Solid-water partitioning

To a solution of the ester amide (160 mg, 0.26 mmol) in methanol (3 mL) and THF (3 mL) was added a 1 M solution of NaOMe in methanol (5 mL). The mixture was stirred at rt for 1.5 d then neutralized with methanolic acetic acid and concentrated in vacuo. The crude material was partitioned between water and CH2CI2. The organic phase was dried over anhydrous magnesium sulfate, filtered, and concentrated in vacuo to afford the bis(ester) 73 as a colorless solid, mp 154.4-155.5 C, [a] -17° (c = 0.3, MeOH). 

The partitioning of As in the aquifer solid-water interface can best be explained with the distribution coefficient, Kd (a ratio of solute adsorbed in sediment to that of dissolved in groundwater). Due to being simplistic in nature, Kd has long been well appreciated as well as applied by geochemical modelers. 

The solid-water partition eoeffieient (Kp) in each compartment (sediment/suspended matter) ean be ealeulated from the Koe value, and the fraction of organic carbon in the compartment (foe)) by predietions outlined in equation 2. 

A mixture of 56.5 mmol of the 2/7-3,l-benzoxazine-2,4(l//)-dione 1 (R1 = H, CH3), 6.53 g (56.5 mmol) of pyridine hydrochloride and 7.15 g (62.2 mmol) of (S )-2-pyrrolidinecarboxylic acid is refluxed in pyridine for 6 h. After cooling and evaporation of the pyridine in vacuo, the resulting semisolid is partitioned between water and CHC13. The organic extract is washed with two 15-mL portions of 1M aq hydrochloric acid, followed by brine, and then dried over MgS04, filtered and concentrated to give a solid which, when triturated with ethyl acetate, gives the analytically pure product. 

Enantiomeric purity was determined to be 96-98% by 1H NMR analysis of the Mosher esters4 of the alcohols 4 and ent-4 obtained by reduction of the aldehydes 5 and ent-5. To an ice-cold solution of aldehyde 5 (0.10 g, 0.44 mmol) in 5 mL of methanol was added solid sodium borohydride (33 mg, 0.88 mmol). After the mixture was stirred for 30 min at this temperature, the TLC in (7 3) cyclohexane-ethyl acetate showed the clean formation of the alcohol 4. The mixture was treated with 0.05 mL of acetone and concentrated to dryness under reduced pressure. The residue was partitioned between water (10 mL) and ethyl acetate (10 mL) and the phases were separated. The aqueous phase was extracted with three 10-mL portions of ethyl acetate. The combined organic phases were dried with anhydrous sodium sulfate and concentrated under reduced pressure. The residue was purified by flash... 

Of course, in a two-phase system,/ + f2 must be equal to 1 (which can be easily checked). Note that Eqs. 3-62 and 3-63 are also valid if one of the phases is a solid (e.g., solid-water partitioning in a lake or in an aquifer, or solid-air partitioning in the atmosphere). In such cases, Kn2 is often expressed by the ratio of mole of i per mass of solid concentration and mole of i per volume concentration, and therefore, rl2 is then given by the ratio of the mass of solid and the volume of the bulk liquid or gas phase present in the system considered. 

Hence, the solid-water partition coefficient can be approximated by (Eq. 9-22) ... 

Since the open water column is nearly pure water (op =1, rs p = 0), for compounds with small to moderate solid-water distribution ratios (Kd < 10 m3kg ), the above equilibrium partition coefficient can be simplified to ... 

The target compounds of ozonation are often found in the water phase, although there are applications in which they are found in the solvent, e. g. highly lipophilic PAHs in dispersed oil droplets, or adsorbed on the solid, e. g. in the regeneration of spent adsorbents or treatment of contaminated soils. Generally, the tendency of a solute to partition between water and solvent or water and solid has to be considered carefully in three-phase systems. 

For air-water systems, this equation is known as Henry s law. For solids-water systems, the equilibrium constant is known as the partition coefficient (Ky) or distribution constant (KA). Partition coefficients are available for many organic chemicals from laboratory and field measurements. As organic carbon (OC) present in water (dissolved organic carbon, or DOC), sediment, or soil is the main sink for hydrophobic organic contaminants, the partition coefficients for these compounds are often adjusted (normalized) with respect to the organic carbon content of these compartments ... 

Partition between compartments within the aqueous environment is typically described through the octanol water partition coefficient, Aiow, or the organic carbon-water partitioning coefficient, (see Chapter 5). This approach assumes that partitioning from water into fish or suspended solids within the water is determined by the availability of organic matter whose properties as a solvent can be described by a parallel with octanol for which partitioning data are widely available... 

Permeability and solubility/dissolution are two major determinants of gastrointestinal drug absorption. The prediction of solubility of molecules is more difficult than for lipophilicity. Solubility critically depends on the solid-state properties of compounds. The same compound can exist in amorphous or in several crystalline states and this can result in very different solubility of molecules. The prediction of crystalline properties, represented, for example, by the melting point, is one of the most difficult problems of physical chemistry. Like the octanol-water partition coefficient, water solubility critically depends on the pH and ionization state of molecules. 

Solid-water exchange of hydrocarbons is a primary control on their aqueous concentration in groundwater and surface aquatic environments (Figures 10 and 11). The specific partitioning of hydrocarbons between solid and aqueous phase could be described by the distribution coefficient (A)j) ... 

An amino acid, tryptophan, was dissolved in SCF ethane for the first time at the 0.1 wt.% level using AOT and octanol. Solubilities are highly adjustable in the solid-liquid-fluid region, where the partitioning of water and surfactant are variable with pressure. It is possible that this type of adjustability could be used to selectively extract and recover hydrophilic substances such as proteins. It could be used also as a means to recover surfactant for recycle, but further woik is needed to understand these complex systems. 

Chemical partitioning also occurs between water and solid phases and between air and solid phases, in a process most generally termed sorption. Types of sorption include adsorption, in which a chemical sticks to the two-dimensional surface of a solid, and absorption, in which a chemical diffuses into a three-dimensional solid. Chemical sorption in the environment is much more difficult to predict than is chemical partitioning between air and water, partly because the types of sorptive solid phases (sorbents) vary enormously, and partly because there are many different mechanisms by which sorption can occur. In this section, only partitioning between water and solid phases is considered. 

Physicochemical models of partitioning at the solid-water interface, such as that used here to model ion exchange, require detailed knowledge about the particles. The surface properties of the mineral phases present, as well as equilibrium constants for ion binding to both fixed and variable charge sites associated with each phase, are required. These data requirements and the uncertainty about modeling sorption in mixtures of minerals (e.g., 48-50) make such models difficult to apply to complex natural systems. This is especially the case for modeling solute transport in soil-water systems, which... 

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