Oxalates, mixed, decompositions

It is well known that a mixed solution of ordinary mercuric chloride and ammonium oxalate undergoes decomposition when exposed to light, mercurous chloride being precipitated and carbon dioxide evolved. The reaction may be represented by the equation... 

Ubaldini and coworkers [79] studied the thermal decomposition of the mixed oxalates (Cei xGdx)2(C204)3-nH20. The mechanisms of decomposition of Ce and Gd oxalate are different, and mixed oxalates behave in an intermediate way. Their dehydration stages are more similar to those of Gd oxalate, because not all the molecules of water are equivalent, as they are in the cerium oxalate. The decomposition leads to (Cei xGdx)02-x/2- For x close to 0 or to 1, two solid... 

Specific Volume of Gases Formed on Explosion. 723ml/g (NG 712ml) (Ref 46) Stabilization. Chromatographically pure Mannitol Hexanitrate was mixed with varying percentages of 22 stabilizers and the mixts tested for stability in the 100° heat test best results were obtained with a mixt of 96% MHN, 2% Amm oxalate, and 2% dicyandiamide (4.07% wt loss after 48 hours, 5.74% after 96 hours) (Ref 56). The use of ethylene oxide as a stabilizer is reported in Ref 27 Thermal Decomposition. Slow heating causes decompn at 150° with evolution of red fumes (Ref 20, p 249)... 

Decompositions of oxalates containing the strongly electropositive metals yield an oxide product but the more noble elements yield the metal. Discussion of the mechanisms of these reactions and, in particular, whether metal formation necessarily involves the intermediate production of oxide which is subsequently reduced by CO has been extended to consideration of the kinetics of pyrolysis of the mixed oxalates [32]. 

Barium acetate converts to barium carbonate when heated in air at elevated temperatures. Reaction with sulfuric acid gives harium sulfate with hydrochloric acid and nitric acid, the chloride and nitrate salts are obtained after evaporation of the solutions. It undergoes double decomposition reactions with salts of several metals. For example, it forms ferrous acetate when treated with ferrous sulfate solution and mercurous acetate when mixed with mercurous nitrate solution acidified with nitric acid. It reacts with oxahc acid forming barium oxalate. 

In an atmosphere of nitric oxide, thermal decomposition produces barium nitrite, Ba(N02)2. Reactions with soluble metal sulfates or sulfuric acid yield barium sulfate. Many insoluble barium salts, such as the carbonate, oxalate and phosphate of the metal, are precipitated by similar double decomposition reactions. Ba(N03)2 is an oxidizer and reacts vigorously with common reducing agents. The solid powder, when mixed with many other metals such as aluminum or zinc in their finely divided form, or combined with alloys such as... 

K. G. Thurnlackh and K. F. von Hayn prepared a mixed soln. of potassium chlorate and chlorite by the action of potassium hydroxide free from chlorine on a soln. of chlorine dioxide. Light was carefully excluded, and the soln. was evaporated in vacuo at 45°-50°—potassium chlorate separated out first, and after further evaporation, alcohol was added, and the clear alcoholic soln. evaporated. Needle-like crystals of potassium chlorite, KC102, were obtained which deliquesced on exposure to air. As already indicated in connection with the preparation of the acid, G. Bruni and G. Levi made the potassium chlorite by reducing a soln. of potassium chlorate with oxalic acid and A. Reychler, sodium chlorite, by the action of chlorine dioxide on a soln. of sodium peroxide. Sodium chlorite, NaClQ2, can be also made by double decomposition by treating a soln. of barium chlorite with sodium sulphate and evaporating the clear soln. in vacuo. 

If a powder which decomposes and forms acid products is mixed with a healthy" powder it causes the latter to decompose. The products of decompostion of smokeless powder were found to contain formic add, hydroxypyruvie acid CH2OH- CO COOH, hydroxyisobutyric acid (CH3)2C(OH)COOH and oxalic acid. All these acids except oxalic acid are hygroscopic, hence by increasing the moisture content in the powder, they hasten its decomposition. Acid products react with alkaline stabilizing components. 

