Self-protonation reactions

Increased acidity of this hydrogen atom may lead to self-protonation reactions with electrogenerated bases (in aprotic solvents or in unbuffered solutions). 

Amatore C, Capobianco G, Famia G, Sandona G, Saveant JM, Severin MG, Vianello E (1985) Kinetics and mechanism of self-protonation reactions in organic electrochemical processes. J Am Chem Soc 107(7) 1815-1824. doi 10.1021/ja00293a003... 

Stereospecific nucleophilic substitution in chiral ion—dipole complexes. Chiral molecules can be discriminated in the Cl source of a CIMS instmment by specific ion-molecule reactions induced by chiral reagent gas. This method has been applied with success to distinguish between enantiomeric and diastereomeric forms of menthols ((lR,2S,5R)-(— )-14, (lS,2R,5S)-(+)-14, and (lR,2R,5S)-(—)-14 in Scheme 11) through the nucleophilic displacement of their hydroxyl group by (5)-2-amino-l-butanol Self-protonation of As... 

The voltammetric reduction of a series of dialkyl and arylalkyl disulfides has recently been studied in detail, in DMF/0.1 M TBAP at the glassy carbon electrode The ET kinetics was analyzed after addition of 1 equivalent of acetic acid to avoid father-son reactions, such as self-protonation or nucleophilic attack on the starting disulfide by the most reactive RS anion. Father-son reactions have the consequence of lowering the electron consumption from the expected two-electron stoichiometry. Addition of a suitable acid results in the protonation of active nucleophiles or bases. The peak potentials for the irreversible voltammetric reduction of disulfides are strongly dependent on the nature of the groups bonded to the sulfur atoms. Table 11 summarizes some relevant electrochemical data. These results indicate that the initial ET controls the electrode kinetics. In addition, the decrease of the normalized peak current and the corresponding increase of the peak width when v increases, point to a potential dependence of a, as discussed thoroughly in Section 2. 

The reduction scheme (equations 85-88) may be complicated by other reactions induced by the initial ET. The most important of these is the selfprotonation, a reaction between an electrogenerated species and the starting material. Self-protonation is the most common case of the so-called father-son reactions. This type of reaction has been characterized both theoretically and experimentally for the case of an initial slow ET by Vianello and co-workers in a study concerning the reduction of Ph2CH-SPh, as shown in equation (89). ... 

Scheme 10.4 Self-assembly of molecular square 10.10 from Pd (en)2+ and 4,4 bipyridine in competition with protonation reactions.

Such self-exchange reactions cannot be followed by optical spectroscopy since no chemical change is involved. However, ESR spectroscopy provides a unique capability to do so because the spin states of the protons in the radical effectively label a particular radical. The reaction leads to broadening of the ESR lines, which is detectable at rates of transfer >10 s. From the dependence of line width on phenolate concentration it was calculated that the rate constant for this self-exchange reaction is 1.9 x 10 ... 

These approaches date back to the classical papers by Onsager(9) and Kirkwood(lO). A self-consistent reaction field (SCRF) was developed and applied to several solvent effects with reasonable success(8, 11). However, it seems to become clear that these models where the solute and the solvent are represented by separated non-overlapping wave functions are too crude in some cases(12). Studies of solvent effects involving the interaction of the solute with a proton donor solvent (the so-called protic solvents) for instance usually leads to hydrogen bonds and therefore neglecting the overlap of the electron densities between the two subsystem is very difficult to justify. A similar difficulty is obtained for those absorptions where electron is trans-... 

Recently, a new category of methods, the cavity model, has been proposed to account for the solvent effect. Molecules or supermolecules are embedded in a cavity surrounded by a dielectric continuum, the solvent being represented by its static dielectric constant. The molecules (supermolecules) polarize the continuum. As a consequence this creates an electrostatic potential in the cavity. This reaction potential interacts with the molecules (supermolecules). This effect can be taken into account through an interaction operator. The usual SCF scheme is modified into a SCRF (self consistent reaction field) scheme, and similar modifications can be implemented beyond the SCF level. Several studies based on this category of methods have been published on protonated hydrates. They account for the solvent effect on the filling of the first solvation shell (53, 69), the charges (69, 76) and the energy barrier to proton transfer (53, 76). 

The can, in turn, attack the minerals causing more Fe(II) to be released that once oxidized and hydrolyzed could produce more protons, thus initiating a self-sustaining reaction, provided enough O2 is present. 

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