Hydrolysis Behaviour of Some Heterocyclic Nitrogen Azomethines

Kinetics of base hydrolysis of some new heterocyclic azomethines derived from aminotriazol and aromatic aldehydes were investigated in the presence of NaOH in 60% (wt/wt) water-ethanol medium. The base hydrolysis of these Schiff bases is strictly first-order with respect to OH^? and Schiff. The rate-determining step is suggested to be the attack of the hydroxide ion on the free base. Effect of the molecular structure of both aldehydes and amines and the nature of organic hydroxylic solvent on the hydrolysis rate was investigated and discussed.     

Kinetics of Hydrolysis of Some Bifunctional Schiff Bases

Kinetics of hydrolysis of some bifunctional Schiff bases, bis(x-benzylidenes)-o-phenylenediamine, have been investigated in aqueous media containing 0.1 mole fraction of ethanol under base and acid conditions. Under base conditions the rate determining step is the hydroxide ion attack on the protonated substrate while under weak acid conditions the attack of water rather than hydroxide ion on the protonated substrate becomes the predominant reaction pathway. The bifunctional Schiff base molecular structure-base or acid hydrolysis reactivity relationship has been examined and discussed. Effect of medium (water content and nature of organic solvents) has been investigated and it is deduced that specific solute-solvent interactions, namely the proton-solvent, play a vital role on such hydrolysis reaction.     

The effect of electron-withdrawing properties of substituents on the hydrolysis of some Schiff bases

The dissociation kinetics of the Schiff bases investigated in the present paper [N,N-bis(X-benzylidenes)ethylenediamine], have been examined under basic and acidic conditions, in aqueous medium 25% acetone in water (wt-wt). The base hydrolysis reaction of these compounds was found to follow second-order kinetics, first-order with respect to each of the Schiff base and the hydroxide ions. The rate-determining step is suggested to be the hydroxide ions attack on the free base. The effect of acetone ratio, in hydrolysis medium, has been studied under alkaline conditions. It is deduced that both the hydrogen bonding formation and solvent-solvent interaction have a pronounced role in such hydrolysis reactions. The acid hydrolysis reaction is strictly second-order kinetics, first-order with respect to the Schiff base and also to the hydrogen ions, and the attack of water molecules on the protonated substrate becomes the rate-determining step. A slower rate of the base hydrolysis was observed through the Schiff base II (p-NO₂), on the other hand, a fast acid hydrolysis rate was detected in the case of compound III (p-COOH). Furthermore, from the effect of temperature on the reaction rate, the various thermodynamic parameters have been also calculated and discussed.     

Synthesis of 2,3-disubstituted thiazolidin-4-ones containing the sterically hindered 4-hydroxy-3,5-di(tert-butyl)phenyl grouping

A series of 2,3-disubstituted thiazolidin-4-ones containing 4-hydroxy-3,5-di(tert-butyl)phenyl groups has been synthesized. For preparation of these sterically hindered compounds the condensation of thioglycolic acid with azomethines — derivatives of 4-hydroxy-3,5-di(tert-butyl)benzaldehyde was used.I. M. Gubkin Russian State University for Petroleum and Gas, Moscow 117917. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 2, pp. 256–260, February, 2000.     

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.     

Synthesis of 3,4-Substituted Phenylmethylene-(2-carboxyphenyl)amines and Their Antitumor Activity

Previously unknown azomethines 3a-z and 4a-j were prepared in methanol by condensation of anthranilic acid 1 with vanillin, vanillal, and esters of these compounds 2.__________Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 164–169, March–April, 2005.     

