Kinetics and mechanism of base-catalyzed hydrolysis of Cu(II)-malonamide complex

A kinetic study of base-catalyzed hydrolysis of Cu(II)-malonamide complex has been performed in sodium hydroxide solution (0.2–1.25M). The reaction follows an irreversible first-order consecutive path: The variation of k_1obs and k_2obs with alkali concentration was found to be in good agreement with the equations: where B₁, B₂, C₁, and C₂ are empirical constants. The mechanism of hydrolysis of Cu(II)-malonamide complex has been discussed and rate equations have been derived. Retardation of rate of hydrolysis due to coordination of Cu(II) with malonamide, in alkaline medium, has been explained in terms of comparatively slow breakdown of the C? N bond of the tetrahedral intermediate (TI). Thermodynamic parameters have also been evaluated.     

Kinetics of the alkaline hydrolysis of fenuron in aqueous and micellar media

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/k_obs = 1/k + 1/(kK[OH^?]), where k_obs 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     

The Ortho Effect on the Acidic and Alkaline Hydrolysis of Substituted Formanilides

The kinetics of formanilides hydrolysis were determined under first‐order conditions in hydrochloric acid (0.01–8 M, 20–60°C) and in hydroxide solutions (0.01–3 M, 25 and 40°C). Under acidic conditions, second‐order specific acid catalytic constants were used to construct Hammett plots. The ortho effect was analyzed using the Fujita–Nishioka method. In alkaline solutions, hydrolysis displayed both first‐ and second‐order dependence in the hydroxide concentration. The specific base catalytic constants were used to construct Hammett plots. Ortho effects were evaluated for the first‐order dependence on the hydroxide concentration. Formanilide hydrolyzes in acidic solutions by specific acid catalysis, and the kinetic study results were consistent with the A_AC2 mechanism. Ortho substitution led to a decrease in the rates of reaction due to steric inhibition of resonance, retardation due to steric bulk, and through space interactions. The primary hydrolytic pathway in alkaline solutions was consistent with a modified B_AC2 mechanism. The Hammett plots for hydrolysis of meta‐ and para‐substituted formanilides in 0.10 M sodium hydroxide solutions did not show substituent effects; however, ortho substitution led to a decrease in rate constants proportional to the steric bulk of the substituent.     

Kinetics of the alkaline hydrolysis of isoproturon in CTAB and NaLS micelles

Kinetics of the alkaline hydrolysis of isoproturon has been studied in the absence and presence of cetyltrimethylammonium bromide (CTAB) and sodium lauryl sulfate (NaLS) micelles. CTAB micelles were found to enhance the rate of reaction, while NaLS micelles inhibited the reaction rate. The reaction obeyed first‐order kinetics in [isoproturon] and was linearly dependent on [NaOH] at lower concentration. The rate of reaction became independent at higher [NaOH]. At lower [NaOH] the reaction proceeded via formation of hydroxide ion addition complex, while at higher [NaOH] the reaction occurred via deprotonation of ? NH? , leading to the formation of isocyanate. The values of k_w, k_m, and K_s were determined by considering the pseudophase ion exchange model. The activation parameters have also been reported. The effect of added salts (NaCl and KNO₃) on the reaction rate has also been studied. © 2006 Wiley Periodicals, Inc. Int J Chem Kinet 39: 39–45, 2007     

Theoretical studies on the alkaline hydrolysis of N-Methylcarbamates

The reaction mechanisms of the alkaline hydrolysis of N-methylcarbamates were studied using the AM1 method by assuming two possible pathways: (1) nucleophilic attack of hydroxide ion on the carbonyl carbon to give a tetrahedral complex followed by its breakdown to carbamic acid (B_AC2); and (2) proton abstraction by hydroxide ion at the nitrogen atom followed by elimination of the alkoxide ion to form N-methyl isocyanate (E1cB). Reaction coordinate analysis showed that the reaction mechanism is determined by both the stability of an intermediate and the energy barrier for elimination.     

A novel synthetic path to a luminescent,dimeric samarium complex induced by the hydrolysis of methyl pyridine-3-carboxylate

A novel path to lanthanide complexes of aromatic carboxylates controlled by the hydrolysis of the corresponding aromatic carboxylate ester has been discovered. A dimeric samarium complex of pyridine-3-carboxylate (NIC) has been obtained using methyl pyridine-3-carboxylate (MNIC) as the starting ligand. With the hydrolysis of MNIC to NIC in the presence of sodium hydroxide, samarium ions coordinate to HNIC to form [Sm(NIC)₃(H₂O)₂]₂. X-ray analysis reveals the dimeric structure formed through bridging oxygen atoms of carboxylate groups. The complex crystallizes in the monoclinic space group P2₁/c with a?=?9.668(3), b?=?11.807(3), c?=?17.512(5)?Å, β?=?92.361(3)°, V?=?1997.3(10)?ų, D _c?=?1.838?Mg?m^?3, Z?=?2, R ₁?=?0.0225. The complex exhibits strong luminescence.     

