Polarography at high pressures

A review of polarography at high pressures is presented.     

Henry condensation at high pressures

The hitherto inaccessible nitroolefin (VII), which is the most convenient intermediate for the synthesis of the psychotropic amine (VIII), has been obtained by the direct condensation at high pressures (up to 1500 MPa) of piperonal (V) with 1-nitropropane (VI). The structure of (VII) was confirmed by direct synthesis from pyrocatechol (X). The amine (VIII) was obtained in three steps from (VII). This synthesis of (VIII) is shorter than that previously reported.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 829–832, April, 1990.     

Grignard reaction at high pressures

Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1937–1938, August, 1991.     

Liquid densities at high pressures

Aalto et al. recently proposed a model for compressed liquid densities. The model was found more accurate than the Hankinson–Brobst–Thomson (HBT) and Chang–Zhao models. However, the pressure region of the data studied was limited to 200 bar maximum. In this work, the recently developed liquid density model is extended to high pressures. The equation describing the pressure dependence of liquid density is reformulated and the required parameters are optimized using a database containing 7478 data points for 31 pure hydrocarbons; maximum pressure in this data set is 8000 bar. The average absolute deviation (AAD) between these data and the recommended model is 0.4636%. A comparison to the results obtained with the HBT and Chang–Zhao models for the same data set shows that the new model is clearly more accurate in the extended pressure range, as well. The revised model is also tested in predicting liquid densities for mixtures; 84 different combinations of mixing rules are studied. The evaluation of the mixing rules is carried out using two compilations of experimental data: the first one contains 6712 points for 47 binary and two ternary mixtures, and the second 3582 points for 11 methane+alkane mixtures. In addition, the predictions are tested with a data set of 1119 points for other miscellaneous mixtures. No binary interaction parameters are used. With the recommended mixing rules, the AAD percentage is 0.5824% for the first set of data. If one simply adopts the mixing rules recommended for the HBT model, the AAD value for the same data set becomes 0.7482%.     

Trimerization of perfluoroheptanonitrile at high pressures

Conclusions A study was carried out on the trimerization of perfluoroheptanonitrile under high pressure conditions at 110 and 124°C. This reaction obeys zero-order kinetics relative to the monomer and first-order kinetics relative to the catalyst.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 8, pp. 1893–1895, August, 1987.     

Infrared and Raman spectroscopy at high pressures

Pressure is accepted theoretically as a useful variable. However in a studies on liquid or solid samples, it is still relatively unusual for pressure to be used as an experimental variable. The reluctance of experimentalists to use this theoretically attractive variable is caused mainly by the technical difficulties associated with the use of sufficiently high pressures. In this talk I will try to show that in many cases the experimental limitations are no longer those introduced by the use of high pressures. High pressure spectroscopic studies clearly imply the use of high pressure spectroscopic cells. A brief account will therefore be given of the various types of high pressure optical cells which are currently being used for spectroscopic studies. Each individual high pressure spectroscopic study has its own special justification. However there are a few quite general observations that can be made which cover many of the specific objectives of individual high pressure spectroscopic studies. For example:(i) pressure induced frequency shifts carry unambiguous information about anharmonic terms in the relevant potential function (i.e. the potential V is a function of distance d. therefore pressure can be used to change d and study V.)(ii) all known materials undergo structural phase transitions if the form which is thermodynamically stable under ambient conditions is compressed to high enough pressures: these high pressure phases should be studied.(iii) as the application of pressure forces a material towards a phase transition, the spectroscopic study can be used to gain information about the approaching structural instability.(iv) virtually all infrared and Raman spectra contain examples of Fermi resonance which confuse the interpretation of the spectra and the effects of pressure are valuable aids to the correct assignment of the resonating levels.(v) pressure induced frequency shifts can often give extra information to help with the more reliable assignment of features within a spectrum.The above points will be discussed and illustrated by examples chosen mainly from recent work by members of the spectroscopy group at King's College London.     

