Basic Aqueous Media Research Articles

Comparative study of 2‐amino and 3‐aminobenzoic acid copolymerization with aniline synthesis and copolymer properties

AbstractPolyanilines soluble in an aqueous basic medium were synthesised by copolymerization of aniline (ANI) with both 2 and 3‐aminobenzoic acids (ABA). Different composition copolymers were prepared by varying the ANI/ABA feed ratio. Poly(aniline‐co‐2‐aminobenzoic acid) (PANI2ABA) and poly(aniline‐co‐3‐aminobenzoic acid) (PANI3ABA) displayed differences in their properties, such as specific charge and fluorescence behavior because the reactivity of 2‐aminobenzoic (2ABA) and 3‐aminobenzoic (3ABA) acids are very different. The new materials were characterized by X‐ray photoelectron, Fourier transform infrared, and Raman spectroscopies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5587–5599, 2004

Zinc phyllosilicates containing amino pendant groups

Two new zinc silicate hybrids were synthesized via sol–gel process from the reaction of zinc ions with trialkoxyaminesilanes in aqueous basic medium at room temperature and at 373 K. The inorganic–organic hybrids obtained, named SILZn ( x=1 or 2) are related to 3-aminopropyl- and N-propylethylenediaminetrimethoxysilane, respectively. From nitrogen content, the number of pendant moles of organic groups in the matrices SILZnx ( x=1 to 2) were determined as 5.14 and 3.25 mmol g −1, respectively. The thermogravimetric curves showed mass losses of 50.7% and 58.0% for the same sequence of hybrids, to give the oxides as residue. X-ray diffraction patterns gave basal distances of 2065 and 2814 pm for SILZnx ( x=1, 2), with well-formed particles of irregular shapes and sizes, as a characteristic of such material obtained from sol–gel process. The infrared spectra confirmed the attachment of the organic moieties on siloxane groups on the inorganic framework.

Cyanide‐Melt Synthesis of Reduced Molybdenum Selenide Clusters.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Electrochemical Oxidation of Silver and Copper in Aqueous Basic Media and in Fused Hydroxide Electrolytes

Electrochemical Oxidation of Silver and Copper in Aqueous Basic Media and in Fused Hydroxide Electrolytes

Formal Bleaching Kinetics of Acid Blue 80 in Weakly Acidic, Neutral, and Basic Aqueous Media

General kinetic relations were established for the first step of oxidation of Acid Blue 80 in weakly acidic, neutral and basic media in the following systems: Fe2+-H2O2, Mn2+-HCO3 --H2O2, and Cu2+-phenanthroline-H2O2. The rate constant for the reaction of hydroxyl radical with the dye and the dependence of the degree of bleaching upon oxidant and catalyst concentrations were determined.

Cyanide-melt synthesis of reduced molybdenum selenide clusters.

The tightly cross-linked Mo(3n)Se(3n+2) (n = 2, 3,... infinity) cluster compounds react with alkali metal cyanide or cyanide salt mixtures at temperatures of 450-675 degrees C to yield cyanide-terminated molybdenum chalcogenide clusters, [Mo6Se8(CN)6]n- (1n-) (n = 6, 7) and [Mo4Se4(CN)12](8-) (2(8-)). The process by which discrete 1(n-) clusters are excised from a CN-linked intermediate chain compound, K6Mo6Se8(CN)5 (3), was investigated, and the cubane cluster 2(7-) plays an essential role. An efficient one-step synthesis for Na8[2(8-)] is presented. These clusters are stable in basic aqueous solutions. Cyclic voltammetric (CV) measurements in basic aqueous media show multiple reversible redox waves corresponding to 1(6-/7-), 1(7-/8-), and 1(8-/9-) redox couples with half-wave potentials of E(1/2) = -0.442, -0.876, and -1.369 V, respectively, versus SHE. Half-wave potentials (E(1/2)) for the [Mo4Se4)(CN)12](6-/7-) and [Mo4Se4(CN)12](7-/8-) couples are 0.233 and -0.422 V, respectively, versus SHE. The 2(8-) compounds are K7Na[2(8-)].5H2O.MeOH, Cs7Na4[2(8-)]Cl3, Na8[2(8-)], and K4Na4[2(8-)].12H2O. The products were characterized by X-ray crystallography, cyclic voltammetry, and UV-vis spectroscopy. Reduction potentials measured by voltammetry are consistent with conditions needed for isolating reduced species on a preparative scale but are much more negative than previously reported values. Na8[1(8-)].20H(2)O was isolated by reduction of 1(7-) with Zn in aqueous NaCN solution. Reduction potentials measured in basic NaCN solutions of 2(8-) also differ widely from previous reported values.

