Donor Properties Of Solvents Research Articles

Entropy and Enthalpy Effects on Metal Complex Formation in Non-Aqueous Solvents: The Case of Silver(I) and Monoamines.

Access to the enthalpy and entropy of the formation of metal complexes in solution is essential for understanding the factors determining their thermodynamic stability and speciation. As a case study, in this report we systematically examine the complexation of silver(I) in acetonitrile (AN) with the following monoamines: n-propylamine (n-pr), n-butylamine (n-but), hexylamine (hexyl), diethylamine (di-et), dipropylamine (di-pr), dibutylamine (di-but), triethylamine (tri-et) and tripropylamine (tri-pr). The study shows that the complex stabilities are quite independent of the length of the substitution chain on the N atom and demonstrates that, in general, the overall enthalpy terms associated with the complex formation are strongly exothermic, whereas the entropy values oppose the complex formations. In addition, we examined the similarity of the formation constants of AgL complexes of the primary monoamines in AN, dimethylsulfoxide (DMSO) and water, which were unexpected on the basis of the difference between the donor properties of solvents.

Chemically Triggered C–ON Bond Homolysis in Alkoxyamines. 6. Effect of the Counteranion

We showed (J. Org. Chem. 2012, 77, 9634) that the activation by methylation of pyridyl-based alkoxyamine 1 increased with the hydrogen bond donor properties of solvents. In this paper, activation of 1 by protonation with acids, CF3COOH and CSA, in tert-butylbenzene (t-BuPh) and in H2O/MeOH afforded, with CF3COOH, k(d) 28-fold larger in H2O/MeOH than in t-BuPh, whereas it was only 4-fold larger when CSA was used. This puzzling observation was ascribed to the dissociation of the intimate ion pair.

Quantum-chemical study of the Grignard reaction mechanism within the cluster model of reaction center

Structure and energy of EtBr adsorption complexes on (0001) magnesium crystal surface in the surrounding of adsorbed solvent molecules L (L=n-pentane, acetonitrile, THF, DMF, DMSO, pyridine, HMPTA) as well as the most probable routes of their transformation with the Grignard reagent (EtMgBr) formation were studied by applying the DFT method (B3PW91/6-31G(d)). Surface complexes were modeled using the Mg50–EtBr, Mg50–L and Mg50–EtBr–L6 clusters. Thermodynamics of elementary reactions of Grignard reagent formation in aprotic solvents on the magnesium surface was studied. It is shown that the overall kinetic rate of the Grignard reagent formation is defined by the competition between the adsorption and desorption steps depending on the donor properties of solvents, while the oxidation step itself is fast. The magnesium oxidation rate correlates with the adsorption energy of oxidizer on a magnesium surface and product’s desorption energy to the reaction mixture volume.

Kinetics and Mechanism of Triphenylphosphine Quarternization with Unsaturated Carboxylic Acids in Various Media

Reactions of tertiary phosphines with unsaturated electrophilic reagents are widely used in synthetic organic chemistry. Typical satellites of these transformations are proton migration processes, which can play decisive role in such reactions. To learn more about proton transfer mechanism, kinetics of reaction of triphenylphosphine with a series of unsaturated carboxylic acids in alcohols, carboxylic acids, and aprotic solvents was studied by spectrophotometry. The form of kinetic equation depends on proton–donor properties of solvent and has a general third order. Proton transfer occurs from the solvent in carboxylic acids; the second molecule of substrate is required in aprotic solvents, and both canals of proton migration take place in alcohols. Existent proton transfer canals are isokinetic, attesting to the invariability of general features of the reaction mechanism independent of proton–donor nature at the last step of the interaction. A stepwise mechanism including initial generation of 1,3-dipole followed by proton transfer to the carbanionic centre from the medium is suggested.

Solvent Swelling of Petroleum Asphaltenes

Volumetric changes of crude oils and derived fractions can cause phase separation. Crude oil asphaltene swelling has been recently reported in the open literature. Solvent swelling processes have been formerly studied in greater detail for coal samples. Important structural and chemical information on coals have been gathered through the use of swelling as a characterization technique. In this study, crude oil isolated asphaltenes were successfully characterized by solvent swelling, employing polar as well as nonpolar solvents. Operationally stable and unstable crude oils, virgin and hydrocracked vacuum residua, and solid deposits from oil production tubings were the selected matrices for asphaltene isolation and characterization. The main factor that governs swelling appears to be dispersive forces, since swelling maxima were observed for alkane type solvents. Consistently, compositional asphaltene parameters like elemental hydrogen and aliphatic chain content significantly influenced the solvent swelling process. However, solvent donor properties and asphaltene acceptor properties also played an important role in the swelling phenomenom. Asphaltene swelling in nonpolar solvents was successfully fitted using the Flory−Rehner equation. This procedure allows to estimate the solubility parameters for the samples, which turned out relatively low. The former results allowed us to present a structural model for solid asphaltenes. This model proposes the solids to be composed of inner aromatic cores that are impermeable to solvents, surrounded by aliphatic moieties capable of incorporating solvents and swell. Kinetic dissolution experiments carried out with solvent swollen asphaltenes show consistency with the proposed model.

