Kinetics of the hydrolysis of mixed cellulose derivatives

By acetylating weakly substituted Na and H carboxymethylcelluloses and methylcellulose we have synthesized acetone-soluble highly substituted mixed derivatives of cellulose — acetocarboxymethylcellulose and acetomethylcellulose. Water-soluble products have been obtained from these esters by subsequent deep hydrolysis. The kinetics of the hydrolysis of the acetyl groups in the mixed derivatives obtained have been studied. Rate constants of the hydrolysis reactions have been calculated. The influence of the substituted groups on the acetylation and hydrolysis reactions has been determined.Tashkent Institute of Chemical Technology. Translated from Khimiya Prirodnykh Soedinenii, Vol. 33, No. 1, pp. 102–106, January–February, 1997.     

Solvation of iron and chromium complexes in alcohol–water mixtures

Solubilities are reported for the perchlorates of five iron(II)-diimine complexes in t-BuOH–H₂O and one in MeOH–H₂O mixtures, for three iron(III)-3-hydroxy-4-pyranonate and three iron(III)-3-hydroxy-4-pyridinonate complexes in MeOH–H₂O and t-BuOH–H₂O, and for two chromium(III)-3-hydroxy-4-pyranonate complexes in MeOH–H₂O. Transfer chemical potentials are thence derived for the various iron(II), iron(III) and chromium(III) complexes, for transfer from H₂O into the respective mixed solvents (at 298.2 K). These results are combined with values reported earlier for related complexes, and for other alcohol–H₂O mixtures, to give an overall picture of solvation, expressed in the thermodynamic format of transfer chemical potentials, for iron(II)-diimine, iron(III)-3-hydroxy-4-pyridinonate and chromium(III)-3-hydroxy-4-pyranonate complexes in H₂O-rich aqueous-alcohol mixtures. Some spectroscopic (¹H-n.m.r.; i.r.) and kinetic (aquation rate constants at 298.2 K) data are reported for the chromium(III) complexes.     

Kinetic,solvation and reactivity studies of iron(II) complexes of monoxime and dioxime ligands

Complexes of Fe^II 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 Fe^II–monoxime complexes follow a rate law with k_obs = k₂[H⁺] + k₃[H⁺]², while kinetics of acid dissociation and base hydrolysis of the Fe^II–dioxime complex follow rate laws with k_obs = k₂[H⁺] and k_obs = k₂[OH⁻]. Acid aquation and base hydrolysis mechanisms are proposed. The solubilities of Fe^II–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 Fe^II in acidic and neutral media, in water and in aqueous alcohols.     

Hydrophobicity and Reactivity of Base Hydrolysis of Some Novel Low Spin Fe(II) Amino Acid Schiff Base Complexes in Some Binary Aqueous Solvent Mixtures

Rate constants for base hydrolysis of bis(naphthylidene isoleucinate)iron (II) (nili), bis(naphthylidene leucinate)iron(II) (nli), bis(naphthylidene serinate)iron(II) (nsi), bis(salicylidene isoleucinate)iron(II) (sili), (salicylidene leucinate)iron(II) (sli), bis(salic- ylidene methioninate)iron(II) (smi), and (salicylidene tryptophanate)iron(II) (sti) have been reported in different binary aqueous mixtures at 298 K. The observed reactivity trends are discussed in terms of the hydrophilic and hydrophobic forms of the complexes investigated, as well as the transfer chemical potentials of hydroxide ion and the complex. Both the solvent–solute and solvent–solvent interactions have been considered. The hydrophobic character of the complexes studied was manifested by enhancing the rate of base hydrolysis at the initial addition of the different cosolvents; further addition led mostly to a decrease in reactivity, but, in some cases, the greater destabilization of OH^– ion by added DMSO and acetone increases the rate of base hydrolysis. The modified Savage–Wood equation, based on the principle of group additivity, was applied to estimate the observed kinetic medium effects.     

Spectrophotometric studies of the thermodynamics of sitting-atop complexation between free base meso-tetraarylporphyrins and titanium(IV) chloride

Titanium(IV) chloride reacts with free base meso-tetraarylporphyrin and its ortho, meta and para-substituted derivatives (H₂T(X)PP; X: OCH₃, CH₃ and Cl) for formation of sitting-atop (SAT) complexes, [TiCl₄(H₂T(X)PP)]. The computer fitting of the variation of the absorbance versus mole ratio by KINFIT program was used for calculation of the formation constants of these complexes in chloroform. Thermodynamic parameters, ΔG°, ΔH°, ΔS°, have been determined and the influence of the temperature and the substituted aryl groups (electronic and steric effects) in the free base porphyrins on the stability of the SAT complexes was studied.     

