Terms Of Solvent Effects Research Articles

Water-DMSO Co–Solvent effect and kinetics of acid catalyzed Hydrolysis of butyl formate and Influence on Activation Parameters

The acid catalyzed hydrolysis of butyl formate in presence of 0.1N-HCI in water and the presence of water-DMSO mixture containing up to 30-70% (v/v) was studied over the temperature ranging from 20-400C. The rate of reaction decreases with decrease of water content of the solvent mixture and reached minima at about 70% of organic solvent. The number of water molecule associated with activated complex was showing decrease in trend with increase of temperature, is an indication of change in mechanism from unimolecular to bimolecular in reaction media. The parameters of thermodynamic activation were also calculated and discussed in terms of solvent effect with help of plots of ΔH* versus ΔS*, the isokinetic temperature was calculated and found to be greater than 300.

Critical assessment of solvent effects on absorption and fluorescence of 3HF in acetonitrile in the QM/PCM framework: A synergic computational and experimental study

Absorption and fluorescence properties of 3-hydroxyflavone (3HF) dissolved in the polar aprotic solvent acetonitrile have been investigated by electronic spectroscopies, associated to mixed quantum mechanical (QM)/classical calculations, where the effect of the solvent is included at the classical level by means of the polarizable continuum model (QM/PCM).Whereas absorption and fluorescence (λexc = 342 nm) spectra confirmed previous results, a detailed spectrofluorimetric investigation of the anion, deriving from solvent-induced deprotonation of the OH group of 3-hydroxyflavone, showed for the first time that a single anionic form is present in solution, differently from what observed in another polar aprotic solvent, DMSO.A detailed computational study based on Density Functional Theory (DFT), using five different functionals, has been carried out in order to reproduce and better understand absorption and emission bands on the different existing forms for 3HF in solution: Normal (N), Tautomer (T), Anion (A).The results are discussed in terms of solvent effects on 3HF spectroscopic properties. It was found that simulations are in good agreement with the spectroscopic data for the N and T forms, whereas for the A form larger discrepancies are observed, especially for absorption properties. The effect of specific solute solvent hydrogen bond interactions involving the CO and OH moieties of 3HF was also explored, aiming to better simulate anionic spectroscopic properties. Results suggest that a more complete description of the whole solvation shell is necessary.

Comparison of the leaving groups during the study of the aquation of halopentaammine cobalt(III) complex in tartarate at different percentage of tert-butanol

The experimental kinetic study of aquation for both complexes bromopentaammine cobalt(III) and chloropentaammine cobalt(III) ions in the presence of tartarate solution in mixed solvent media of water with tert-butanol (10-50%, v:v) was examined spectrophotometrically at different temperatures (30-60 °C) by comparing the special effects of the leaving group of chloro and bromo on the rate constant of aquation. Comparison of kip (rate constant of ion-pairing) for both complexes and show the non-linear plots of log (kip) ion-pair rate constants against the reciprocal of the dielectric constant D. The thermodynamic analyses of the kinetic data for both complexes have been discussed in terms of solvent effect on the ion-pair aquation reactions. The obtained isokinetic temperatures of these systems indicate the existence of compensation effect arising from solute-solvent interaction. The excessive change of ΔHip* and ΔSip* with the mole fraction of the co-solvent can be recognized to the change of the physical properties of the solvent-water mixture with the solvent structure. Undersized changes in ΔGip* with the mole fraction of the co-solvent was found, representing a compensating effects between ΔHip* and ΔSip*.

Solvent Effects on the Electrochemical Behavior of TAPD-Based Redox-Responsive Probes for Cadmium(II)

Two tetralkylated phenylenediamines (TAPD)1and2have been prepared by reductive alkylation ofpara-dimethylaminoaniline with furfural or thiophene 2-carboxaldehyde, respectively. Their chelation ability has been evaluated as electrochemical guest-responsive chemosensors for Cd(II) in acetonitrile (ACN), dimethylformamide (DMF), propylene carbonate (PC), and nitromethane (NM). The voltamperometric studies showed that these compounds are able to bind the Cd(II) cation with strong affinities except in DMF. The redox features of the chemosensors changed drastically when they are bounded to Cd(II) to undergo important anodic potential peak shifts comprised between ca. 500 and ca. 900 mV depending on the solvent. The addition of ∼4–10% molar triflic acid (TfOH) was found to be necessary to achieve rapidly the cation chelation which is slow without the acid. The electrochemical investigations suggested the formation of 1 : 2 stoichiometry complexes [Cd(L)2]2+. The results are discussed in terms of solvent effects as a competitive electron donating ligand to the cation. The reaction coupling efficiency (RCE) values were determined and were also found to be solvent-dependent.

