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1.
The kinetics of the acid hydrolysis reaction of Fe(II)‐bis(salicylidene) complexes were followed under pseudo–first‐order conditions ([H+] >> [complex]) at 298 K. The ligands of the studied azomethine complexes were derived from the condensation of salicylaldehyde with different five α‐amino acids. The hydrolysis reactions were studied in acidic medium at different ratios (v/v) of aqua–organic mixtures. The decrease in the dielectric constant values of the reaction mixture enhances the reactivity of the reaction. The transfer chemical potentials of the initial and transition states (IS–TS) from water into mixed solvents were determined from the solubility measurements combined with the kinetic data. Nonlinear plots of logkobs versus 1/D (the reciprocal of the dielectric constant) suggest the influence of the solvation of IS–TS on the reaction reactivity. Furthermore, the acid hydrolysis reactions were screened in the presence of different concentrations of cationic and anionic tensides. The addition of surfactants to the reaction mixture accelerates the reaction reactivity. The obtained kinetic data were used to determine the values of δmΔG# (the change in the activation barrier) for the studied complexes when transferred from “water to various ratios (v/v) of water–co‐organic binary mixtures” and from “water to water containing different [surfactant].” It was found that the reactivity of the acid hydrolysis reaction was controlled by the hydrophobicity of the studied chelates.  相似文献   

2.
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   

3.
The kinetics of the hydrolysis of fenuron in sodium hydroxide has been investigated spectrometrically in an aqueous medium and in cationic micelles of cetyltrimethylammonium bromide (CTAB) medium. The reaction follows first‐order kinetics with respect to [fenuron] in both the aqueous and micellar media. The rate of hydrolysis increases with the increase in [NaOH] in the lower concentration range but shows a leveling behavior at higher concentrations. The reaction followed the rate equation, 1/kobs = 1/k + 1/(kK[OH?]), where kobs is the observed rate constant, k is rate constant in aqueous medium, and k is the equilibrium constant for the formation of hydroxide addition product. The cationic CTAB micelles enhanced the rate of hydrolytic reaction. In both aqueous and micellar pseudophases, the hydrolysis of fenuron presumably occurs via an addition–elimination mechanism in which an intermediate hydroxide addition complex is formed. The added salts decrease the rate of reaction. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 638–644, 2007  相似文献   

4.
Complexes of FeII with monoxime and dioxime ligands have been isolated and characterised. Kinetic results and rate laws are reported for acid aquation and base hydrolysis of these complexes in H2O and in MeOH–H2O mixtures. Kinetics of acid catalysed aquation of FeII–monoxime complexes follow a rate law with kobs = k2[H+] + k3[H+]2, while kinetics of acid dissociation and base hydrolysis of the FeII–dioxime complex follow rate laws with kobs = k2[H+] and kobs = k2[OH]. Acid aquation and base hydrolysis mechanisms are proposed. The solubilities of FeII–monoxime and –dioxime complex salts are reported and transfer chemical potentials of their complex cations are calculated. Solvent effects on reactivity trends have been analysed into initial and transition state components. These are determined from transfer chemical potentials of reactant and kinetic data. Rate constant trends from these complexes are compared and discussed in terms of ligand structure and solvation properties. Our kinetic results give information relevant to the application of these ligands as analytical reagents for trace FeII in acidic and neutral media, in water and in aqueous alcohols.  相似文献   

5.
Kinetics of aquation of some Fe(II) Schiff base amino acid complexes was followed spectrophotometrically. The Schiff base ligands were derived from salicylaldehyde and isoleucine, leucine, serine, methionine, tryptophan, or histidine. The reaction was studied in aqueous media, aqua–propanol mixtures, and in the presence of different concentrations of KBr. Moreover, the activation parameters were calculated and discussed for structures and other physical properties observed. The reaction was acid catalyzed and the general rate equation was suggested as follows: rate = kobs [complex], where kobs = k2 [H+]. © 2010 Wiley Periodicals, Inc. Int J Chem Kinet 42: 372–379, 2010  相似文献   