Preparation and properties of the layered organic derivatives of γ-zirconium phosphate,Zr(CH3−(OCH2CH2)n−OPO3) (HPO4) (n=1–3)

New kinds of organic derivatives of layer structured -zirconium phosphate Zr(HPO₄)₂·2H₂O are prepared by the exchange of the interlayer phosphate groups with phosphoric ester groups having oxyethylene chains, CH₃–(OCH₂CH₂)_n–OPO₃ ^2– (n=1–3). Half of the interlayer phosphate groups are exchanged topochemically, the oxyethylene chains being grafted onto the phosphate layers through the ester bonds in the resulting derivatives. The derivatives behave like crown ethers, and form complexes with alkali salts of soft base anions such as SCN^– and I^–. Alkali salts of hard base anions such as Br^– and NO₃ ^– do not form complexes with the derivatives. The alkali iodide complexes of the organic derivatives can be used for the halogen exchange reaction. n-Butyl bromide is converted into n-butyl iodide in the presence of the alkali iodide complexes. The reactivities for the halogen exchange reaction increase with the number of the oxyethylene units.     

Study of the Complexation of Octakis(diethoxyphosphoryloxy)-tetramethylcalix[4]resorcinarene with Benzene Derivatives by the RP HPLC Method

Stability constants of the host–guest complexes of octakis(diethoxyphosphoryloxy) tetramethylcalix[4]resorcinarene (RA) with different benzene derivatives (alkyl benzenes, halogenated benzenes, substituted aldehydes, phenols and benzoic acids) were determined by the reversed phase high-performance liquid chromatography (RP HPLC) method (Separon SGX C 18, UV detector at 254 nm and acetonitrile-water, 86 : 14, v/v, as mobile phase) from the relationship between the aromatic guest capacity factors and the RA host concentration in the mobile phase. The constants are within the range 17–596 M^–1, dependent on the size, nature, position and quantity of the substituents in the benzene ring of the guest molecules.     

The base hydrolysis ofmer-[Co(1,5-diamino-3-azapentane)(amino acidate)X]+ (X = Cl or NO2) complexes and base hydrolysis of complexed peptides in the coordination sphere of the [Co(dien)]3+ moiety

Summary A variety ofmer-[Co(dien)(AA)X]⁺ (AA = amino acidate, dien = 1,5-diamino-3-azapentane) andmer-[Co(dien)(dipeptideOR)X]²⁺ complexes (X = Cl or NO₂) have been prepared and characterised. Base hydrolysis of the peptide bond in the carbonyl bonded glycyl peptides has been studied at 25°C and I = 0.1 mol dm^–3. The rate constants k_OH for peptide bond hydrolysis fall within the 0.67–0.88 mol dm^–3s^–1 range. Base hydrolysis of the complexed peptide isca. 2×10⁴ times faster than for the uncomplexed peptide ligand at 25 °C. The base hydrolysis of the chloro- and nitro-ligands in these complexes has also been studied. Very rapid hydrolysis occurs if the dien ligand adopts amer-configuration and the reactions are 10²–10⁴ times faster than for analogous complexes where the dien ligand adopts afac-configuration. These results are in agreement with Tobe's criteria for rapid base hydrolysis in cobalt(III) complexes.The following abbreviations are used thoughout this paper; dien 1,5-diamino-3-azapentane - dpt 1,7-diamino-4-azaheptane - glyO glycinate - glyOH glycine - glyOR glycine ester - glyNH₂ glycine amide - glyglyO glycylglycinate - glyglyOR glycylglycine ester - glyglyglyOH triglycine - -alaO -alaninate     

Oxomolybdenum(VI) and (V) complexes with 6–methyl-4–hydroxypyrimidinyl hydrazones

Dioxomolybdenum(VI) complexes [MoO2(L)H2O] and oxomolybdenum(V) complexes [Mo2O3(LH)2Cl2] (where LH2=hydrazones derived from 6–methyl-4–hydroxy-2–hydrazinopyrimidine with salicylaldehyde, 5–methyl-, 5–chloro-, 5–bromo-, 3–methoxy-salilcylaldehyde, or 2–hydroxy-1–naphthaldehyde) have been prepared and characterised by spectroscopic and physico-chemical methods. The MoVI complexes are diamagnetic octahedral structures, whilst the MoV complexes are paramagnetic and probably dimeric, via oxobridging.     