A computational study of the formation of 1,3,2-dioxaborolane from the reaction of dihydroxy borane with 1,2-ethanediol

Boronic acids are well known to form covalent linkages with compounds containing 1,2- or 1,3-diol moieties that lead to 5- or 6-membered cyclic boronate esters, respectively. In the present study, we use density functional theory at the B3LYP/6-311++G** computational level to discuss formation of the representative 5-membered cyclic ester 1,3,2-dioxaborolane, HB(–O–CH 2–CH 2–O–), from the dehydration reaction of dihydroxy borane, HB(OH) 2, and 1,2-ethanediol, HOCH 2–CH 2OH. Calculations support a stepwise mechanism in which the monoester HB(OH)–O–CH 2–CH 2OH is formed in an initial bimolecular dehydration; this is followed by a unimolecular elimination in which HB(–O–CH 2–CH 2–O–) is formed. Since diol complexations with boronic acids are typically carried out either in aprotic solvents using a dehydrating agent or in basic aqueous media, the effects of acetonitrile and various Lewis bases on the thermodynamic and kinetic parameters of these dehydration and elimination reactions are also discussed.

Water‐Mediated Transition‐Metal‐Free Tsuji—Trost‐Type Reaction.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Water-mediated transition-metal-free Tsuji–Trost-type reaction

Abstract The treatment of 1-acetoxy-1,3-diphenylpropene ( 1 ) by C-, O-, S- and N-nucleophiles in basic aqueous media produced the corresponding substitution products in the absence of a transition-metal catalyst. Mechanistic studies, using ( S )- 1 and p -MeC 6 H 4 CH(OAc)CHCHPh as substrates, led to propose a B AL 1 cleavage of the ester function leading to a stabilized allylic carbocation as intermediate.

Properties of amphoteric polyurethane waterborne dispersions: II. Macromolecular self-assembly behavior

Amphoteric polyurethane (APU) samples used in this paper were composed of hydrophobic soft segments and pendent COOH and CH 2N(CH 3) 2 groups on the hard segments, which present the properties of both amphoteric polyelectrolytes and amphiphilic block copolymers. APU macromolecules can self-assemble into micelles in acidic and basic aqueous media by hydrophobic/hydrophilic interaction. The self-assembly behavior of APU in acidic and basic media was studied by transmission electron microscopy and light scattering methods. The spherical and hollow micelles of APU were observed respectively in acidic and basic aqueous media. The results indicate that the size and size distribution of APU self-assembly micelles largely depend on the ratio of COOH to CH 2N(CH 3) 2 groups, density of ionizable groups, concentration of APU, and types of acid and base in the media.

Vanadium Chloroperoxidase as a Catalyst for Hydrogen Peroxide Disproportionation to Singlet Oxygen in Mildly Acidic Aqueous Environment

AbstractChemiluminescence studies show that the enzyme vanadium chloroperoxidase from the fungus Curvularia inaequalis is a highly efficient catalyst for the production of singlet oxygen from hydrogen peroxide in a mildly acidic aqueous environment, with a maximum turnover frequency of 100 s−1 with respect to H2O2 consumption. The enzyme studied here can be regarded as a supplementary catalyst to inorganic molybdate, which operates in basic aqueous media. The enzyme system is 103 – 104 times faster than the molybdate system when compared at their optimal pH. The enzyme is very stable against singlet oxygen, in contrast to heme‐containing peroxidases which, due to inactivation by singlet oxygen, only produce a short burst, presumably by oxidation of the labile cofactor. The vanadium chloroperoxidase was compared with vanadium bromoperoxidase from the seaweed Ascophyllum nodosum and was found to be even more stable; it is stable towards a continuous flow of singlet oxygen for at least 1 hour and also it is not inactivated by 500 mM H2O2. An important difference with vanadium bromoperoxidase is that the vanadium chloroperoxidase is able to effectively use chloride as a cocatalyst (20 s−1) instead of bromide. This offers an important advantage from an application point of view; using chloride, no side products are observed when the chemical trap anthracene‐9,10‐bis(ethanesulphonate) is fully converted by singlet oxygen into its corresponding endoperoxide. By contrast, when bromide is used, 20% side product is formed. During the conversion the enzyme remains fully stable for 25,000 turnovers.

Easy and environmentally friendly uncatalyzed synthesis of β-hydroxy arylsulfides by thiolysis of 1,2-epoxides in water

The title compounds were prepared via thiolysis of alkyloxiranes by arylthiols in basic aqueous medium at 30 °C. The nucleophilic addition is anti diastereoselective and occurs on the less substituted carbon of the oxirane ring. The aqueous medium was reused and crystalline sulfides were isolated by filtration carrying out a solventless process. The protocol was used for a one-pot synthesis of hexahydrodibenzo[1,4]oxathiepinone 9.

