Modeling the Solubility in Water

Based on the Langmuir-Herman-Amidon model, the solubility, in water was given by the following expression ... 

Modeling the Solubility in Water of Environmentally Important Organic Compounds... 

Modeling the Solubility in Water of Environmentally Important Organic Compounds by Ernesto Estrada, Eduardo J. Delgado and Yamil Simon-Manso. Email estrada66 yahoo.com... 

CHAPTER 2 Modelling the solubility in water of environmentally important... 

The study of the variation of the solubility with the selenite concentration is stated to have been carried at the constant ionic strengths 0.01 and 0.3 M. How this was accomplished was not clear from the information in the paper. The data in the tables rather seem to indicate that the ionic strength varied and reached 0.03 and 0.5 M, respectively, in the solution with the highest selenite concentrations. The analysis of the data was made with an equilibrium model that comprised the solubility equilibrium and the formation of the complex 0(8003)2 T us the formation of CoSe03(aq) was not included in the model. The analysis led to values of the solubility product at the two ionic strengths that appear to be inconsistent with the value obtained from the solubility in water. This result together with the improbable model made the review reject the outcome of the equilibrium analysis. 

The surface area model for solubility in water or any solvent can be further investigated by measuring the effect of temperature or added salt. Preliminary measurements indicate that some of the above models are not satisfactory. We find that the solubility of butanol in water decreases while the magnitude of surface tension of aqueous NaCl solution increases. These kinds of data are important for such systems as EOR (enhanced oil recovery). 

The LLE data of the ternary system composed of water + ethanol + cyclohexane were measmed at different temperatures of 298.2, 303.2, 308.2, and 313.2 K. The UNIQUAC model was used to correlate the experimental LLE data. The optimum UNIQUAC interaction parameters between water, ethanol, and 2-etyl-l-hexanol were determined using the experimental (liquid + liquid) data. The average rmsd value between the observed and calculated mole fractions with a reasonable error was 1.70% for the UNIQUAC model. The solubility of water in cyclohexane increases with amoimts of ethanol added to water + 2-ethyl-hexanol mixtore. 

The identification of (5) is based on several analytical techniques, one being the direct comparison with model p-hydroxysulfonates synthesized by Bakker and Cerfontain [29]. As indicated above, in AOS manufacturing aging is introduced to avoid the poorly water-soluble 1,2-sultone-derived 2-hydroxy-l-sulfonates. In contrast with AOS the end products derived from internal olefins obtained after direct neutralization without any aging showed good solubilities in water [4]. 

In Eqs. (27) and (28), p is the contribution of the substrate water molecules, p that of the adsorbate polar head, and p that of the hydrophobic moiety of the adsorbed molecules. Consistently, 8i, 82, and 83 are the effective local permittivities of the free surface of water and of the regions in the vicinity of the polar head and of the hydrophobic group, respectively. The models have been used in a number of papers on adsorbed monolayers and on short-chain substances soluble in water. " Vogel and Mobius have presented a similar but more simplified approach in which p is split into two components only. " Recently some improvements to the analysis using Eq. (27) have been proposed. " An alternative approach suggesting the possibility of finding the values of the orientation angle of the adsorbate molecules instead of local permittivities has been also proposed.""... 

In our ongoing efforts to develop oxidation catalysts that are functional in water as environmentally berrign solvent, we synthesized a water-soluble pentadentate salen ligand with polyethylene glycol side chairts (8). After coordination of copper(II) ions to the salen ligand, a dinuclear copper(II) complex is obtained that is soluble in water, methanol and mixtures of both solvents. The aerobic oxidation of 3,5-di-tert.-butylcatechol (DTBC) into 3,5-di-terr.-butylqitinone (DTBQ) was used as a model reaction to determine the catalytically active species and initial data on its catalytic activity in 80% methanol. 