Dimerization and polymerization of isoprene at high pressures

The high-pressure reactivity of isoprene has been studied at room temperature up to 2.6 GPa by using the diamond anvil cell technique in combination with Fourier transform infrared spectroscopy. Both dimerization and polymerization reactions take place above 1.1 GPa. At this pressure, the two processes are well separated in time, the dimerization being the only one occurring in the first 150 h. Both processes simultaneously occur as the pressure increases. The reaction product is composed of a volatile fraction, identified as sylvestrene, and a transparent rubberlike solid formed by cis-1,4- and 3,4-polyisoprene. The activation volume of the dimerization reaction has been obtained from the kinetic data. The photoinduced reaction, studied at room temperature for two different pressures, takes place through a two-photon absorption process, and the threshold pressure is lowered to 0.5 GPa. At this pressure, both the dimerization and polymerization processes occur, but the dimerization is not as selective as in the purely pressure-induced reaction. 4-Ethenyl-2,4-dimethylcyclohexene is obtained in addition to sylvestrene. By increasing the pressure, the photoinduced reaction becomes more selective, and the monomer is quantitatively transformed into the same polymer obtained in the purely pressure-induced reaction.     

Concentrated electrolyte solutions at high temperatures and pressures

A survey is given of recent experimental results obtained from high-temperature, high-pressure investigations with water, aqueous solutions, and ionic fluids. Data on the static dielectric constant of water to 550°C and 5 kbar are given and discussed with respect to their relation to water structure. Infrared and Raman spectra of HDO in pure water have been obtained to 400°C and 4 kbar, which give information on hydrogen bonding. Xe–H₂O and CO₂–H₂O mixtures were investigated in the infrared. Ni(II) and Cu(II) complexes were investigated by absorption spectroscopy in aqueous solutions of high chloride content to 350°C and 2–6 kbar. The gas-liquid critical point of ammonium chloride was found at 880°C and 1635 bars. This fluid appears to be predominantly ionic even in the critical region. The possibility of converting pure polar fluids such as ammonia and water into concentrated ionic solutions by self-ionization at very high pressures is mentioned.This paper was presented at the symposium, The Physical Chemistry of Aqueous Systems, held at the University of Pittsburgh, Pittsburgh, Pennsylvania, June 12–14, 1972, in honor of the 70th birthday of Professor H. S. Frank.     

Sulphate ion dynamics in α-alums studied by esr at high pressures

The variation of zero-field splitting and linewidth of Cr³⁺ ion in KCr and KAI alums with hydrostatic pressure and with temperature is investigated. A model for the apparent phase transition is proposed on the basis of the reorientational motion of the SO^2?₄ groups.     

Some kinetic characteristics of glycosylation at high pressures

The effect was studied of pressure up to 1400 MPa on the stereospecificity of glycosylation during the condensation of 1,2-0-exocyanoethylidene-3,4,6-tri-O-acetyl--D-glucopyranose (I) with 2,4,6-tri-O-acetyl-3-O-trityl--methyl-D-glucopyranoside (II) in the presence of tritylium perchlorate, as a result of which a mixture of disaccharides containing an a- and -glycoside bond is formed. It was shown that in the liquid phase (up to 1300 MPa) there is a smooth increase in the stereospecificity of glycosylation ( ) and in the rate of glycosylation (V ₀ =–8 cm³/mole) as the pressure increases. Upon reaching a pressure that causes crystallization of the solvent (CH₂Cl₂, 1400 MPa, 20°C) the stereospecificity and glycosylation rate increase sharply and under these conditions the reaction takes place almost completely stereospecifically.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2804–2809, December, 1989.     

Adsorption phenomena at high pressures and temperatures.

Equilibrium isotherms of adsorption of methane on crystalline Rho zeolite were measured with the use of a precision volumetric gravimetric setup that was developed for determining the equilibrium and Kinetic parameters of adsorption in the pressure range of 0.1–160 MPa and temperature range of 300–600 K. The method of determining the accessible volume of an adsorption system (free volume + micropore volume) and the micropore volume of a sorbent was used. Two independent methods for calculation of micropore volume on the basis of the isotherms of excess adsorption were used. The discrepancy in the results of the calculation of the micropore volume by three independent methods is within the limits of the calculation accuracy. An evaluation of a change in the isosteric heats of the excess and absolute adsorption of methane on Rho zeolite was carried out in relation to filling and temperature. An evaluaton of the adsorption volume above the outer surface of the zeolite crystals was performed. The results of experimental investigations of methane adsorption on Rho zeolite can be used to solve the problem of encapsulation of gases by solid sorbents. kg]Key words kw]adsorption kw]micropore volume kw]surface kw]isostere kw]heat kw]zeoliteFor Part 1 see Ref. I.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 568–573, March, 1996.     