Living Radical Polymerization. 1. The Case of Atom Transfer Radical Polymerization of Acrylamide in Aqueous-Based Medium

Atom transfer radical polymerization (ATRP) of acrylamide has been carried out in water or in glycerol−water (1:1 v/v) medium at 130 °C using water-soluble initiators, viz. 2-chloropropionamide (2-Cl-PA) or 2-bromopropionamide (2-Br-PA) and CuX (X = Cl, Br) bipyridine complex as catalyst. Extraneous addition of CuX2 (20 mol % of CuX) and/or excess X- ions (1 M alkali halide) in the reaction mixture helps to reduce molecular weight polydispersity (PDI). However, even under the best conditions (using both CuX2 and X- ion additives), the PDI is high, ca. 1.6−1.7. Also, the GPC traces show shoulders. The chain extension experiment, however, confirms the living nature of the polymers. Replacement of glycerol−water with water as the medium results in sluggish polymerization. The ln M0/M vs t plots are curved to start with but become linear after polymerization proceeds to variable extents depending on the additives used. The molecular weights tend to agree with the theoretical values as conversion increases. A ...

First determination of absolute rate constants for the reaction of aroyl-substituted benzyl carbanions in water and DMSO.

The prompt generation of carbanions II and III within the duration of the nanosecond laser pulse provides a way of evaluating absolute rate constants for their two decay pathways, protonation and cyclization, the latter resulting from an intramolecular nucleophilic carbanion displacement of iodide tethered at the end of the lateral alkyl chain. Absolute rate constants are given for both carbanions (II and III) and show that the intra-S(N)2 reaction is favored in aprotic media, such as dimethyl sulfoxide (DMSO), while protonation is the dominant reaction in basic aqueous media.

Synthesis and photophysics of purine-capped Q-CdS nanocrystallites.

Purine-capped Q-CdS has been synthesised in aqueous basic medium in the presence of excess Cd2+. XRD analysis suggests the presence of CdS is in both its cubic and wurtzite structural forms along with Cd(OH)2. IR and NMR studies indicate core CdS binds purine through H-bonding interaction involving the OH of Cd(OH)2 and N(9) of purine. A further uptake of purine occurs through protonated N(7). The amount of purine controls the size of the clusters in a dynamic equilibrium. These clusters exhibit size-dependent electronic properties. Purine binds to the deep defects involved in non-radiative transition and enhances the bandgap emission. Emission decays in a complex process and consists of three distinct time domains in the sub-nanosecond and nanosecond range. Relaxation kinetics of the charge carriers monitored as a function of emission energy reveal a distribution of traps to varying depths on the surface of the particles. These particles were highly photoactive. Their illumination results in the production of smaller particles. Thermolysis of these colloids induces the growth of particles by removing the weakly bound purine.

Kinetics and Mechanism of the Cobalt(III) Tetraammine Complex-Promoted Hydrolysis of 4-Nitrophenyl Glycinate

Abstract The kinetics of the hydrolysis of 4-nitrophenyl glycine ester (PNPG) catalysed by [Co(OH)(trien)(OH2)]2+, [Co(OH)(tren)(OH2)]2+ and [Co(OH)(en)2(OH2)]2+ complexes has been studied spectrophotometrically in weakly basic aqueous media (pH = 6.5 to 7.4). Kinetic experiments were carried out as a function of the pH, complex concentration and temperature. The rate of hydrolysis increases linearly with the complex concentration with a trend to wards rate saturation, suggesting the formation of associative species in a pre-equilibrium step. The pseudo-first order rate constant, kobs, increases rapidly with a decrease in the hydrogen-ion concentration. The complexes promote the hydrolysis of 4-nitrophenyl glycinate significantly, and the acceleration rate is about 400–600. An attack of external OH- on the chelated ester is suggested as a probable mechanism for the hydrolysis. The lower rate enhancements observed in the present study could probably be ascribed to a weaker cobalt(III) alkoxy carbonyl interaction in the chelate, owing to a decreased nucleophilicity of the carbonyl oxygen in the p-nitrophenyl ester. The activation parameters for all three complex-promoted reactions are found to be comparable, thus suggesting a common mechanism operative in all complex catalysed reactions.

