Mixtures partitioning

To evaluate the effects of salts or organic cosolvents on air-water (or more correctly, air-aqueous phase or air-organic solvent/water mixture) partitioning, we may simply apply the approaches discussed in Section 5.4 (Eqs. 5-27 and 5-29). Thus, knowing how salt affects a compound s aqueous solubility, while having no effect on its saturation vapor pressure, we deduce that the impact of salt on Ki3V/ may be expressed by ... 

To a solution of LDA (40mmol) in THF (200ml) cooled at -45°C, methyl dithioacetate (3.92 ml, 40 mmol) was added dropwise. The yellow colour rapidly disappeared. The mixture was stirred for 5 min. 2-Cyclohexenone (3.92 ml, 40 mmol) was then added dropwise. A yellow colour appeared. The resulting mixture was stirred for 15 min. An aqueous solution of ammonium chloride was added and the mixture partitioned between ether and brine. The organic layer was washed with brine, dried with magnesium sulfate and concentrated. Methyl (cyclohexanone-3-yl)dithioacetate (3) (6.75 g, 33.4 mmol, 83%) was isolated by flash chromatography on silica gel using cyclohexane/ethyl acetate (9 1) as the eluent. 

After the reaction was complete, the reaction mixture was slowly added to a mechanically stirred, pre-cooled (0°-5°C) quench mixture of ethyl acetate (1.7 L) and water (800 mL). At the same time, 50% (w/w) aqueous sodium hydroxide (185 mL) was added to the quench mixture at such a rate that the pH was maintained between 3-5 and the internal temperature was maintained below 25°C. The pH was then further adjusted to 7.0-7.5 with additional sodium hydroxide, and the mixture stirred for 1 h at 30°C. The mixture was filtered to remove the sodium sulfate, and the filter cake washed with ethyl acetate (300 mL). The filtrate and cake washes were combined, and the mixture partitioned. The aqueous (lower) phase was extracted once with ethyl acetate. The organic (upper) phases were combined and then concentrated in vacuo (10 mBar, 50°C) to a volume of 100 mL. Hexane (300 mL) was added slowly, and the mixture stirred for 1 h at 20°-22°C. The mixture was filtered, and the product cake washed with hexane (1 bed volume). The product was air-dried, then dried in vacuo (100 mBar, nitrogen sweep, 30°-35°C) to constant weight. Yield 31.0 g (95% based on HPLC wt % purity) of crude acetamidosulfone as a white solid. The crude product also contains a small amount of acetamide and sodium acetate. 

Many current protein separation operations involve exposure of a protein to interfaces, sometimes as the primary purpose of the process step and sometimes as a secondary consequence of that step. In either case, the extent to which a protein partitions between bulk solution and the interface greatly affects the process, and how multicomponent mixtures partition is even more important and even less understood and less predictable. Protein transport processes are also significant and not well understood, especially in confined or highly concentrated domains such as interstices in porous media and faces of membranes. 

In many process situations, it is desirable that all or most proteins have minimal interaction with surfaces. In other cases, the surface interaction may serve as the primary mechanism of separation. What is the relationship between the physical and chemical structure of a surface and the partitioning of particular proteins to that surface How will a protein mixture partition in the presence of a surface with a certain density and organization of charges or hydrophobic groups What minimum of experimental data is required... 

Wasylkiewicz et al. (1993) present a method to find regions where mixtures partition in two or more liquid phases. They base it on the Gibbs tangent plane test (Michelsen, 1982, 1993) to decide if a current composition resides in a single- or a multiple-liquid phase region. 

The stationary phase is an inert solid which has been impregnated with a high-boiling liquid. The sample is passed into the column in a gas stream, and the components of the mixture partition themselves between the liquid in the stationary phase and the gas stream. The gas stream then acts to develop and elute the column. The method may be used for a wide variety of compounds, since the temperature of the tube may be raised and since the tube may be operated under reduced pressure. 

