Solute-solvent interaction parameters by gas chromatography

Gas-liquid distribution coefficients at ideal dilution in non-volatile solvents can be measured by gas chromatography. The numerical value of a coefficient depends on the choice of the concentration unit in the solvent and in the gas phase. The relationships between different coefficients characterizing gas-liquid equilibria are discussed and summarized. Coefficients determined at several temperatures permit calculation of the standard chemical potential difference of the solute with the ideal gas phase as reference as a function of temperature, the g-SPOT. Following the proposal of Kirchhoff the latter can be formulated as an equation with three constants. As in the gas phase the molecules of the solute have no interacting partners, the three constants, deltaH, deltaS and deltaC, characterize the interaction between solvent and solute molecules. They will be called the "solute-solvent interaction parameters". In the same system the values of these parameters depend on the choice of the distribution coefficient. Five different distribution coefficients result five sets of interaction parameters. It is shown that conversion of a parameter set to another implies additive corrections independent of the nature of the solute. If g-SPOT-s are measured in a series of solvents, the data may be used to calculate the corresponding liquid-liquid partition coefficients by electing one of the solvents as reference (l-SPOT). The corresponding "relative interaction parameters" can be calculated by simple substraction. In a second chapter the precautions are summarized, necessary for gas chromatographic determination of distribution coefficients and examples are given for interaction parameters in different systems. It is concluded that there are significant differences between g-SPOT-s related to different distribution coefficients. On the other hand, differences between l-SPOT-s are negligible.     

Systematic and random errors in ion affinities and activation entropies from the extended kinetic method

An evaluation of the extended kinetic method with full entropy analysis was conducted using RRKM theory to simulate data for collision-induced dissociation under single-collision conditions. A rigorous method for analyzing kinetic method data, orthogonal distance regression, is introduced and compared with previous methods in the literature. The results demonstrate that the use of the extended kinetic method is definitely superior to the standard kinetic method, but final ion affinities and activation entropies differ intrinsically from the correct values. Considering the effects of both systematic and random error in Monte Carlo simulations of the full entropy analysis, error distributions of +/-4 to +/-12 kJ mol(-1) for ion affinities and of +/-9 to +/-30 J mol(-1) K(-1) for activation entropy differences are found (+/-2 standard deviations of the sample populations). The systematic errors in ion affinities are larger for systems with large activation entropy differences. These uncertainties do not include any error in the absolute calibration of the reference ion affinity scale. We argue that application of an empirical correction factor is inadvisable.     

Chemically modified silicon dioxide surfaces. Wetting properties of compact n-alkyl-dimethylsiloxy layers,and their mixed surface crystals. The Question of Wetting of Molecularly Rough and of Swollen Surfaces

By means of contact angle measurements, it has been shown that compact alkyl-dimethyl-siloxy layers can be obtained on the surface of acid leached glass using the method previously developed for fume silica. Subsequently, a series of densest possible alkyl-dimethylsiloxy layers were prepared having non-branched alkyl substituents, C_zH_2z+1, (with z=1, 2, 3, 6, 10, 14, 18 and 22) and wetting angles were measured as a function of the temperature. On surfaces coated with longer alkyl substituents the formation of mixed crystals, consisting of the sparse chemically bonded alkyl layer and a n-alkane acting as a wetting agent, has been observed at low temperatures. At higher temperatures such surfaces appeared to be «molten», and at the same time swollen by the wetting agent. Equations have been derived to deduce the free surface energies and to account for the wetting properties of rough and swollen surfaces. Application of the results to the data presented in this paper revealed that glass surfaces covered with short alkyl chains (methyl, ethyl and propyl) are rough and those covered with long chains (tetradecyl, octadecyl and docosyl) are swollen. Surfaces formed by hexyl- and decyl-dimethylsiloxy substituents exhibit intermediate properties.     

Die photokolorimetrische Bestimmung des Palladiums mit 2-Mercapto-5-Anilin-1,3,4,-thiodiazol

Zusammenfassung Pd(II) gibt mit 2-Merkapto-5-anilin-1,3,4-thiodiazol eine Komplexverbindung; diese ist löslich und intensiv gelb gefärbt. Das stöchiometrische Verhältnis der beiden Komponenten beträgt 12. Die Komplexkonstante hat den Wert 4,17·10^–10. Eine empfindliche kolorimetrische Bestimmungsmethode für 0,12 bis 30 ppm Pd(II) wurde angegeben. Das UV-Spektrum der Komplexverbindung wurde ermittelt und der molare Extinktionskoeffizient bestimmt.

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Summary 2-Mercapto-5-aniline-1,3,4-thiodiazole yields a complex compound with palladium(II). This product is soluble and has an intense yellow color. The stoichiometric ratio of the components is 12; the complex constant is 4,17 ·10^–10. A sensitive colorimetric method for determining 0.12–30 ppm of palladium(II) is given. The ultraviolet spectrum of the complex compound has been mapped and also the molar extinction coefficient has been determined.