6.
Salt effects on the kinetics of acid hydrolysis of some novel hydrophilic iron(II) complexes have been investigated in aqueous medium. The ligands are derived from the condensation of amino acids (glycine, L-alanine, L-leucine, L-isoleucine, DL-methionine, DL-serine or L-phenylalanine) and sodium 2-hydroxybenzaldehyde-5-sulfonate. The reaction was studied under conditions of pseudo first order kinetics. The general rate equation was suggested as follows: rate = k obs[complex], where k obs = k 2[H+]. The reaction rate decreases with an increase of the salt concentration.  相似文献   

7.

Two Schiff base Mn(III) complexes containing polyether side chain were synthesized and characterized. The catalytic hydrolysis of p‐nitrophenyl picolinate (PNPP) by the two complexes in the buffered CTAB micellar solution in the pH range of 6.60–8.20 was investigated kinetically in this study. The influences of acidity, temperature, and structure of complex on the catalytic cleavage of PNPP were also studied. The mechanism of PNPP hydrolysis catalyzed by Schiff base manganese(III) complexes in CTAB micellar solution was proposed. The relative kinetic and thermodynamic parameters were determined. Comparied with the pseudo‐first‐order rate constant (k 0) of PNPP spontaneous hydrolysis in water, the pseudo‐first‐order rate constants (k obsd) of PNPP catalytic hydrolysis are 1.93×103 fold for MnL1 2Cl and 1.06×103 fold for MnL2 2Cl in CTAB micellar solution at pH=7.00, T=25°C, and [S]=2.0×10?4mol · dm?3, respectively. Furthermore, comparing the k obsd of PNPP catalytic hydrolysis by metallomicelles with that of PNPP hydrolysis catalyzed only by metal complexes or CTAB micelle at the above‐mentioned condition, metallomicelles of MnL2(L=L1, L2) Cl/CTAB exhibit notable catalytic activities for promoting PNPP hydrolysis, and MnL1 2Cl/CTAB system is superior in promoting cleavage of PNPP relative to MnL2 2Cl/CTAB system under the same experimental conditions. The results indicate that the rate of PNPP catalytic cleavage is influenced by the structures of the two complexes, the acidity of reaction systems, and the solubilization of PNPP in CTAB micelles.  相似文献   

8.
Kinetics of the base hydrolysis of 6-nitro-2H-chromen-2-one (NC) and 6-nitro-2H-chromen-2-one-3-carboxylic acid (NCC) in water-methanol and water-acetone mixtures was studied at temperature range from 283 to 313 K. The activation parameters of the reactions were evaluated and discussed. The change in the activation barrier of the investigated compounds from water to water-methanol and water-acetone mixtures were estimated from the kinetic data. The base hydrolysis of NC and NCC in the water-methanol and water-acetone mixtures follows a rate law with k obs = k 2[OH] and k obs = k 1 + k 2[OH], respectively. The decrease in the rate constants of NC and NCC hydrolysis, as the proportion of methanol and acetone increases, is accounted for by the destabilization of the OH ion. The activation and thermodynamic parameters were determined.  相似文献   

9.
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: kobs1 + 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   

10.
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   

11.
The nucleophilic second-order rate constant (kOH) for the reaction of ōH with ionized N-hydroxyphthalimide (S?) appears to follow a reaction mechanism similar to that for reactions of ōH with neutral phthalimide and its N-substituted derivatives. Kinetically indistinguishable terms, kw[H2O][S?] and kōH[ōH][SH] (SH represents nonionized N-hydroxyphthalimide), which constitute the pH-independent rate region of the pH-rate profile, are resolved qualitatively. It is shown that the term kōH[ōH][SH], rather than kw[H2O][S?], is important in these reactions. The rates of ōH-catalyzed cleavage of S? were studied at 32° in the presence of micelles of sodium dodecyl sulphate (SDS). At a constant [ōH], the observed pseudo first-order rate constants (kobs) increase linearly with [SDS]T (total SDS concentration). These data are explained in terms of the pseudophase model of micellar effects on reactivity. The linear dependence of kobs with [SDS]T (within [SDS]T range of 0.0–0.2 or 0.3 M) is attributed to the occurrence of the reaction between the exterior boundary of Stern layer and Gouy-Chapman layer.  相似文献   