Water-soluble mono- and star-shaped hexanuclear functional organo-iron catalysts for nitrate and nitrite reduction in water: syntheses and electroanalytical study

Ten functional sandwich complexes [Fe II(η 5-C 5H 4CO 2H)(η 6-(arene)][PF 6] and [Fe +(η 5-C 5H 5)(η 6-(C 6(CH 2CH 2C 6H 4OH) 6)][PF 6] have been synthesized to provide water-soluble redox catalysts with a range of redox potentials for the Fe II–Fe I redox couple. The CpFe + induced CH benzylic activation and the carboxylation of hexamethylbenzene, the CpFe + induced one-pot polymethylation of mesitylene and hexamethylbenzene, and the one-pot CpFe + induced hexa- p-methoxybenzylation of hexamethylbenzene have led to the desired functionalized complexes. These compounds catalyze the cathodic reduction of nitrate and nitrite in a basic aqueous medium on a Hg cathode. The rates of the rate-limiting steps of the redox-catalytic processes involving the homogeneous reduction of nitrate and nitrite by the ‘19-electron’ states of the redox catalysts have been measured using enhancement of the intensity of the monoelectronic cathodic wave Fe II→Fe I in the presence of the substrate by cyclic voltammetry, polarography and chronoamperometry. For six iron sandwich complexes without excessive bulk around the iron center, a linear Marcus-type correlation between the kinetics and the thermodynamics was found by plotting the logarithm of this rate constant versus the redox potential, which indicates that the homogeneous electron-transfer from the 19-electron catalyst to the substrate is rate-limiting. With four complexes in which chains of the arene ligand introduced more bulk around the iron center, the rates were found to be an order of magnitude lower, showing the crucial effect of the distance on the outer-sphere electron transfer. A small inner-sphere contribution cannot be discarded, however. When the redox catalysts are attached to the termini of the branches of hexa-branch star-shaped cores, the rate constants are close to those of unencumbered catalysts, i.e. no significant loss of activity is observed.

The Mechanism of Aqueous Hydrolysis of Nitro Derivatives of Phenyl Phenylmethanesulfonate. An Organic Laboratory Experiment

This paper describes the preparation, characterization, and hydrolysis reactions in aqueous basic medium of three nitro derivatives of a simple sulfonate ester, phenyl phenylmethanesulfonate, C6H5-CH2-SO2-O-C6H5. The three nitro esters are p-nitrophenyl phenylmethanesulfonate, C6H5-CH2-SO2-O-C6H4-NO2-p, ester 1; phenyl p-nitrophenylmethanesulfonate, p-O2N-C6H4-CH2-SO2-O-C6H5 ester 2; and p-nitrophenyl p-nitrophenylmethanesulfonate, p- O2N-C6H4-CH2-SO2-O-C6H4-NO2-p ester 3. Laboratory experiments involving this system include ester synthesis, purification and characterization, and visual observations and kinetic analysis of hydrolysis reactions of ester 2 using a digital visible spectrophotometer.Experimental data are interpreted in light of chemical principles already familiar to students, which enables them to construct a plausible mechanism for the hydrolytic process. These principles are all encountered during the first semester organic chemistry course, and the students should therefore be able to see connections between lecture concepts and their laboratory observations.

Keto–enol/enolate equilibria in the 2-acetylcyclopentanone system. An unusual reaction mechanism in enol nitrosation

The keto–enol equilibrium of 2-acetylcyclopentanone (ACPE) was studied in water by analysing the effect that aqueous micellar solutions produce in the UV absorption spectrum of this compound. Aqueous solutions of anionic, cationic, or nonionic surfactants forming micelles have been used. The quantitative treatment of absorbance changes measured at the maximum absorption wavelength as a function of surfactant concentration gave the keto–enol equilibrium constant, KE. In the same sense, the analysis of spectral changes measured as a function of pH in aqueous basic media allowed us to determine the acidity equilibrium constant, Ka. The combination of both equilibrium constants gives the acidity constant of the enol ionizing as an oxygen acid, pKEa=7.72 and the acidity constant of the ketone ionizing as a carbon acid, pKKa=8.12. The kinetic study of the nitrosation reaction of ACPE has been realized in aqueous strong acid media under several experimental conditions. As expected, the reaction is first-order with respect to ACPE concentration, but in sharp contrast to other β-dicarbonyl compounds, the dependence of both [H+] or [X−] (X−=Cl−, Br−, or SCN−) is not simple first-order; instead a fractional order which varied from 1 to 0 was observed. The kinetic interpretation of these experimental facts has been done on the basis of a reaction mechanism that considers the formation of an intermediate in steady-state, which has been postulated as a chelate-nitrosyl complex. The quantitative treatment of the experimental data gave the values of every rate constant appearing in the proposed reaction mechanism.

Electrochemical reduction of benzil and salicylaldehyde at stainless steel cathode in basic aqueous ethanol medium

The electrochemical reduction of the benzil and salicylaldehyde was carried out at the controlled potential in 1.0 M. acetate buffer at pH 9.0 for the purpose of investigating this type of reduction as a possible synthetic procedure for the preparation of 1,2-glycols. The products formed during electrolysis at constant cathode potential are reported.