Kinetics and mechanism of aquation of bromopentammine cobalt(III) cation assisted by ion-pairing succinate anion in ethane-2-diol-water mixtures

The aquation kinetics of bromopentammine cobalt(III) ion has been investigated in the presence of different concentrations of succinate ion in aqueous medium and that mixed with ethane-1,2-diol (up to 50%, w/w) within the temperature range (35-65 o C). The ion-pairing succinate ion concentration (L) and the observed rate constant have been determined at different experimental conditions. The thermodynamic parameters of activation have been calculated and discussed in terms of solvent effects. Also the extrathermodynamic analyses of the obtained results have been discussed on the basis of solute-solvent and solvent-solvent interactions. An empirical correlation between the rate coefficient and the concentration of the ion-pairing succinate ligand (L) has been established and a suggested reaction mechanism is proposed.

Studies on ion-pairing effects of the kinetics of aquation of bromopentaammine cobalt(III) complex in malonate media

The aquation of bromopentaamminecobalt(III) ion in the presence of ion-pairing malonate anion in mixed solvent media of water with tert -butanol (10%-50%) v/v have been investigated spectrophotometrically at different temperatures (30-60 o C). Nonlinear plots of Log (k ip ) ion-pair rate constants against the reciprocal of the dielectric constant D, Log of water concentration and Grunwald-Winstein Y values were found. The thermodynamic and extrathermodynamic analyses of the kinetic data have been discussed in terms of solvent effect on the ion-pair aquation reactions. The obtained isokinetic temperatures of these systems indicate the existence of compensation effect arising from solute-solvent interaction. The extrema found in the change of ∆H ip * and ∆S ip * with the mole fraction of the co-solvent can be attributed to the change of the physical properties of the solvent-water mixture with the solvent structure. Application of a free energy cycle is performed to compare between the stability of the initial and the transition state of the complex. However, small changes in ∆G ip * with the mole fraction of the co-solvent was found, indicating a compensating effects between ∆H ip * and ∆S ip *

Kinetics of Ion-Pair Effect of Aquation of Bromopentaammine Cobalt(III) Complex in Different Dicarboxylate Media

The rate of aquation of bromopentaammine cobalt(III) ion in the presence of different types of dicarboxylate solutions containing tert-butanol (40% V/V) have been measured spectrophotometrically at different temperatures (30-600°C) in the light of the effects of ion-pairing on reaction rates and mechanism. The thermodynamic and extrathermodynamic parameters of activation have been calculated and discussed in terms of solvent effect on the ion-pair aquation reaction. The free energy of activation ∆Gip* is more or less linearly varied among the studied dicarboxylate ion-pairing ligands indicating the presence of compensation effect between ∆Hip* and ∆Sip*. Comparing the kip values with respect of different buffers at 40% of ter-butanol is introduced.

Thermodynamics of Binary and Ternary Solutions of Multivalent Electrolytes with Formation of 1:1 and 1:2 Complexes, within the Mean Spherical Approximation

The mean activity (γ±) and osmotic (Φ) coefficients for binary and ternary aqueous solutions of trivalent electrolytes (mainly made up of lanthanide salts) are described in the framework of the primitive model of ionic solutions, using the binding mean spherical approximation (BiMSA). This model, based on the Wertheim formalism, accounts for (chemical or electrostatic) association of ions. In this work, the multivalent cation and the anion are allowed to form 1:1 (pairs) and 1:2 (trimers) complexes. Expressions for γ± and Φ are given which satisfy the Gibbs−Duhem relation. The model involves concentration-dependent cation size and effective relative permittivity, variations that can be interpreted in terms of solvent effects. The theory is applied to aqueous solutions of binary and ternary mixtures at 25 °C with common anion.

Aggregation of Alcohols Ethoxylates in n‐Heptane

AbstractThe solubility and aggregation process of polyethoxylated non‐ionic surfactants, of general formula CiH2i+1–(O–CH2–CH2)j–OH with i = 6, 8, 10 and j = 3–6 (CiEOj), in heptane were studied. The aggregation of CiEOj surfactants in heptane was investigated by using methylene blue (MB) as an absorption probe. In solutions of MB in the presence of these surfactants in heptane, at concentrations larger than the re‐dissolution concentration, the UV bands associated to free MB (A1) and MB–EO complex (A2) were detected. The ratio of these intensities A2/A1, was used to study the kinetics of the complex formation in pure surfactant. The value of A2/A1 depends on the surfactant structure and the media wherein MB is dissolved, being larger in the pure surfactant than in heptane solutions. These results are explained in terms of solvent effect and aggregate structures on the complex formation.

