Repeatability dissolution

Fluorozirconate Crystallization. Repeated dissolution and fractional crystallization of potassium hexafluorozirconate was the method first used to separate hafnium and zirconium (15), potassium fluorohafnate solubility being higher. This process is used in the Prinieprovsky Chemical Plant in Dnieprodzerzhinsk, Ukraine, to produce hafnium-free zirconium. Hafnium-enriched (about 6%) zirconium hydrous oxide is precipitated from the first-stage mother Hquors, and redissolved in acid to feed ion-exchange columns to obtain pure hafnium (10). 

The first is, the conformity Salts have with earth and water, or the properties they possess in common with both. The second is, that all Salts may be actually resolved into earth and water by sundry processes particularly by repeated dissolutions in water, evaporation, dessica-tion, and calcination. 

The total content of residual solvent is determined by partially dissolving a weighed sample of the powder in a solvent (a mixture of alcohol and ether) and adding water so as to precipitate the nitrocellulose from the solution in llocculant form. The weight of this nitrocellulose is determined by evaporation to dryness, repeated dissolution and precipitation with water, and by final drying. The difference between the weight of the powder sample and that of the nitrocellulose is the weight of the residual solvent. 

Quinoxaline-2,3-dithiol [1199-03-7] M 194.1, m 345°(dec). Purified by repeated dissolution in alkali and re-pptn by acetic acid. 

Figure 8. Repeated dissolution tests over 24 days on the same sample of cristobalite 1.10 grams of 9.1 sq. meters/gram = 10 sq. meters of total surface area in 500 ml- of solvent.

Boron trifluoride etherate (2.5 equiv. with respect to the alkenylsilane) was added dropwise to a stirred suspension of the appropriate alkenylsilane and iodosylbenzene (2.5 equivalent with respect to the alkenylsilane), in dichloromethane, under nitrogen. A yellow colour developed, while the mixture was stirred for 15 min to 7 h, at 0°C or room temperature, according to the substrate. A saturated aqueous sodium tetrafluoroborate solution was added and the mixture was stirred vigorously for 0.5 h. The reaction mixture was poured into water and extracted with dichloromethane. The organic layer was concentrated to give an oil which was washed several times with hexane and/or ether by decantation. Further purification was accomplished by repeated dissolution of the salt in dichloromethane or ethyl acetate followed by slow precipitation with hexane or ether. 

Mass or heat transfer between fluid and particles is related not only to fluid-particle contacting, but also to the exchange between the dense and the dilute phases. Therefore, further efforts are needed to unravel how the latter effect, which is characterized by repeated dissolution and reformation of particle aggregates, should be incorporated in order to evaluate the overall mass or heat transfer process. 

The polystyrene is isolated by removing the solvent on the rotary evaporator, dissolving the polymer in the minimum volume of dichloromethane, and then pouring this solution into a beaker containing aqueous methanol (1 4, ca. 10 X volume). Further purification is achieved by repeated dissolution in dichloromethane, followed by re-precipitation into methanol finally, the white solid is dried in a vacuum oven at 60°C. 

Repeated dissolution and recrystallization of these salts leads to the mechanical disruption of the masonry structure. Since the salts will concentrate in the more porous material, either the brick or the mortar will be more seriously affected, depending on their relative porosity. 

Pterin-6-carboxylic acid (2-amino-4-oxo-3,4-dihydropteridine-6-carboxylic acid) [948-60-7] M 207.2, m >360 , pKj 1.43, pK 2.88, pKf 7.72. The acid gives yellow crystals by repeated dissolution in aqueous NaOH and adding aqueous HCl. It has UV with Xniax at 235,260 and 265nm (ell, 000,... 

Benzene, Acetone, EtOH Repeated dissolution in Et20 and precipitation with light petroleum IR,UV,H- NMR,GC (29)... 

The last type causes subsidiary phenomena in many labeling reactions and for most purposes a label introduced in this way must be removed again in order to avoid false conclusions this is done by repeated recrystallization from protonic solvents or by repeated dissolution in and recovery (by evaporation) from such solvents (see Section 2.3). 

Type III process consists of the repeated dissolution and precipitation of phase B from the Type II case. It is typically assumed in these calculations that (a) the system is closed to fluid, (b) the stoichiometry of the solid remains constant, (c) the isotopic fractionation factor between the freshly formed portion of the mineral and the fluid is constant (not necessarily equilibrium), and (d) isotopic exchange before dissolution and after precipitation is negligible. As a basis for their modeling, Dubinina and Lakshtanov... 

The ideal is to determine the reproducibility from repeated dissolution experiments under identical conditions, on the same batch. This will add to the cost of the experiment but it will probably be necessary. Nevertheless before considering doing this we should use at least what information we have to the full, and there are two important sources of information on the reproducibility of the experiment already available. 

Chlorotrimethylstannane 2.32 g (11.6 mmol) is dissolved in 20 mL of THF and added to the Na[Co(CO)3 P(OPh)3 ] solution while stirring vigorously. After 30 min the THF is completely removed under vacuum ( — 20°C, 0.5 mm). The residue is then repeatedly extracted with 20-mL portions of hexane until the latter becomes colorless. The orange-yellow hexane solution is filtered and reduced to dryness under vacuum to leave a dark yellow solid. If necessary, further purification can be accomplished by repeated dissolution of the product in a minimum volume hexane, followed by rapid cooling to — 30°C in a Dry Ice-acetone bath. The crystals are dried in vacuo for 2h... 

As already demonstrated, for relatively recent sedimentary rocks and weathering crusts (20-200 Ma), the characteristic sequence of silica transformation is silica gel —> opal-A —> opal-CT —> chalcedony —> quartz. This is a well studied, polymorphous transformation of the solid phase transition type (a-cristobalite —> a-quartz) (Plyusnina 1983,1986,1990). One aspect of the solid phase transformations is the gradual transition of one silica phase to another and the gradual transformation of morphological features down the stratigraphic column with increasing burial depth and age (similarly in weathering crusts). The observed sequential cristobalite-quartz ratio would be unlikely to occur in rocks with repeated dissolution and crystallization from solution (Plyusnina 1983). 

The thorium atom in ThCLc4DMA appears, on the basis of the cone-angle approach to steric crowding (p. 1130), to be very overcrowded, and it is probable that this complex should be written as [ThCl3(DMA)4] Cr, even though its conductivity in nitromethane is very low. Repeated dissolution of this complex in THF and reprecipitation with a mixture of n-pentane and toluene yields the tris complex, [ThCl4(DMA)3]. ... 

While SEC aims to separate a polymeric mixture only with respect to size (hydro-dynamic volume), investigations of substituent distribution requires a separation with respect to the chemistry of the constituents. Spurlin, very early on, recognized this problem and fiactionated cellulose nitrate by repeated dissolution and precipita-tion. The fractions obtained showed increasing viscosities and, related to this, increasing flexibihty of solution-cast thin films. Saake et al. also made use of this common principle in polysaccharide isolation, in particular the (stepwise in this instance) precipitation of CMC by ethanol from aqueous solution. ... 

After less than 10% conversion the reaction tubes were cooled and the vacuum was released. The viscous solution was then precipitated in excess of dry hexane. The polymers were further purified by repeated dissolution and precipitation from THF into n-hexane so as to remove the unreacted comonomers and initiator species. 

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