Phenyl benzoate ions, decomposition

From a study of the decompositions of several rhodium(II) carboxylates, Kitchen and Bear [1111] conclude that in alkanoates (e.g. acetates) the a-carbon—H bond is weakest and that, on reaction, this proton is transferred to an oxygen atom of another carboxylate group. Reduction of the metal ion is followed by decomposition of the a-lactone to CO and an aldehyde which, in turn, can further reduce metal ions and also protonate two carboxyl groups. Thus reaction yields the metal and an acid as products. In aromatic carboxylates (e.g. benzoates), the bond between the carboxyl group and the aromatic ring is the weakest. The phenyl radical formed on rupture of this linkage is capable of proton abstraction from water so that no acid product is given and the solid product is an oxide. 

Figure 5.191 uses the sodium benzoate-induced melt crystallization of bisphenol A-polycarbonate to illustrate its catalyzed decomposition. There are kinetic and product specific indications that rearrangements of phenyl salicylates are forming o-phenoxybenzoates. The phenyl salicylates are created by sodium salicylates that form from carboxylate ions of sodium phenolate. Pyrolysis/mass spectroscopic investigations showed the ultimate formation of cyclical trimmers, dimers, and/or tetramers of bisphenol A-polycarbonate caused by intermolecular transesterifications and/or homolytic reactions [673]. 

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