Carboxylate decomposition, residual

Though salt dehydration was not accompanied [27] by particle disintegration, the anhydrous pseudomorph was shown by X-ray diffiaction measurements to be very poorly crystallized (a characteristic feature of many nickel carboxylates). Decomposition in air (554 to 631 K) proceeded at a constant rate (0.1 < nr < 0.8 and = 96 kJ mol" ), ascribed to the operation of an autocatalytic mechanism. The reaction in vacuum (562 to 610 K) gave a sigmoid ar-time curve which was fitted by the Prout-Tompkins equation. Because the activation energy was the same as that for reaction in air, it was concluded that the same mechanism operated. The reaction in air yielded residual nickel oxide, while reaction in vacuum gave the carbide with excess carbon and some oxide. In addition to carbon dioxide, the volatile products of decomposition included water and acetic acid. 

The chemical properties of the residual solid products from metal carboxylate decomposition are largely controlled by the reactant cation present and may include one or more of the following metal, carbide, oxide or oxides, carbonate. 

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. 

The products of decomposition of metal carboxylates vary to some extent with the constituent cation and the final residue is usually either the metal or an oxide, occasionally the carbide and sometimes some elemental carbon deposit. Dollimore et al. [94] have described the use of Ellingham diagrams for the prediction of the composition of the solid products of oxalate decompositions. The complete characterization of residual material can be difficult, however, since the solids may be finely divided, pyrophoric [1010], metallic and amorphous to X-rays. 

After the reaction, 1 ml of water was added to the reaction mixture, and the mixture was adjusted to a pH of 1.0 with concentrated hydrochloric acid while being cooled, and then stirred for 30 minutes, The insoluble matters were filtered off, and the filtrate was adjusted to a pH of 5.5 with triethylamine. This solution was concentrated under reduced pressure, and the residue was diluted with 20 ml of acetone to precipitate white crystals. The crystals were collected by filtration and washed with ethanol to obtain 1.46 g of white crystals of 7-[D(-)-a-amino-(4-hydroxyphenyl)acetamido]-3-methyl-3-cephem-4-carboxylic acid having a decomposition point of 197°C. 

About 23 g (0.095 mol) of l-ethyl-6,7-methylenedioxy-4(lH)-oxocinnoline-3-carbonitrile were added to a mixture of 200 ml of concentrated hydrochloric acid and 200 ml of acetic acid. The resultant reaction mixture was heated under reflux for 18 hours. The excess acids were removed under vacuum, and the residue was taken up in 150 ml of a 5% sodium bicarbonate solution. The resultant solution was treated with 5 g of charcoal and filtered. The filtrate was made acidic by the addition of hydrochloric acid and the resulting precipitate was removed by filtration. 23 g, representing a yield of 91.6% of l-ethyl-6,7-methylenedioxy-4(lH)-oxocinnoline-3-carboxylic acid as light tan crystals which melted at 261°C to 262°C with decomposition were recovered. 

Cyclopropyl-6-fluoro-4-oxo-7-(l-piperazinyl)-l,4-dihydro-3-quinolinecarboxylic acid was synthesized by heating of a mixture of 7-chloro-l-cyclopropyl-6-fluoro-l,4-dihydro-4-oxo-quinolin-3-carboxylic acid and 30.1 g dry piperazine in 100 ml DMSO for 2 hours at 135-140°C. DMSO was evaporated in high vacuum. The residue was heated with 100 ml of water, and was dried over CaCI2 in vacuum. Cyclopropyl-6-fluoro-4-oxo-7-(l-piperazinyl)-l,4-dihydro-3-quinolinecarboxylic acid obtained has a temperature of decomposition 255-257°C. 

The inclusion of heat stabilizers is essential to protect the system against thermal decomposition at elevated temperatures during processing. For this purpose, tin carboxylate esters or liquid calcium-zinc stabilizers are preferred. Thio-tin compounds are very effective as heat stabilizers but must be regarded with caution, bearing in mind that they can lead to unpleasant and unacceptable residual odours. Secondary stabilizers that can be used include epox-idized soya bean oil. 

Esterification of the carboxyl group is usually performed by heating with a 25% solution of HC1 in methanol at 70°C for 30 min and the residue is acylated with TFA anhydride [298,299], Although the acylation proceeds under very mild conditions (20°C) and satisfactory results have been obtained for micromole amounts with the use of the FID, decomposition of the derivatives during the process has been observed when working at the picomole level with the ECD. 

Fig. 1. a-Oxidation of amino acids. Hydroxyl radical (or other reactive radical) abstracts hydrogen atom from the a-carbon. The C-centered free radical formed may react with other amino acid residues or dimerize in the absence of oxygen, which leads to protein aggregation. In die presence of oxygen the carbon-centered radical forms peroxyl radical. Reduction of peroxyl radical leads to protein hydroperoxide. Decomposition of hydroperoxide leads to formation of carbonyl compounds via either oxidative deamination or oxidative decarboxylation. Oxidation of the new carbonyl group forms a carboxyl group. 

Schmitt et worked out an interesting procedure, applicable on a large scale, for introducing alkylaminoalkyl residues in position 10, via the esters of phenothiazine-lO-carboxylic acid (136). On thermal decomposition, the latter eliminate CO2 and give the deri-... 

As seen from Table 6.7.18, the thermal decomposition of poly(methacrylic acid) generates at lower temperature the anhydride, and at higher temperatures undergoes decarboxylation. It can be assumed that the process leads to the formation of unsaturated chains that further decompose to form small hydrocarbon molecules and some aromatic compounds. Residual carboxyl groups may be retained on some of these molecules. 

Decompositions of metal carboxylates (see Chapter 16) can lead to the formation of metal, metal oxide, or metal carbonate, as residual products ... 

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