The value of the tris(pyrazolyl)hydroborato complexes [TpRR ]ZnOH is that they are rare examples of monomeric four-coordinate zinc complexes with a terminal hydroxide funtionality. Indeed, [TpBut]ZnOH is the first structurally characterized monomeric terminal hydroxide complex of zinc (149). As such, the monomeric zinc hydroxide complexes [TpRR ]ZnOH may be expected to play valuable roles as both structural and functional models for the active site of carbonic anhydrase. Although a limitation of the [TpRR ]ZnOH system resides with their poor solubility in water, studies on these complexes in organic solvents... 

The spectra we have so far discussed were recorded using CDC13> the best allround solvent for organic molecules. However, many molecules, especially biomolecules, are only soluble in water biological systems often remain stable only in aqueous solution. Thus NMR measurements in water are extremely important our model compound is also water-soluble, so that we can use it to demonstrate some important experiments. 

Physical and Chemical Properties. Most of the important physical-chemical properties of acrylonitrile have been determined (see Chapter 3). However, the partitioning of acrylonitrile between the air and water has been evaluated by using an estimated value for a Henry s law constant. This general approach assumes that the concentration of the chemical in water is low. Because acrylonitrile is relatively soluble in water, this approach may not be accurate. Experimental measurement of the partition coefficient for acrylonitrile at water-air interfaces would be useful in refining models on the behavior of acrylonitrile in the environment. 

Much effort has been expended on models that can be used to predict the solubility behavior of solutes, with good success being attained using a semi-empirical, group contribution approach [75]. In this system, the contributions made by individual functional groups are summed to yield a composite for the molecule, which implies a summation of free energy contributions from constituents. This method has proven to be useful in the prediction of solubility in water and in water-cosolvent mixtures. In addition to the simplest methodology, a variety of more sophisticated approaches to the prediction of compound solubility have been advanced [68]. 

Influence of Organic Cosolvents. Rao et al. (49) have recently presented a solvophobic model for estimating the sorption of a hydrophobic solute from a mixed solvent. This model is based on the work of Yalkowsky et al. (27), who developed an empirical relationship between the solubility in a mixed solvent system, Sm, and that in pure water given by... 

Between 1906 and 1908 the breakdown of fatty acids to acetone was detected by Embden in perfused livers. Only fatty acids with even numbers of carbon atoms produced this effect. The acetone was postulated to have originated from acetoacetate. For the next 30 years the 6-oxidative route of fatty acid oxidation was generally unchallenged. By 1935-1936 however much more accurate determinations of the yields of acetoacetate per mole of fatty acid consumed (Deuel et al., Jowett and Quastel) indicated convincingly that more than one mole of acetoacetate might be obtained from 6C or 8C fatty acids. (Octanoic acid was often used as a model fatty acid as it is the longest fatty acid which is sufficiently soluble in water at pH 7.0 for experimental purposes.) The possibility had therefore to be entertained that 2C fragments could recondense (MacKay et al. 1942). 

This model assumes the absence of specific solute-solvent interactions and is based upon a linear relationship between the free energy of solution and solute surface area. It assumes that the overall solubility is simply the sum of the solubilities in the individual solvent components. This model treats the cosolvent and the water as distinct entities and neglects any interaction between them [19,145,226,253,261]. 

A realistic boundary condition must account for the solubility of the gas in the mucus layer. Because ambient and most experimental concentrations of pollutant gases are very low, Henry s law (y Hx) can be used to relate the gas- and liquid-phase concentrations of the pollutant gas at equilibrium. Here y is the partial pressure of the pollutant in the gas phase expressed as a mole fraction at a total pressure of 1 atm x is the mole fraction of absorbed gas in the liquid and H is the Henry s law constant. Gases with high solubilities have low H value. When experimental data for solubility in lung fluid are unavailable, the Henry s law constant for the gas in water at 37 C can be used (see Table 7-1). Gas-absorption experiments in airway models lined with water-saturated filter paper gave results for the general sites of uptake of sulfur dioxide... 

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