Formic acid from methane

Whereas acetic acid was formed in good yield from ethane, the analogous formation of formic acid from methane proceeded only in low yield because of the general instability of the latter acid under the reaction conditions. Since formic acid is a much less desirable product from methane than is methanol, the possibility of halting the oxidation of methane at the methanol stage was examined. 

Atmospheric oxidation of methane, 81 dimethyl peroxide from, 81 formaldehyde from, 81 formic acid from, 81... 

In formulating a theory for the production of formic acid front methane in the presence of metallic oxides such as copper subaxide at temperatures ranging from 200° to 500° C., Nielson27 assumed the intermediate formation of carbon monoxide and water which then reacted to formic... 

Several hypotheses have been advanced for the mechanism of the aromatization reaction. Heard et al. (1956) suggested that enolization of the 3-0X0 group occurred first, followed by oxidation of the angular C-19 methyl group. Since the removal of methane (from testosterone), methyl alcohol (from 19-hydroxy compounds), or formic acid (from 10-carboxy compounds) is not commonly observed, whereas the splitting off of formaldehyde from the 19-oxo compound is much more likely. Heard con-... 

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). 

Labeling studies indicated that the obtained formic acid was originated from both substrate and solvent. When the catalyst was supported onto silica to provide a heterogeneous catalyst, methane is oxidized at 80 °C and 32 bars CH4 to CH2O (up to 1.1 TON) and HCOOH (up to 27.3 TON). 

A calculation of the temperature dependence of the free energy for the reactions in Eqs. (15)-(18), and hence the electrochemical potential, showed that with an increase in temperature, formic acid formation became more unfavorable.4 In the case of formaldehyde, methanol, and methane formation, the calculation indicated a positive shift in the reduction potential, but of very small magnitude ca. 30 mV for a temperature change from 300 to 500 K, and ca. 20 mV from 500 to 1200 K.4... 

Acetic acid can be synthesized from methane using an aqueous-phase homogeneous system comprising RhCI as catalyst, CO and 02.17 Side-products included methanol and formic acid, although yields of acetic acid increased upon addition of either Pd/C or iodide ions. The active species is thought to be a CH3-Rh(l) derivative, formed from the C-H activation of methane. The activation of ethane was also achieved, although selectivities were lower, with products including acetic and propionic acids and ethanol (Equation (9)). 

Multiple products are possible from C02 hydrogenation, but all of the products are entropically disfavored compared to C02 and H2 (Scheme 17.1). As a result, the reactions must be driven by enthalpy, which explains why formic acid is usually prepared in the presence of a base or another reagent with which formic acid has an exothermic reaction. Of the many reduction products that are theoretically possible, including formic acid, formates, formamides, oxalic acid, methanol, CO, and methane, only formic acid and its derivatives are readily prepared by homogeneous catalysis. 

Vanadium-catalyzed hydroxylation of benzene and cyclohexane has also been obtained with in situ generation of hydrogen peroxide from H2/O2 in the presence of palladium. A similar process has been settled for methane oxygenation to methyl trifluoroacetate and formic acid. Monoperoxovanadate, as well as copper hydroperoxides, have been indicated as the active species for the activation of the C—H bond of methane. 

Another important class of organic compounds that we shall meet frequently, even in the early chapters of the text, are the carboxylic acids. These compounds are characterized by the carboxyl group, — COOH (7). As their names suggest, these compounds are acids. The most common example is acetic acid, CH3COOH (8 formally, ethanoic acid), the acid that gives vinegar its sharp taste. Another simple carboxylic acid is formic acid, HCOOH (9 formally, methanoic acid), the acid of ant venom. Note how the systematic (formal) names of the carboxylic acids are derived from the parent hydrocarbons (ethane and methane, respectively) by adding -anoic acid as a suffix to the stems eth- and meth-. 

Order the following substances from the least to most oxidized carbon Formaldehyde, carbon dioxide, methane, formic acid, methanol. Use the open-chain form of glucose and the structural formula for decanoic acid and this scheme to determine the aver-... 

