Acetic oxygen exchange with

If a zeolite with a low Si/AI ratio is exchanged with a large monovalent cation, e.g. Cs+ in zeolite X, one obtains a weakly basic catalyst (CsX). The basic sites in this case are the oxygen framework atoms of the zeolite itself. Much stronger basic sites are formed when a zeolite or MCM-41 support is overexchanged or impregnated with, e.g. Cs acetate, and subsequently calcined (34). This results in formation of Cs20 oxidic particles. 

The initial step in the microbiological metabolism of lysine to acetate, butyrate, and ammonia is the reversible interconversion of L-lysine and L-jS-lysine via exchange of the a-amino group and a /8-proton catalyzed by lysine 2,3-aminomutase (Scheme 49). The reaction has been observed in several species of Clostridium, Nocardia, and Streptomyces (218, 219), but the mechanistic studies have concentrated on the enzyme from Clostridium subterminale SB4, which has been purified and characterized (220). The enzyme is extremely sensitive to reversible oxygen inactivation, with reactivation achieved by anaerobic incubation with a thiol and Fe(II), and a protein-bound Fe(II) is apparently required for activity (220). The exchange reaction is also accelerated by S-... 

Mesityl oxide is oxygenated under irradiation in methanol in the presence of copper(II) sulfate to give a peroxy acetal via photoenolization and stabilization of the s-cis conformation of dienol by Cu(II) the intermediate peroxyhemiacetal undergoes exchange with the solvent to generate the peroxyacetal (Scheme 19) [43]. 

If the carbonyl oxygen of methyl and ethyl acetate exchanges with the solvent under the conditions of acid-catalyzed hydrolysis in the same way as ethyl benzoate, and if it is assumed that exchange and hydrolysis go by the same intermediate, then the mechanism is the slow bimolecular addition to the ester protonated on the carbonyl oxygen. Asknes and Prue (1959) have presented other evidence suggestive of carbonyl-oxygen protonation. 

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