The global expansion of industrial and consumer-oriented societies is linked to large-scale industrial production and consumerism that utilize a vast array of numerous chemical compounds. The listings of such chemicals are too vast to present in this paper but some examples will be discussed here. Environmental contaminants in nature typically involve complex mixtures, partitioning factors, chemical transformations, and abiotic and biotic interactions. The biological and environmental effects are complex and may be additive, synergistic and even antagonistic in nature. 

Gas chromatography is primarily an analytical separation technique. However, since the basic process is an equilibration of a solute between two immiscible phases, the chromatographic technique may be used to measure such physical properties as activity coefficients, second virial coefficients of gas mixtures, partition coefficients, adsorption and partition isotherms, and complex formation constants. Other properties which can be measured with less accuracy, from secondary measurements or from temperature variation studies, include surface areas, heats of adsorption, and excess enthalpies and excess entropies of solution. A number of reviews and discussions on these measurements have appeared in the literature. The present work is restricted to a review of activity-coefficient measurements. 

Of particular interest is the aforementioned interfacial partitioning technology. It has been demonstrated that small particles in a mixture partition differently to the interface of a suitable liquid-liquid system, such that (1) a particle-stabilised interfacial layer develops, and (2) that particles with a high-affinity displace those with lower affinities [34,35]. This opens possibilities for the development of a particle fractionation technology to produce essentially pure particles from a mixture, as is shown schematically in Fig. 9. 

The favourable partitioning of the desired solute between the rafiSnate and the extract phases is dependant on the relative affinities (physical interactions) of the solute species for the two phases. This is expressed through a ratio of the distribution coefficients for the separation of an aliphatic-aromatic mixture, partitioning between two phases, known as the selectivity (5) [22], as defined below ... 

Most essential oils are complex mixtures of terpenic and sesquiterpenic hydrocarbons and their oxygenated terpenoid and sesquiterpenoid derivatives (alcohols, aldehydes, ketones, esters, and occasionally carboxylic acids), as well as aromatic (benzenoid) compounds such as phenols, phenolic ethers, and aromatic esters. So-called terpeneless and sesquiterpeneless essential oils are commonly used in the avor industry. Many terpenes are bitter in taste, and many, particularly the terpenic hydrocarbons, are poorly soluble or even completely insoluble in water-ethanol mixtures. Since the hydrocarbons rarely contribute aitything of importance to their avoring properties, their removal is a commercial necessity. They are removed by the so called washing process, a method used mostly for the treatment of citrus oils. This process takes advantage of the different polarities of individual essential oil constituents. The essential oil is added to a carefully selected solvent (usually a water-ethanol solution) and the mixture partitioned by prolonged stirring. This removes some of the more polar oil constituents into the water-ethanol phase (e.g., the solvent phase). Since... 

Lipid extracts obtained from biological samples, as aforementioned, tend to contain significant amounts of nonlipid contaminants, such as sugars, amino acids, urea, and salts. These must be removed before the lipids are analyzed. A common and classical approach is to use a simple washing procedure devised by Folch, Lees and Sloane Stanley [17], in which a chloroform-methanol (2 1, v/v) extract is shaken and equilibrated with one-fourth its volume of saline solution (i.e., 0.88% potassium chloride in water). The mixture partitions into two layers, of which the lower phase is comprised of chloroform-methanol-water in a proportion of 86 14 1 (by volume) and contains virtually all of the lipids, while the upper phase consists of the same solvents in the proportion of 3 48 47 (by volume), respectively, and contains much of the nonlipid contaminants. It is important that the proportion of chloroform, methanol, and water in the combined phases should be as close as possible to 8 4 3 (by volume), otherwise selective losses of lipids may occur. If a second wash of the lower phase is needed to remove any remaining contaminants, a mixture of similar composition to that of the upper phase should be used, i.e., methanol-saline solution (1 1, v/v). 

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