Relative Thermodynamic Stabilities of Isomeric Vinyl Ethers Derived from 2-Acetyland 2-Isobutyryltetrahydrofurans. An Experimental and DFT Study

The relative thermodynamic stabilities of four isomeric vinyl ethers obtained by acid-catalyzed cleavage of MeOH from the dimethyl acetals of both 2-acetyltetrahydrofuran and 2-isobutyryltetrahydrofuran have been determined by chemical equilibration in cyclohexane solution. In addition, the structures and relative energies of many of these compounds have also been studied theoretically by DFT calculations. In each series of compounds, the endocyclic isomers, 5-(1-methoxyethyl)-2,3-dihydrofuran and 5-(1-methoxy-2-methylpropyl)-2,3-dihydrofuran, respectively, show the highest thermodynamic stabilities. This is particularly prominent for the vinyl ethers derived from 2-isobutyryltetrahydrofuran in which the equilibrium mixture consists of 90% of the endocyclic isomer at room temperature. The geometrical (exocyclic) isomers of the latter series of compounds show unexpected relative thermodynamic stabilities, but on the basis of the geometry-optimized structures provided by the DFT calculations, a reasonable explanation can be found.     

Complex Formation of 1,10-Dibenzyl-1,10-diaza-18-crown-6 with Ni2+, Cu2+, Ag+ and Cd2+ Metal Cations in Acetonitrile–dimethylformamide Binary Solutions

Conductance measurements are reported for nickel(II), cupper(II), silver(I) and cadmium(II), salts in acetonitrile (AN)–dimethylformamide (DMF) binary solvents containing macrocyclic ligand, 1,10-dibenzyl-1,10-diaza-18-crown-6 (DBDA18C6) at different temperatures. The changes in molar conductance caused by addition of DBDA18C6 to solutions were analyzed by non-linear least squares to give stability constants of 1:1 metal cation–DBDA18C6 complexes. The results show that the stabilities of the complexes are sensitive to solvent composition and in some cases the sequence of stabilities is changed with changing the composition of the mixed solvents. The values of thermodynamic quantities (ΔH°c and ΔS°c) for formation of DBDA18C6-Ni²⁺, DBDA18C6-Cu²⁺, DBDA18C6-Ag⁺ and DBDA18C6-Cd²⁺ complexes were obtained from temperature dependence of the stability constants and the results show that the values of ΔH°c and ΔS°c for these complexes are sensitive to the nature and composition of AN–DMF binary solutions, but they do not vary monotonically with the solvent composition.     

Complexes of nickel(II) withS-carboxyalkyl-L-cysteines in aqueous medium. Determination of enthalpies by thermometric titrimetry

Summary Molar heats for the reaction of nickel(II) with sulphur-containing amino acids,S-carboxymethyl-L-cysteine andS-carboxyethyl-L-cysteine, have been determined by thermometric titrimetry. The data refer to aqueous solutions at 25°C andI=2.0m. From these enthalpies and equilibrium constants, the corresponding entropies have been calculated. The present thermodynamic data are complementary to previous spectrophotometric data in explaining the structures of the complexes. In particular, the importance of solute-solvent external factors in determining different stabilities for successive steps of complex-formation is stressed.     

Relative thermodynamic stabilities of 2-substituted 4-methylene-1,3-dioxolanes and 4-methyl-1,3-dioxoles

The relative thermodynamic stabilities of 24 pairs of carbon-carbon double-bondexo-endo isomeric 2-substituted 4-methylene-1,3-dioxolanes (a) and 4-methyl-1,3-dioxoles (b) have been determined by base-catalyzed chemical equilibration in DMSO solution. In all cases, theendo isomer (b) is the favored species at thermodynamic equilibrium. A single alkyl substitutent on C-2 gives only a negligible contribution to the relative stability of the isomeric forms, but the presence of two alkyl groups on C-2 increases the relative stability of theendo isomer by 2–3 kL mol^–1. A still higher effect in favor of theendo isomer is produced by introduction of a single alkoxy group on C-2; this effect is further slightly accentuated by 2,2-dialkoxy substitution at C-2. The origin of the favorable effect of 2-alkoxy substitution on the relative stability of theendo isomer is not clear, but it seems to arise from an unexpected stability of theendo isomer rather than from an enhanced destabilization of theexo form.     

