Disproportionation equilibrium constants

The disproportionation equilibrium constant Kiiap has been estimated to be 10.34 (AGdi8p° = -5.79 kJ mol-1), which is small compared to a / dispof3.2 x 10, found in rans-[Ruv(14TMC)(0)2] +. ... 

Disproportionation equilibrium constants" for 2RH,+ R2+ + R as determined from 1/2 data... 

Disproportionation mechanisms have been proposed for protonation reactions and intramolecular rearrangements (see Sec. III.B and III.D) [50,51]. Their prominent feature is that follow-up processes at the level of the dianion can already take place at potentials corresponding to radical anion formation. In order to evaluate data for disproportionation reactions it is necessary to know the value of the disproportionation equilibrium constant. 

The cation radical of thianthrene (LVII" ") has been subject of extensive investigation [3, 187]. Voltammetric experiments with thianthrene (LVII) when carried out in the presence of TEA and its anhydride or activated neutral alumina gave reversible oxidation potentials in a variety of solvents, and disproportionation equilibrium constants, Xd,sp, were calculated [190]. Accurate values of X isp are important in the mechanistic evaluation for the reaction of LVII" with nucleophiles and have been used to rule out the disproportionation pathway, such as the reaction with water [191]. 

Eq. (2.56)] is determined solely by thermodynamic stability of intermediate species, which, in turn, is expressed by the equilibrium formation constant (or, alternatively, the disproportionation equilibrium constant) of the intermediate valence compound. 

Table 8.6 Disproportionation equilibrium constant of Cu ions in various solvents.

The equilibrium constant for this reaction is very favourable in each case 10 for ClO , lO for BrO , and 10 ° for IO . However, particularly in the case of ClO , the rate of disproportionation is slow at room temperature and only becomes appreciable above 70°. Similarly, the disproportionation... 

A wide range of nitroxidcs and derived alkoxyamincs has now been explored for application in NMP. Experimental work and theoretical studies have been carried out to establish structure-property correlations and provide further understanding of the kinetics and mechanism. Important parameters are the value of the activation-deactivation equilibrium constant K and the values of kaa and (Scheme 9.17), the combination disproportionation ratio for the reaction of the nilroxide with Ihe propagating radical (Section 9.3.6.3) and the intrinsic stability of the nitroxide and the alkoxyamine under the polymerization conditions (Section 9.3.6.4). The values of K, k3Cl and ktieact are influenced by several factors.11-1 "7-"9 ... 

Use the information in Appendix 2B to determine the equilibrium constant for the disproportionation of copper(l) ions in aqueous solution at 25°C to copper metal and copper(ll) ions. 

Additional data were obtained from the study of kinetics of the slow disproportionation of the living dimers of methyl methacrylate. The progress of this reaction is shown in Fig. 8 which displays also the respective rates and equilibrium constants. 

In contrast to disproportionation, in the dimerization equilibrium at lower temperatures the reaction product is favored. The contributions coming from partition functions and from the exponential term are presented together with the temperatures and logarithms of equilibrium constants of the reaction (103) in Table XI. 

Rate Constants (in M 1s 1) and Equilibrium Constants and Activation Parameters for Iron(III)-TAML Catalyzed Disproportionation of Hydrogen Peroxide (Eq. (17)) at 25°C and 0.1 M Phosphate... 

When one of the aromatic groups of the triarylmethyl free radical is replaced by an alkyl group, a decrease in stability due to a loss of resonance stabilization is to be expected. The paramagnetism and reactions associated with these less stable radicals will therefore appear only when the ethane is heated well above room temperature, the dissociation being endothermic. The rate of formation, but not the equilibrium constant, is experimentally accessible for these radicals since the radical once formed is subject to rearrangement, cleavage, and disproportionation reactions ... 

The equilibrium constant for the disproportionation reaction, KD, may be expressed as a function of the standard potentials of the two-electrode electron transfer reactions according to... 

Barnett and co-workers recently reported that it might be possible to utilize hydrocarbons directly in SOFC with Ni-based anodes. " ° First, with methane. they observed that there is a narrow temperature window, between 550 and 650 °C. in which carbon is not as stable. The equilibrium constant for methane dissociation to carbon and Hz is strongly shifted to methane below 650 °C. and the equilibrium constant for the Boudouard reaction, the disproportionation of CO to carbon and COz, is shifted to CO above 550 °C. Therefore, in this temperature range, they reported that it is possible to operate the cell in a stable manner. (However, a subsequent report by this group showed that there is no stable operating window for ethane due to the fact that carbon formation from ethane is shifted to lower temperatures. ) In more recent work, this group has suggested that, even when carbon does form on Ni-based anodes, it may be possible to remove this carbon as fast as it forms if the flux from the electrolyte is sufficient to remove carbon faster than it is formed.Observations by Weber et al. have confirmed the possibility of stable operation in methane. Similarly, Kendall et al. showed that dilution of methane with COz caused a shift in the reaction mechanism that allowed for more stable operation. 

Szwarc and coworkers have reported equilibrium constants for the disproportionation reaction given in equation 40 ... 

Under these circumstances, it seems reasonable to look for alternative explanations for the polysulfide reactions and in this connection it is interesting to note that a bimolecular mechanism is in better agreement with the data reported for the trisulfide disproportionation discussed above. This reaction has been followed by H n.m.r. spectroscopy at different temperatures and initial concentrations. Equimolar amounts of diethyl and di-n-propyl trisulfide were used and after the equilibrium had been established the equilibrium constant... 

Chlorine, when dissolved in water, undergoes rapid disproportionation (i.e., it oxidizes and reduces itself simultaneously) to hypochlorous acid and hydrochloric acid, with an equilibrium constant of 5 x 10 4 mol2 L 2 ... 

The disproportionation is crucial in determining the action of superoxide anion as a base. According to equation 1, in aqueous solution stoichiometric amounts of the strong bases HO and HO are formed, and the equilibrium constant for this process indicates that superoxide is effective in extracting protons from acids of pK up to 24. In contrast O itself is a weak base (the pK of its conjugate acid, HOj, is 4.69). 

Cyclic voltammetric methods, or other related techniques such as differential pulse polarography and AC voltammetry,3 provided a convenient method for the estimation of equilibrium constants for disproportionation or its converse, comproportionation. In this respect, the experimentally measured quantity of interest in a cyclic voltammetric experiment is E>A, the potential mid-way between the cathodic and anodic peak potentials. For a one-electron process, E,A is related to the thermodynamic standard potential Ea by equation (4).13 In practice, ,/2 = E° is usually a good approximation. 

There have been extensive investigations into the kinetics of disproportionation reactions involving chlorofluorocarbon compounds.4-6 Phase equilibrium constants in relation to contact time and temperature have been determined and reported in various publications.1-3... 

The most common electrochemical effects exerted in bulk solution are related to association (solvation, ion-pairing, complex formation, etc.) with the electroactive substance or electrochemically generated intermediates [4,19]. The importance of solvation can be gauged by comparing calculated and measured values of the parameter AE1/2 (defined as the difference, in volts between the half-wave potentials of the first and second polarographic waves) exhibited by polycyclic aromatic hydrocarbons (PAH) in dipolar aprotic solvents [46,47], It can be shown that AE1/2 is related to the equilibrium constant for disproportionation of the aromatic radical anion into neutral species and dianion, that is,... 

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