Formates, decomposition

The subscripts c, r,f, d, and i denote chain, ring, formation, decomposition, and isomerization, respectively. and F, are the amoimts of nitrogen derived from the arenediazoazide and arylpentazole, respectively. 

Bircumshaw and Edwards [1029] showed that the rate of nickel formate decomposition was sensitive to reactant disposition, being relatively greater for the spread reactant, a—Time curves were sigmoid and obeyed the Prout—Tompkins equation [eqn. (9)] with values of E for spread and aggregated powder samples of 95 and 110 kJ mole-1, respectively. These values are somewhat smaller than those subsequently found [375]. The decreased rate observed for packed reactant was ascribed to an inhibiting effect of water vapour which was most pronounced during the early stages. 

References to a number of other kinetic studies of the decomposition of Ni(HC02)2 have been given [375]. Erofe evet al. [1026] observed that doping altered the rate of reaction of this solid and, from conductivity data, concluded that the initial step involves electron transfer (HCOO- - HCOO +e-). Fox et al. [118], using particles of homogeneous size, showed that both the reaction rate and the shape of a time curves were sensitive to the mean particle diameter. However, since the reported measurements refer to reactions at different temperatures, it is at least possible that some part of the effects described could be temperature effects. Decomposition of nickel formate in oxygen [60] yielded NiO and C02 only the shapes of the a—time curves were comparable in some respects with those for reaction in vacuum and E = 160 15 kJ mole-1. Criado et al. [1031] used the Prout—Tompkins equation [eqn. (9)] in a non-isothermal kinetic analysis of nickel formate decomposition and obtained E = 100 4 kJ mole-1. 

It is believed [1135,1136] that the decomposition of metal complexes of salicyaldoxime and related ligands is not initiated by scission of the coordination bond M—L, but by cleavage of another bond (L—L) in the chelate ring which has been weakened on M—L bond formation. Decomposition temperatures and values of E, measured by several non-isothermal methods were obtained for the compounds M(L—L)2 where M = Cu(II), Ni(II) or Co(II) and (L—L) = salicylaldoxime. There was parallel behaviour between the thermal stability of the solid and of the complex in solution, i.e. Co < Ni < Cu. A similar parallel did not occur when (L—L) = 2-indolecarboxylic acid, and reasons for the difference are discussed... 

Co (I I) complex formation is the essential part of copper wet analysis. The latter involves several chemical unit operations. In a concrete example, eight such operations were combined - two-phase formation, mixing, chelating reaction, solvent extraction, phase separation, three-phase formation, decomposition of co-existing metal chelates and removal of these chelates and reagents [28]. Accordingly, Co (I I) complex formation serves as a test reaction to perform multiple unit operations on one chip, i.e. as a chemical investigation to validate the Lab-on-a-Chip concept. 

The following rather different type of catalytic cycle involving formate decomposition explains our observations on the water gas shift reactions catalyzed by M(CO) (M = Cr, Mo, and W) in the presence of a base ... 

Ruthenium carbonyl decomposes the formate ion in basic media, but at a rate slower than the rate of the WGSR. At 100° and 0.10 mM Rug(C0)] 2 under 3 atm N2> the rate of decomposition of trimethyl ammonium formate to H2 and CO2 is 0.6 mmol/hr. Under 5 atm CO the rate is slower (<0.1 mmol/hr), but the overall rate of H2 production is >0.4 mnol/hr. At this low CO pressure, the rate of H2 production directly from CO and H2O is more than three times that from formate decomposition. Furthermore, since increases in CO pressure result in improved H2 production rates (10 mnol/hr at 50 atm CO), while apparently inhibiting the rate of formate decomposition, it may be concluded that formate decomposition has little mechanistic significance in the WGSR activity of Ru (CO)... 

However, while ruthenium carbonyl was found to decompose the formate ion in basic media, the rate was slower (<0.1 mmol trimethyl ammonium formate to H2 and C02 per hour) than the rate of the water-gas shift reaction (>0.4 mmol H2/hr) at 5 atm CO and 100 °C. Increasing CO pressure decreased the formate decomposition rate. However, it was observed that increasing the CO pressure from 5 atm CO to 50 atm increased the H2 production rate to 10 mmol/hr. They proposed, in a similar manner to Pettit et al.,34 a mechanism that involved nucleophilic attack by amine (instead of hydroxide). Activation of the metal carbonyl (e.g., Ru3(CO) 2 cluster to Ru(CO)5) was suggested to be favored by dilution, increases in CO pressure, or, in the case of Group VIb metal carbonyl complexes, photolytic promotion. The mechanism is shown below in Scheme 9 ... 

Bimolecular formate decomposition HC02" + H20 <-> C02 + OH + H2 Leuckart reaction 6... 

Madix and coworkers—facile formate formation/decomposition over Cu (110). In 1979-1981, Madix and coworkers219 220 226 studied formic acid adsorption and decomposition over Cu(l 10) and they showed facile formate production. TPD studies indicated that formate decomposed to yield C02 and H2 at temperatures as... 

Table 53 Suggested link between formate decomposition and the water-gas shift rate257,261...

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