Isolation of 1,2,3,4-tetrahydrobenzo[f]quinolin-2-ones on the reaction of 2-arylidenenaphthylamines with 4-hydroxycoumarin. IV

The reaction of 2-arylidenenaphtylamines with 4-hydroxycoumarin results in Hoffman-Martius type rearrangement yielding 2H-benzo[f][1]benzopyrano[4,3-b]quinolin-2-ones I and the compounds II. This work describes the structure elucidation of the compounds II. The structure was confirmed using ir, nmr and X-ray spectroscopy.     

A cyclization reaction in the electron-impact induced fragmentation of some N-propargylic oxoquinazolines and anilines

Evidence for an acetylenic rearrangement, involving the ring-closure of ions containing the N-propargylaniline substructure to the corresponding quinoline ions, has been obtained in a study of the electron-impact induced fragmentation of 1,4-dihydro-4-oxo-2-phenyl-1-propargylquinazoline (I) and 1,2,3,4-tetrahydro-2-oxo-3-phenyl-1-propargylquinazoline (II). The N-propargylaniline moiety is formed from compounds I and II through the RDA process. N-Methyl-N-propargylaniline (III), which was examined as a model compound, was also found to undergo this rearrangement but N-methyl-N-propargyl-2,6-xylidine (IV), on the other hand, exhibits a quite different fragmentation pattern due to its blocking methyl groups, which prevent the rearrangement. Exact mass measurement and specific deuterium labelling were used to establish the fragmentation routes.     

Experimental and Quantum‐Chemical Studies on the Thermochemical Stabilities of Mercury Carbodiimide and Mercury Cyanamide

Calorimetric dissolution measurements of the solid compounds mercury carbodiimide HgNCN(I ) and mercury cyanamide HgNCN(II ) in aqueous HCl that targeted at their thermochemical stabilities show the cyanamide species HgNCN(II ) to be the more stable phase in terms of both enthalpy and Gibbs energy with an enthalpy difference of 2–3 kJ mol^?1. While the stability ranking of HgNCN(I ) and HgNCN(II ) thus perfectly matches Pearson's HSAB concept, quantum‐chemical stability predictions using common parametrizations of density functional theory appear to be fundamentally flawed. An analysis of the error is attempted on the basis of correlated wave functions for related molecules.     

Density Functional Study of the Reaction Mechanism of Two Oxiimine Alcohol Formations and Their Novel Rearrangements

In this study, the reaction mechanisms of isonitrosoacetophenone (inapH) with ethanolamine (ea) and 1‐phenylethanolamine (pea) have been investigated theoretically using B3LYP/6‐311G(d,p) method to explain why the formation and unexpected rearrangement products occur or not occur. While the reaction between isonitrosoacetophenone (inapH) with ethanolamine gives oximine alcohol ( Ib ), the reaction of 1‐phenylethanolamine with inapH results in the formation of oximine alcohol with a different substituent ( Ia ) and amido alcohol ( IIa ), which is the unexpected rearrangement product. The rearrangement driving forces of compounds from Ia to IIa are calculated as ca. 28 and 23 kJ/mol in the gas and EtOH phases, respectively. These driving forces have been calculated ca. 46 and 45 kJ/mol for the rearrangement of compound Ib to obtain IIb in the same phases, respectively. This high driving force shows that the compound IIb cannot be obtained from rearrangement of compound Ib as described experimentally in the literature. In addition, as the DFT functionals poorly describe dispersion effects, dispersion correction for reaction heat and free‐energy barrier was estimated using the wB97X‐D/6‐311G(d,p). In general, the relative free energies of all molecules calculated from wB97XD method are lower than performed from B3LYP level. The changes of thermodynamic properties for all molecules with temperature ranging from 100 to 500 K have been obtained using the statistical thermodynamic method.     

