摘要:

AbstractWe have performed a systematic study of liquid‐liquid phase equilibria in aqueous and non‐aqueous solutions of tetraalkylammonium salts up to about 500 K, covering a large number of hydrogen‐bonding, dipolar aprotic and non‐polar solvents. There appear to be two different types of liquid‐liquid phase equilibria resulting from long‐range Coulombic and from short‐range specific forces, respectively. These may be denoted asCoulombicandsolvophobic unmixing. Coulombic unmixing is observed in solutions of 1:1‐electrolytes in solvents of low dielectric constant, as is exemplified for solutions in hydrocarbons and long‐chain alcohols. It appears to be closely related to a general instability of ionic fluids at low reduced temperatures. Increase of the dielectric constant results in complete miscibility, as is demonstrated for salts dissolved in short‐chain alcohols and some common dipolar aprotic solvents. Solvophobic unmixing occurs if salts with large cations and anions are dissolved in water. A phenomenological analysis shows that this phase separation results from those thermodynamic pecularities which are usually attributed to the hydrophobic nature of the cations. Some cation‐anion association appears also to play a role. Similar immiscibilities have been observed with other hydrogen‐bonding solvents of high cohesive energy density, namely glycerol, ethylene glycol, 1,3‐propanediol, formamide and monoethanolamine, suggesting the existence of a more general so

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951201

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractA small‐size high‐temperature, high‐pressure Raman cell of about 1.6 cm3internal volume with four sapphire windows is described. It can be used to 400°C and 3000 bar. The OD‐stretching bands around 2600 cm−1of HDO diluted in H2O have been measured from 25°C to 400°C and in a density range between 0.04 g·cm−3to 1.0 g·Cm−3. The critical temperature of waterTcis 374°C, the critical density ϱC= 0.32 g°cm−3. At the supercritical temperature of 400°C the OD‐band was determined at densities from 0.04 to 0.8 g·cm−3. At nearly constant densities between 1.0 and 0.8 g·cm−3the band was recorded from 25 to 400°C. Thus the OD‐band, which depends on hydrogen bonding, could be studied in a wide range of temperatures and pressures, avoiding the immediate critical region.—At 400°C and low density the sharp narrow OD‐band has a maximum frequency of 2727 cm−1. It becomes broader and shifts to 2668 cm−1at 0.8 g·cm−3. A very broad band occurs at 25°C and 1 g·cm−3at 2530 cm−1. Depolarization ratios were measured, local field corrections were applied and permitted the determination of isotropic and anisotropic spectra. The transition of band shape in the wide range of temperature and density is always smooth with no prominent features. As compared with a two‐component hydrogen‐bonded and non‐bonded “mixture” model a description with a “continuum”‐model as proposed by Efimov et al. appears to be preferable.

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951202

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractA and B diffuse from opposite sides into a finite slice of solid C. After a certain diffusion time the solubility product of a product phase, AB, may be reached and AB precipitates. The location of the first nuclei formation is calculated as a function of the solubilities and the diffusion coefficients of A and B in the matrix C, and of the solubility product. Chemical diffusion coefficients of A and B, which are either constant or proportional to their own concentration, or proportional to the concentration of the other diffusing species are considered. For some sets of typical system parameters the diffusion profiles are calculated and the time and coordinate for first precipitation are shown.—Further growth of small nuclei is given by further diffusion of A and B into the matrix C and to the precipitate, which constitutes a sink for A and B. The precipitate grows in the diffusion field with a preference for certain directions. These directions and the initial growth rate of the precipitate depend on the transport properties of both the matrix and the precipitate, as well as on the thermodynamic conditions of phase coexistence of precipitate and matrix. Limiting cases of an infinitely fast or negligible material transport inside the precipitated phase are considered and the initial growth of a single precipitate in the diffusion field and its shape evolution during growth are calculated.—The global morphology of the assembly of AB precipitates for long diffusion times is discussed by considering the morphological evolution of an intermediate AB la