205T1-NMR and UV-Visible spectroscopic determination of the formation constants of aqueous thallium(I) hydroxo-complexes

The hydrolysis of T1(I) has been studied at 25°C using²⁰⁵T1-NMR spectroscopy and UV-Vis spectrophotometry in aqueous solutions with ionic strengths maintained by NaC10₄ at 2, 4, 6, and 8M. The formation constant and the spectral characteristics for the hydroxo complex, T10Hℴ have been determined. At high hydroxide ion concentrations there is clear evidence from the UV-Vis data for the formation of a T1(OH)₂-species. The spectrum and an estimated formation constant for this second hydroxo complex are also reported.     

Kinetics and mechanism of ninhydrin reaction with copper(II) complexes of glycine and α-alanine. Elucidation of the template mechanism

Ninhydrin has been found to react with Cu(glycine)⁺ and Cu(alanine)⁺ in the ratio of 1:1. The kinetic studies of the reaction were carried out at different concentrations of the reactants at 80°C (pH = 5.0). The reaction proceeds through the formation of a ternary labile complex of ninhydrin with Cu(II) complexes of glycine and alanine. The kinetics were found to follow pseudo-first-order reaction path with respect to Cu(II)-complex in presence of excess [Ninhydrin]. Formation of a ternary labile complex indicates a template reaction mechanism based on the reactions with coordinated ligands. The variation of pseudo-first-order rate constants with [ninhydrin] was found to be in good agreement with equation where B₁ and B₂ are the unknown empirical parameters. The [acetate ion] has no significant effect on the rate constants. On the basis of observed data a probable mechanism has been proposed. © 1993 John Wiley & Sons, Inc.     

Radical and anionic homopolymerization of maleimide and N-n-butylmaleimide

The rate of homopolymerization of maleimide has been measured in dimethylformamide solution at 60°C. in the presence of azobisisobutyronitrile; it has been compared to that of N-n-butylmaleimide. The overall rates of polymerization are equal to R_p = k[M]^1.1–1.2 [In]^0.8 for maleimide, and R_p = k'[M] [In]^0.5 for the N-substituted imide. The difference of behavior has been interpreted on the basis of an intramolecular tautomery of the terminal group of the maleimide growing chain and the formation of a resonance-stabilized succinimidyl radical. The relative ease of polymerization of these monomers and of maleic anhydride has been discussed. In the presence of sodium tert-butoxide at 20°C. in dimethylformamide solutions, maleimide polymerizes with hydrogen isomerization. The percentage of N-substituted isomerized units was evaluated at 70–75% by measurement of the rate of hydrolysis in 0.005N sodium hydroxide and comparison with succinimide and N-butylsuccinimide. N-n-butylmaleimide undergoes ring opening together with anionic polymerization in the presence of sodium tert-butoxide at 20°C. and butyllithium at -40°C. Unlike the radical-initiated polymerization, it was impossible to obtain anionic copolymers of maleimide and N-butylmaleimide with acrylonitrile and methyl methacrylate.     

Die Hydrolyse des Ga3+-Ions; potentiometrische Untersuchungen in 3m NaClO4 bei 60°C

The hydrolysis of the ion Ga³⁺ has been investigated at 60°C by potentiometric titrations in a sodium perchlorate medium of the constant ionic strength 3 m. Solutions of various total gallium concentrations B were alkalified by means of a coulometric technique. The concentrations h of the free hydrogen ions were measured with the aid of a glass electrode. From the experimental data, Z, the average number of OH bound per Ga was calculated. The mathematical analysis of the curves Z(logh)_B is consistent with the following formulation of the hydrolysis reactions with log*β_l = log k₀ k^l = ?1,7 ? 11,55 l.     

Kinetic Study of Complex Formation of by 2‐Nitroso‐1‐naphthol with Cobalt (II) Ion in Presence of Cetyltrimethylammonium Bromide Surfactant

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.     