Raman study of solvent-solute interactions in solutions of mercury(II)-thiocyanate complexes

Raman spectra of the Hg(SCN)2, [Hg(SCN)3]- and [Hg(SCN)4]2- complex species in solution were investigated for 10 donor solvents in the ν(CN) and ν(CS) wavenumber regions. Attempts were made to relate the solvent donor strength to overall vibrational properties of the complexes. A good correlation of ν(CN) with ν(HgS) and consequently with solvent donor properties was found in solutions of Hg(SCN)2 and [Hg (SCN)3]-. Wavenumber differences Δν˜(CN), calculated as the difference between wavenumbers of coordinated and free SCN- ligands, correlate well with the solvent donor strength scale, DS. The Δν˜(CN) values for Hg(SCN)2 and [Hg(SCN)3]- can be used as an indicator of solvent donor capacity. Data derived from the Δν(CN) shifts show a better correlation with solvent donor ability than those obtained from the ν(CS) wavenumber. The spectral properties of [Hg(SCN)4]2- complex depend only on the electrophilic properties of the solvent and not on its donor strength, because solvent molecules cannot penetrate into the first coordination sphere and donate an electron pair to Hg(II). Solvent electrophilic interaction with coordinated thiocyanate is proportional to its acceptor number. ©1998 John Wiley & Sons, Ltd.

A critical view on the Lewis-donor (nucleophilic) properties of solvents

Abstract Parameters which claim to reflect the Lewis-type donor properties of solvents are reviewed. It will be shown that the original concept of Lewis, where one partner supplies one electron-pair for a chemical bond and the other partner accepts this electron-pair, is limited to “hard-hard” interactions. “Soft-soft” interactions, where both solute and solvent donate and accept electron pairs cannot be accounted for by parameters derived from model substances, which are based on the classical Lewis concept. Disregard of the different chemical behaviour of “hard-hard” and “soft-soft” interactions has led to misinterpretation of solvent parameters and to deviations in correlations of kinetic and thermodynamic properties with solvent parameters.

4- and 5-Coordinate Dinuclear Copper(II) Complexes with the Tetraacetylethanediide and an N-Alkylated Diamine or a Triamine

Six dinuclear copper(II) complexes have been prepared, Cu2(taet)(plam)2X2 where taet = 1,1,2,2-tetraacetylethanediide, plam = N-alkylated polyamine such as tmen = N,N,N′,N′-tetramethylethylenediamine or pmdt = N,N,N′,N′,N′-pentamethyldiethylenetriamine, X = a monovalent anion such as ClO4 - , NO3 - or Cl-. These complexes are classified into two categories from the results of electronic spectra, IR spectra, and X-ray single crystal structure analysis as follows: (1) 4-coordinate-4-coordinate dinuclear, [Cu2(taet)(tmen)2]X2 (where X = ClO4 - or NO3 -), (2) 5-coordinate-5-coordinate dinuclear, [Cu2(taet)(tmen)2Cl2], and [Cu2(taet)(pmdt)2]X2 (where X = ClO4 - , NO3 - , or Cl- ). The crystal structure of Cu2(taet)(tmen)2(ClO4)2 · H2O (1) has been determined by the single crystal X-ray diffraction technique; monoclinic space group P21/a with a = 26.478(3), b = 8.744(1), c = 15.601(3) Å, β = 106.195(9)°, and V = 3468.9(8) Å3 for Z = 4. The final agreement factors are R = 0.097 ( Rw = 0.099). The geometry of each Cu(II) moiety in the dinuclear cation (1) is 4-coordinate square planar with a N2O2 donor set. This tmen-dinuclear complex exhibits a very weak C u (II)-Cu (II) interaction (J = -0.5 cm-1), and shows characteristic ESR spectra with seven hyperfine peaks in 1,2-dichloroethane solution at room temperature. This is not found for the corresponding pmdt-dinuclear complex. All complexes obtained in this study are very soluble in many organic solvents. The tmen-dinuclear complexes show pronounced solvatochromic behavior-dependent on the solvent donor properties. This is not found for the corresponding pmdt-dinuclears, which are stable as 5-coordinated species.