Kinetics of solvolysis and of formation of tetrachloroplatinate(II) in alcohol: Water mixtures

Summary Rate constants are reported for the reaction of [PtCl₄]^2– with hydrochloric-perchloric acid mixtures, in aqueous methanol and aqueous t-butanol at 308.2 K. The observed first-order rate constants are, from their dependence on chloride concentration, divisible into forward and reverse rate constants for the equilibrium: [PtCl₁₄]^2–+H₂O[PtCl₃(OH₂)]^–+Cl^–. The solvent dependence of aquation rates for [PtCl₄]^2– is compared with those for other chlorotransition metal complexes, and discussed in terms of the Grunwald-Winstein method of mechanism diagnosis in organic systems. The solvent dependence of rates of [PtCl₄]^2– formation is compared with the rates of formation of other metal complexes; differences between this platinum reaction and, for example, nickel(II) formation, are rationalised in terms of the reactant charge product difference and consequent solvent permittivity effects on rate trends.     

Metal Ion Buffer Systems for Ionometry in Water-Ethanol Mixtures and Micellar Medium of Sodium Dodecyl Sulfate

The concentration dissociation constants of nitrilotriacetic acid and the concentration stability constants of Cd(II) complexes with the nitrilotriacetic acid anion in water-ethanol mixtures and of Cu(II) and Cd(II) complexes with o-phenanthroline and 2,2′-bipyridine in micellar solutions of sodium dodecyl sulfate were determined potentiometrically. Based on the concentration constants determined, Cd²⁺ and Cu²⁺ buffer solutions were developed for calibration of a Cd²⁺-selective electrode in water-ethanol mixtures and Cd²⁺ and Cu²⁺-selective electrodes in micellar solutions of sodium dodecyl sulfate within the ranges pCu 9.7–13.5 and pCd 7.5–11.8.__________Translated from Zhurnal Prikladnoi Khimii, Vol. 78, No. 2, 2005, pp. 273–278.Original Russian Text Copyright © 2005 by Chernysheva, Loginova, Bazilyanskaya.     

Synthesis,characterization and electrochemical behavior of mononuclear,binuclear nickel(II) and heterobinuclear zinc(II)nickel(II) complexes derived from novel macrobicyclic tricompartmental ligands: kinetics of the catalytic hydrolysis of 4-nitrophenyl phosphate by the complexes

Mononuclear, binuclear Ni^II and heterobinuclear Zn^IINi^II complexes have been derived from lateral macrobicyclic tricompartmental ligands embracing three different donor sets: (i) O₂N₂-donor set, derived from ether oxygens and tertiary amine nitrogens; (ii) N₂O₂-donor set, derived from tertiary amine nitrogens and phenolic oxygens; (iii) O₂N₂-donor set, derived from phenolic oxygens and azomethine nitrogens. Cyclic voltammograms of the mononuclear Ni^II complexes showed irreversible one-electron reduction processes in the –1.2 to –1.3 V region and an irreversible oxidation process in the range +0.8 V potential region. The binuclear complexes showed quasireversible two-step single electron reduction processes around the –1.3 and –1.7 V potential regions. The anodic potential region showed an irreversible oxidation process at +1.0 V. The heterobinuclear Zn^IINi^II complex showed an irreversible reduction of the Ni^II species at –1.55 V. The catalytic hydrolysis towards 4-nitrophenyl phosphate by the mononuclear, binuclear Ni^II complexes and the heterobinuclear complex were found to be appreciable. The pseudo-first order rate constant for the catalytic hydrolysis catalyzed by the binuclear and heterobinuclear complexes were found to be higher (9.8 × 10^–4 s^–1) than that of the corresponding mononuclear complexes (1.3 × 10^–5 s^–1), which ascertain the requirement of two metal ions in close proximity for the binding of the nucleophilic OH and the phosphate group.     