12.
The kinetics of hydrolytic cleavage of saccharin has been studied at 60°C within the [ōH] range of 0.1 to 3.0 M. The observed pseudo first-order rate constants, kobs, follow an empirical relationship: kobs = B[ōH] + [C[ōH]]2. The B and C terms are attributed to the formation of dianionic and trianionic tetrahedral intermediates on the reaction path. It is concluded that the ionized form of saccharin is the major reacting species under the present experimental conditions. The positive ionic strength effect and the negative effect of 1,4-dioxan on the rate of hydrolysis favor the proposed reaction mechanism. The analysis of the observed activation parameters indicates that the increase in the contribution of C term to kobs causes the slight increase in both ΔH* and ΔS*. A significantly large negative value of ΔS* favors the proposed mechanism.  相似文献   

13.
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   

14.
Complexes of the type [Ni(L)(H2O)]Cl2·nH2O, where L = 2‐pyridyl‐3‐isatinbishydrazone ligands, have been synthesized and characterized on the bases of elemental analysis, molar conductance, IR, electronic spectra, and thermal analysis (TGA and DTA). Acid‐catalyzed aquation of the Ni(II) isatin‐bishydrazone complexes was followed spectrophotometrically in various water–methanol and water–acetone mixtures at temperature 298 K. Kinetic behavior of the acid aquation is a linear rate law, indicating that the acid‐catalyzed aquation of these complexes in water–methanol and water–acetone mixtures follows a rate law with kobs = k2[H+]. The effect of the mole fraction of the ganic solvent, i.e., methanol and acetone, on the acid aquation has been analyzed; the decrease in the rate constant values with increasing of the methanol or acetone ratios is attributable to the effect of the co‐organic solvent on the initial states of the acid aquation by the destabilization of the H+ ion.  相似文献   

15.
The kinetics of the aqueous cleavage of N‐ethoxycarbonylphthalimide (NCPH) in CH3NHOH buffers of different pH reveals that the cleavage follows the general irreversible consecutive reaction path NCPH ENMBC A B , where ENMBC, A , and B represent ethyl N‐[o‐(N‐methyl‐N‐hydroxycarbamoyl)benzoyl]carbamate, N‐hydroxyl group cyclized product of ENMBC, and o ‐(N‐methyl‐N‐hydroxycarbamoyl)benzoic acid, respectively. The rate constant k1 obs at a constant pH, obeys the relationship k1 obs = kw + knapp [Am]T + kb[Am]T2, where [Am]T is the total concentration of CH3NHOH buffer and kw is first‐order rate constant for pH‐independent hydrolysis of NCPH. Buffer‐dependent rate constant kb shows the presence of both general base and general acid catalysis. Both the rate constants k2 obs and k3 obs are independent of [Am]T (within the [Am]T range of present study) at a constant pH and increase linearly with the increase in aOH with definite intercepts. © 2001 John Wiley & Sons, Inc. Int J Chem Kinet 34: 95–103, 2002  相似文献   