Extrapolation of molar equilibrium constants to zero ionic strength and parameters dependent on it. Copper(II), nickel(II), hydrogen(I) complexes with glycinate ion and calcium(II), hydrogen(I) complexes with nitrilotriacetate ion

The stability constants of the complexes of glycinate ion with copper(II), nickel(II) and hydrogen(I) and of nitrilotriacetate ion with calcium(II) and hydrogen(I) and the ionic product of water (K(w)) were determined potentiometrically. The measurements were carried out at 25.0 degrees C in four different ionic strengths up to I (= I(c)) = 2.50 and two different ionic media (KNO(3) and (CH(3))(4)NNO(3)). Extrapolation of equilibrium constants to zero ionic strength and ionic strength corrections to equilibrium constants were carried out with the data obtained from both media using the TEC (thermodynamic equilibrium constant) equation and computer program. The constants of the potassium complexes with nitrilotriacetic acid at low ionic strength are also given. Successful attempts to predict equilibrium constants for other ionic media using TEC parameters and the procedure of the specific ion-interaction theory (SIT) are given. The variations of equilibrium constants with the ionic strengths and ionic media are demonstrated.     

A Triazacyclononane‐Based Bifunctional Phosphinate Ligand for the Preparation of Multimeric 68Ga Tracers for Positron Emission Tomography

For application in positron emission tomography (PET), PrP9 , a N,N′,N′′‐trisubstituted triazacyclononane with methyl(2‐carboxyethyl)phosphinic acid pendant arms, was developed as ⁶⁸Ga³⁺ complexing agent. The synthesis is short and inexpensive. Ga^III and Fe^III complexes of PrP9 were characterized by single‐crystal X‐ray diffraction. Stepwise protonation constants and thermodynamic stabilities of metal complexes were determined by potentiometry. The Ga^III complex possesses a high thermodynamic stability (log K_[GaL]=26.24) and a high degree of kinetic inertness. ⁶⁸Ga labeling of PrP9 is possible at ambient temperature and in a wide pH range, also at pH values as low as 1. This means that for the first time, the neat eluate of a TiO₂‐based ⁶⁸Ge/⁶⁸Ga generator (typically consisting of 0.1 M HCl) can be directly used for labeling purposes. The rate of ⁶⁸Ga activity incorporation at pH 3.3 and 20 °C is higher than for the established chelators DOTA and NOTA. Tris‐amides of PrP9 with amino acid esters were synthesized to act as models for multimeric peptide conjugates. These conjugates exhibit radiolabeling properties similar to those of unsubstituted PrP9 .     

A POTENTIOMETRIC STUDY OF METAL CHELATES WITH TETRAETHYLENEPENTAAMINEHEPTA-ACETIC ACID

Abstract

The protonation constants of tetraethylenepentaamineheptaacetic acid, TPHA, were determined by potentiometric titration in aqueous solution at an ionic strength of 0.10 M KNO₃ and at 25°C. The formation constants of various metal-TPHA complexes were also obtained by titrating mixtures of metal to ligand in molar ratios of 1 :1 and 2:1. Calculations were performed with the computer program BEST. Individual stability constants are reported for Co(II). Ni(II), Cu(II), Zn(II), Cd(II), Hg(II) and Pb(II) with TPHA as well as their related pro-tonated species. The stabilities of the 1:1 complexes parallel to those of similar complexes with DTPA and TTHA. However the 2: 1 complexes have significantly larger log K _ML's than their TTHA counterparts. The extra stability of the 2:1 metal-TPHA complexes is explained in terms of ligand denticity and steric effects. Mercury(II)-TPHA complexes exhibited the highest formation constants and the copper-TPHA complexes had slightly higher log K _ML's than those for Co(II), Ni(II), Zn(II), Cd(II) and Pb(II).     

