Low Temperature Condensation of High

Low temperature condensation of high temperature species as a synthetic method. P. L. Timms, Adv. Inorg. Chem. Radiochem., 1972,14,121-171 (143). 

Low Temperature Condensation of High Temperature Species as a Synthetic Method P. L. Timms... 

Lowry-Bronsted acidity of bridge hydrogens, 18 135 of carboranes, 18 132-136 Low-temperature condensation, of high-temperature species, 14 121-171 activation enthalpy in, 14 128-129 atomic species in, 14 123-125 condensation process in, 14 129-130 experimental methods in, 14 130-141 formation of high temperature species, 14 131-139... 

Low-temperature condensation of high-temperature species as a synthetic method (P. 

A number of conventional synthetic procedures have been used to prepare polyimides [1—4]. These are the low-temperature condensation of 3,5-diaminoanisole with acid dianhydrides, conducted in amide solvents, followed by thermal imidisation of the poly(o-carboxy)-amides (PCA) formed low temperature condensation of 3,5-diaminoanisole with acid dianhydrides, conducted in amide solvents, followed by catalytic imidisation of PCA using a 1 1 pyridine-acetic anhydride complex as a catalyst and high temperature (160-180 °C) condensation of 3,5-diaminoanisole with acid dianhydrides, conducted in m-cresol, using quinoline, isoquinoline or benzoic acid as a catalyst. 

Pyrans. - Highly fluorinated 27/-pyrans have been synthesized by low-temperature condensation of the perfluoralkene (18) with an alkyl aryl ketone (19 R = CN, COCF3, or COCF2CF3). 2,4,6-Triarylpyrylium salts are converted, in good yield, into 2-alkoxy-2,4,6-triaryl-2/f-pyrans or 2-amino-2,4,5-triaryl-2//-pyrans on treatment with sodium alkoxides or... 

Many of the high-pressure forms of ice are also based on silica structures (Table 14.9) and in ice II, VIII and IX the protons are ordered, the last 2 being low-temperature forms of ice VII and III respectively in which the protons are disordered. Note also that the high-pressure polymorphs VI and VII can exist at temperatures as high as 80°C and that, as expected, the high-pressure forms have substantially greater densities than that for ice I. A vitreous form of ice can be obtained by condensing water vapour at temperatures of — 160°C or below. 

Accumulatory pressure measurements have been used to study the kinetics of more complicated reactions. In the low temperature decomposition of ammonium perchlorate, the rate measurements depend on the constancy of composition of the non-condensable components of the product mixture [120], The kinetics of the high temperature decomposition [ 59] of this compound have been studied by accumulatory pressure measurements in the presence of an inert gas to suppress sublimation of the solid reactant. Reversible dissociations are not, however, appropriately studied in a closed system, where product readsorption and diffusion effects within the product layer may control, or exert perceptible influence on, the rate of gas release [121]. 

Ice I is one of at least nine polymorphic forms of ice. Ices II to VII are crystalline modifications of various types, formed at high pressures ice VIII is a low-temperature modification of ice VII. Many of these polymorphs exist metastably at liquid nitrogen temperature and atmospheric pressure, and hence it has been possible to study their structures without undue difficulty. In addition to these crystalline polymorphs, so-called vitreous ice has been found within the low-temperature field of ice I. It is not a polymorph, however, since it is a glass, i.e. a highly supercooled liquid. It is formed when water vapour condenses on surfaces cooled to below — 160°C. 

Low-temperature/high-pressure distillation. Rather than use a low-temperature single-stage condensation or refluxed condenser, a conventional distillation can be used. To carry out the separation under these circumstances will require a low-temperature condenser for the column, or operation at high pressure, or a combination of both. 

The instanton method takes into account only the dynamics of the lowest energy doublet. This is a valid description at low temperature or for high barriers. What happens when excitations to higher states in the double well are possible And more importantly, the equivalent of this question in the condensed phase case, what is the effect of a symmetrically coupled vibration on the quantum Kramers problem The new physical feature introduced in the quantum Kramers problem is that in addition to the two frequencies shown in Eq. (28) there is a new time scale the decay time of the flux-flux correlation function, as discussed in the previous Section after Eq. (14). We expect that this new time scale makes the distinction between the comer cutting and the adiabatic limit in Eq. (29) to be of less relevance to the dynamics of reactions in condensed phases compared to the gas phase case. 

Low-temperature reactions of metal atoms have also been studied extensively by vibrational and electronic spectra. In most studies, a noble gas has been used as a diluent for a mixture of metal atoms and compound condensed on a window cooled to 20 K or lower. This permits controlled diffusion of reacting species and gives high quality spectra of reaction products (90). Alternatively, metal atoms can be condensed with the vapor of a pure ligand on a cooled window. This technique works best when the ligand can be subsequently pumped away to leave a thin film of an organometallic compound, the spectra of which can be measured. 

The procedure given here represents a high-yield reproducible synthesis for salts of [Ni6(CO)12]2- with several counterions, and affords fairly pure products. It involves the reduction of Ni(CO)4 with alkali hydroxide in N, N-dimethylformamide (DMF) as solvent and the use of a low-temperature condenser to prevent Ni(CO)4 loss due to the stripping action of the evolving carbon monoxide. 

The number of superimposed atom layers can be estimated on the following basis. According to Beeck and others (29), metal films condensed at low temperature in a high vacuum and warmed to room temperature are composed of crystallites with different orientations. The mirrors obtained in this way show the same optical behavior as crystalline compact material (47), especially after annealing in a high vacuum at an elevated temperature. The temperature coefficient of resistance, too, even that of the transparent nickel films in Table I, has the same order of magnitude as that of the compact metal therefore, it seems correct to use the atomic volume of the crystalline metals for estimating the... 

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