Secondary kinetic electrolyte effect

Although these effects are often collectively referred to as salt effects, lUPAC regards that term as too restrictive. If the effect observed is due solely to the influence of ionic strength on the activity coefficients of reactants and transition states, then the effect is referred to as a primary kinetic electrolyte effect or a primary salt effect. If the observed effect arises from the influence of ionic strength on pre-equilibrium concentrations of ionic species prior to any rate-determining step, then the effect is termed a secondary kinetic electrolyte effect or a secondary salt effect. An example of such a phenomenon would be the influence of ionic strength on the dissociation of weak acids and bases. See Ionic Strength... 

A kinetic electrolyte effect ascribable solely to the influence of the ionic strength on activity coefficients of ionic reactants and transition states is called a primary kinetic electrolyte effect. A kinetic electrolyte effect arising from the influence of the ionic strength of the solution upon the pre-equilibrium concentration of an ionic species that is involved in a subsequent rate-limiting step of a reaction is called a secondary kinetic electrolyte effect. A common case encountered in practice is the effect on the concentration of a hydrogen ion (acting as catalyst) produced from the ionization of a weak acid in a buffer solution. 

When the source of the catalytically active hydrogen ion is a weak acid, one has to consider the weak electrolyte equilibrium involved and the change of the dissociation constant with electrolyte concentration, medium, and temperature. Br0nsted (7) termed this phenomenon secondary kinetic salt effect, but the writer would prefer to omit the word kinetic and substitute electrolyte for salt. The understanding of these... 

The rate constants of chemical reactions the yield and the selectivity of a reaction, as well as the conditions for refining or recycling of products can be optimized by the choice of appropriate solvents. Discussion in this section is restricted to reaction mechanisms involving electrolytes or single ions. The role of electrolyte solutions in primary and secondary kinetic salt effects is not considered. For this problem see Refs. s. 

Aroyl esters of anthracene-9-methanol are photolysed in methanol to give products consistent with the anthracene-9-methyl cation as an intermediate.41 Rate constants for the solvolyses of secondary alkyl tosylates in fluorinated solvents were analysed in terms of the possible involvement of very short-lived carbocation-tosylate ion pair intermediates.42 The effect of added electrolytes on the rate of solvolysis of cumyl chloride and its -methyl derivative was studied in 90% aqueous acetone and 80% aqueous DMSO, with the results revealing a combination of a special salt effect and a mass law effect.43 Kinetic parameters obtained for the solvolysis of (8) (R1 = R2 = Me and R1 = Ar, R2 = H) show that there is substantial n, n participation in the transition state [e.g. (9). 44... 

In contrast to unfractionated heparin, the factor Xa inhibitor tick anticoagulant peptide (TAP) effectively inhibited coronary arterial thrombosis in a canine electrolytic injury model (57). TAP was also effective in inhibition of the procoagulant properties of whole blood clots in vitro however, it was stated that TAP might be not optimal due to its slow binding kinetics (54). Meanwhile, several low molecular weight direct factor Xa inhibitors are in clinical development (Table I), some of them specifically for the treatment and secondary prevention of ACS. DX-9065a, ZK-807834 and otamixaban have been intensively characterized in vitro and in vivo and are in clinical investigations for the treatment of acute arterial thrombosis. 

The secondary current distribution is calculated by including the effects of the ohmic drop in the electrolyte and the effects of sluggish electrode kinetics. While the secondary distribution may be a more realistic approximation, its calculation is more difficult therefore, we need to assess the relative importance of electrode kinetics to determine whether we can neglect them in a simulation. 

In the case of CdSe/polysulfide system, solution activity, conductivity, efficiency of the photoanode (fill factor), charge-transfer kinetics at the interface, and the stability of the photoelectrode are known to exhibit improvements in the trend Li > Na > K > Cs > for alkali polysulfide electrolyte. This trend is explained in terms of the secondary cation effect on electrochemical anion oxidation in concentrated aqueous polysulfide electrolytes [39]. In the case of Cd(Se,Te)/polysulfide system, the efficiency of light energy conversion is improved by using a polysulfide electrolyte without added hydroxide because of the combined effect of increasing the solution transparency, relative increase of 4 , and decrease in 83 in solution. For the same photoelectrode-electrolyte system, an optimum photoeffect was observed for a solution containing a sulfur-sulfide ratio of 1.5 2.1 with 1 2 molal... 

We will consider only the influence of activation overpotential or overvoltage on secondary current distribution. It is useful to regard the slope of the polarization curve dE /di (if any effect of concentration overpotential can be ignored) as a polarization resistance R. This represents the slowness of charge transfer across the interface and is based on the electrode kinetics of the reaction. If acts in series with R, the resistance of the electrolyte, we can distinguish between two situations. If R R, then the kinetics of charge transfer and not electrolyte resistance determine the current distribution, i.e., secondary current distribution dominates. Conversely, if R R, primary current distribution dominates. Secondary current distributions tend to smooth out the severe nonlinear variations of current associated with primary distributions and they eliminate infinite currents associated with electrode edges. 

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