Carboxylate decompositions, secondary reactions

The experiments of Schwenker and Beck also throw further light on the mechanism of the secondary reactions. In these experiments, cellulose was pyrolyzed in atmospheres of air, nitrogen, and helium, and essentially the same products were obtained, regardless of the conditions of pyrolysis. Therefore, it was concluded that the secondary decomposition reactions must, by-and-large, be non-oxidative in nature, in contrast with the primary reactions of cellulose on slow heating, which involve oxidation of the compound to provide carbonyl and carboxyl groups. 

Decompositions of other metal carboxylates, such as acetates and other anions containing hydrocarbon radicals, give a more complicated range of volatile products and the solid product may also contain the metal carbide, identified as being formed by secondary reactions. It is useful to be able to predict, on thermodynamic grounds, the probable solid product which, in turn, may provide information about the gaseous products to be expected. 

Reactions of carboxylates containing the more electropositive cations yield product carbonates, or sometimes the basic carbonates. Some of these salts, e.g., those of the alkali metals, melt before decomposition. The oxide products from decomposition of the lanthanide compounds may contain carbon deposited as a result of carbon monoxide disproportionation. Kinetic measurements must include due consideration of the possible retention of carbon dioxide by the product (as COj ) and the secondary reactions involved in carbon deposition. 

The kinetics of the decomposition [17] of thorium tetraformate to ThOj can be described by the Prout-Tompkins equation with = 150 kJ mol" from 498 to 553 K. The autocatalytic process was ascribed to participation of the oxide in breakdown of the carboxyl groups at the reaction interface to yield ThOj, formaldehyde and carbon dioxide as the primary products of reaction. The volatile products could, however, react further on the surface of the active solid to yield a number of secondary products amongst which the following gases were identified Hj, CO, HjO, CHjOH, HCOOCHj, HCOOH and (CHj). Addition of nickel formate to the reactant not only accelerated decomposition but also influenced the composition of the gases evolved, yielding predominantly CO, COj and H2 (which are the main products of nickel formate decomposition). 

Because oxidative decarboxylation of carboxylic acids by lead tetraacetate depends on the reaction conditions, the co-reagents, and the structures of the acids, a variety of products such as acetate esters, alkanes, alkenes, and alkyl hahdes can be obtained. Mixed lead(IV) carboxylates are involved as intermediates as a result of their thermal or photolytic decomposition decarboxylation occurs and alkyl radicals are formed. Oxidation of alkyl radicals by lead(IV) species gives carbocations a variety of products is then obtained from the intermediate alkyl radicals and the carbocations. Decarboxylation of primary and secondary acids usually affords acetate esters as the main products (Scheme 13.41) [63]. 

Reaction (a) represents the ketone decomposition, reaction (b) the acid decomposition. E and Ei can be used to represent a variety of different groups. The exact relation of E to the carboxyl group with which it is combined is of secondary importance, as long as it does not change in the course of the reaction. The distribution of the charges, or the valence of the atoms follows from the principles already given. In reaction (6), the acid decomposition, there is apparently no oxidation or reduction involved. This reaction involves the use of concentrated alcoholic alkali, a reagent which is supposed to cause or assist oxida-... 

Mild Hydrolysis. Acetates of primary and secondary alcohols such as cyclopropyl acetate [205] and methyl or ethyl carboxylates (such as the labile cyclopentadiene ester [206]) can be selectively hydrolyzed under mild conditions using PLE, avoiding decomposition reactions which would occur during a chemical hydrolysis under acid or base catalysis (Scheme 2.22). For example, this strategy has been used for the final deprotection of the carboxyl moiety of prostaglandin Ei avoiding the destruction of the delicate molecule [207, 208],... 

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