Formation of peroxide compounds on the oxidation of lignin by oxygen in an organic solvent

The results are given of a determination of the steady-state concentrations of peroxide compounds on the oxidation of lignin by oxygen in dioxane. An iodometric method of determining peroxides was used, with spectrophotometric control of the amount of iodine formed. It was established that the achievable steady-state concentration of peroxide compounds on the oxidation of lignin is 0.28–0.44 wt. % of O_act (oxygen pressure 1 atm, temperature 50–80°C). With a rise in the temperature, the steady-state concentration of peroxide compounds decreased. The addition of water (30 vol. %) to the organic solvent led to an increase in the rate of accumulation of peroxide compounds. It has been shown that the presence of alkaline and acidic catalysts exerts no appreciable influence on the achievable steady-state concentration and the rate of accumulation of peroxide compounds during the oxidation of lignin.Bratsk Industrial Institute. All-Union Scientific Production Combine of the Pulp and Paper Industry, Leningrad. Translated from Khimiya Prirodnykh Soedinenii, Nos. 3,4, pp. 413–417, May–August, 1992.     

Cyclic azomethines and their hydrogenated derivatives. (Review)

The literature data on the methods of synthesis and chemical properties of cyclic azomethines, mainly isoquinoline derivatives, have been correlated. Examples of biologically active compounds of the 3,4-dihydro- and 1,2,3,4-tetrahydroisoquinoline are given.Institute of Technical Chemistry, Russian Academy of Sciences, Ural Branch, Perm 614600, Russia; Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 579–604, May, 2000.     

Kinetics and Mechanism for Hydrolysis of α-Amino Acid Esters in Mixed Ligand Complexes with Zn(II)–Nitrilo-tris(methyl phosphonic Acid)

The kinetics of base hydrolysis of the alanine ethyl ester, in addition to glycine, histidine and methionine methyl esters in the presence of the Zn-NTP complex, were studied in aqueous solution by the pH-potentiometric technique, where NTP denotes the nitrilo-tris(methyl phosphonic acid) ligand. The kinetic data fits assumed that hydrolysis proceeds through formation of a M–OH complex, followed by an intramolecular OH⁻ attack. The effect of an organic solvent on the hydrolysis of coordinated esters was investigated by measuring the rate of hydrolysis in dioxane–water solutions of different compositions at t=25.0 °C and I=0.1 mol⋅dm⁻³. The kinetics of base hydrolysis of the glycine methyl ester was studied at different temperatures. Activation parameters for the base hydrolysis of the complexes were evaluated.     

Synthesis of 2-(pyridylazo)-2-furyl-and 2-(pyridylazo)-2-thienylmethines and other heterocyclic Schiff bases in the presence of molecular sieves

The reactions of 2-furaldehyde, 2-thiophenecarbaldehyde, and their 5-methyl derivatives with 2-aminopyridines and some other amines in the presence of molecular sieves as a dehydrating agent and acid catalyst have been studied. A series of new heterocyclic azomethines was synthesized. Proposals were made for the mechanism of the condensation involving 2-aminopyridines and the structure of the intermediates in these processes.Latvian Institute of Organic Synthesis, Riga LV-1006, Latvia. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 890–897, July, 2000.     

Hydrolysis of 1,2-disubstituted imidazolines in aqueous media

The kinetics of hydrolysis of 1,2-disubstituted imidazolines in aqueous media was studied (pH 2.0—12.5, T = 25—90 °C) by UV spectroscopy. The hydrolysis products were identified. The introduction of a branched substituent into position 2 of the imidazoline ring increases the hydrolytic stability of the compounds. The effect of the pH on the hydrolysis rate of imidazolines is discussed.     