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951203

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractKinetic and mechanistic details of the imidazole‐catalyzed hydrolysis of substituted phenyl benzoates in 10% acetonitrile in water (V/V) were examined. The following 4 ester series were studied: p‐nitrophenyl p‐X‐benzoates (X = CH3, H, Cl, CN, NO2, series I), p‐Y‐phenyl p‐nitrobenzoates (Y = CH3, H, Cl, CN, NO2, series II), 2, 4‐dinitrophenyl p‐X‐benzoates (X = CH3O, H, Cl, CN, NO2, series III) and p‐Y‐phenyl 2,4‐dinitrobenzoates (Y = CH3, H, Cl, CN, NO2, series IV). Based on: catalytic rate constants, activation parameters, kinetic solvent isotope effects, Hammett (δ) values and the spectroscopic detection of the reaction intermediates, the following conclusions were reached: a) imidazole acts as a nucleophilic catalyst, i.e., the hydrolysis occurs via the intermediate formation of acylimidazole; b) the leaving group is the phenoxide ion; c) the rate limiting step is the decomposition of the tetrahedral intermediate that precedes the acylimidazole (series I, II and IV) or the attack of imidazole on the acyl group

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951204

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractThe collisional behaviour of the optically metastable, electronically excited calcium atom, Ca(4s4p(3P1)), 1.888 eV above its 4s2(1S0) electronic ground state, is investigated in the time‐resolved mode following its generation by pulsed dye‐laser excitation at elevated temperature from calcium vapour in the presence of CH3I and excess helium buffer gas in a slow flow system, kinetically equivalent to a static system. The removal of Ca(43P1) is monitored by time‐resolved atomic fluorescence at the resonance wavelength ( λ = 657.3 nm, Ca(43P1) → Ca(41S0) +hv), following rapid Boltzmann equilibration within the 43P1spin‐orbit manifold using boxcar integration. Electronically excited CaI in the A2Π and B2Σ+states, respectively 1.9372 (186.9 kJ mol−1) and 1.9466 eV (187.8 kJ mol−1) above the X2Σ+ground state, was also monitored by time‐resolved molecular chemiluminescence of the A, BX systems under identical conditions to those employed for characterising the decay profiles of Ca(43P1). Both atomic and molecular chemiluminescence emissions showed exponential decay profiles, characterised by first‐order decay coefficients which were found to be equal under the same experimental conditions. CaI(A2II) and CaI(B2Σ+) are thus shown to arise from direct production on the collision of Ca(43P1) with CH3I where these processes are energetically favourable:\documentclass{article}\pagestyle{empty}\begin{document}$$ \begin{array}{l} \begin{array}{*{20}c} \begin{array}{l} {\rm Ca(4}^{\rm 3} {\rm P}_{\rm J} {\rm ) + CH}_{\rm 3} {\rm I}{\rm } \to {\rm CaI(A}^{\rm 2} \Pi {\rm ) + CH}_{\rm 3} \\ \Delta {\rm H = - 16}{\rm .2 kJ mol}^{{\rm - 1}} \\ \end{array} & {(1)} \\ \end{array} \\ \begin{array}{*{20}c} \begin{array}{l} {\rm Ca(4}^{\rm 3} {\rm P}_{\rm J} {\rm ) + CH}_{\rm 3} {\rm I}{\rm } \to {\rm CaI(B}^{\rm 2} \sum ^ + {\rm ) + CH}_{\rm 3} \\ \Delta {\rm H = - 15}{\rm .3 kJ mol}^{{\rm - 1}} \\ \end{array} & {(2)} \\ \end{array} \\ \end{array} $$\end{document}As with complementary measurements that have been reported on the collisional behaviour of Ca(43PJ) with CH3I under single‐collision conditions in molecular beams, where the AX and BX chemiluminescence of CaI was recorded, it was not possible to resolve the AX and BX profiles individually in view of spectroscopic overlap between these two close lying electronic states where vibrational population in higher levels of the A and B states at these elevated temperatures (900 K) also complicates the chemiluminescence spectra, as well as the spin‐orbit components in CaI(A2II1/2, 3/2). Time‐resolved chemiluminescence from CaI(A, BX) is hence employed the to monitor the global emission from these two electronically excited states. Thus, the A, BX emission can be used as an overall spectroscopic marker for Ca(43PJ) in the time‐domain and can be used to estimate a reaction rate constant for the overall collisional removal of Ca(43PJ) by CH3I of ca. 2 · 10−11cm3molecule−1s−1atT= 900 K though this must be viewed with caution on account of reaction of ground state Ca(41S0) with CH3I in the flow system prior to dye laser excitation. Broad band chemiluminescence is recorded for the Ca(43P1)CH3I system as well as laser‐induced fluorescence by excitation of the X2Σ+state which is also generated on reaction of the excited atom. The principal conclusion of the present investigation in the time‐domain is the direct production of CaI(A2Π, B2Σ+) on the collision of Ca(43P1) with CH3I, in accord with complementary observations that have been made hitherto under single‐collision conditions and which are compared with the present investigation. The present results for CaI(A2Π, B2Σ+) are further compared with chemiluminescence measurements for analogous collisional processes for Ca(43P1) involving O, H, F, Cl and Br‐atom abstraction in the time‐domain and under mole

