Oxalic pyrolysis

Boldyrev et al. [46] identified the C - C link as the least stable bond, which may be broken as the initial step during oxalate pyrolysis ( 204 - 2CO ). These radicals (COj") may react in three ways (i) revert to oxalate, (ii) form (OCOCOj) COj + CO, or (iii) reduce the cation (-+ M + 2CO2). The common initial step explains the similar values of for decompositions of several oxalates (often about 170 kJ mol ). This is lower than the energy of rupture of the C - C bond... 

NaOH at approx. 200 C. Pyrolysis then gives sodium oxalate. 

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]. 

Finely divided oxide may be obtained by pyrolysis of cadmium salts of carboxylic acids, such as cadmium formate or oxalate ... 

A variety of pyrrole ring closure reactions are conveniently formulated as proceeding via nitrene intermediates, although it is doubtful whether a free nitrene is involved. Pyrolysis of o-nitrobiphenyls with iron(II) oxalate (61T(16)80), or reduction under milder conditions with triethyl phosphite (65JCS4831) or tris(trimethylsilyl) phosphite (79TL375), leads to the carbazole, as does the pyrolysis or photolysis of 2-azidobiphenyls (Scheme 3) (75JA6193). 

Muchall et al. (98CC238) have recently investigated the gas-phase thermolysis of 2,5-dihydro-2,2-dimethoxy-2,5,5-trimethyl-l//-l,2,4-oxadiazole (75) by PE spectroscopy. Decomposition of 75 was induced by means of a continuous wave (CW) C02 laser as directed heat source at 26 W, which corresponds to a temperature of 500 50°C. When the PE spectra of acetone, tetramethoxyethene, and dimethyl oxalate were subtracted from the pyrolysis spectrum, a sim-ple spectrum remained that could be identified as that of dimethoxycarbene. Thermolysis in solution (94JA1161) had shown formation of tetramethoxyethene, and FVP experiments (92JA8751) gave dimethyl oxalate, both of which arise from the common precursor, dimethoxycarbene. Thermolysis of oxadiazolines similar to 75 in solution affords dialkoxycarbenes via an intermediate carbonyl ylide (94JOC5071). 

Because of the low reactivity of chromium(III) oxide, lithium chromium(III) oxide is prepared by pyrolysis of the oxalate Li[Cr(H20)2(C204)2], which is prepared by the reduction of chromium(VI) oxide.3... 

During their attempts to synthesize disaccharides, Freudenberg and WolP discovered that the pyrolysis of bis(2,3 5,6-di-O-isopropylidene-D-mannofuranosyl) oxalate afforded a low yield of bis(2,3 5,6-di-0-isopro-pylidene-D-mannofuranosyl) carbonate, with the elimination of carbon monoxide. 

A similar cyclization occurs also on pyrolysis with a reducing agent (e.g., ferrous oxalate) of the nitroether (9), proceeding through an intermediate monoaminodiphenyl ether.30... 

Dry methods and postcalcination methods The industrial micron sized R2O3 powder is commonly made by thermal pyrolysis of rare earth carbonates or oxalates at a temperature of 600-1000 °C. The dry methods usually result in fine powders with a relatively wide size distribution. After the sintering, the surface OH and other solvent related species are generally removed, therefore, the powder may exhibit better luminescence efficiency and longer decay time. Nano-sized rare earth oxide products could be obtained from finely selected precursors like hydroxides gels, premade nanostructures, through heat treatment, spray pyrolysis, combustion, and sol-gel processes. 

CdO is obtained by burning the metal in air or by pyrolysis of nitrates, carbonates, formate, or oxalate the last two, in... 

Carbon dioxide, 0=C=6 , mp —57°C (5.2 atm), bp —79 °C (sublimes), is obtained from the combustion of carbon and hydrocarbons in excess air or oxygen or by the pyrolysis ( calcination ) of CaCOs (limestone). The photosynthesis in plants reduces CO2 to organic matter, but the similar reduction of CO2 in a nonliving system ( in vitro ) appears to be very difficult. However, CO2 can be reduced electrochemically to methanol, formate, oxalate, methane, and/or CO depending upon the conditions. Numerous transition metal complexes of CO2 are known,which exhibit the modes of metal-C02 bonding depicted in Figure 2. 

This method can also be used in the determination of the DA of chitin based on reactive pyrolysis gas chromatography in the presence of oxalic acid aqueous solution. The DA could be determined from chromatography of the characteristic products of thermal decomposition of chitin in the absence of oxygen. 

Acylation of ketones by diethyl oxalate (cf. method 203) gives a,"/-diketo esters from which (5-keto esters are obtained by pyrolysis at 175° over powdered glass and powdered iron, ... 

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. 

The Naval Ammunition Depot (NAD) at Crane, Indiana has developed improved fire-retardant phenolic foams containing blends of boric/oxalic acids as catalysts, as described above. The resultant foams were found to be extremely efficient fire barriers due to their high heat absorptivity, the amount of carbon and/or coke produced during pyrolysis, and the adhesion of the char to the burned materials. Other advantages of the foam during flaming and nonflaming pyrolysis are its low smoke emissions and lack of toxic fumes other than carbon monoxide. It takes one hour to reach 230°F (110°C) when a 13 Ib/tf (208 kg/m ) phenolic foam specimen 2.9 inches (7.4 cm) is exposed to a fully developed fire (41). 

---