Donator Acceptor Map of Psittacofulvins and Anthocyanins: Are They Good Antioxidant Substances?

Psittacofulvins represent an unusual class of pigments (noncarotenoid lipochromes), which are found only in the red, orange, and yellow plumage of parrots. Anthocyanins are flavonoids, and they are one of the primary types of colorants found in plants. Blue butterflies acquire blue and UV hues on their wings, owing to the presence of flavonoids. It is assumed that these natural pigments are valuable antioxidants because they are able to scavenge free radicals. The aim of this investigation is to rationalize the scavenging activity of psittacofulvins and anthocyanins, in terms of the one electron transfer mechanism, taking into account that to prevent oxidative stress, substances must either donate or accept electrons. Density functional approximation calculations are used to obtain ionization potentials, electron affinities, electrodonating, and electroaccepting power indexes. Taking these values, a donator acceptor map (DAM) was constructed, indicating that anthocyanins are good electron donors, whereas psittacofulvins are good electron acceptors. Anthocyanins and vitamins are antioxidants, whereas psittacofulvins and carotenoids are antireductants (oxidants). In terms of solvent effects, animal pigments (carotenoids, psittacofulvins, and anthocyanins) are much better electron acceptors in water than in either the gas phase or benzene. Solvent effects do not alter the electron donor capacity of vitamins, but anthocyanins become effective electron acceptors in water, rather than effective electron donors. The information presented here may also be valuable for the design and analysis of further experiments.

Solvent Effect in Binary Copolymerization

Recently published experimental data concerning the solvent effect in binary copolymerization are re‐analyzed. Newer, more accurate, reactivity ratios were calculated using a non‐linear method (PROCOP), which involves all experimental data, conversion values included. The differences between the reactivity ratios provided by the recalculated values are discussed in terms of solvent effect. Based on the existing experimental data, the solvent effect was identified only for a few binary copolymerization systems.

The use of heat transfer fluids in the synthesis of high-quality CdSe quantum dots,core/shell quantum dots, and quantum rods

Fluorescent semiconductor nanoparticles, or quantum dots, have potential uses as anoptical material, in which the optoelectronic properties can be tuned precisely by particlesize. Advances in chemical synthesis have led to improvements in size and shape control,cost, and safety. A limiting step in large-scale production is identified to be the rawmaterials cost, in which a common synthesis solvent, octadecene, accounts for most of thematerials cost for a batch of CdSe quantum dots. Thus, less expensive solvents are needed.In this paper, we identify heat transfer fluids, a class of organic liquids commonlyused in chemical process industries to transport heat between unit operations, asalternative solvents for quantum dot synthesis. We specifically show that two heattransfer fluids can be used successfully in the synthesis of CdSe quantum dotswith uniform particle sizes. We show that the synthesis chemistry for CdSe/CdScore/shell quantum dots and CdSe quantum rods can also be performed in heattransfer fluids. With the aid of a population balance model, we interpret theeffect of different HT fluids on QD growth kinetics in terms of solvent effects, i.e.,solvent viscosity, CdSe bulk solubility in the solvent, and surface free energy.

Effects of long-chain alkyl substituents on the protolytic reactions of naphthols

Kinetics and mechanism of excited-state proton-transfer reactions of 1-naphthol (1N) and 2-octadecyl-1-naphthol (2O1N) were studied in aqueous acetonitrile and absolute ethanol. Dissociation of 1N and 2O1N in the singlet excited state was characterized by similar rate and equilibrium constants ( k 1 ∼ 0.5 ns −1, p K ∼ 1) in contrast to the ground state, where 2O1N is a weaker acid than 1N (Δp K = 0.6 in an acetonitrile–water mixture 2:1, v/v). Main features of the ground and excited-state p K and p K* and excited-state protolytic dissociation rate constants k 1 and k R were rationalized in terms of solvent effects on the energetics of equilibrium between hydrogen bonded complex and ion pair and in terms of electron donating effects of alkoxy group in the ground state and aromatic system in the excited singlet state. An efficient deactivation process competing with the excited-state proton transfer (ESPT) was observed both for 1N and 2O1N. This needs more complicated kinetic analysis, yet provided a deeper insight into mechanisms of the excited-state proton-transfer reactions. A simple kinetic scheme including transient formation of excited hydrogen-bonded complex and geminate ion-pair and fast deactivation of both transients provided a good description of the protolytic photodissociation for the compounds studied. The rate constants for proton transfer and induced deactivation were determined for photodissociation of excited 1N and 2O1N in aqueous acetonitrile and their reactions with acetate anion in absolute ethanol. A remarkable decrease of ESPT rate constant and a substantial increase of the radiationless decay rate constant was observed in aqueous acetonitrile as compared to water. The origin of dissimilar solvent effects on these rate constants was discussed.

