Acid-catalyzed ionic decomposition

Acid-catalyzed, ionic decompositions have been reported for peroxyesters, RC(0)—OOR, in which the R group can form a particularly stable carbonium ion, eg, tropybum ion (213). 

For the modeling of the decomposition of glycerol in near- and supercritical water on the basis of elementary reactions, we assumed a combination of a free-radical thermal decomposition model and an acid-catalyzed ionic decomposition model [128]. This is supported by some studies in the hterature, which also include the... 

The reaction chemistry of simple organic molecules in supercritical (SC) water can be described by heterolytic (ionic) mechanisms when the ion product 1 of the SC water exceeds 10" and by homolytic (free radical) mechanisms when <<10 1 . For example, in SC water with Kw>10-11 ethanol undergoes rapid dehydration to ethylene in the presence of dilute Arrhenius acids, such as 0.01M sulfuric acid and 1.0M acetic acid. Similarly, 1,3 dioxolane undergoes very rapid and selective hydration in SC water, producing ethylene glycol and formaldehyde without catalysts. In SC methanol the decomposition of 1,3 dioxolane yields 2 methoxyethanol, il lustrating the role of the solvent medium in the heterolytic reaction mechanism. Under conditions where K klO"11 the dehydration of ethanol to ethylene is not catalyzed by Arrhenius acids. Instead, the decomposition products include a variety of hydrocarbons and carbon oxides. 

The most numerous cases of homogeneous catalysis are by certain ions or metal coordination compounds in aqueous solution and in biochemistry, where enzymes function catalytically. Many ionic effects are known. The hydronium ion H3O and the hydroxyl ion OH catalyze hydrolyses such as those of esters ferrous ion catalyzes the decomposition of hydrogen peroxide decomposition of nitramide is catalyzed by acetate ion. Other instances are inversion of sucrose by HCl, halogenation of acetone by H and OH , hydration of isobutene by acids, hydrolysis of esters by acids, and others. 

The acid-catalyzed decomposition of /i-superoxo complexes of the type [Co(III)2(/>t02)(en)4(NH3)2] involves intramolecular electron transfer with AV around 20cm moP. Reductions by [Fe(CN)e] of [Co(edta)] and [Co(NH3)5py] are outer sphere but, in the latter case, detection of an outer-sphere precursor allows evaluation of A V for electron transfer of 23.9cm moP comparable with other values/ Attempts to rationalize this suggest almost complete electron transfer in the transition state. Similar activation volumes for electron transfer are found in reduction of [(NH3)5CoOH2] by [FeCCN) ], but there is a marked discrepancy in reaction volumes for precursor formation with those of other cobalt(III) oxidants. Such differences may be due in part to solvation effects which vary with ionic strength and the necessity of studying ionic strength dependencies of activation volumes for electron transfer reactions between complex ions has been pointed out. ... 

Kennerly and Patterson (13) studied the effect of several organic sulfur compounds, including thiols, sulfides, a disulfide, sulfonic acids, and a zinc dialkyl dithiophosphate, on the decomposition rate of cumene hydroperoxide in white mineral oil at 150 °C. In each case they found phenol as the major product. They suggested that the most attractive mechanism by which to explain these results involves ionic rearrangement catalyzed by acids or other electrophilic reagents (10) as... 

Proton transfer may proceed directly or via a six-membered cyclic transition state involving a molecule of water. A calculation of the intermediate zwitter-ionic concentration for the hydrolysis of methyl phosphate monoanion, based on the pKa values for methanol and methyl phosphate dianion, predicts the first-order rate coefficient for zwitterion decomposition to be ca. 10 sec-1 at 100°C. This value is in good agreement with the observed rate of hydrolysis and, considering the assumptions involved, with the rate of P-O bond fission of the presumed zwitterionic intermediate (2) formed in the Hg(II) catalyzed solvolysis of phosphoenolpyruvic acid, a model reaction for pyruvate kinase10. 

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