Polymer‐supported metal complexes as antibacterial agents: synthesis,characterization and thermal degradation kinetics

Polymeric metal complexes were prepared using a synthesized novel terpolymer ligand involving anthranilic acid–o‐toluidine–formaldehyde by a polycondensation technique. The synthesized ligand and its metal complexes were characterized using elemental analysis and molar conductivity measurements, and FT‐IR, electronic, electron spin resonance and NMR (¹H and ¹³C) spectral methods. The surface morphology and the nature of the synthesized compounds were examined using scanning electron microscopy and X‐ray diffraction. The thermal stabilities of the ligand and its metal complexes were determined using thermogravimetric analysis (TGA). From the TGA results, various kinetic parameters, i.e. activation energy and order of reaction, and thermodynamic parameters, i.e. entropy change, apparent entropy, frequency factor and free energy change, were determined using the Freeman–Carroll and Sharp–Wentworth methods. In addition, a thermal degradation model was also proposed using the Phadnis–Deshpande method. The thermal stability of the ligand and its metal complexes was found to be appreciably high; in particular, the ligand showed very high stability compared to its metal complexes due to intramolecular hydrogen bonding. Furthermore, the synthesized compounds were subjected to in vitro antibacterial studies with various microorganisms. The results of the studies confirmed that the compounds showed better antibacterial results than a standard antibacterial drug. Copyright © 2014 John Wiley & Sons, Ltd.     

Geltungsbereich und Mechamismus der durch Silberionen katalysierten Propargylester-Allenylester-Umlagerung nach Saucy und Marbet

The mechanism of the catalysis of the reversible (propargyl ester)/(allenyl ester) rearrangement ( 10 ? 11 ) by silver(I) ions was investigated, using optically active and diastereoisomeric esters as well as ¹⁴C- and ¹⁸O-labelling. In order to work with crystalline materials, mainly p-nitrobenzoates ( 10 , 11 : R⁴ = p? O₂N? C₆H₄) were used. In some cases the rearrangement 10 ? 11 was studied using acetates (R⁴ = CH₃). The alkyl substituents R¹, R², R³, were widely varied (cf. Tables 1, 2). The solvents in which the rearrangements were performed were in most cases dry chlorobenzene and 96% aqueous dioxane. Silver tetrafluoroborate, the benzene complex of the latter, and silver trifluoroacetate (in chlorobenzene) as well as silver nitrate (in aqueous dioxane) served as catalysts. The amounts of the silver catalysts used varied between 0,5 and 10 mol-%; reaction temperatures applied were in the range 35–95°, The results obtained are as follows:

• 1 The rate-determining step of the (propargyl ester)/(allenyl ester) rearrangement ( 10 ? 11 ) occurs in a silver(I) complex with the substrates ( 10 , 11 ), which is formed in a pre-equilibrium. This follows from kinetic experiments (cf. Fig. 6, 7, 8, 10) and the fact that the rate of rearrangement (of 10a ) is strongly decreased when cyclohexene is added (cf. Fig. 9). In solvents which are known to form complexes with silver(I) ions the rate of rearrangement (of 10a )is much slower than in solvents with similar dielectric constants but with small capacity for complex formation with silver(I) ions (cf. Table 4). Taking into account what is known about silver(I)-alkene and -alkyne complexes (cf. [18]), it is obvious that the (propargyl ester)/(allenyl ester) rearrangement occurs in a π-complex of the silver(I) ion with the triple bond in the propargyl ester or one of the two C,C double bonds in the allenyl ester, respectively.
• 2 The shift of the carboxyl moiety in the reversible rearrangement 10 ? 11 occurs intramolecularly. p-Nitrobenzoic acid-[carboxyl-¹⁴C] is not incorporated during the rearrangement, neither in the reactant 10 nor in the product 11 and vice versa. A crossing experiment gave no mixed products (cf. Scheme 2, p. 882).
• 3 An internal ion pair can be excluded for the rearrangement 10 ? 11 because the ¹⁸O-carbonyl label in the reactant is found exclusively in the alkoxy part of the product (cf. Scheme 3, p. 886, and Table 9). Thus, the rearrangement 10 ? 11 occurs with inversion of the carboxyl moiety.
• 4 The rearrangement of optically active propargyl esters ( 10g , 10i ) leads to completely racemic allenyl esters ( 11g , 11i ). However, rearrangement of erythro- and threo- 10j -[carbonyl-¹⁸O] (Scheme 3) shows that the stereospecifically formed allenyl esters erythro- and threo- 11j -[¹⁸O]-epimerize rapidly in the presence of silver(I) ions. This epimerization is twice and forty times, respectively, as fast as the rearrangement of the corresponding propargyl esters (cf. Fig. 1–5). During epimerization or racemization the ¹⁸O-label is not randomized (cf. also Scheme 4, p. 898).
• 5 The equilibrium of the rearrangement 10 ? 11 depends on the bulkiness of the substituents R¹, R², R³ and of the carboxyl moiety (cf. Table 2).