Temperature coefficients of electrode potentials and Gibbs energies, entropies and enthalpies of transfer of Ag+, Na+ and Tl+ from N,N-dimethylformamide to its mixtures with N,N-dimethylthioformamide and with water

Gibbs energies of transfer for Ag+, Na+ and Tl+ from N,N-dimethylformamide (DMF) into its mixtures with N,N-dimethylthioformamide (DMTF) and with water were derived from electrochemical measurements on the basis of the bis(biphenyl)chromium assumption. Transfer entropies were obtained from the temperature coefficients of the half-wave potentials or electrode potentials employing the assumption of a negligible thermal-diffusion potential. Gibbs energies and entropies of transfer were used to calculate transfer enthalpies.The Gibbs energies of Ag+, Na+ and Tl+ into these two solvent mixtures are interpreted on the basis of hard and soft solvent donor properties. The entropies were influenced by the structure of the solvents. The transfer enthalpies were affected by both the solvent donor properties and the solvent structure.

ChemInform Abstract: Recent Aspects of Single Ion Transfer Properties

Gibbs energies, entropies and enthalpies of transfer for several cations and anions from acetonitrile into various solvents formed the basis for investigations on general trends in the interactions of solvent molecules with positively and negatively charged ions. Gibbs energies of transfer for Na+, K+, Rb+, Cs+, Cuff T1+ and Ag+ obtained from different assumptions, experimental techniques and research groups together with a large number of recen ly pu lishe energies of transfer for Li+, Ba2+, Cu, Zn9+, Cd9+,GiHbgb5+ and Pb2+ based on the bis (bipheny1)chromium assumption - were employed to study the interactions of hard and soft donor solvents with hard, soft and borderline cations. Solvent effects on anions were deduced from the Gibbs energies of transfer for Cl', Br-, I- and SCN-. Parameters proposed to account for hard and soft donor properties or for acceptor properties of the solvents were compared with the Gibbs energies of transfer. Parameters representing hard donor properties of solvents correlated with Gibbs energies of transfers for cations into hard solvents, but transfer properties of soft and borderline cations into soft solvents called for a different solvent parameter. The Gibbs energies of transfer for anions related to such solvent parameters that characterized acceptor properties. The solvent induced changes in the Gibbs energies of transfer of hard and soft cations as well as the respective data for anions were explained within the framework of a donor-acceptor model of ion-solvent interactions, including the principle of hard and soft acids and bases. The current status on enthalpies and entropies of transfer is discussed.

Effect of solvent and strong base on electrochemical and chemical behaviour of copper tetraaza macrocyclic complex

Reactions of copper(II) complex with tetrabenzo- [b,f,j,n] [1,3,9,13]tetraazacyclohexadecine (TAAB) as a Lewis acid have been studied. Coordination of solvent molecules and stabilization of the copper(II) oxidation state according to solvent donor properties has been confirmed. The product of hydroxyl ion nucleophilic addition has been isolated and characterized. Differences in electrochemical as well as chemical reduction and reoxidation of the complex in acidic and basic medium have been investigated and the reaction mechanism is discussed.

Recent aspects of single ion transfer properties

Abstract

Solvation and complex formation in strongly solvating solvents

Abstract

Furcate intra- and intermolecular interactions in 1,1,1,3,3,3-hexachloroisopropanol

The effect of electron donor properties of solvents on the infra-red absorption spectra of 1,1,1,3,3,3-hexachloroisopropanol was investigated. Furcate molecular interactions in which the hydroxyl proton is capable of two, three, and four co-ordination bonding were proved.

Solvent effects on thermodynamics and mechanism of dissociation of the monocomplex of nickel(II) with thiocyanate

Rate constants and associated activation parameters for dissociation of (NiSCN)+ were measured kinetically in methanol and dimethylsulfoxide by stopped-flow spectrophotometry using copper(II) as the decomposing ion. The data along with previous results by others on dissociation of (NiSCN)+ in water, acetonitrile, and N,N-dimethylformamide are discussed mechanistically by considering the effect of solvent donor properties on the activation enthalpy for the dissociation process. Rate constants for dissociation at a single temperature are not systematically related to the Gutmann donor number of the solvent, but the enthalpy of activation for the dissociation process shows a linear inverse relation to the donor number. Pathways for dissociation of (NiSCN)+ in these solvents are accommodated within an Id-type mechanism.