Synthesis and Characterization of Tris(tetraethylammonium) Pentacyanoperoxynitritocobaltate(III)

We report the first synthesis of a stable complex of peroxynitrite coordinated to a transition‐metal ion. Solid tris(tetraethylammonium) pentacyanosuperoxocobaltate(III) reacts with 1 equiv. of gaseous nitrogen monoxide to yield tris(tetraethylammonium) pentacyanoperoxynitritocobaltate(III) ( 1 ). This novel complex is characterized by a UV absorption band at 280 nm (ε≈2000 M ⁻¹ cm⁻¹) in H₂O. The IR spectrum of the sodium salt of the complex, 2 , shows vibration bands due to peroxynitrite. Nitrated and hydroxylated products are observed when the complex is dissolved in H₂O in the presence of phenol. The rate constant of hydrolysis is k=4.9×10⁻⁶ s⁻¹. The complex is less stable in MeCN and in MeOH and perhaps reacts with these solvents.     

A study on the hydrolysis of bis(nitrophenyl)phosphate catalyzed by N‐methyldiethanolamine‐Ce(III) complex

The hydrolysis of bis(p‐nitrophenyl)phosphate (BNPP) catalyzed by N‐methyldiethanolamine‐Ce(III) complex in the presence and absence of cetyltrimethylammonium bromide (CTAB) and Brij35 surfactants at pH 7.20 and 303 K has been studied. The experimental results indicate that N‐methyldiethanolamine‐Ce(III) complex remarkably accelerates the hydrolysis of BNPP. The observed first‐order rate constant of the hydrolysis of BNPP catalyzed by N‐methyldiethanolamine‐Ce(III) complex at pH 7.20 and 303 K is 1.22 × 10^?2 s^?1, which is 1.09 × 10⁹ times of that of spontaneous hydrolysis of BNPP at pH 7. It is close to the activity of natural enzyme. A general quantitative treatment of the catalytic reaction involved a ternary complex as M_mL_lS has also been proposed in this paper. Applying this method to the catalytic hydrolysis of BNPP, we have obtained its thermodynamic and kinetic parameters. CTAB and Brij35 surfactant micelles obviously influence the rate constants of the catalytic hydrolysis of BNPP. Brij35 micelles promote the catalytic hydrolysis of BNPP, while CTAB micelles inhibit it. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 687–692, 2004     

Rate Study of the Alkline Hydrolysis of Nicotinamide Using an Ammonia Gas-Sensing Electrode

Abstract

The hydrolysis of nicotinamide in alkaline solutions was studied. An ammonia gas-sensing electrode was used to follow the formation of ammonia. A technique making use of simulated reactions has been developed to calibrate the electrode under dynamic conditions overcoming problems arising because of the relatively slow response of the sensor. A general expression has been derived for the pseudo first-order rate constant valid over the concentration range 0.005 to 0.10 M nicotinamide, 0.1 to 0.5 M hydroxide and the temperature range 22° to 31° C, under constant ionic strength (0.5 M NaOH + NaC1O₄).     

Micellar effects upon the basic hydrolysis of 2,7-bis(diethylamino)phenazoxonium chloride

The effect of cationic and anionic surfactants on the reaction of Basic Blue 3 (2,7-bis(diethylamino)phenazoxonium chloride, 1) with hydroxide ion has been studied. Cetyltrimethylammonium bromide (CTAB), cetyl and tetradecyltrimethylammonium chloride (CTAC and MTAC) enhance the rate of basic hydrolysis whereas sodium dodecyl sulfate (SDS) has an inhibitory effect. The extent of micellar catalysis is reduced by the addition of organic solvents. The results have been analyzed on the basis of the pseudophase ion-exchange model [1–3].     

The temperature dependence and the mechanism of the SO2 (3B1) quenching reactions

The Arrhenius parameters have been determined for the SO₂(³B₁) quenching reaction (9), SO₂(³B₁) + M → (SO₂ ? M), for 21 different molecules as quenching partner M. The rate constants were calculated from phosphorescence lifetime measurements made over a range of reactant pressures and temperatures. Excitation of the SO₂ (³B₁) molecules was accomplished by two very different methods: (1) a 3829 Å laser pulse generated the triplet directly through absorption within the “forbidden” SO₂ (³B₁) → SO₂ (¹A₁) band; (2) a broadband Xe-flash system generated SO₂(³B₁) molecules and triplets were formed subsequently by intersystem crossing, SO₂(¹B₁) + M → SO₂(³B₁) + M. The measured rate constants were independent of the method of triplet formation employed. For the atmospheric gases, the activation energies (kcal/mole) were identical within the experimental error: N₂, 2.9 ± 0.4; 0₂, 3.2 ± 0.5; Ar, 2.8 ± 0.6; CO₂, 2.8 ± 0.4; CO, 2.7 ± 0.4; CH₄, 2.5 ± 0.6. This energy corresponds to the first region of the SO₂(³B₁) → SO₂(¹A₁) absorption spectra in which Brand and coworkers observe strong perturbations. It is suggested that the quenching in these cases results largely from the physical process involving potential energy surface crossing to another electronic state. Activation energies for SO₂(³B₁) quenching by the paraffinic hydrocarbons show a regular decrease in the series ethane, neopentane, propane, n-butane, cyclohexane, and isobutane, which parallels closely the decrease in C? H bond energies in these compounds. These and other data are most consistent with the dominance of chemical quenching in these cases. The rate constants for the olefinic and aromatic hydrocarbons and nitric oxide show only very small variations with temperature change, and they are near the kinetic collision number. These data support the hypothesis that quenching in these cases is associated with the formation of a charge-transfer complex and subsequent chemical interactions between the SO₂(³B₁) molecule and the π-system of these compounds.     