Co-hydrolysis products of tetraethoxysilane and methyltriethoxysilane in the presence of tetramethylammonium ions

Tetracethoxysilane (TEOS) and methyltriethoxysilane (MTEOS) have been co-hydrolyzed in methanolic solutions containing tetramethylammonium ions that only affect polymerization of silicate species (hydrolysis products of TEOS) to form the Si₈O ₂₀ ^8– cubic octameric silicate species. The effects of water content and TEOS-to-MTEOS molar ratio on the distribution of species formed in the solutions have been investigated with the trimethylsilylation technique and ²⁹Si n.m.r. spectroscopy. Formation of Si₈O ₂₀ ^8– and the cubic octameric species consisting of both Si(O^–)₄ and CH₃Si(O^–)₃ units, (CH₃)_nSi₈O _20–n ^(8–n)– (n=1–5), is found in the solutions. The increase of water content in the solutions solely results in increasing yield of Si₈O ₂₀ ^8– in spite of the presence of hydrolysis products of MTEOS together with those of TEOS, suggesting that water in the solutions plays an important role in the formation of Si₈O ₂₀ ^8– with the aid of tetramethylammonium ions. The TEOS-to-MTEOS molar ratio varies the distribution that is kept under control by the water content, increasing yields of (CH₃)_nSi₈O _20–n ^(8–n)– (n=1, 2). It is found that the water content and TEOS-to-MTEOS molar ratio determine the reaction conditions effective for the formation of CH₃Si(O^–)₃ unit-containing cubic octameric species.     

The interaction of alkaline solutions of potassium borohydride with LaNi4.5M0.5 (M = Ni,Mn, Cr,Co, Fe,Cu, Al) intermetallic compounds

The behavior of LaNi_4.5M_0.5 (M = Ni, Mn, Cc Co, Fe, Cu, Al) interinctallic compounds (IMC) in alkaline solutions of KBH₄ (0.1; 1.0; 4.0 mol L^–1 KOH) Was investigated in the temperature range 298–318 K. The catalytic hydrolysis of KBH₄ is zero order with respect to KBH₄ and not order with respect to IMC. Activation energies of the catalytic hydrolysis of KBH₄ in the presence of' IMC are in the range of 60–65 U mol^–1. The rate of hydrolysis of KBH₄ increases with the concentration of the KOH solution. The hydrogenation of LaNi_4.5M_0.5 in alkaline solutions of KBH₄ yields -hybride phases for M = Min, Cr, Co, Cu, Al and -hybride phases for M = Ni, Fe.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1632–1635, July, 1996.     

Acceleration Effect of Fe(II), Co(II), Ni(II) and Cu(II) on the Hydrolysis Rate of Ortho- or Para-Hydroxy Schiff Bases

The kinetics of hydrolysis of ortho- or para-hydroxybenzylidene-4-benzidine Schiff bases have been examined in the pH range 1.70–11.90, in aqueous media containing 20wt% dioxane, at 20 °C. In basic media, pH > 8.47, a slight increase in the hydrolysis reaction rate of the Schiff bases is observed. In such basic media, the rate-controlling step is the attack of hydroxide ion on the ionized Schiff base. Below pH 6.82, the rate-determining step is ascribed to be the attack of water molecules on the protonated substrate. The effects of Fe(II), Co(II), Ni(II) and Cu(II) ions on the hydrolysis reaction rate of the Schiff bases have been studied and discussed on the basis of formation of a monocyclic chelate rings. The various thermodynamic parameters have also been evaluated and discussed.     

A calorimetric study of the ultrasound-stimulated hydrolysis of solventless TEOS-water mixtures

The kinetics of ultrasound-stimulated and HCl-catalyzed hydrolysis of solventless TEOS-water mixtures was studied as a function of temperature ranging from 10°C up to 65°C by means of flux calorimetry measurements. A specially designed device was utilized for this purpose. The exothermic peak arising few minutes after sonication began has been attributed mainly to the hydrolysis reaction. The overall hydrolysis process, which was measured through the irradiation time up to the hydrolysis peak, was found to be thermally activated, with an apparent activation energy E=36.4 kJ/mol. The alcohol produced at the early hydrolysis due to sonication seems to further enhance the reaction, via a parallel autocatalytic path, which is controlled by a faster pseudo second order rate constant (k). Our modeling yielded k=6.3×10^–2M^–1min^–1 at 20°C, which is in a reasonable agreement with the literature, and an activation energy E=40.4 kJ/mol for the specific process of hydrolysis in presence of alcohol.     