Cobalt(II) and cadmium(II) chelates with nitrogen donors and O 2 bonding to Co(II) derivatives

The formation of Cd(II) and Co(II) complexes with N-methylethylenediamine (men) has been studied at 298 K in dimethylsulfoxide (dmso) in an ionic medium set to 0.1 mol dm −3 with Et 4NClO 4 in anaerobic conditions by means of potentiometric, UV–Vis, calorimetric and FT-IR technique. Mononuclear ML j (M=Cd, Co; j=1–3) complexes are formed in exothermic reactions, whereas the entropy changes oppose the complexes formation. The results are discussed in terms of different basicities and steric requirements and the whole of the thermodynamic data reported till now for the two ions with a number of diamines are summarized to visualize the selectivity of the ligands. The dioxygen uptake of Co(men) 2 species has also been studied by means of UV–Vis and EPR techniques. The kinetic parameters and stability constants obtained for the formation of the superoxo and μ-peroxo species are discussed in terms of solvent effect and steric hindrance due to methyl group. Cyclic voltammetry was used to confirm the stability constant for the Co(dmen) 2 (dmen= N, N ′-dimethylethylenediamine) superoxo adduct formation but was not successful to investigate this Co(men) 2–O 2 system.

Cobalt(II) and cadmium(II) chelates with nitrogen donors and O2 bonding to Co(II) derivatives

The formation of Cd(II) and Co(II) complexes with N-methylethylenediamine (men) has been studied at 298 K in dimethylsulfoxide (dmso) in an ionic medium set to 0.1 mol dm−3 with Et4NClO4 in anaerobic conditions by means of potentiometric, UV–Vis, calorimetric and FT-IR technique. Mononuclear MLj (M=Cd, Co; j=1–3) complexes are formed in exothermic reactions, whereas the entropy changes oppose the complexes formation. The results are discussed in terms of different basicities and steric requirements and the whole of the thermodynamic data reported till now for the two ions with a number of diamines are summarized to visualize the selectivity of the ligands. The dioxygen uptake of Co(men)2 species has also been studied by means of UV–Vis and EPR techniques. The kinetic parameters and stability constants obtained for the formation of the superoxo and μ-peroxo species are discussed in terms of solvent effect and steric hindrance due to methyl group. Cyclic voltammetry was used to confirm the stability constant for the Co(dmen)2 (dmen=N,N′-dimethylethylenediamine) superoxo adduct formation but was not successful to investigate this Co(men)2–O2 system.

Conformational Analysis of Poly(propylene sulfide)

Conformational characteristics of poly(propylene sulfide) (PPS, [CH2C*H(CH3)S]x) have been investigated. Proton and carbon-13 NMR vicinal coupling constants observed from its monomeric model compound, 1,2-bis(methylthio)propane (BMTP, CH3S−CH2−C*H(CH3)−SCH3), were analyzed to yield bond conformations of the S−C, C−C*, and C*−S bonds. Ab initio molecular orbital (MO) calculations at the MP2/6-311+G(3df,2p)//HF/6-31G(d) and B3LYP/6-311+G(3df,2p)//B3LYP/6-31G(d) levels were carried out for BMTP to evaluate free energies and dipole moments of all the possible conformers. Conformational energies and bond dipole moments of BMTP were estimated therefrom. Conformational energies of BMTP and PPS were also determined by simulations based on the rotational isomeric state scheme for experimental observations of bond conformations of BMTP, characteristic ratio of atactic PPS, and dipole moment ratios of isotactic and atactic PPS. The first-order interaction energies for the S−C (Eσ) and the C−C* (Eα and Eβ) bonds were obtained as follows: Eσ = −1.0 to −0.60 kcal mol-1, Eα = 0.5−0.6 kcal mol-1, and Eβ = 1.1−1.2 kcal mol-1. The second-order ω1 and ω2 interactions, representing intramolecular C−H···S interactions, are repulsive: Eω1 = 0.6−0.9 kcal mol-1 and Eω2 = 1.0−1.2 kcal mol-1. The S−C, C−C*, and C*−S bonds were found to prefer the gauche, trans, and trans states, respectively. The conformational characteristics of unperturbed PPS are similar to those of poly(ethylene sulfide) but significantly different from those of its corresponding polyether, poly(propylene oxide) (PPO), although isotactic PPS and PPO are isomorphous. The conformational characteristics of PPS are discussed in terms of solvent effect, crystal structure, and thermal properties.