Kinetics of aquation and base hydrolysis ofcis-(carboxylato) (ethylamine)bis(ethylenediamine)cobalt(III) ions

Summary The aquation ofcis-[Co(en)₂(NH₂Et)O₂CR]²⁺ [R=H or Me] is strongly acid-catalysed and the rate and activation parameters for this process are reported. No significant rate difference is observed in the spontaneous aquation path for the complexes. The acetato complex undergoes acid catalysed aquation at a rate comparable to the of the corresponding formato complex, in contrast with the relative basicities of the coordinated formate and acetate. This result is interpreted in terms of relative solvation effects of the initial and transition states of both complexes.The base hydrolysis of both complexes obeys overall second order kinetics in the 0.05[OH^–]_T 0.35 mol dm^–3 range (I=0.5 mol dm^–3). The formato complex reacts five times faster than its acetato analogue under comparable conditions, which is fully consistent with the dissociative mode of activation of the amido conjugate base involving Co–O bond heterolysis. A substantially large positive value for the activation entropy supports SN₁CB mechanism for base hydrolysis.     

Solvation of iron(II) complexes of hexadentate tris-diimine Schiff base tripod ligands in alcohol–water and DMSO–water mixtures

Solubilities of the perchlorate salt of the iron(II) complex of the tripodal ligand derived from tris(2-aminoethyl)amine and pyridine 2-carboxaldehyde, [Fe({pyH}₃tren)](ClO₄)₂, have been determined in MeOH-, i-PrOH-, t-BuOH-, and DMSO–H₂O mixtures. Solubilities of [Fe({pyMe}₃tren)](ClO₄)₂ and of [Fe({pyPh}₃tren)](ClO₄)₂, analogues derived from 2-acetylpyridine and 2-benzoylpyridine, respectively, have been determined in MeOH–H₂O mixtures. Transfer chemical potentials for the three complexes have been calculated from these solubilities, and solvation trends for these complexes discussed in relation to the overall pattern for iron(II)-diimine complexes in binary aqueous solvent mixtures. The crystal structure of [Fe({pyH}₃ tren)](ClO₄)₂ has been determined.     

Potentiometric Determination of the First Hydrolysis Constant of Gallium(III) in NaCl Solution to 100°C

The hydrolysis equilibrum of gallium (III) solutions in aqueous 1 mol-kg^–1 NaCl over a range of low pH was measured potentiometrically with a hydrogen ion concentration cell at temperatures from 25 to 100°C at 25°C intervals. Potentials at temperatures above 100°C increased gradually because of further hydrolysis of the gallium(III) ion, followed by precipitation. The results were treated with a nonlinear least-squares computer program to determine the equilibrium constants for gallium(III)–hydroxo complexes using the Debye–Hückel equation. The log K (mol-kg^–1) values of the first hydrolysis constant for the reaction, Ga³⁺ + H₂O GaOH²⁺ + H⁺ were –2.85 ± 0.03 at 25°C, –2.36 ± 0.03 at 50°C, –1.98 ± 0.01 at 75°C, and –1.45 ± 0.02 at 100°C. The computed standard enthalpy and entropy changes for the hydrolysis reaction are presented over the range of experimental temperatures.     

Potentiometric Studies on Some α-Amino Acid-Schiff Bases and Their Manganese(III) Complexes in Dimethyl Sulfoxide–Water Mixtures at 25°C

In this study the stoichiometric protonation constants were determined for some -amino acids (glycine, L-alanine, L-methionine, L-phenylalanine, and L-threonine), the Schiff bases derived from them and 2-hydroxy-1-naphthaldehyde, along with the stoichiometric stability constants of Schiff base–Mn(III) complexes. These equilibrium constants were determined potentiometrically using a combined pH electrode system calibrated in concentration units of the hydrogen ion at 25°C, and at an ionic strength of 0.10 mol-dm^–3 NaCl in 30 and 50% dimethyl sulfoxide–water mixtures. The calculations of these constants were carried out using the PKAS and the BEST computer programs. In addition, the effects of solvent composition and structures on the protonation and the complex formation constants were investigated. The mole ratio of Mn(III) to amino acid-Schiff bases was also determined and it was found that the complexes were of the MnL₂ type.     