The thermal analysis of polymers at high pressures

The extension of two techniques of thermal analysis into the region high pressures (50–100 MPa) are discussed. One is the extension of dilatometry (thus becoming pressure-volume-temperature measurements, PVT). This technique has been well established over the past few years. Some results obtained on typical polymer systems are presented and discussed. The second is the extension of the differential thermal analysis (DTA) principle to high pressures, trying to maintain some of the advantages of the DTA technique when compared to the PVT method, such as small sample size and productivity. DTA determinations of the pressure dependence of the melting points of pure metals and polymers are presented and compared with results from the PVT technique. Satisfactory agreement is obtained. The advantages and limitations of our current high-pressure DTA method are discussed.We gratefully acknowledge the partial financial support of the high-pressure DTA development by Metler Instrumente AG, Switzerland.     

Recent studies of phase equilibria at high pressures

In its first part the present review considers the dependence of phase transition temperatures of some selected liquid crystals on pressure up to 300 MPa with differential thermal analysis (DTA) and diamond anvil techniques; here also pressure-induced phases as well as tricritical and reentrant phenomena will be discussed. In the second part the most important types of high-pressure phase diagrams of fluid mixtures are shortly reviewed. Here recent results on binary systems (containing trifluoromethane, tetrafluoromethane, nitrogen etc) will be presented and compared with data that are calculated from an equation of state. The results will be discussed in relation to some applications e.g. in fluid extraction and supercritical fluid chromatography (SFC).     

Solid-liquid transitions of sodium chloride at high pressures

We investigate solid-liquid transitions in NaCl at high pressures using molecular dynamics simulations, including the melting curve and superheating/supercooling as well as solid-solid and liquid-liquid transitions. The first-order B1-B2 (NaCl-CsCl type) transition in solid is observed at high pressures besides continuous liquid structure transitions, which are largely analogous to the B1-B2 transition in solid. The equilibrium melting temperatures (T(m)) up to megabar pressure are obtained from the solid-liquid coexistence technique and the superheating-supercooling hysteresis method. Lindemann's vibrational and Born's mechanical instabilities are found upon melting. The Lindemann frequency is calculated from the vibrational density of states. The Lindemann parameter (fractional root-mean-squared displacement) increases with pressure and approaches a constant asymptotically, similar to the Lennard-Jones system. However, the Lindemann melting relation holds for both B1 and B2 phases to high accuracy as for the Lennard-Jonesium. The B1 and B2 NaCl solids can be superheated by 0.18T(m) and 0.24T(m), and the NaCl liquid, supercooled by 0.22T(m) and 0.32T(m), respectively, at heating or cooling rates of 1 K/s and 1 K/ps. The amount of maximum superheating or supercooling and its weak pressure dependence observed for NaCl are in accord with experiments on alkali halides and with simulations on the Lennard-Jones system and Al.     

Room-temperature structures of solid hydrogen at high pressures

By employing first-principles metadynamics simulations, we explore the 300 K structures of solid hydrogen over the pressure range 150-300 GPa. At 200 GPa, we find the ambient-pressure disordered hexagonal close-packed (hcp) phase transited into an insulating partially ordered hcp phase (po-hcp), a mixture of ordered graphene-like H(2) layers and the other layers of weakly coupled, disordered H(2) molecules. Within this phase, hydrogen remains in paired states with creation of shorter intra-molecular bonds, which are responsible for the very high experimental Raman peak above 4000 cm(-1). At 275 GPa, our simulations predicted a transformation from po-hcp into the ordered molecular metallic Cmca phase (4 molecules∕cell) that was previously proposed to be stable only above 400 GPa. Gibbs free energy calculations at 300 K confirmed the energetic stabilities of the po-hcp and metallic Cmca phases over all known structures at 220-242 GPa and >242 GPa, respectively. Our simulations highlighted the major role played by temperature in tuning the phase stabilities and provided theoretical support for claimed metallization of solid hydrogen below 300 GPa at 300 K.