Formic acid synthesis from carbon dioxide

The turnover frequency (TOF = mole of product per mole of catalyst per hour) of this rapid reaction is rather high, with values up to 1400. This reaction, carried out at 50 °C in SC-CO2, is 18 times faster than in conventional tetrahydrofuran under otherwise identical reaction conditions. This formic acid synthesis can be coupled with subsequent reactions by addition of methanol or dimethylamine, this supercritical reaction system provides a highly efficient one-pot route to methyl formate and A,A-dimethylforma-mide, respectively [918]. Another example of a reaction in which carbon dioxide acts as both reactant and reaction medium is the formation of tetraethyl-2-pyranone from hex-3-yne and CO2 in the presence of an Ni(II)-diphosphane catalyst at 102 °C under supercritical reaction conditions [919]. 

The synthesis of cellulose by A. xylinum from various polyalcohols14 is accompanied by the formation of carbon dioxide, formic acid, nonvolatile acids, ketoses and sometimes ethanol. The much greater variety of substrates suitable for cellulose synthesis, as compared with the small number for dextran or levan, may account for the widespread natural occurrence of cellulose. 

From Acetic and Formic Acids.—A fourth method of synthesis from acetic and formic acid esters will be explained in detail in connection with the next acid. All of these syntheses prove the constitution of pyro-racemic acid as an a//>/fa-ketone acid as given. It may be considered as aceto formic acid which is in accord with the fourth method of synthesis. As an acid it forms all acid derivatives and as a ketone it undergoes the characteristic ketone reactions, e.g.y with phenyl hydrazine and hydroxyl amine. On heating to 150° with dilute sulphuric acid in a sealed tube it loses carbon dioxide and yields acet aldehyde. 

Catabolism of tyrosine and tryptophan begins with oxygen-requiring steps. The tyrosine catabolic pathway, shown at the end of this chapter, results in the formation of fumaric acid and acetoaceticacid, Iryptophan catabolism commences with the reaction catalyzed by tryptophan-2,3-dioxygenase. This enzyme catalyzes conversion of the amino acid to N-formyl-kynurenine The enzyme requires iron and copper and thus is a metalloenzyme. The final products of the pathway are acetoacetyl-CoA, acetyl-Co A, formic add, four molecules of carbon dioxide, and two ammonium ions One of the intermediates of tryptophan catabolism, a-amino-P-carboxyrnuconic-6-semialdchydc, can be diverted from complete oxidation, and used for the synthesis of NAD (see Niacin in Chapter 9). 

CO2 reduction at metallic electrodes is generally poorly selective [151]. Monoelec -tronic reduction of carbon dioxide may occur at a platinum cathode in non-aqueous solvents, but at very negative potentials. Catalytic activation of CO2 has been described (e.g. at a cathode modified by a rhenium complex in a hydroorganic solvent) the observed conversions did correspond to the formation of CO and formic acid. In organic synthesis, CO2 was mainly used as an electrophile (toward electrogenerated anions from jt -acceptors or electrogenerated nucleophiles when adequate transition metals ions were present in situ) for the purpose of carboxylation. 

Leitner, W. Carbon-Dioxide as a Raw-Material - The Synthesis of Formic-Acid and Its Derivatives from CO2, Angew. Chem. Int. Ed. Engl. 1995, 34, 2207. (c) Tanaka, K. Carbon dioxide fixation catalyzed by metal complexes Adv. Inorg. Chem. 1995, 43, 409. (d) Ayers, W. M. Ed. Catalytic Activation of Carbon Dioxide, ACS Symposium Series 363, Washington, DC 1988. (e)... 

The carbon dioxide produced from formic acid is then recycled back to the plasma-chemical synthesis (9-61). The cycle (9-61) and (9-62) of lydrogen production from water is especially interesting because the plasma-chemical stage (9-61) does not require thermodynamically sigiuficant energy input. Most of the energy reqtrired for hydrogen... 

Non-Thermal Plasma Synthesis of Formic Acid in CO2-H2O Mixture. Determine the minimum energy efficiency of the plasma-chemical HCOOH synthesis in the CO2-H2O mixture (9-60) required for effective hydrogen production in the double-step cycle (9-60) and (9-61). Assume that thermodynamically about 70% of the total energy required for hydrogen production from water should be consumed in this case for decomposition of formic acid (9-61) to form hydrogen and to recycle carbon dioxide back to the plasma process. 

W Leitner. Carbon dioxide as a raw material the synthesis of formic acid and its derivatives from CO2. Angew Chem Int Ed Engl 34 2207-2221, 1995. 

While efficient avenues for releasing hydrogen from formic acid have been demonstrated, the efficient synthesis of formic acid continues to be a challenge [55]. This state of affairs is smprising, if one considers that the electroreduction of carbon dioxide to formic acid has been studied for more than 140 years, and the first report on the process was published by Royer as early as in 1870 [127]. By the begirming of World War 1, an additional three papers had been released [128-130]. Nevertheless, the process still needs to be optimised for energy efficiency and selectivity [131,132]. 

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