Solvation of inorganic complexes: transfer chemical potentials for mono- and bi-nuclear cobalt(III) complexes to methanol + water mixtures

Solubilities in MeOH--H₂O mixtures at 298.2 K are reported for a number of salts of mono- and bi-nuclear cobalt(III) complexes. From these solubilities and published single ion transfer chemical potentials, on the TPTB (Ph₄P⁺ = BPh^– ₄ ) assumption, transfer chemical potentials have been derived for these mono- and bi-nuclear cobalt(III) complexes. The results and trends are discussed in relation to those for other complexes and ions in these binary aqueous solvent mixtures.     

Kinetics and mechanism of ligand interchange in the [RuIII(edta)L] complexes; L=Cysteine and related thiolates

Complexes of the [RuIII(edta)SR]n series, with SR–= deprotonated cysteine, N- acetylcysteine, 2–mercaptoethanol, glutathione and penicilamine, were prepared from [Ru(edta)H2O]– and the corresponding RSH thiols, at pH=5.5. The complexes exhibit intense visible absorption bands at ca. 520nm (3500M–1 cm–1), associated with LMCT from the sulfur ligands bound to RuIII. The kinetics of the formation reactions were first order in [RuIII(edta)H2O]– and thiol reactants, with k1 values ca. 1–5×102 M–1s–1 (25°C) for all the sulfur ligands except penicilamine, which reacted slower by a factor of 10. Activation parameters suggest an associative mechanism, as for the coordination of other S- and N-bound ligands to [RuIII(edta)H2O]–. A reactivity decrease is apparent at low and high pH's (ranges 1–3 and 8–10, respectively), associated with acid-base equilibria involving the less reactive [RuIII(Hedta)H2O] and [RuIII(edta)OH]2– species. A significant rate increase was found for cysteine and penicilamine at ca. pH=8.0, because the thiol reactants deprotonate. The equilibrium constants for all the ligands showed that robust complexes were formed, with K=ca. 1×105 M–1 (25°C). The dissociation rate constants, k–1, were in the 10–3–10–4 s–1 range. The influence of nucleophilic and steric effects increasing and decreasing the formation rates, respectively, is discussed for the thiolate ligands, with adequate comparisons with other L species bound to [RuIII(edta)H2O]–.     

Thermodynamics of coordination of pyridine and its substituted derivatives to osmium tetroxide

Complexation of osmium tetroxide (OsO₄) with pyridine and its substituted derivatives (i.e. 4-picoline, 3 -picoline, 4-tertbutylpyridine, methyl nicotinate, 3,4-dimethylpyridine, 3-chloropyridine, and 3-phenylpyridine) has been studied at different temperatures in benzene. Spectrophotometric measurements have been carried out to obtain the equilibrium constants and thermodynamic parameters. The equilibrium constants of the resulting 1:1 complexes are found to vary in the order 3,4-Me₂Py > 4-^tBuPy > 4-MePy > 3-MePy > Py > 3- PhPy > 3-C(O)OMePy ≈ 3-ClPy. All complexes are enthalpy stabilized whereas the entropy changes counteract the complexation. The results are discussed in terms of different basicities of the substituted pyridines.     

Cobalt(II) Schiff Base Complexes Bearing Aza Crown Ether Pendants as Synthetic Hydrolase Catalyzing PNPP Hydrolysis

Two Co^II complexes with aza crown ether substituted salicylaldimine Schiff base, CoL¹ ₂ and CoL² ₂, have been synthesized and employed as models to mimic hydrolase in catalytic hydrolysis of a carboxylic ester. The specific change of u.v.–vis. absorption spectra of the hydrolytic reactive systems has been observed, which indicates that key intermediates are formed by PNPP and Co^II complexes. The kinetics and the mechanism of PNPP hydrolysis have been investigated. The kinetic mathematical model for PNPP cleavage catalyzed by the Co^II complexes has been proposed. The results show that, compared with the crown-free analogous CoL³ ₂, the bis(aza crown ether)s Co^II complexes CoL¹ ₂ and CoL² ₂ exhibit high activity in the PNPP catalytic hydrolysis; the rate of the PNPP hydrolysis catalyzed by the complexes increases with the increase of pH of the buffer solution; the pseudo-first-order rate constants (k _ob) of PNPP hydrolysis catalyzed by the complexes is 1000 times more than that of spontaneous hydrolysis of PNPP.