Protonic acids decomposition

More recently Hand et al. (ref. 9) have studied the decomposition reaction of N-chloro-a-amino acid anions in neutral aqueous solution, where the main reaction products are carbon dioxide, chloride ion and imines (which hydrolyze rapidly to amine and carbonyl products). They found that the reaction rate constant of decarboxylation was independent of pH, so they ruled out a proton assisted decarboxylation mechanism, and the one proposed consists of a concerted decarboxylation. For N-bromoamino acids decomposition in the pH interval 9-11 a similar concerted mechanism was proposed by Antelo et al. (ref. 10), where the formation of a nitrenium ion (ref. 11) can be ruled out because it is not consistent with the experimental results. Antelo et al. have also established that when the decomposition reaction takes place at pH < 9, the disproportionation reaction of the N-Br-amino acid becomes important, and the decomposition goes through the N,N-dibromoamino acid. This reaction is also important for N-chloroamino compounds but at more acidic pH values, because the disproportionation reaction... 

The impact which was made by the writer s revival of the old ester mechanism in the context of polymerisations is attested by the number of polymer chemists who set about examining the validity of the theory experimentally. For example, Bywater in Canada confirmed that during the progress of a polymerisation of styrene by perchloric acid the acid could not be distilled out of the reaction mixture, but after exhaustion of the monomer it could be. This regeneration of the initiating acid after the consumption of the monomer is an often attested characteristic of pseudocationic polymerisations with many different protonic acids it is most simply explained by the decomposition of the ester to an alkene and the acid, i.e., a reversal of the initiation, when the monomer has been consumed. Enikolopian in the USSR found that the effect of pressure on the rate of polymerisation in the same system was not compatible with the propagation step involving an ion, and... 

The mechanism proposed by Schwab for the formic acid decomposition is that two protons of the hydrogen atoms of this compound intrude into interlattice spaces of the catalyst, that the electrons dissolve in the... 

Cince the catalytic activity of synthetic zeolites was first revealed (1, 2), catalytic properties of zeolites have received increasing attention. The role of zeolites as catalysts, together with their catalytic polyfunctionality, results from specific properties of the individual catalytic reaction and of the individual zeolite. These circumstances as well as the different experimental conditions under which they have been studied make it difficult to generalize on the experimental data from zeolite catalysis. As new data have accumulated, new theories about the nature of the catalytic activity of zeolites have evolved (8-9). The most common theories correlate zeolite catalytic activity with their proton-donating and electron-deficient functions. As proton-donating sites or Bronsted acid sites one considers hydroxyl groups of decationized zeolites these are formed by direct substitution of part of the cations for protons on decomposition of NH4+ cations or as a result of hydrolysis after substitution of alkali cations for rare earth cations. As electron-deficient sites or Lewis acid sites one considers usually three-coordinated aluminum atoms, formed as a result of dehydroxylation of H-zeolites by calcination (8,10-13). 

Fig. 8.5. Proton-induced decomposition of W-substituted carbamic acid C into carbon dioxide and a primary ammonium hydrochloride—a reaction occuring in the course of acidic hydrolysis of organic isocyanates.

Fig. 8.6. Proton-induced decomposition of /(/-substituted carbamic acid B into carbon dioxide and a primary ammonium trifluoroacetate—a reaction occuring during the acidic deprotection of a Boc-pro-tected amine.

This is not, of course, the end of the reaction as R+ is very reactive and we shall see the sort of things it can do in Chapters 17 and 19. More commonly, some sort of catalysis is involved in decomposition reactions. An important example is the decomposition of tertiary alcohols in acid solution. The carbon-oxygen bond of the alcohol does not break by itself but, after the oxygen atom has been protonated by the acid, decomposition occurs. 

Acidity in zeolites, particularly Bronsted or proton acidity, was shown many years ago by Rabo, Pickert and co-workers (1 ) to be more complex than was originally proposed. Later it was shown that the thermal treatment of NH4Y zeolite produces a zeolite containing hydroxoaluminum cations as the stable end product, rather than solely protons, in order to balance framework negative charges following the decomposition of the ammonium ions, as established by Breck and Skeels in 1976 (2. ... 

Hydrogen peroxide is formed from (a) the dimerization of hydroxyl radicals (equation 63), (b) the proton-induced decomposition of superoxide ions (equation 64), (c) the reductive electrolysis of O2 in acidic media (eqnation 65), and (d) the base-induced reduction of O2 by 1,2-disubstituted hydrazines (equation 66). ... 

Catalysis by protonic acids accounts for the hydrolysis of fluorides, such as trityl fluoride [31], or elimination of hydrogen fluoride from various systems (Chapter 6), frequently being autocatalytic. The hydrolysis of benzyl fluoride is roughly proportional to the Hammett acidity function [32], which is consistent with the scheme indicated in Figure 5.14 [1, 33]. Indeed, the decomposition of benzyl fluoride, on storage, may be violent [34]. 

The photochemical decomposition of sulfonium or diarylhalonium salts can also lead to the formation of protonic acids subsequently initiating polymerization ) ... 

Reaction with protonic acids 1.5.3.1.3 Thermal decomposition to NH3 ... 

Methods which realize mercury-hydrogen exchange in organomercurials include homolytic decomposition in solvents capable of hydrogen atom transfer, protonolysis by protonic acids and reduction. 

The protonic acid-catalysed decomposition of azides is conceived of tis involving an initial protonation of the a-nitrogen atom, subsequent to which nitrogen may be eliminated either in a non-concerted or a concerted process. 

Acidity and Catalytic Activity of In-SAPO Obtained via Template Induced RSSIE The template decomposition in SAPO s goierates proton acidity that was characterized... 

Significant replacement of monovalent metal cations on layer silicate clay surfaces by protons can occur if the electrolyte concentration is very low. The long-term result, beyond hydrolytic exchange, is acidic decomposition of the clay structure in part, and release of structural AP or Mg + to solution. These multivalent cations may then readsorb onto exchange sites, influencing the rheological properties of clays in very dilute salts. Some of the anomalous behavior of Na -smectites suspended in... 

Sulfided Mo-Y and Ni-Mo-Y catalysts were tested in thiophene hydrodesulfurization and hydrogenation of pentene-1 and cyclopentene. Catalysts were prepared by thermal decomposition of supported Mo(CO)g encaged in Y and stabilized Y zeolites. Cracking ability in both reactions is related to the surface acidity of catalysts but is not parallel to their HDS activity. H S generates protonic acidity over NaY and KY zeolites. Synergetic effect between Ni and Mo sulfided species in HDS reaction was observed. The presence of extra-lattice aluminum in stabilized forms of Y-zeolites favours selectivity towards formation of isopentane and cyclopentane during hydrogenation. 

We now report results of a study of the thermal decomposition patterns in the 4 methyl-substituted ammonium (MA) exchanged Y-type faujasites, detailed transformation of the TTMA form, and the resulting generation of protonic acidity. 

Thus, the differences in activities of protonic acids are due to the quality of the corresponding anion or to its tendency to form chemical bonds with the carbon cation. If the anion is unable to form such bonds without extensive regrouping or decomposition, the addition of the proton is followed by polymerization. Should the reactivity of the anion be suppressed by solvation, the tendency to polymerize is enhanced. Consequently, the efficiencies of protonic acids depend very much upon... 

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