Acetate ion, decomposition

Ab initio methods, 147-49 Acetate ion, decomposition, 135 Acetylene, interaction with palladium, tunneling spectroscopy, 435,437f Acid-dealuminated Y zeolites catalytical properties, 183 sorption, 175-78 Acid sites, on zeolites, 254 acidification effects, 266 Acoustic ringing, in NMR, elimination, 386 Active sites, nature, 104 Activity measurements, Co-Mo catalysts, 74 Adsorbed molecules,... 

Metastable 1- and 2-tetralol ions have been found to lose water by specific 1, 4 and 1, 3 eliminations, respectively. Using a type of internal reference method, an isotope effect of 2.0 on loss of water relative to total metastable ion decompositions was obtained for 1-tetralol [345]. The acetoxy derivatives of 1- and 2-tetralol lose acetic acid by specific mechanisms and no isotope effect was observed in either case [923]. 

No dimerization of acetic anhydride has been observed in either die liquid or solid state. Decomposition, accelerated by heat and catalysts such as mineral acids, leads slowly to acetic acid (2). Acetic anhydride is soluble in many common solvents, including cold water. As much as 10.7 wt % of anhydride will dissolve in water. The unbuffered hydrolysis rate constant k at 20°C is 0.107 min 1 and at 40°C is 0.248 min-1. The corresponding activation energy is about 31.8 kj/inol (7.6 kcal/mol) (3). Aldiougli aqueous solutions are initially neutral to litmus, they show acid properties once hydrolysis appreciably progresses. Acetic anhydride ionizes to acetylium, CH CO+, and acetate, CH - CO, ions in the presence of salts or acids (4). Acetate ions promote anhydride hydrolysis. A summary of acetic anhydride s physical properties is given in Table 1. 

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. 

It is possible that some acetate radicals are formed by the direct discharge of the ions as, it will be seen shortly, is the case in non-aqueous solutions but an additional mechanism must be introduced, such as the one proposed above, to account for the influence of electrode material, catalysts for hydrogen peroxide decomposition, etc. It is significant that the anodes at which there is no Kolbe reaction consist of substances that are either themselves catalysts, or which become oxidized to compounds that are catalysts, for hydrogen peroxide decomposition. By diverting the hydroxyl radicals or the peroxide into an alternative path, viz., oxygen evolution, the efficiency of ethane formation is diminished. Under these conditions, as well as when access of acetate ions to the anode is prevented by the presence of foreign anions, the reactions mentioned above presumably do not occur, but instead peracetic acid is probably formed, thus,... 

In non-aqueous solutions the Kolbe electrosynthesis takes place with high eflSciency at platinized platinum and gold, as well as at smooth platinum, anodes increase of temperature and the presence of catalysts for hydrogen peroxide decomposition, both of which have a harmful effect in aqueous solution, have relatively little influence. The mechanism of the reaction is apparently quite different in non-aqueous solutions and aqueous solutions in the former no hydroxyl ions are present, and so neither hydroxyl radicals nor hydrogen peroxide can be formed. It is probable, therefore, that direct discharge of acetate ions occurs at a potential which is almost independent of the nature of the electrode material in a given solvent. The resulting radicals probably combine in pairs, as in aqueous solution, to form acetyl peroxide, which subsequently decomposes as already described. ... 

All these papers, however, have really been concerned with the use of model substances rather than proteins, and it is doubtful whether extrapolation of the results is justified. Thus Zahn and Golsch (1962) studied the alkali decomposition of cystine, cysteine, cystine dihydantoin, lanthio-nine, and lanthionine dihydantoin. It was concluded that cystine decomposes either by mechanism given in Section IV,A,5,a or b, whereas the dithiohydantoin undergoes 8-elimination. The mechanism of decomposition of lanthionine dihydantoin was apparently even more complex and depended on the acetate ion concentration. 

The population of surface defects and coordination vacancies drives alkoxide and carboxylate formation and decomposition. When cations have at least two coordination vacancies, bimolecular reactions are possible (e.g., acetone from acetate ions, dimethylether from methoxy groups). 

Although the emphasis in this chapter is placed on the use of acid anhydrides in the Pummerer reaction, a number of other activating reagents, e.g. acids, in particular p-toluenesulfonic acid, and trial-kylsilyl halides, have been employed. Mention of these reagents is made in cases where their use leads to an improvement in yields or selectivity, or to a transformation which is not possible using an acid anhydride. Acetyl chloride is usually not employed in the Pummerer reaction because of the simultaneous presence of acetate ion and chloride ion in the reaction medium. The product of these reactions is predominantly the thioacetal derived from spontaneous decomposition of the initially formed a-acetoxy sulfide. 

Decomposition of the acetate ion isolated in a potassium iodide matrix was studied [38] (753 to 847 K) by infrared measurements of the quantities of acetate or formate (product) ions present. Reaction, suggested to be controlled by the step ... 

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