Mechanistic investigation of the oxidation of vitamin B1 with sodium N-chlorobenzenesulfonamide in presence of ruthenium(III) catalyst in hydrochloric acid medium: a kinetic approach

The oxidative cleavage of vitamin B₁ (thiamine hydrochloride, THM) with sodium N-chlorobenzenesulfonamide (chloramine-B, CAB) has been kinetically investigated in HCl medium in presence of ruthenium(III) catalyst at 308 K. The oxidation reaction follows the rate law, −d[CAB]/dt = k [CAB] [Ru(III)] [H⁺] [THM]^a [Cl⁻]^b, where a and b are less than unity. Variation of ionic strength of the medium and addition of the reaction product, benzenesulfonamide (BSA) had no significant effect on the reaction rate. The change in relative permittivity of the medium affected by changing the solvent composition with acetonitrile has been studied. The stoichiometry of the reaction was found to be 1:1, and N-[(4-amino-2-methylpyrimidine-5-yl)methyl]benzensulfonamide and 2-(4-methylthiazol-5-yl)ethanol were identified as the oxidation products of vitamin B₁. The reaction constants involved in the mechanism were computed. The reaction was studied at different temperatures and the overall activation parameters have been evaluated. C₆H₅SO₂NHCl has been postulated as the reactive oxidizing species. The observed results have been explained by plausible mechanisms and the relative rate laws have been deduced. Correspondence: Kikkeri Narasimhasetty Mohana, Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570 006, India.     

Mechanism of hydrolyzable metal ions effect on the zeta potential of fine quartz particles

The effects of ion species, cation valence, ionic strength, and hydrated ionic radius on the zeta potential of quartz have been systematically studied through the measurement of zeta potential, sedimentation rate, and aggregation observation. The results show that the interaction between hydrolysis components and quartz particles results in three critical points – CR₁, CR₂, and CR₃. The results of sedimentation and aggregation observation are in good agreement with the changes of the zeta potential in 0.1?M MgCl₂, the maximum sedimentation rate being 99.26% at pH 10.85. When the pH is around 6.25 or 10.00, the sedimentation rate is relatively lower and the size of aggregation smaller. The adsorption of hydrolyzable multivalent metal ions on the quartz surface is a combination of three adsorption forms, namely electrostatic adsorption, hydroxyl complex adsorption, and hydroxide precipitation adsorption. Then the hydrolysis properties of metal ions and the surrounding environment determine the action of the hydrolysis components and the main form of adsorption.     

Kinetic study on acid‐base catalyzed hydrolysis of azimsulfuron,a sulfonylurea herbicide

Pseudo‐first‐order rate constants (k_obs) 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: k_obs =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 (k_obs) for hydrolysis of AZS within the [H⁺] range from 2.5 × 10⁻⁶ to 1.4 M follow the relationship: k_obs = (α₁K _a + B₁[H⁺] + B₂[H⁺]²)/([H⁺] + K_a) where pK_a = 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     

Synthesis and characterization of copolymers from 4-halo(chloro, bromo) salicylic acid

Copolymers have been prepared by condensing a mixture of either 4-chloro or 4-bromosalicylic acid and any one of the comonomer like salicylic acid,p-hydroxybenzoic acid,p-aminosalicylic acid,p-aminobenzoic acid,p-cresol andp-halo(chloro, bromo)phenol with formaldehyde in the presence of 5M H₂SO₄. Copolymer composition of each of the copolymer has been estimated on the basis of halogen content and/or on the basis of results of non-aqueous titrations of the copolymer against standard sodium methoxide and/or tetra-n-butylammonium hydroxide. The IR spectral characteristics of copolymers have been noted. The viscometric and thermal studies of copolymers have also been carried out.