Proton exchange reactions system

Exchange studies were carried out by solvolysing a series of butyl chlorides in 2m solutions of antimony pentafluoride in fluoro-sulfonic acid at —50° and —78°. The acid contained tracer levels of TjO and small amounts of water to provide sufficient nucleophiles to catalyse proton exchange reactions with some of the intermediates formed in the butyl system (Kramer, 1970, 1973). 

In this example, one key objective would be to determine the concentrations of [AB], [A], and [B] that fit with the equilibrium constant. The values of ion activities, not shown (discussed later), will also be dependent on these concentrations at equilibrium. It is generally assumed that while most natural systems are far from equilibrium conditions, if the reactions between reactant and product states are rapid, equilibrium can be applied (Butcher and Anthony, 2000). For example, in aquatic systems, NH4+ and NH3(aq) are considered to be in equilibrium, as shown below, because the proton exchange reaction is so rapid (Quinn et al., 1988) ... 

To evaluate whether our experimental system can detect the contribution of a direct reaction, we substituted the highly charged emitter with the neutral one, 0-naphthol. The protonation cycle of Bromo Cresol Green, in the presence of 0-naphthol, is depicted in Figure 30. Calculations that did not account for the contribution of the direct proton exchange (reaction 31) gave unsatisfactory simulations. However, including the rate constants of reaction (30) in the differential rate equations... 

The reaction between the above carbodiimides and the sodium caprolactamate takes place in part in the liquid system, producing a resonance-stabilized guanidine anion (Scheme 27). In the initiation of the polymerization, the guanidine anion rearts with the lactam monomer by a proton exchange reaction... 

Yong MacDonald (1998) show that upon apparent completion of metal sorption, measurements of the equilibrium pH of the system generally showed a reduction below initial pH. This reduction in pH was attributed to the resultant effect of the many reactions in the system. These reactions included the release of hydrogen ions by metal/proton exchange reactions on surface sites, hydrolyses of metals in the soil solution, and precipitation of metals. It was apparent that more detailed information was needed to distinguish between surface and solution reactions responsible for release of hydrogen ions. However, it was evident that if surface complexation models are to be used, the relationship between metal adsorption and proton release needs to be established. That is, net proton release or consumption is due to all the chemical reactions involving proton transfer. 

Nagypal, I. and Fabian, I. (1982) NMR relaxation studies in solution of transition metal complexes. V. Proton exchange reactions in aqueous solutions of VO -oxalic acid, -malonic acid systems. Inorg. Chim. Acta, 61, 109-113. 

Singh, U.C., Kollman, P.A. A combined ab initio quantum mechanical and molecular mechanical method for carrying out simulations on complex molecular systems Applications to the CH3CI 4- Cl exchange reaction and gas phase protonation of polyethers. J. Comput. Chem. 7 (1986) 718-730. 

Singh U C and P A Kollman 1986. A Combined Ab Initio Quantum Mechanical and Molecule Mechanical Method for Carrying out Simulations on Complex Molecular Systems Applicatior to the CHsQ + Cr Exchange Reaction and Gas Phase Protonation of Polyethers. Journal Computational Chemistry 7 718-730. 

The suggested reaction mechanism involves a nucleophilic attack of the imine nitrogen at the activated triple bond, followed by a proton exchange, to give a benzimidazolinium system which, by intramolecular attack at the carbonyl group, leads to an epoxide that ring opens to the observed product. For the ethyl derivative (R = Et) a tub conformation could be established by X-ray crystallographic analysis.33... 

The authors developed a multi-layered microreactor system with a methanol reforma- to supply hydrogen for a small proton exchange membrane fiiel cell (PEMFC) to be used as a power source for portable electronic devices [6]. The microreactor consists of four units (a methanol reformer with catalytic combustor, a carbon monoxide remover, and two vaporizers), and was designed using thermal simulations to establish the rppropriate temperature distribution for each reaction, as shown in Fig. 3. 

The values obtained for the proton transfer in these four systems (Table IV) are typically as expected for these rapid processes. Examples from the literature where similar reactions were studied in metal complexes include the [Cr(OH)(OH2)]2+ (62) and [VO(OH2)5]2+ (63) systems. In the proton exchange study of the hexaaqua aluminate(III) system a bimolecular process, similar to that proposed for the systems in this study, for the exchange between the [Al(OH2)6]3+ and [Al(OH2)5(OH)]2+ (64) complexes was postulated. 

The semi-empirical descriptions of adsorbate/solid interactions are based on net changes in system composition and, unlike surface complexation models, do not explicitly identify the details of such interactions. Included in this group are distribution coefficients (Kp) and apparent adsorbate/proton exchange stoichiometries. Distribution coefficients are derived from the simple association reaction... 

Table 19 reports multicollisional dissociation thresholds of the selected complexes. A direct correlation exists between them and the proton affinity (PA) of the guest. However, although chiral specificity has been observed in similar systems using ligand-exchange reactions (see previous sections), the results of Table 19 show no such specificity. The differences in binding of the Ala and Phe enantiomers are evidently too small to be measured with this method. 

In order to study the dependence of the exchange reaction (a) on the proton concentration alone, i.e. on the acidity of the solvent, MacLean el al. (1958) chose the system pentamethylbenzene-CFs. CO. OH-H2O.BF3. 

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