Formic acid, catalyzed decomposition

Thermolysis of D-fructose in acid solution provides 11 and 2-(2-hydrox-yacetyl)furan (44) as major products. Earlier work had established the presence of 44 in the product mixtures obtained after acid-catalyzed dehydrations of D-glucose and sucrose. Eleven other products were identified in the D-fructose reaction-mixture, including formic acid, acetic acid, 2-furaldehyde, levulinic acid, 2-acetyl-3-hydroxyfuran (isomaltol), and 4-hydroxy-2-(hydroxymethyl)-5-methyl-3(2//)-furanone (59). Acetic acid and formic acid can be formed by an acid-catalyzed decomposition of 2-acetyl-3-hydroxyfuran, whereas levulinic acid is a degradation prod-uct of 11. 2,3-Dihydro-3,5-dihydroxy-6-methyl-4//-pyran-4-one has also been isolated after acid treatment of D-fructose.The pyranone is a dehydration product of the pyranose form of l-deoxy-D-eo f o-2,3-hexodiulose. In aqueous acid seems to be the major reaction product of the pyranone. 

Although sulfur is ordinarily considered a catalyst poison, it has been found to actually accelerate the decomposition of formic acid catalyzed by rhodium (26). In Figure 10 the rate of this reaction, as measured by the evolution of gas, is plotted against the amount of sulfur present. The break in the curve at approximately 5 mg. of sulfur may indicate that a sulfide of rhodium is a more efficient catalyst for this reaction than is rhodium itself. 

Anhydrous, monomeric formaldehyde is not available commercially. The pure, dry gas is relatively stable at 80—100°C but slowly polymerizes at lower temperatures. Traces of polar impurities such as acids, alkahes, and water greatly accelerate the polymerization. When Hquid formaldehyde is warmed to room temperature in a sealed ampul, it polymerizes rapidly with evolution of heat (63 kj /mol or 15.05 kcal/mol). Uncatalyzed decomposition is very slow below 300°C extrapolation of kinetic data (32) to 400°C indicates that the rate of decomposition is ca 0.44%/min at 101 kPa (1 atm). The main products ate CO and H2. Metals such as platinum (33), copper (34), and chromia and alumina (35) also catalyze the formation of methanol, methyl formate, formic acid, carbon dioxide, and methane. Trace levels of formaldehyde found in urban atmospheres are readily photo-oxidized to carbon dioxide the half-life ranges from 35—50 minutes (36). 

PCSs obtained by dehydrochlorination of poly(2-dilorovinyl methyl ketones) catalyze the processes of oxidation and dehydrogenation of alcohols, and the toluene oxidation207. The products of the thermal transformation of PAN are also catalysts for the decomposition of nitrous oxide, for the dehydrogenation of alcohols and cyclohexene274, and for the cis-tnms isomerization of olefins275. Catalytic activity in the decomposition reactions of hydrazine, formic acid, and hydrogen peroxide is also manifested by the products of FVC dehydrochlorination... 

Several compensation effects have been reported for the decomposition of formic acid on metals (231) particular interest has been shown in the silver-catalyzed reaction (19, 35, 232, 233). The available data for this rate process do not, however, define a single compensation relation, and, even for groups of closely related reactions, it is difficult to decide which of the various possible calculated lines provides the most meaningful representation of the kinetic measurements. Values of B and e, obtained from various sets of reported results, extend over a significant range and, moreover, there is an apparent tendency for an increase in the value of one of these parameters to be offset by a diminution in the other. Such behavior can, in the widest sense of the word, be described as compensatory. To illustrate the difficulties inherent in this analysis of the published data, some calculated values of B and e derived from possible alternative groups of observations are discussed here. Values of (log A, E) reported by Sosnovsky (35), for the decomposition of formic acid on silver, may be considered either as the three different lines, Table III, K, L, and M for reactions on the (111), (110), and (100) planes, respectively, or as the single line,Table III, N. These combined data (Table III, N and x on Fig. 6) intersect with the line obtained from a different set of results... 

