5) ( 3c ) as nucleophiles in aqueous solution, by means of cyclic voltammetry and controlled‐potential coulometry. The results indicate the participation of electrochemically generated o‐benzoquinones ( 2 ) in Michael‐type reaction with aza‐crown ethers ( 3 ) to form the corresponding new o‐benzoquinone‐aza‐crown ether adducts ( 5 ). Based on ECE mechanism, the observed homogeneous rate constants (kobs) of the reaction of o‐bezoquinones ( 2 ) with aza‐crown ethers ( 3 ) were estimated by comparing the experimental cyclic voltammograms with the digital simulated results. The calculated observed homogeneous rate constants (kobs) was found to vary in the order DA18C6>DA15C5>A15C5. 相似文献
18.
The kinetics of oxidation of cis‐[CrIII(phen)2(H2O)2]3+ (phen = 1,10‐phenanthro‐ line) by IO4? has been studied in aqueous acidic solutions. In the presence of a vast excess of [IO4?], the reaction is first order in the chromium(III) complex concentration. The pseudo‐first‐order rate constant, kobs, showed a very small change with increasing [IO4?]. The dependence of kobs on [IO4?] is consistent with Eq. (i). (i) The pseudo‐first‐order rate constant, kobs, increased with increasing pH, indicating that the hydroxo form of the chromium(III) complex is the reactive species. An inner‐sphere mechanism has been proposed for the oxidation process. The thermodynamic activation parameters of the processes involved are also reported. © 2011 Wiley Periodicals, Inc. Int J Chem Kinet 43: 563–568, 2011 相似文献
19.
The chromium(III)-quinolinato complexes, [Cr(quinH)3]0, [Cr(quinH)2(H2O)2]+ and [Cr(quinH)(H2O)4]2+ (where quinH = N,O-bonded quinolinic acid anion), were obtained and characterized in solution. The tris-quinolinato complex
undergoes acid-catalyzed aquation to give the diaqua-product, whereas subsequent ligand liberation processes are exceptionally
slow. Kinetics of the aquation were studied spectrophotometrically over the 0.1–1.0 M HClO4 range, at I = 1.0 M. The first aquation stage, the chelate-ring opening at the Cr-N bond, is much faster than the second one. The following rate
laws were established: k
obs = k
1 + k
−1/Q
1[H+] and k
obs = k
2
Q
2[H+]/(1 + Q
2[H+]), where k
1 and k
2 are the rate constants for the chelate-ring opening and the ligand liberation, respectively, k
−1 is the rate constant of the chelate-ring closure, Q
1 and Q
2 are the protonation constants of the pyridine nitrogen and 3-carboxylate group in the one-end bonded intermediate, respectively.
Kinetic parameters have been determined and the mechanism has been discussed. 相似文献
20.
Yongqing Zhai Hongmei Liu Baosheng Liu Yukai Liu Jia Xiao Weisong Bai 《Transition Metal Chemistry》2007,32(5):570-575
The kinetics and mechanism of ruthenium(III) catalyzed oxidation of tetrahydrofurfuryl alcohol (THFA) by cerium(IV) in sulfuric
acid media have been investigated spectrophotometrically in the temperature range 298–313 K. It is found that the reaction
is first-order with respect to CeIV, and exhibits a positive fractional order with respect to THFA and RuIII. The pseudo first-order ([THFA]≫[CeIV]≫[RuIII]) rate constant k
obs decreases with the increase of [HSO
4
−
]. Under the protection of nitrogen, the reaction system can initiate polymerization of acrylonitrile, indicating the generation
of free radicals. On the basis of the experimental results, a reasonable mechanism has been proposed and the rate equations
derived from the mechanism can explain all the experimental results. From the dependence of k
obs on the concentration of HSO
4
−
,
has been found as the kinetically active species. Furthermore, the rate constants of the rate determining step together with
the activation parameters were evaluated. 相似文献