Taking into account these facts (points 1–5), the reversible (propargyl ester)/(allenyl ester) rearrangement promoted by silver(I) ions can be described as a [3s, 3s]-sigmatropic reaction occurring in a silver(I)-π-complex with the C,C triple bond in 10 and a C,C double bond in 11 . It is suggested that complex formation in 10 and 11 occurs with the π-bond which is not involved in the quasicyclic (containing six orbitals and six electrons) transition state of the rearrangement (Fig. 11). Thus, the rearrangement is of a type which has recently been called a charge-induced sigmatropic reaction (cf. [26]). Therefore, in our case, the catalysis by silver(I) ions is of a different type from that of transformations of strained cyclic molecules promoted by silver(I) ions (cf. [14] [16] [27]–[31]). Side reactions. Whereas the rearrangement of propargyl esters 10 in presence of silver tetra- fluoroborate in chlorobenzene or silver nitrate in aqueous dioxane leads to the corresponding allenyl esters 11 , the rearrangement of 10 with silver trifluoroacetate, especially in the presence of trifluoroacetic acid, results in the formation of the dienol esters 12 and 13 , which clearly are derived from 11 (see Scheme 1, p. 881). As shown by the rearrangement of 11 in the presence of p-nitrobenzoic acid-[carboxyl-¹⁴C], 12 and 13 arise in part from a not isolated di-p-nitrobenzoate (cf. Scheme 6, p. 905), since radioactivity is found in 12 and 13 .     

Preparation and properties of 1-ethoxy-2,2,2-trifluoroethyl esters of acrylic and methacrylic acids and of their polymers

1-Ethoxy-2,2,2-trifluoroethyl esters of acrylic ( I ) and methacrylic ( II ) acids were synthesized from 1-ethoxy-2,2,2-trifluoroethanol and acryloyl- and methacryloylchloride, respectively, and their densities, mass, ¹H- and ¹³C-NMR spectra were measured and the rate constants of hydrolysis were determined. Poly( I ) and poly( II ) were prepared by radical homopolymerization; the rates of polymerization, specific volume contractions in polymerization, limiting viscosity numbers, average number degrees of polymerization, temperature dependences of the heat capacities both in glass and liquid state, glass transition temperatures, and the initial temperature of the spontaneous thermal decomposition of homopolymers were determined. The monomer reactivity ratios of the styrene (S) copolymerizations, S? I and S? II , and the Alfrey–Price copolymerization constants e and Q for I and II were calculated from the composition of copolymers of I and II with styrene.     

Iron succinate coordination compounds. Simulation of formation processes

The complexation of Fe(II) and Fe(III) with succinate anions was studied by the oxidation potential method. Using the oxidation function and the proposed principle of simulation of equilibrium from experimental data, we determined the composition, stability, the regions of existence, and accumulation rates of iron succinate coordination compounds. The calculated model parameters can be used as reference data in the targeted synthesis of complexes and thermodynamic calculations.     

Thermal decomposition reactions of nickel(II) complexes under quasi-equilibrium conditions

The stoichiometry of thermal decomposition and thermal (thermodynamic) stability was studied for the Werner clathrates [Ni(4-Mepy)₄(NCS)₂]·G, whereG = benzene(I), toluene(II) andp-xylene(III). The loss of the volatile components occurs in five steps in compounds I and II and in four steps in the complex III. According to the quasi-equilibrium data the thermodynamic stability of these compounds can be ordered in the following sequence: I<II<III. The increasing host-guest interaction (larger positive band shift in the visible spectra) was accompanied by increasing in the quasi-equilibrium temperature (T _D) for the complexes under study.     