Compensation trends found for decomposition of formic acid on metal (and other) catalysts are represented diagrammatically in Fig. 7. Line I (Table III, Q) refers to reactions over nickel and copper (3, 190, 194, 236), gold (5,189,237), cobalt (137,194), and iron (194) the observations included in this group were obtained by selection, since other metals, which showed large deviations, were omitted [see also (5), p. 422], Line I is close to that calculated for the reaction catalyzed by nickel metal (Table III, R) (3, 137, 189-194, 238). Lines II (19,233) and III (3, 234, 235) (Table III, O and P) refer to decomposition on silver. The other lines were found for the same rate process on IV, copper-nickel alloys (190) V, oxides (47, 137), VI, tungsten bronzes (239) and VII, Cu3Au (Table III, S) (240a). 

Trillo et al. (47,137) have reported compensation behavior in oxide-catalyzed decomposition of formic acid and the Arrhenius parameters for the same reactions on cobalt and nickel metals are close to the same line, Table V, K. Since the values of E for the dehydration of this reactant on titania and on chromia were not influenced by doping or sintering, it was concluded (47) that the rate-limiting step here was not controlled by the semiconducting properties of the oxide. In contrast, the compensation effect found for the dehydrogenation reaction was ascribed to a dependence of the Arrhenius parameters on the ease of transfer of the electrons to the solid. The possibility that the compensation behavior arises through changes in the mobility of surface intermediates is also mentioned (137). 

Several reports of catalysis of the decomposition of formic acid involving homogeneous transition metal complexes and proceeding by means of metalloformate intermediates have recently appeared in the literature. For example, Rh(C6H4PPh2)(PPh3)2 (8) catalyzes the decomposition of formic acid to C02 and H2 via the intermediacy of the product of oxidative-addition of HCOOH, Rh(HC02)(PPh3)3 (56). -Elimination of the hydride from the... 

The complex /rara-PtH(02CH)[PEt3]2 catalyzes the decomposition of formic acid in the presence of sodium formate. A mechanism based on the equilibria described in Scheme 2 has been proposed by Paonessa and Trogler (60). The role of formate ion is to promote catalysis by reaction with the platinum dimer (10) or the solvated complex [frans-PtH(S)L2]+, where S = acetone, to reform the catalytically active monomeric species 11 and 12. 

If the catalyst to be studied has acidic sites, formic acid may decompose into carbon-monoxide and water according to a class A mechanism (dehydration). We may assume the mechanism of decomposition to be that of an acid catalyzed decarboxylation 63> ... 

For example, Fahrenfort et al. [42] considered the possible role of the intermediate formation of nickel formate in the nickel catalyzed decomposition of formic acid. They showed that when the volatile reaction products were rapidly removed, the carbon monoxide concentration was greater than that expected from the water-gas equihbriiun. When the gaseous products remained in contact with the residual solid, containing catalytically active nickel metal, the [C0]/[C02] ratio was that expected from the water-gas equilibrium. The composition of the primary products thus... 

Reports of investigations of metal-catalyzed decompositions of formic acid have discussed the participation of the metal formate as a reaction intermediate, for example in the decomposition of Ni(OOCH)2 [73]. This indicates the possible value of complementary investigations of both classes of heterogeneous rate processes crystolysis and metal surface chemistry. There is an extensive literature concerned with the decompositions of adsorbed species, including formic acid, at low coverages on almost perfect metal crystal faces. Results of such work may not, however, be directly applicable to the more crowded states existing at solid state reaction interfaces. 

Nitriles [1, 725-726, after citation of ref. 23]. The original method of Backeberg and Staskun23 for conversion of a nitrile to an aldehyde does not proceed well with hindered nitriles in this case, use of moist Raney nickel in formic acid is recommended.233 The formic acid serves as a source of hydrogen, and the nickel catalyzes both decomposition of the acid and reduction of the nitrile. 

As it appeared that the main reactions on different catalytic systems had many features in common, the decomposition of formic acid will in the following chapters be discussed along the lines given by the two main reaction paths. Thus the dehydrogenation both on metals and oxides will be treated in the first part and the second part will be devoted to the dehydration reaction. As the latter reaction is also largely catalyzed in the liquid phase by strong acid, a short discussion of this phenomenon has been included. 

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