Formic acid HCO

Formic acid—HCO,OH—46—occurs in the acid secretion of red ants, in the stinging hairs of certain insects, in the blood, urine, bile, perspiration, and muscular fluid of man, in the stinging-nettle, and in the leaves of trees of the pine family. It is produced in a number of reactions by the oxidation of many organic substances sugar, starch, flbrin, gelatin, albumin, etc. by the action of potash upon chloroform and kindred bodies by the action of mineral acids in hydrocyanic acid during the fermentation of diabetic urine by the direct union of carbon mon-... 

From their Lewis structures, determine the number of o-and 7T bonds in each of the following molecules or ions (a) CO2 (b) thiocyanate ion, NCS (c) formaldehyde, H2CO (d) formic acid, HCO(OH), which has one H and two O atoms attached to C. 

The formyl cation, HCO, is also likely to be an intermediate in the modification of the Koch reaction whereby formic acid reacts with olefins to give carboxyhc acids (20) ... 

Intermediate formation of formyl chloride is not necessary since the actual alkylating agent, HCO", can be produced by protonation of carbon monoxide or its complexes. However, it is difficult to obtain an equimolar mixture of anhydrous hydrogen chloride and carbon monoxide. Suitable laboratory preparations involve the reaction of chlorosulfonic acid with formic acid or the reaction of ben2oyl chloride with formic acid ... 

The decarbonylation of aromatic aldehydes with sulfuric acid" is the reverse of the Gatterman-Koch reaction (11-16). It has been carried out with trialkyl- and trialkoxybenzaldehydes. The reaction takes place by the ordinary arenium ion mechanism the attacking species is H and the leaving group is HCO, which can lose a proton to give CO or combine with OH from the water solvent to give formic acid." Aromatic aldehydes have also been decarbonylated with basic catalysts." When basic catalysts are used, the mechanism is probably similar to the SeI process of 11-38. See also 14-39. 

Methanol still proceeds through an initial C H bond scission, but reacts with water before the OH bond breaks. Alternatively, formaldehyde formation likely occurs along the same pathway as CO formation. This is true if HCO is an intermediate in the decomposition pathway. Furthermore, the lack of a kinetic isotope effect for CH3OD indicates that formaldehyde is not the product of an initial O-H scission.94 Because formaldehyde and formic acid are not the thermodynamically favored products of methanol oxidation, they must be the result of kinetic limitations preventing the full oxidation to C02, analogous to the production of H202 for the reduction of oxygen (see next section). 

HCO.O.OH mw 62.03, OB 0.0%. Prepd as a 90% soln by distilling a mixture of formic acid, lt)0% hydrogen peroxide and sulfuric acid (Ref 2). The soln is more volatile than formic acid, is miscible with water, ale, eth and readily sol in benz or chlf. 

For the calculations in the fourth and sixth columns of Table II we used kn +ferricyanide/k B. +HCO," = 20. This was obtained from the previous results (44) in 0.047 M formic acid (no HuSCh) after [HC02 ], calculated from the pK of formic acid, has been corrected for the effect of the ionic strength. In the more acid region, this correction is larger and less... 

Using the photoionization technique, Matthews and Warneck (j ) measured the appearance potentials of HCO (g) from formaldehyde, formic acid and acetaldehyde as 11.95, 12.79 and 11.79 eV, respectively, whose average yields AjH (CHC0, g, 0 K) - 197.7 1.5 kcal mol", based on the following A H (0 K) data (in units of kcal mol" ) 51.63 for H(g), 9.35 for OH(g), 35.62 for CHg(g), -26.78 for HgCOCg) (2), -88.74 for HCOOH(g) (3) and -37.14 for CHgCHO (4). The appearance potentials obtained from photoionization are several tenths to 1 eV lower than the recent electron impact data (5, 6, 7, 8, 9). The appearance potentials determined by the electron impact method tend to be high because the fundamental nature of the process does not lead to a sharp o pet in contrast to the step-function behavior of photoionization onset. 

The carboxyl group withdraws electron density from the aromatic ring, which implies that the ring donates electrons to the carboxyl group as illustrated by structures 5 and 6 in Scheme 5.11. Such behaviour is acid weakening and benzoic acid (pKa 4.17) is weaker than formic acid (methanoic acid, HCO,H pKa 3.75). Note that electron donation by the phenyl group is apparently less than that of a methyl group, since acetic acid (ethanoic acid pKa 4.76) is a weaker acid than benzoic acid. 

Because of the great potential of methanol as a fuel for low-temperature fuel cells, the electro-oxidation of methanol on Pt or Pt-based alloy electrodes has been studied extensively in the past decades [112-115]. It is generally accepted that methanol is oxidized to CO2 by the so-called dual-path mechanism [112] via adsorbed CO (poison) and non-CO reactive intermediates. The formation of CO by dehydrogenation of methanol has been well confirmed, but no consensus has been reached so far on the nature of the reactive intermediates in the non-CO pathway. Various adsorbates such as CHxOH [116], -COH [116], formyl (-HCO), [117] carboxy (-COOH) [117], a dimer of formic acid [35], and COO [38] have been claimed to be the reactive intermediates from IRAS and other physicochemical measurements. However, the spectra of the reaction intermediates are not well reproduced by other groups. 

The photochemistry of formic acid itself, in ap-H2 matrix, promoted by irradiation at 193 nm, was investigated by Paulson et al Ther authors observed production of HOCO, HCO and atomic hydrogen, besides CO and CO2. The subsequent association reaction between H and formic acid was also investigated in detail and shown to be qualitatively different at 4.3 and 1.9 K. 

Formic acid = methanoic acid HCO H. Acetone = 2-propanone. 

---