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951205

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractThe CO2laser induced multiphoton dissociation of CF2Cl2takes place in atomic and molecular chlorine elimination channels, with about 8% of the reaction by the latter channel. Time resolved experiments show a fast formation of :CF2from the primary reaction, followed by a secondary slow growth from the decomposition of CF2Cl. The experimental rates are consistent with the RRKM rate constants with an excitation energy of nearly 343 kJ/mol in CF2Cl2. At high laser fluences, addition of argon has improved the dissociation yield, due to rotational hole filling mechanism. The internal energy of CF2Cl2decreases from 356 to 343 kj/mol on addition of argon as buffer gas. The nascent vibrational temperature of the CF2is 950 K, whereas an overall temperature of the thermalized ensemble in milliseconds time is computed to be 480 K.

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951206

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractA detailed investigation on the reduction of 2‐(1‐naphthylhydrazono)dimedone (1‐NHD) and 2‐(2‐naphthylhydrazone)dimedone (2‐NHD) in 0.1 M TEAI‐DMSO was made using various electroanalytical techniques. Each of the two compounds gave two well‐defined polarographic waves/cyclic voltammetric (CV) peaks. The first one‐electron diffusion‐limited wave/peak arises out of the formation of the corresponding anion radical and has been characterised to be of oxy type from in‐situ EPR studies. However, the second wave/peak is attributed to an EC reaction involving a fast reverse disproportionation reaction by which the anion radical is regenerated, as confirmed from CV studies and also from the non‐integralnvalue obtained for the second wave from microcoulometry. Macroscale CPE experiments carried out at the limiting regions of the first and second polarographic waves of 1‐NHD and 2‐NHD afforded the corresponding naphthylamines as the major product. Based on these results, a plausible mechanism for the electroreduction of 1‐NHD and 2

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951207

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractThe far infrared absorption spectra of furan in liquid solutions with carbon disulphide, carbon tetrachloride and benzene, are to the first time presented, along with the absorption spectra of neat furan at three different temperatures. The spectral behaviour of the absorption curves is studied for each solvent at three mole fractions of furan. The results are qualitatively discussed in terms of the intermolecular geometry in the solution, as determined by the structure characteristics of the non‐polar solvents, and also in terms of the interaction between solvent and solute, producing under certain circumstances an interaction induced contribution to the permanent dipole moment of the furan molecul

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951208

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractThe plastic nature of the highest‐temperature metastable phase of CH3NH3Br obtainable above 483 K was studied by X‐ray diffraction, differential scanning calorimetry, and1H NMR spin‐lattice and spin‐spin relaxation time measurements. The CsCl‐type cubic structure determined for this phase implies the presence of highly disordered cationic orientations in accordance with the reported results in the other ionic‐plastic crystals.1H NMR relaxation times observed in this phase were well explained by the motional model of the slow translational self‐diffusion and rapid overall rotation of the CH3NH3+cations. The obtained activation energy (51 kJ mol−1) and correlation times (1.1 · 10−8s at the melting point) were shown to be reasonable values as compared with those in stable plastic crystals. The melting condition derived from the dynamic parameters obtained in molecular and ionic plastic crystals was g

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951209

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY

摘要:

AbstractPhase boundaries for mixtures of dodecylammonium chloride (DDACl) and sodium dodecyl sulfate (NaDS) are determined over a wide range of concentrations. The phase behavior strongly depends on the molar ratio and concentration of surfactant present. In the range of concentrations where monomer‐micelle equilibrium prevailed the mixed micelles of different composition are formed. The addition of oppositely charged surfactant enhance the apparent degree of counterion dissociation (α). Results reveal the existence of asymmetry on NaDS‐rich systems; more pronounced shift of CMCNaDSwith DDACl addition, higher increase of αNavalues and the two regions of mixed micelles formation. The deviation of precipitate‐solubility boundary from linearity is explained by phase transitions from precipitate and coacervate to mixed micelles. The concentrations at which coacervate is formed are lower than it would be found in the absence o

ISSN:0005-9021    

DOI:10.1002/bbpc.19910951210

出版商:Wiley‐VCH Verlag GmbH&Co. KGaA    

年代:1991

数据来源: WILEY