Proton theory

Although the protonic theory is not confined to aqueous solutions, it does not cover aprotic solvents. The solvent system theory predates that of Bronsted-Lowry and represents an extension of the Arrhenius theory to solvents other than water. It may be represented by the defining equation ... 

B) From the foregoing, it is clear that the Arrhenius or solvents theory cannot work for aprotic solvents most adequate here is the Bransted-Lowry or proton theory, in which an acid is defined as a proton donor and a base as a proton acceptor, and under conditions such that the acid by donating its proton is converted into its conjugate base, and the base by accepting a proton is converted into its conjugate acid. This mutual relationship is illustrated by the following equilibrium reaction ... 

This example shows also that the proton theory, in addition to being valid for aprotic solvents, also works for amphiprotic solvents, and so represents a more general theory. How in an acid-base titration the theory works out can be followed from the titration of a certain amount of HC1 gas introduced into pyridine as an aprotic solvent ... 

An analogue of the proton theory is found in systems where the oxygen ion O2- is merely split off (without solvation), as illustrated by the following equilibrium reaction ... 

The above solvents theory (A) and proton theory (B) have shown that in theory the neutrality point (of the pure solvent) lies for the amphiprotic solvents at pH = pKs and for the aprotic protophilic solvents at a pH somewhere between the highest acidity (of the protonated solvent) and an infinitely high pH. However, the true pH of the neutrality point of the solvent can only be obtained from a reliable pH measurement and the problem is whether and how this can be achieved. For water as a solvent, the true pH = - logaH+ = colog aH+ is fixed by the internationally adopted convention E°m ( H2(latm) = 0... 

C) The Bronsted-Lowry or proton theory interprets the acid-base reaction as a mere proton exchange between the acid (proton donor) and the base (proton acceptor) however, the Lewis theory or electron theory interprets the reaction as a donation and acceptance of a lone pair of electrons, where the... 

From our previous treatment of the Arrhenius, Bransted and Lewis acid-base theories, the importance of the choice between the divergent solvent types clearly appeared if we now confine ourselves to solvents to which the proton theory in general is applicable, this leads to a classification of eight classes as already proposed by Bronsted35,36 (Table 4.3). 

Lowry is best known to chemistry students through the tradition of eponymony, since the proton theory of acidity is known as the "Bronsted/Lowry theory" of proton donors. His most important experimental investigation likely was a long series of studies on optical rotatory dispersion.49 For our purposes, there is special interest in his discovery of mutarotation in camphor derivatives and his theory of dynamic tautomerism, which led him to an ionic theory of organic reaction mechanisms. 

From the above it is evident that the proton theory of acids has made possible considerable progress in acidic and basic catalysis and even permitted the quantitative prediction of the activity of new catalysts after a few experiments with other acids or bases. In some cases the prediction can be quite accurate (Kilpatrick and Kilpatrick, 42). 

At the same time, based on the proton theory by Bronsted and Lowry, Edward Armand Guggenheim (1901-1970) and John N. Scatchard (1892-1973) formed a specific ion interaction theory. At its basis is a concept of close interactions between individual ions, which are measured by values of interaction coefficients. This theory subsequently formed the foundation of the model of state of real water solution. 

According to proton theory by Johannes Nicolaus Bronsted (1879-1947) and Thomas Martin Lowry (1874-1936), substance exchange by H ions is a very important reaction called acid-base or protolytic (or simply protolysis). 

Bronsted, Johannes Nicolaus (1879-1947) Danish physical chemist in 1923 he introduced the protonic theory of acid-base reactions, simultaneously with the English chemist Thomas Martin Lowry. 

The proton theory emphasizes the important fact that acid-base phenomena can be observed in any solvent or even in the absence of a solvent. It also takes into account the experimental fact that there are many other substances besides the hydroxyl ion which exhibit typical basic properties. Yet it does not recognize the complementary data with regard to acids. The followers of Br0nsted have maintained that only substances capable of giving up protons can be called acids. 

The modern one-element theory of acids and bases is usually credited to Br0nsted and Lowry. They proposed the proton theory independently in 1923. But G. N. Lewis, who set forth his electronic definitions of acids and bases in the same year, also explained the proton-donor concept as a special case of his broader theory. According to the proton theory, an acid donates a proton to a base, and a base accepts a proton from an acid. The acid and base may be either compounds or ions, as shown in the following examples ... 

The proton theory of acids and bases recognizes the existence of a large number and variety of bases, both molecular and ionic hydroxyl ion, amide ion, ethoxide ion, piperidine and other amines alcohols, ethers, acetate ion, hydrosulfide ion, cyanide ion, bisulfate ion, ketones, and many others. It also recognizes that acid-base phenomena do not depend upon the solvent. But its great weakness is that it ignores a large body of experimental data by restricting the use of the word acid to proton donors. For a time the only alternative to the proton theory seemed to be the theory of solvent systems. 

This example is only one of many which could be given to show that the electronic theory of acids and bases includes the proton theory as a special case. The simultaneous coordination and ionization pictured by the electronic theory is equivalent to the pro-ton-transfer mechanism of the Br0nsted theory. The bases of the... 

Such reactions, as well as those of electrolysis and of amphoteric behavior, have been observed in other solvents. Reactions that occur in ammonia, sulfur dioxide, acetic acid, hydrogen sulfide, hydrogen fluoride, phosgene, selenium oxychloride, alcohols, and sulfuric acid are analogous to those that take place in water. Some of them have been interpreted according to the solvent-systems theory others, according to the proton theory. AU of them may be understood more clearly on the basis of the electronic theory of acids and bases. Only a few examples will be discussed here. 

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