     

New Molybdenum(V) Complexes Prepared by the Oxidation of Dinuclear Quadruply-Bonded Molybdenum(II) Monothiocarboxylates

Oxidation of molybdenum(II) thiopivalate and thiobenzoate in the presence of -picoline or pyridine results in the formation of dinuclear molybdenum(V) complexes of the general formulae [Mo₂O₂(-O)₂(-SO₄)L₄] with L = -picoline or pyridine and [Mo₂O₂(-O)(-S)(-SO₄)L₄] with L = -picoline. As determined by X-ray structure analysis, two complexes with -picoline differ in their bridging cores: In one complex, two Mo atoms are doubly bridged through two oxygen atoms; in the other, one Mo atom is doubly bridged through oxygen and sulfur atoms. However, they both crystallize together. The product is solvated with -picoline and water molecules. Molybdenum atoms exhibit distorted octahedral coordinations. The same complexes were prepared also through direct reactions of [Mo₂O₃(O₂CCH₃)₄] with thiopivalic and thiobenzoic acid in the presence of -picoline or pyridine. The appearance of the oxo-oxygens and sulfido-sulfur as well as sulfato ligand is explained by the molybdenum-catalyzed oxidation of thiocarboxylates.     

Synthesis,Characterization, and Crystal Structure of Mononuclear and Dinuclear Dioxomolybdenum(VI) Complexes with Tridentate Schiff‐base Ligands. Part 2

Mononuclear [MoO₂LD], and dinuclear [MoO₂L]₂ or [MoO₂L]₂ · D dixomolybdenum(VI) complexes have been prepared by the reaction of tridentate Schiff‐base ligands L with [MoO₂(acac)₂]. The Schiff‐base ligands have been synthesized from salicylaldehyde ( 1 , 1a , 1c , 1d ), 2‐hydroxy‐1‐naphthaldehyde ( 2 , 2c ) and 2‐hydroxy‐3‐methoxybenzaldehyde ( 3a , 3b , 3c , 3d , 3e ) with 2‐amino‐p‐cresol. All prepared complexes consist of cis‐MoO₂²⁺core coordinated by Schiff‐base ligand through two deprotonated hydroxyl groups and one imino nitrogen atom. The usual octahedral coordination around the molybdenum atoms is completed by the neutral ligand D (methanol, ethanol, dimethyl sulfoxide, imidazole or 4, 4′‐bipyridine). All compounds were characterized by elemental analyses, IR spectroscopy and some of them by X‐ray crystallography ( 1a , 2c , 3a , 3b , 3c and 3e ).     

Microcanonical analysis of the kinetic method. the meaning of the "apparent entropy"

A rigorous analysis of the kinetic method is carried out using Rice-Ramsperger-Kassel-Marcus (RRKM) theory of microcanonical statistical unimolecular dissociation rates. The model employs a kinetics treatment appropriate for metastable ion dissociation. Proton-bound alkoxide dimer anions are used as model systems, with realistic vibrational and rotational parameters calculated by ab initio methods for the cluster ion and transition states leading to the competitive dissociation channels. The numerical simulations show that the kinetic method plots of ln(I2/I1) versus AAH are nearly linear but can exhibit significant curvature. The apparent entropy obtained in the extended kinetic method is not approximately equal to the thermodynamic entropy difference for dissociation, AAS(T), or for activation, deltadeltaS++(T), either at the effective temperature or at any fixed equilibrium temperature. Instead, the apparent entropy term can be related to the ratio of the microcanonical sum of states of the dissociation transition states for the kinetically selected internal energy of the dissociating ions.     

5,12-Diacylated-5,6,11,12-tetrahydrodibenzo[b,f][1,4]-diazocines and related compounds

Both N,N′ -(o-phenylene)diformamide (1) and N,N′ -(4-chloro-1,2-phenylene)diformamide (30) reacted with α,α-dibromo-o-xylene (2) in DMF at 95–100° to give 5,6,11,12-tetrahydrodibenzo-[b,f][1,4]diazocine-5,12-dicarboxaldehyde (3a) and the corresponding 2-chloro derivative (3b). With potassium hydroxide in ethylene glycol at 110°, 3a and 3b were selectively saponified to the 5-carboxaldehyde derivatives (4) and either 21a or 22a. Reacylation of the latter led to a series of 5,12-unsymmetrically diacylated derivatives, 5–18. Additionally, 4 was subjected (a) to a basecatalyzed addition to acrylonitrile to give the 12-cyanoethyl derivative (19) and (b) alkylation with α-bromotoluene to give the 12-benzyl compound (20). Saponification of both carboxaldehyde groups in 3a,b required potassium hydroxide in ethylene glycol at 135° and gave the N,N′ -unsubstituted heterocycles (23 and 24) ; these were subsequently reacted with several aldehydes to yield the 5,12-methano derivatives (25–29) .     

Threshold collision-induced dissociation of hydrogen-bonded dimers of carboxylic acids

Energy-resolved competitive collision-induced dissociation is used to investigate the proton-bound heterodimer anions of a series of carboxylic acids (formic, acetic, and benzoic acid) and nitrous acid with their conjugate bases. The dissociation reactions of the complexes [CH3COO.H.OOCH]-, [CH3COO.H.ONO]-, [HCOO.H. ONO]-, [C6H5COO.H.OOCH]-, and [C6H5COO.H.ONO]- are investigated using a guided ion beam tandem mass spectrometer. Cross sections of the two dissociation channels are measured as a function of the collision energy between the complex ions and xenon target gas. Apparent relative gas-phase acidities are found by modeling the cross sections near the dissociation thresholds using statistical rate theory. Internal inconsistencies are found in the resulting relative acidities. These deviations apparently result from the formation of higher-energy conformers of the acids within the complex ions induced by double hydrogen bonding, which impedes the kinetics of dissociation to ground-state product acid conformations.