The simplest alcohol, methanol, is commonly known as wood alcohol, because it was once obtained by heating wood in the absence of air, a process that also produced charcoal. Now methanol is synthesized from methane in natural gas. Methanol itself has a relatively low toxicity. However, methanol is oxidized (metabolized) in the liver to formaldehyde and then to formic acid, both of which are much more toxic. 

As follows from the above, at short contact times (below 2.9 s) the monooxygenase activity of the mimic remains low, whereas catalase activity is maximal (molecular oxygen yield exceeds 90 wt.%). Methanol yield and methane conversion increase with contact time up to r = 10 s and then stabilize at a level of 49-50 wt.% with —96% selectivity. Formaldehyde and formic acid are side products, giving total 2.7 wt.% no CO and C02 are detected in gaseous products. 

In complete combustion, the products from burning wood are carbon dioxide, water, and ash. Other gases and vapors that may be present due to incomplete combustion include carbon monoxide, methane, formic acid, acetic acid, glyoxal, and saturated and unsaturated hydrocarbons (46). The aerosols can alsa contain various liquids such as levoglucosan and complex mixtures. The solids can consist of unburned carbon particles and high-molecular-weight tars. 

The first comprehensive study was made by Taylor and Blacet,20 who studied the nature of the products at 3130 A. at temperatures from 60 to 140°C. and in the presence of large pressures of oxygen (10-124 mm.) Table V. Conditioning of the cell walls by photooxidation or by boric acid helped to reduce the considerable scatter in their experimental results. Analyses, performed mass spectrometrically, gave the main products as carbon monoxide, carbon dioxide, formaldehyde, and water, while minor products were methanol, acetic acid, and a polymeric substance that gradually accumulated on the walls. No methane, ethane, or formic acid was deteoted. 

Figure 5.1.6 Comparison of the energy efficiencies and current densities for C02 reduction to formic acid, syngas, and hydrocarbons (methane and ethylene) reported in the literature with those of water electrolyzers. Efficiencies of electrolyzers are total system efficiencies, while the CO2 conversion efficiencies only include cathode losses and neglect anode and system losses. Adapted from [17],...

Occurrence.—The members of this series of acids are derived from the methane series of hydrocarbons and occur very commonly in nature. In a few cases they are found free as formic acid in ants and nettles and valeric acid in the root of Valeriana. In most cases the acids are combined with alcohols as esters and as such are found in ethereal oils, fats and waxes. This has given them the name fatty acids. 

Methane from Formic Acid by Dii ect Reduction, Arch, Biochem, Biophys, (1960) 91, 159-162. 

Recently, Sen has reported two catalytic systems, one heterogeneous and the other homogeneous, which simultaneously activate dioxygen and alkane C-H bonds, resulting in direct oxidations of alkanes. In the first system, metallic palladium was found to catalyze the oxidation of methane and ethane by dioxygen in aqueous medium at 70-110 °C in the presence of carbon monoxide [40]. In aqueous medium, formic acid was the observed oxidation product from methane while acetic acid, together with some formic acid, was formed from ethane [40 a]. No alkane oxidation was observed in the absence of added carbon monoxide. The essential role of carbon monoxide in achieving difficult alkane oxidation was shown by a competition experiment between ethane and ethanol, both in the presence and absence of carbon monoxide. In the absence of added carbon monoxide, only ethanol was oxidized. When carbon monoxide was added, almost half of the products were derived from ethane. Thus, the more inert ethane was oxidized only in the presence of added carbon monoxide. 

Simply changing the solvent in the Pd-based catalytic system from water to a mixture of water and a perfluorocarboxylic acid (some water is necessary for the reaction see Scheme 6) had no significant effect on product composition formic acid was still the principal product from methane. However, the addition of Cu or Cu chloride to the reaction mixture had a dramatic effect. Methanol and its ester now became the preferred products, with virtually no acetic and little formic acid being formed [40 b]. The activation parameters for the overall reaction determined under the condition when the rate was first order in both methane and carbon monoxide were A = 2 X [O sfa = 15.3 kcal mol . Since methyl trifluoro-acetate is both volatile and easily hydrolyzed back to the acid and methanol, it should be possible to design a system where the acid is recycled and methanol is the end product. Lee and co-workers have recently reported on the further characterization of the catalyst in this bimetallic Pd/Cu system [41]. 

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