Aqueous solution, protonation

In acidic aqueous solution, protonation reactions of tetracyanodioxotech-netate(V) give a complicated equilibration, leading to formation of [TcO(OHXCN)4]- and [TcO(H2OXCN)4] . At pH values less than 1, these monomer species are fairly stable, while at pH 2-5, [Tc203(CN)8]4 is formed rapidly. This complicated feature is seen in a plot of /cobsd against pH (Fig. 4). When thiocyanate ion is added to this system at pH 1, it replaces a water molecule or hydroxy group in the coordination site. 

Reductants and oxidants are defined as electron donors and proton acceptors (Sect. 2.2.2). Because there are no free electrons, every oxidation is accompanied by a reduction and vice versa. In aqueous solutions, proton activities are defined by the pH ... 

More recent studies of the kinetics of bromination of imidazoles coordinated to cobalt(III) have implied that, in aqueous solution, proton-abstraction from a Wheland intermediate is rate-determining at acidic pH values. In more nearly neutral conditions bromine addition becomes rate-... 

In aqueous solution, protons (actually present as hy-dronium ions) or hydroxide ions are the catalysts most commonly used for nonenzymatic reactions. The way in which acid or base catalysts work in ester hydrolysis is illustrated in Figure 10b and c. As a result of the electronegativity of... 

In aqueous solution, proton transfer to tile first formed intermediate is very rapid. However, again for illustrating die stepwise changes that must occur on the way from reactants to products using curved-arrow notation, these steps are shown independently. 

Campbell JM, von Sonntag C, Schulte-Frohlinde D (1974) Photolysis of 5-bromouracil and some related compounds in solution. Z Naturforsch 29b 750-757 Candeias LP, Steenken S (1989) Structure and acid-base properties of one-electron-oxidized deoxy-guanosine, guanosine, and 1-methylguanosine. J Am Chem Soc 111 1094-1099 Candeias LP, Steenken S (1992a) Electron adducts of adenine nucleosides and nucleotides in aqueous solution protonation at two carbon sites (C2 and C8) and intra- and intermolecular catalysis by phosphate. J Phys Chem 96 937-944... 

Candeias LP, Steenken S (1992) Electron adducts of adenine nucleosides and nucleotides in aqueous solution Protonation at two carbon sites (C2 and C8) and intra- and intermolecular catalysis by phosphate. / Phys Chem 96 937-944. 

Fig. 28. Gas-phase ab initio protonation energies (<5A p) versus aqueous solution protonation energies (dAG,.q, (a) methylpyrazoles, (b) methylimidazoles. Lines A, iV-methyl-substituted azoles lines B, C-methyl-substiluted azoles. All values relative to the corresponding unsubstituted parent compounds (84JOC4379).

This ionic liquid, having A AiAi-trimethylglycine as cation and being practically the oxidized form of choline, is able to dissolve large amounts of metal oxides. This metal solubilizing power is selective, making possible separation of metals. Moreover, the metals can be stripped from the ionic liquid by treatment with an acidic aqueous solution. Protonated betaine bis(trifluoromethylsulfonyl)imide can be switched from a hydrophobic IL to a hydrophilic one by temperature or pH control. At high temperature, or under basic condition (pH > 8), this IL and water form a sole phase whereas... 

In the classical chemistry of aqueous solutions, proton dissociation is treated as a simple first-order reaction. Actually it is a very complex... 

In aqueous solution, protons are solvated and so it is more correct to write [H30] (aq) than H (aq). Even this is oversimplihed because the oxonium ion is further hydrated and species such as [H502] (see Figure 9.1), [Hv03] and [Hg04] are also present. 

Fig. 8. Summary gas phase protonation energy, hydration energy and aqueous solution protonation energy for most stable hydromorphone and oxymorphone species.

To calculate rate constants of protolytic dissociation of hydroxyaromatic compounds in the singlet excited state in the micellar phase we studied the dependence of fluorescence quantum yields and fluorescence kinetics of undissociated (f>) and dissociated (p ) forms of hydroxyaromatic compounds in the micellar solutions on the concentration of hydroxo-nium ions in the solution. Similarly to aqueous solutions proton transfer photoreactions in micellar solutions can be described by simple kinetic scheme ... 

In neutral aqueous solutions protonation reaction of ArO can be neglected, since its pseudounimolecular rate constant ( calculated as a product of the diffusion rate constant... 

In aqueous solutions, protonation of one of the nitrogen atoms — preferably at the N = N double bond — causes a considerable reduction in the activation barrier. Inversely, hydroxide ions decrease the reaction rate. To study thermal Z—> isomerization rates of unprotonated azobenzenes in aqueous solutions, the pH of the solution should be clearly above the threshold where protonation influences the rate. The dependence of Iq of 4-(phenylamino)-4 -nitroazobenzene on H5O concentration in acetone/ water (1 1, v/v) mixtures corresponds to a titration curve (see Figure 89.6). - The flash-photolytic preparation of thermally unstable Z-isomers offers the interesting possibility of determining their pKj-data by means of kinetic experiments. 

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