Oxalic and formic acids

In the reaction of oxalic acid with iodate, the oxidising species are molecular iodine and hypoiodous acid (principally the latter). The induction period observed in the reaction is due to build-up of the oxidising species it is shortened by exposure to light or by the presence of metal ions. As soon as the iodine concentration is appreciable, the reaction rate accelerates rapidly on account of the sequence of reactions 

Abel and Hilferding studied the kinetics of the reaction, and showed that the oxidations of oxalic acid and its monoanion by hypoiodous acid are second-order. 

The reaction of formic acid with iodate is similar to the reaction of oxalic acid. Abel and Bildermann studied the kinetics, and showed that molecular iodine and hypoiodous acid are the oxidising species. 

---

Ozonization of phenol in water resulted in the formation of many oxidation products. The identified products in the order of degradation are catechol, hydroquinone, o-quinone, cis,ds-muconic acid, maleic (or fumaric) and oxalic acids (Eisenhauer, 1968). In addition, glyoxylic, formic, and acetic acids also were reported as ozonization products prior to oxidation to carbon dioxide (Kuo et al, 1977). Ozonation of an aqueous solution of phenol subjected to UV light (120-W low pressure mercury lamp) gave glyoxal, glyoxylic, oxalic, and formic acids as major products. Minor products included catechol, hydroquinone, muconic, fumaric, and maleic acids (Takahashi, 1990). Wet oxidation of phenol at 320 °C yielded formic and acetic acids (Randall and Knopp, 1980). 

CASRN 56-40-6 molecular formula C2H5NO2 FW 75.07 Chemical/Physical Products identified from the oxidation of glycine and OH radicals (generated from H2O2/UV) in oxygenated water were oxalic acid, formic acid, and ammonium ions. In oxygen-free water, oxalic and formic acids were not produced, i.e., glycine oxidized directly to ammonium ions. The rate constant for the reaction of OH radicals with the zwitterion ion is 1.7 X 10 /M-sec and with the anionic form is 1.9 x 10 /M-sec (Vel Leitner et al., 2002). 

For reductions in aprotic media, tetraalkylammonium salts of derivatives of oxalic and formic acid may be employed in many cases the reaction may then be performed in an undivided cell, as the reaction at the counterelectrode (oxidation of the anion to carbon dioxide) generally does not interfere with the cathodic reaction [452]. 

Figure 21.6 The photocatalytic mechanism of decomposition of oxalic and formic acids by the Fe203/P25 composite. (Reproduced with permission from Ref. [95].)...

In organic analysis, the oxidizing power of permanganate ions in neutral or weakly alkaline medium permits the determination of some alcohols, oxalic and formic acids, and their salts with the production of carbon dioxide. In these pH conditions, permanganate ions react faster than in acidic medium. 

Positive results in both tests may be given by some nitro-and polyhalogenophenols, some simple acid anhydrides, and some very readily hydrolysable esters (e.g. methyl and ethyl esters of oxalic and formic acid methyl oxalate is a white crystalline solid). For distinguishing test for esters and anhydrides, see pages 58, 59. 

Oxidation. Maleic and fumaric acids are oxidized in aqueous solution by ozone [10028-15-6] (qv) (85). Products of the reaction include glyoxyhc acid [298-12-4], oxalic acid [144-62-7], and formic acid [64-18-6], Catalytic oxidation of aqueous maleic acid occurs with hydrogen peroxide [7722-84-1] in the presence of sodium tungstate(VI) [13472-45-2] (86) and sodium molybdate(VI) [7631-95-0] (87). Both catalyst systems avoid formation of tartaric acid [133-37-9] and produce i j -epoxysuccinic acid [16533-72-5] at pH values above 5. The reaction of maleic anhydride and hydrogen peroxide in an inert solvent (methylene chloride [75-09-2]) gives permaleic acid [4565-24-6], HOOC—CH=CH—CO H (88) which is useful in Baeyer-ViUiger reactions. Both maleate and fumarate [142-42-7] are hydroxylated to tartaric acid using an osmium tetroxide [20816-12-0]/io 2LX.e [15454-31 -6] catalyst system (89). 

Reduction of carbon dioxide takes place at various metal electrodes. The main products are formic acid in aqueous solutions and oxalate, CO, and formic acid in nonaqueous solutions. An indium electrode is the most potential saving for C02 reduction. Due to the difference in optimum conditions between those for C02 reduction to formic acid and those for formic acid reduction to further reduced products, direct reduction of C02 in aqueous solutions without a catalyst to highly reduced products seems to be difficult at metal electrodes. However, catalytic effects of metal electrodes themselves have recently become more clear for example, on Cu, methane was detected, while on Ag and Au, CO was produced effectively in aqueous solutions. Furthermore, at a Mo electrode, methanol was obtained. The power efficiency is, however, still low at any electrode. 

The kinetic parameters for the oxidation of a series of alcohols by ALD are shown in Table 4.1 (74). Methanol and ethylene glycol are toxic because of their oxidation products (formaldehyde and formic acid for methanol and a series of intermediates leading to oxalic acid for ethylene glycol), and the fact that their affinity for ALD is lower than that for ethanol can be used for the treatment of ingestion of these agents. Treatment of such patients with ethanol inhibits the oxidation of methanol and ethylene glycol (competitive inhibition) and shifts more of the clearance to renal clearance thus decreasing toxicity. ALD is also inhibited by 4-methylpyrazole. 

Chemical/Physical. Wet oxidation of 4-nitrophenol at 320 °C yielded formic and acetic acids (Randall and Knopp, 1980). Wet oxidation of 4-nitrophenol at an elevated pressure and temperature gave the following products acetone, acetaldehyde, formic, acetic, maleic, oxalic, and succinic acids (Keen and Baillod, 1985). 

Reactions with organic acids such as formic, acetic, benzoic, oxalic, and salicylic acids produce their corresponding ammonium salts concentrated ammonia solution in excess forms ammonium stearate, CH3 (CH2)i6 COONH4 with stearic acid. 

In a series of transition metal oxide semiconductor powders, photochemical activity in the decarboxylation of oxalic acid was controlled by surface properties and the presence of recombination centers, which in turn depended on the preparation method Similar effects have also been noted in the photodecarboxylation of pyruvic acid and formic acid... 

Studies of the solubility of polonium(IV) in formic, acetic, oxalic and tartaric acids have provided evidence of complex formation,48 with the acetato complex emerging as more stable than the hexachloro anion. Other studies of the solubility of polonium(IV) hydroxide in carbonate49 and nitrate50 solution, together with investigations51 of the ion exchange behaviour of polonium(IV) at high nitrate ion concentration, have been discussed in terms of the formation of anionic complex species. 

---