16.
The effect of cationic micelles of cetyltrimethylammonium bromide (CTAB) on the kinetics of interaction of copper dipeptide complex [Cu(II)‐Gly‐Gly]+ with ninhydrin has been studied spectrophotometrically at 70°C and pH 5.0. The reaction follows first‐ and fractional‐order kinetics, respectively, in complex and ninhydrin. The reaction is catalyzed by CTAB micelles, and the maximum rate enhancement is about twofold. The results obtained in the micellar medium are treated quantitatively in terms of the kinetic pseudophase and Piszkiewicz models. The rate constants (kobs or kΨ), micellar‐binding constants (kS for [Cu(II)‐Gly‐Gly]+, kN for ninhydrin), and index of cooperativity (n) have been evaluated. A mechanism is proposed in accordance with the experimental results. The influence of different inorganic (NaCl, NaBr, Na2SO4) and organic (NaBenz, NaSal) salts on the reaction rate has also been seen, and it is found that tightly bound/incorporated counterions are the most effective. © 2007 Wiley Periodicals, Inc. Int J Chem Kinet 39: 556–564, 2007  相似文献   

17.
Summary The reduction of chloro-, bromo- and iodopentacyanocobaltate(III) anions by aquatitanium(III) has been studied in aqueous solution with ionic strength, I = 1.0 mol dm-3 (LiCl, KBr or KI) at T = 25 °C. The dependence of the observed second-order rate constant, k obs, on [H+] has been investigated over the acid range 0.005–0.100 mol dm –3 and is of the general limiting form: k obs k 0 + k[H +] –1, where k 0 is appreciable in all cases and k is a composite rate constant. Using values of K a (associated with the TiIII hydrolytic equilibrium constant), obtained from the kinetic data for the TiIII/CoIII redox reactions, and comparison of the rate constants obtained with those for the corresponding VII reductions of the same CoIII complexes, it is concluded that the TiIII reductions of these halopentacyanocobaltate(III) complexes proceed via an outer-sphere mechanism.Author to whom all correspondence should be directed, who is presently on leave of absence from Obafemi Awolowo University.  相似文献   

18.
The hydrolysis reaction of O,O‐diethyl Op‐nitrophenylphosphate (Paraoxon) with the octanohydroxamate ion (OHA?) was studied in a cationic oil‐in‐water (O/W) microemulsion system over a pH range 7.5–12.0 at 300 K. The O/W systems are stabilized by using cationic surfactant, cetyltrimethylammonium bromide (CTAB), and n‐butanol as cosurfactants. In a microemulsion, the rate enhancement by OHA? is greater toward the cleavage of paraoxon than its spontaneous (2.1 × 107 s?1) hydrolysis. The kobs values for the reaction of paraoxon with OHA? were determined in different microemulsion compositions with varying chain length of alcohols (n‐butanol, n‐pentanol, n‐octanol, and n‐dodecanol) and alkanes (n‐hexane, n‐heptane, and n‐decane). The effects of water content, pH, and size of the oil pool have been discussed.  相似文献   

19.
In the present paper, kinetics of alkaline degradation of well known drug, indomethacin (2-[1-(4-chlorobenzoyl)-5-methoxy-2-methylindol-3-yl]acetic acid), was studied in presence of excess [NaOH]. The rate of hydrolysis of substrate was independent of the [indomethacin] though it increased linearly with increasing the hydroxide ion concentration with a positive slope, suggesting the following rate law: kobs = k1[OH]. Cationic surfactants having non-reactive ions (cetyltrimethylammonium bromide, CTAB and cetyltrimethylammonium sulfate (CTA)2SO4) first increased the rate constants at lower concentrations and then decreased it at higher concentrations while in case of the surfactant with reactive counterions (cetyltrimethylammonium hydroxide, CTAOH) the rate increases sharply at lower concentrations of surfactant until it reaches to a plateau in contrast to the appearance of maxima in case of CTAB and (CTA)2SO4. Anionic surfactant, sodium dodecyl sulfate (SDS), inhibited the reaction rate at all concentrations used in the study. Pseudophase ion-exchange model was used for analyzing the effect of cationic micelles while the inhibition by SDS micelles was fitted using the Menger–Portnoy model. The effect of salts (NaCl, NaBr and (CH3)4NBr) was also seen on the hydrolysis of indomethacin and it was found that all salts inhibited the rate of reaction. The inhibition followed the trend NaCl < NaBr < (CH3)4NBr.  相似文献   

20.
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   

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