Synthesis, spectral and redox properties of tetraammine dioxolene ruthenium complexes †

A series of species [RuIII(NH3)4(Cat-R)]n+ have been synthesized where Cat-R is a catecholate dianion having the substituent R = CO2−, CO2H, OMe or H. These so-called parent species were characterized by their electronic spectra, FTIR, mass spectrum, cyclic voltammetry and EPR. Controlled potential reduction yields [RuII(NH3)4(Cat-R)](n − 1)+ while controlled potential oxidation yields [RuII(NH3)4(Q-R)](n + 1)+ (Q-R = substituted quinone). Density Functional Theory (DFT) was primarily used to explore the electronic structures of these complexes. Application of the INDO semi-empirical model proved less useful. Time dependent density functional response theory was used to calculate the electronic spectra of the species with R = H. The electronic spectra of the closed shell species are well reproduced by the calculations. The physical properties of these complexes indicate a charge delocalized system reminiscent of a delocalized organic molecule. The simple valence descriptions noted above are convenient to use but do not reflect the actual electronic structure. The electronic spectra of the parent species are temperature dependent. The visible region charge transfer band shifts by about 1500 cm−1 to higher energy in acidic media at liquid nitrogen temperature. This is interpreted in terms of solvent effects rather than valence tautomerism. The electrochemical properties of [RuIII(NH3)4(Cat-R)], in aqueous solution, reveal the first example of a reversible and stable Ru–quinone species in that medium. The pKa values for several dioxolene species, with R = CO2−, are derived from a Pourbaix diagram.

Effect of mixed H2O−CH3CN solvent on intramolecular general base-catalyzed cleavage of ionized phenyl salicylate in the presence of DL-proline

Nucleophilic second-order rate constant (Knms) for the reaction of DL-proline with ionized phenyl salicylate (PS−) shows a nonlinear decrease with the increase in the content of CH3CN in mixed aqueous solvents at ≤50% v/v CH3CN. The values of knms show a mild increase with the increase in the content of CH3CN at >50% v/v CH3CN. The effect of solvent on knms is explained in terms of solvent effect on the pKa of the conjugate acids of leaving group (i.e. phenolate ion) and DL-proline.

Sensitized ring-opening reactions of 3-(1-naphthyl)-2-(1-naphthalenemethyl) oxaziridine

The benzophenone (BP)-sensitized photolysis of the title compound (1) in oxygen-free acetonitrile and benzene gave 1-naphthaldehyde and N-(1-naphthoyl)-1-naphthalenemethylamine as main products along with small amounts of unidentified products. The occurrence of triplet-triplet energy transfer between BP and 1 at the diffusion-limited rate suggests the participation of triplet 1, from which the N-O bond cleavage as well as the N-O and C-N bond fissions in the three-membered ring proceeds to eventually yield the amine and the aldehyde, respectively. Control experiments using 1-naphthalenemethylazide showed the involvement of a triplet nitrene intermediate in appearance of the latter product. On the other hand, the 9,10-dicyanoanthracene (DCA)-sensitized reaction of 1 in nitrogen-purged acetonitrile was found to occur by an electron-transfer mechanism giving the product distribution that is different from that of the BP-sensitized reaction. No occurrence of the reaction in benzene confirms that the dissociated oxaziridine cation radical is a precursor of the products obtained. Significantly, the electron-transfer sensitization of 1 in acetonitrile afforded 1 -(nitromethyl) naphthalene as one of the products, being consistent with the mechanism in which atomic oxygen derived from the deoxygenation of the nitrone cation radical is captured by the nitrene intermediate. However, the deoxygenation reaction was not observed in methanol where only the aldehyde was detected. This interesting result was explained in terms of solvent effects on the stability of the oxaziridine cation radical as well as of the nitrene cation radical that was generated by the ring-opening reaction of the former cation radical.

Kinetics of the solvolysis of the Chloropentakis(methylamine)cobalt(III) Ion in Water–Methanol and Water–Propan-2-ol Mixtures†

The solvolysis kinetics of [Co(NH 2 Me) 5 Cl] 2+ in water–methanol and water–propan-2-ol mixtures are discussed in terms of solvent effects and the structure of the complex.