Ternary complexes involving copper(II) and amino acids,peptides and DNA constituents. The kinetics of hydrolysis of α-amino acid esters

Binary and ternary complexes of copper(II) involving picolylamine (Pic) and amino acids, peptides (HL) or DNA constituents have been investigated. Ternary complexes of amino acids or peptides are formed by simultaneous reactions. Amino acids form the Cu(Pic)L complex, whereas peptides form Cu(Pic)L and Cu(Pic)(LH_–1). The ternary complexes of copper(II) with picolylamine and DNA are formed in a stepwise process, whereby binding of copper(II) to picolylamine is followed by ligation of the DNA components. The stability of the ternary complexes is compared with the stabilities of the corresponding binary complexes. The hydrolysis of glycine methyl ester (MeGly) is catalysed by the Cu(pic)²⁺ complex. The kinetic data is fitted assuming that the hydrolysis proceeds in two steps. The first step, involving coordination of the amino acid ester by the amino and carbonyl groups, is followed by rate-determining attack by the OH^– ion. The second step involves equilibrium formation of the hydroxo-complex, Cu(pic)(MeGly)(OH), followed by intramolecular attack.     

Voltammetric determination of methyl parathion, ortho, meta and para nitrophenol with a carbon paste electrode modified with C18

Summary The determination of methyl-parathion (MPT), ortho (ONP), meta (MNP) and para nitrophenol (PNP) has been studied by differential pulse voltammetry with a carbon-paste electrode modified with 50% (w/w) of C₁₈. A study of the influence of the pH in the preconcentration cell and the measurement cell was carried out for an electrode with 50% modifier and an accumulation time of 5 min. The voltammograms were recorded with a sweep rate of 40 mV s^–1 and a pulse amplitude of 50 mV. With the optimum conditions of pH for both of the steps, various other variables were studied. The variables for each compound were optimized and the possibility of application to the determination of a mixture of the four compounds was investigated. The determination limits found for all the compounds are: 2 ng ml^–1 for ONP, 5 ng ml^–1 for MNP, 4.3 ng ml^–1 for PNP and 7.9 ng ml^–1 for MPT. The method was applied to samples of a small lake which gathers rain water and water filtered from land on which cereals are grown.     

Synthesis and study of the properties of some azomethine compounds

8 azomethine compounds hitherto undescribed in the literature, which are derivatives of salicylaldehyde and amines from the group sulfanilamide, acridine, tolidine, and some other compounds, are synthesized. The acid dissociation constants of the azomethines are determined spectrophotometrically (using the isobestic points method), and by the solubility method. These constants are of the order 10^–7--10^–11.     

Determination of Impurity Arsenic in High-Purity Sulfur by Electrothermal Atomic-Absorption Spectrometry with the Use of Solvent Extraction

A procedure was developed for determining impurity arsenic in high-purity sulfur with a detection limit of 1 × 10^–7 wt %. The samples of sulfur to be studied were dissolved in nitric acid in an autoclave, and then the arsenic impurity was extracted with toluene and back-extracted with distilled water. Arsenic was determined in the back-extract by electrothermal atomic-absorption spectrometry.     

Physicochemical Study of New Mono- and Binuclear Copper(II) Complexes with Sterically Hindered Acylhydrazones and Azomethines

Series of new binuclear copper(II) complexes with acylhydrazones and azomethines of substituted derivatives of salicylaldehyde containing bulky tert-butyl substituents were synthesized. The target dimerization of the monomeric fragments of the complexes caused by the steric factors was shown to predetermine the specific features of their magnetochemical behavior. The calculated exchange parameters for the complexes based on acylhydrazones range from –110 to –138 cm^–1 and those for the complexes based on azomethines lie in the interval from –400 to –500 cm^–1.