Loss of a carbon atom from the precursor need not always result. Barton and Crich have introduced a related procedure based on the chemistry of mixed oxalates, an example of which is provided in Scheme 49.159 Double decarboxylation is involved in the decomposition of oxalate precursors, such as (39). Unfortunately, there are indications that this method may to be limited to tertiary alcohols one secondary alcohol derived mixed oxylate did not fragment completely to the alkyl radical. 

In the case of transition metal oxides, mixed-valence compounds may resnlt if the decomposition is carried out in air. Thus, highly pure NiO and MnO can be obtained by heating the respective carbonates in vacno while nearly stoichiometric FeO is obtained by the decomposition of its oxalate but it will rapidly pickup oxygen when exposed to air. Conversely, decomposition of Fe2(Ox)3 yields Fe203. 

Ceda-based oxides can be obtained by the decomposition of some compound precursor, such as hydroxide, nitrate, halides, sulfates, carbonates, formates, oxalates, acetates, and citrates.For example, nanosize or porous cerium oxide particles have been prepared at low temperatures by pyrolysis of amorphous citrate," which is prepared by the evaporation of the solvent from the aqueous solution containing cerium nitrate (or oxalate) and citric acid. In the case of mixed oxides, the precursor containing some cations in the same solid salts is prepared. In the same manner of ceria particles, the precursors complexing some cations with citrates are useful to synthsize ceria-zirconia mixed oxides and their derivatives. Also. Ce02-Ln203 solid solutions, where Ln = La. Pr, Sm. Gd. and Tb, have been synthesized from the precursors obtained by the evaporation of nitrate solutions at 353 K in air from an intimate mixture of their respective metal nitrates. The precursors are dried and then heated at 673 K to remove niU ates, followed by calcination at 1073 K for 12h. 

One of the simplest methods of preparation is by decomposition of a thermally unstable compound. The nitrate or chloride is often preferred, sulphates tend to decompose at higher temperatures. Where the presence of residual traces of anion is to be avoided, the metal salts of organic acids are particularly useful. Formates, oxalates, acetates etc, decompose at low temperatures and often reduce the metal at the same time. For the preparation of catalysts from anions, the ammonium salt is frequently used. Metallic salts of complex acids can be used as a source of metal oxide mixtures. Decomposition of the appropriate chromate, tungstate, molybdate or vanadate will produce the mixed oxide. 

An interesting mixed-ligand complex is [Tc(dppe)2(ox)j, prepared by the reduction of TCO4 by dppe in hot ethanol in the presence of oxalic acid. The average Tc-0 bond distances of 2.13(1) and 2.12(1) A in two independent molecules are somewhat longer than those found in other oxalato complexes (197). Reaction of (NH4)2[Tc Clg] with diethyl phenylphosphonite in the presence of BH4" yields the yellow octahedral rans-[Tc HPhP(OEt)2 4Cl2l, with Tc-P and Tc-Cl bond distances both 2.41(1) A. The low measured magnetic moment of 1.4 BM has been ascribed to partial decomposition (198). 

Behaviour depends on the cation present. Studies of the decompositions of some mixed formates, e.g. Ni - Mg [22], Zn - Ba [23] and Cu - Ba [23], have been reported. Sodium and potassium formates melt prior to anion decomposition and reaction is believed [24] to proceed through the intermediate COj". In the absence of oxygen, this entity dimerizes to yield the oxalate, whereas in the presence of oxygen the dismutation reaction, which produces carbon monoxide and carbonate, is preferred. 

Iron(n) oxalate dihydrate loses water above 420 K to yield the anhydrous salt [53] in an inert atmosphere, but in the presence of oxygen FejOj may be formed [54]. At about 590 K the anhydrous oxalate decomposed slowly to yield magnetite and iron but no wustite was detected [53]. Kadlec and Danes [55] showed that the ar-time curves are sigmoidal and Zr, = 167 kJ mol. During decomposition of the mixed (Fe-Mg) oxalates, magnesium may stabilize the wustite product against either oxidation or reduction [56]. 

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