Carboxylates, ammonium decompositions

Many of these salts melt or sublime before or during decomposition and reaction temperatures generally increase with molar mass. Thermal analyses for a selection of ammonium carboxylates have been given by Erdey et al. [915] who conclude that the base strength of the anion increases with temperature until it reaches that of NH3. Decompositions of ammonium acetate (>333 K) and ammonium oxalate (>473 K) proceed through amide formation. Ammonium benzoate and ammonium salicylate sublime (>373 K) without decomposition but ammonium citrate decomposes (>423 K) to yield some residual carbon. 

Initiation takes place by rapid reaction of an ammonium salt with the anhydride (Eq. (46)) whereby ammonium carboxylate is formed. In the propagation step, the carboxylate anion opens an epoxy ring and forms an ammonium alcoholate (Eq. (47)). The latter reacts with the anhydride to yield another ester bond, and ammonium carboxylate is recovered (Eq. (48)). Termination occurs through decomposition of the ammonium counter ion, the alkoxide anion abstracting a proton from the quaternary nitrogen with the formation of a deactivated tertiary amine. 

Many of these salts melt or sublime either before or accompanying anion breakdown, or other reaction. Decomposition temperatures generally increase with molar mass. Thermal analyses for several ammonium carboxylates have been given... 

The selection of this reagent was based partly on the observation [209] that, because various quaternary ammonium carboxylates undergo thermal decomposition to methyl esters, such esters could be formed in situ in good yield by the simple injection of a methanolic solution of the quaternary ammonium carboxylate above 250°C. Thus, the use of the quaternary ammonium hydroxide in the transesterification scheme described above permits the simultaneous conversion of both glycerides and fatty acids to methyl esters. 

A ring enlargement process was used effectively to access the enantiopure pyrrolo [ 1,4]oxazepine-9a(7//)-carboxylate derivatives 142 and 143. The sequence involved copper (Il)-catalysed decomposition of an a-diazocarbonyl derivative attached to a chiral morpholinone, and a carbenoid, spiro-[5,6]-ammonium ylide, Stevens [1,2] rearrangement sequence. The Stevens and related rearrangements have considerable further potential for novel heterocyclic syntheses <00TA3449>. 

Additional work was carried out by the GE group on optimization of the reaction yield and to eliminate unwanted linear oligomers [14], Three side reactions which interfere with synthesis of cyclics were identified reaction of the amine with acid chloride to form an acyl ammonium salt, followed by decomposition to an amide (Equation (3.2)) reaction with CH2CI2 to form a salt (Equation (3.3)) hydrolysis of the acid chloride, forming carboxylate via catalysis... 

Catalysts suitable specifically for reduction of carbon-oxygen bonds are based on oxides of copper, zinc and chromium Adkins catalysts). The so-called copper chromite (which is not necessarily a stoichiometric compound) is prepared by thermal decomposition of ammonium chromate and copper nitrate [50]. Its activity and stability is improved if barium nitrate is added before the thermal decomposition [57]. Similarly prepared zinc chromite is suitable for reductions of unsaturated acids and esters to unsaturated alcohols [52]. These catalysts are used specifically for reduction of carbonyl- and carboxyl-containing compounds to alcohols. Aldehydes and ketones are reduced at 150-200° and 100-150 atm, whereas esters and acids require temperatures up to 300° and pressures up to 350 atm. Because such conditions require special equipment and because all reductions achievable with copper chromite catalysts can be accomplished by hydrides and complex hydrides the use of Adkins catalyst in the laboratory is very limited. 

Its nitrogen readily becomes pentavalent, forming quaternary ammonium salts. Some derivatives of known properties, useful for qualitative identification are the hydrochloride, white crystals melting at 272° with decomposition the nitrate, m.p. 184-185° the picrate, yellow rhombic prisms (from absolute alcohol) melting at 221-222° to a red oiB the />-toluidine, m.p. 150° and the anilide , m.p. 85°. Alkyl iodides readily react with it to form water-soluble compounds. The carboxylic group of nicotinic acid behaves typically, forming salts with alkalies, alkaline earth hydroxides or heavy metals the latter salts are quite insoluble and their preparation is useful to separate nicotinic acid from mixtures. 

Oxalic and malonic acids, as well as a-hydroxy acids, easily react with cerium(IV) salts (Sheldon and Kochi, 1968). Simple alkanoic acids are much more resistant to attack by cerium(IV) salts. However, silver(I) salts catalyze the thermal decarboxylation of alkanoic acids by ammonium hexanitratocerate(IV) (Nagori et al., 1981). Cerium(IV) carboxylates can be decomposed by either a thermal or a photochemical reaction (Sheldon and Kochi, 1968). Alkyl radicals are released by the decarboxylation reaction, which yields alkanes, alkenes, esters and carbon dioxide. The oxidation of substituted benzilic acids by cerium(IV) salts affords the corresponding benzilic acids in quantitative yield (scheme 19) (Hanna and Sarac, 1977). Trahanovsky and coworkers reported that phenylacetic acid is decarboxylated by reaction with ammonium hexanitratocerate(IV) in aqueous acetonitrile containing nitric acid (Trahanovsky et al., 1974). The reaction products are benzyl alcohol, benzaldehyde, benzyl nitrate and carbon dioxide. The reaction is also applicable to substituted phenylacetic acids. The decarboxylation is a one-electron process and radicals are formed as intermediates. The rate-determining step is the decomposition of the phenylacetic acid/cerium(IV) complex into a benzyl radical and carbon dioxide. 

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