Water pseudo-organic solvent

As suggested by the lower dielectric constant, high-temperature water behaves like a pseudo-organic solvent, dissolving organic compounds that are much less soluble at ambient temperatures. This property was exploited for the hydrolysis of naturally... 

An objective of our work is to study biomimetic reactions in an aqueous environment at temperatures between 100 and 300 °C. Water has a dielectric constant which decreases from 78 at 25 °C, to 20 at 300 °C (1,9), this latter value being comparable with that of solvents such as acetone at ambient temperature. Thus water can behave as a pseudo-organic solvent, dissolving otherwise insoluble organic compounds at elevated temperatures. This property has allowed us to study the behavior of naturally occurring organic compounds in water directly, without the requirement that such molecules first be derivatized with characteristic water-... 

First, mention should be made of the metathetical reaction, replacing an anion of a pyrylium salt by another-, when the solubility of the latter salt is lower than that of the former, the conversion is easy. In the opposite case, one has to find a solvent in which the solubilities are reversed (perchlorates are less soluble in water than chloroferrates or iodides, but in concentrated hydrochloric or hydroidic acids, respectively, the situation is reversed For preparing chlorides which are usually readily soluble salts, one can treat the less soluble chloroferrates with hydrogen sulfide or hydroxylamine. Another method is to obtain the pseudo base in an organic solvent and to treat it with an anhydrous acid. 

By using cyclic voltammetry, Schiffrin and coworkers [26, 186, 187, 189] studied electron transfer across the water-1,2-dichloroethane interface between the redox couple FefCNls /Fe(CN)6 in water, and lutetium(III) [186] and tin(IV) [26, 187] diphthalocyanines and bis(pyridine)-me50-tetraphenylporphyrinato-iron(II) or ru-thenium(III) [189] in the organic solvent. An essential advantage of these systems is that none of the reactants or products can cross the interface and interfere with the electron transfer reaction, which could be clearly demonstrated. Owing to a much higher concentration of the aqueous redox couple, the pseudo-first order electron transfer reactions could be analyzed with the help of the Nicholson-Shain theory. However, though they have all appeared to be quasireversible, kinetic analysis was restricted to an evaluation of the apparent standard rate constant o. which was found to be of the order of 10 cm s [186, 189]. Marcus [199] has derived a relationship between the pseudo-first-order rate constant for the reaction (8) and the rate... 

The simpler equation (4) embodies the Ostwald conception with the difference that Km is not the true dissociation constant but the apparerd constant of the indicator since it represents the product of the true dissociation constant and the equilibrium constant for the normal and aci-forms. The latter equilibrium favors the normal compound in the case of p-nitrophenol so that this substance appears to be a very weak acid. With o-nitro-phenol, however, the existence of the aci-form is favored so that this compound behaves as a stronger acid. The ratio of aci to normal is so large in the case of picric acid that relatively much of the aci- or ionogen form, as compared with the pseudo-compound, is present in aqueous solution. Consequently this substance is a rather strong acid. As the apparent dissociation constant increases, the intensity of the yellow color of aqueous solutions must likewise grow because more of the aci-form will be found in solution. This statement can be confirmed easily. Picric acid in water solutions is yellow, but colorless in organic solvents due to the predominance of the pseudo-form. 

With metal ions, some organic reagents form coloured compounds that are sparingly soluble both in water and in organic solvents. They are either polynuclear complexes, such as formed by phenylfluoron with Sn(IV) or with Ge(IV), or adsorption-type compounds such as those formed by titanium yellow with Mg. In such cases, the absorbance is measured for suspensions of coloured pseudo-solutions stabilized with protective colloids [e.g., gum arabic, gelatine, poly(vinyl alcohol)]. 

To date, the water soluble and stable complexes have not yielded values as high as in organic solvents but their preparation has very often allowed microscopy studies, illustrating the interest to develop and optimise such structures for these applications. For instance, Charbonni re et al. reported a pyrazolyl-pyridine ligand (L Scheme 5.2) that possesses a two-photon cross-section of 28.6 GM at 705 nm [89]. In this context, Wong et al. published a pseudo on/off two-photon system (L Scheme 5.2) that enables the detection of Saxitoxin [90]. With such a ligand, the authors showed an increase of the two-photon... 

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