A study of the tautomerism of the N-butyl-4(2)-methoxycarbonyl-pyrrolid-3-ones and their hydrochlorides

The tautomerism of N-butyl-2-methoxycarbonyl-4-methylpyrrolid-3-one (I), N-butyl-4-methoxycarbonylpyrrolid-3-one (II), N-butyl-4-methoxycarbonyl-2-methylpyrrolid-3-one (III), N-butyl-4-methoxycarbonylpyrrolid-3-one hydrochloride (IV), and N-butyl-4-methoxy-carbonyl-2-methylpyrrolid-3-one hydrochloride (V) has been studied by UV and IR spectroscopy. It has been found that the esters I–V are highly ionized in aqueous and ethanolic solutions at concentrations of 10^?2–10^?3 M. On passing from methyl cyclopentran-1-one-2-carboxylate to the esters II and III the position of the equilibrium in heptane and CCl₄ shifts in the direction of the keto form. On passing from the esters II and III to the esters IV and V, the position of the equilibrium shifts in the direction of the enol. Meyer's relationship is not satisfied for the esters II and III, while it is satisfied for the esters IV and V. Hypotheses have been put forward on the causes of the phenomena mentioned.     

Determination of reactivity by MO theory. 27. Molecular orbital study of the gas-phase decarboxylation of but-3-enoic acid

The MINDO /3 calculations were performed on the potential energy profile involved in the equilibrium Optimized structures of stable molecules and transition states have been determined; thermodynamic stabilities of pure acids and barriers indicated that the equilibrium can be set up from any acids. It was argued that direct decarboxylation is only conceivable from (I), since in this process a 1, 5-hydrogen shift is involved, whereas a higher barrier process of 1, 3-hydrogen shift is required in direct decarboxylations from other acids. Direct interconversion of (I) and (III) was found to be unfavorable due to a high barrier involved.     

Crystal polymorphism of local anaesthetic drugs

Crystal polymorphs of pramocaine hydrochloride (PRCNC) and pramocaine (PRCN) free base were produced and characterized by means of thermomicroscopy, differential scanning calorimetry (DSC), FTIR- and FT-Raman-spectroscopy as well as X-ray-powder diffractometry. The relative thermodynamic stabilities of all forms were determined and are represented in semi-schematic energy/temperature diagrams. PRCN, which is a viscous liquid at room temperature and insoluble in water, was found to exist in two different crystal forms with the melting points 23.5°C (mod. I°) and 12.5°C (mod. II). The water-soluble PRCNC crystallizes in three different crystal modifications. Mod. II° is the thermodynamically stable form at room temperature and is present in commercial products. This form is obtained by crystallization from solvents and transforms on heating at about 95°C into the high temperature form mod. I which melts at 171.0°C. Both compounds show conformational polymorphism with forms of low kinetic stability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Thermodynamics of complex formation in dimethyl sulfoxide with ligands coordinating via N,P, As,Sb, OR Bi : III. A comparison between aromatic and aliphatic amines and phosphines

The stabilities of the complexes formed by silver(I), cadmium(II) and zinc(II) with tri-n-butylamine and tri-n-butylphosphine have been determined in dimethyl sulfoxide (DMSO). For the two latter metal ions, it has also been found that complexes are not formed in appreciable amounts with the triphenyl compounds Ph₃X, X = N, P and, in the case of cadmium(II), also As.From these and earlier measurements referring to DMSO as well as aqueous solutions, it was found that the stepwise stability constants increase by roughly one power of ten for each aromatic ring replaced by an aliphatic group, evidently as a consequence of the improved donor properties of the coordinating atoms. Further, for ligands of the same type, the stabilities are always markedly lower in DMSO than in aqueous solution. This is certainly due to the fact that the solvent molecules compete more strongly for the coordination sites in DMSO than in water, as reflected by the larger heats of solvation found in the former solvent for the metal ions concerned.