Oxalic acid, detection

Sulphuric add test. To 0-5 g. of oxalic acid or of an oxalate, add I ml. of cone. H2SO4 and warm CO and COg are evolved (cf. formic acid). The CO burns with a blue flame. Detect the COg by passing the mixed gases evolved into lime-water. It is essential to test for the COj in a separate reaction, or (if the same test-tube is used) before testing for CO. 

The kinetics of the Ce(IV) sulphate oxidation of oxalic acid are simple second order although the rate coefficient is inversely proportional to both hydrogen and bisulphate-ion concentrations, and it is also reduced at very high oxalic acid concentrations. Values of the activation energy from 13.4+1.5 (ref. 411) to 16.5+0.4 (ref. 409) kcal.mole have been reported. An intermediate has been detected spectroscopically " this decays in first-order fashion with E = 10.5+0.5 kcal.mole" and with a rate independent of acidity. However, the extent of formation of this complex is reduced as the acidity is increased ", and it appears that a less reactive dioxalato complex is formed at higher substrate concentrations ". 

Urea was treated with oxalic acid and carbon. The operation was carried out in the presence of anhydrous copper sulphate in order to detect the water formed, and gases were expected to bubble through a barium hydroxide solution to be able to see carbon dioxide. Unfortunately, the apparatus was closed by mistake. It detonated due to the large quantity of gases formed in the reaction ... 

Mayer, W. J. and Greenberg, M. S., A comparison of differential pulse and D. C. amperometric detection modes for the liquid chromatographic determination of oxalic acid, /. Chromatogr Sci., 17, 614, 1979. 

The first catalysts reported for the electroreduction of C02 were metallophthalocyanines (M-Pc).126 In aqueous solutions of tetraalkylammonium salts, current-potential curves at a cobalt phthalocyanine (Co-Pc)-coated graphite electrode showed a reduction current peak whose height was proportional to the C02 concentration and to the square root of the potential sweep rate at a given C02 concentration. On electrolysis, oxalic acid and glycolic acid were detected, but formic acid was not. Mn and Pd phthalocyanines were inactive, while Cu and Fe phthalocyanines were slightly active. At the potentials used for C02 reduction, M-Pc catalysts would be in their dinegative state, and the occupied dz2 orbital of the metal ion in the metallophthalocyanine was suggested to play an important role in the catalytic activity. 

Cobalt porphyrin derivatives were also reported129 to be active for electrochemical reduction of C02 to formic acid at an amalgamated Pt electrode. More recently, Becker et al have reported130 that Ag2+ and Pd2+ metalloporphyrins acted as homogeneous catalysts for C02 reduction in dry CH2C12 oxalic acid and H2 (its source was not clear) were produced, but no CO was detected. 

While oxidation of p-coumaric acid was occurring, the major intermediates formed are p-hydroxybenzaldehyde and p-hydroxybenzoic acid. Low concentrated aromatic intermediates such as phenol and p-hydroxybenzyl alcohol and traces of hydroxylation products such as, 3,4- dihydroxybenzaldehyde and 3,4-dihydroxybenzoic acid were detected. Furthermore, formic and oxalic acids were the ring-cleavage compounds detected. 

The profile is characterized by substantial amounts of dicarboxylic acids, mainly formed in the oxidation of polyunsaturated Cl8 acids (linoleic acid, 08 2 and linolenic acid, 08 3), which are no longer detected after ageing. The presence of short chain dicarboxylic acid, and in particular of oxalic acid, is also characteristic of aged lipid layers. Moreover, in the 30 35 min interval, several peaks are detected and attributed to oxidized species of unsaturated 08 acids. Figure 7.7 reports the mass spectrum of the peak at 31.84, attributed to 13-OH-9-octadecenoic acid or 14-OH-9-octadecenoic acid. Its... 

It was observed that glutamate and aspartate are diverted predominantly to the synthesis of cell substance rather than to the formation of oxalate. It is not inconsistent to see oc-ketoglutarate being formed from glutamate, while no oxaloacetic acid can be detected in the medium containing aspartate, as the oxaloacetic acid is known to be extremely unstable (2), (62), (Hi). The relatively low yields of oxalic acid, derived... 

Thus maleic acid forms from the hydroquinone and oxalic acid forms from pyrocatechol. However, the intermediate compounds are triplets, so the intermediate steps are spin-resistant and may not proceed in the manner indicated. The intermediate maleic acid and oxalic acid are experimentally detected in this low-temperature oxidation process. Although many of the intermediates were detected in low-temperature oxidation studies, Benson [59] determined that the ceiling temperature for bridging peroxide molecules formed from aromatics was of the order of 300°C that is, the reverse of reaction (3.128) was favored at higher temperatures. 

Oxalic acid was identified as a constituent in a variety of composted organic wastes. Detectable concentrations were reported in all 21 composts extracted with water. Concentrations ranged from 0.60 mmol/kg in a straw + dairy cattle manure to 21.89 mmol/kg in straw + wood bark + dairy cattle manure. The overall average concentration was 9.67 mmol/kg (Baziramakenga and Simard,... 

Spectrophotometry (or colorimetry) has been used to measure chlorine dioxide in water using indicators that change colors when oxidized by chlorine dioxide. Spectrophotometric analyzers determine the concentration of chlorine dioxide by measuring the optical absorbance of the indicator in the sample solution. The absorbance is proportional to the concentration of the chlorine dioxide in water. Indicators used for this technique include jV,jV-diethyl-p-phenylenediamine, chlorophenol red, and methylene blue (APHA 1998 Fletcher and Hemming 1985 Quentel et al. 1994 Sweetin et al. 1996). For example, chlorophenol red selectively reacts with chlorine dioxide at pH 7 with a detection limit of 0.12 mg/L. The interferences from chlorine may be reduced by the addition of oxalic acid, sodium cyclamate, or thioacetamide (Sweetin et al. 1996). 

Other model reactants are simple organic molecules, for example, formic acid [381, 382]. Pt(lll) exerts lower catalytic influence on HCOOH oxidation than do Pt(lOO) and Pt(llO) faces. However, in the presence of Pb adatoms on Pt(lll) a strong catalytic influence has been observed [383]. The poisonous species production in HCOOH oxidation is then inhibited. Electrochemical reduction of CO2 to glycolate/glyoxylate and oxalic acid has been studied [384]. Other products such as formic acid accompanied by CO and methane have also been detected [385]. In the latter case, the efficiency of the competing process of hydrogen evolution has been suppressed to less than 3.5%. 

The aniline blue test was used for the detection of oxalic acid (13). 

An indirect competitive ELISA has been also developed for the determination of streptomycin and dihydrosticptomyciri in milk (24). Prior to the analysis, the milk sample was skimmed and treated with oxalic acid. The antiserum was raised in rabbits using streptomycin linked to a bacterial protein as the antigen. To perform the test, microtiter plates were coated with streptomycin, and antiserum and milk samples were mixed to be added in the wells where they were incubated for 1 h. Depending on the amount of residues in the sample, more or less antibody remained available for binding to the streptomycin coat. A pig antirabbit antibody-enzyme conjugate was subsequently added and incubated for 90 min. Using a suitable substrate, streptomycin and dihydrostreptomycin could be detected down to 1.6 ppb, whereas quantification could be made possible up to 100 ppb when samples were used undiluted. 

---