Oxalic acid stabilizer

In acidic solution, the degradation results in the formation of furfural, furfuryl alcohol, 2-furoic acid, 3-hydroxyfurfural, furoin, 2-methyl-3,8-dihydroxychroman, ethylglyoxal, and several condensation products (36). Many metals, especially copper, cataly2e the oxidation of L-ascorbic acid. Oxalic acid and copper form a chelate complex which prevents the ascorbic acid-copper-complex formation and therefore oxalic acid inhibits effectively the oxidation of L-ascorbic acid. L-Ascorbic acid can also be stabilized with metaphosphoric acid, amino acids, 8-hydroxyquinoline, glycols, sugars, and trichloracetic acid (38). Another catalytic reaction which accounts for loss of L-ascorbic acid occurs with enzymes, eg, L-ascorbic acid oxidase, a copper protein-containing enzyme. 

In context with the formation of peraminosubstituted 1,4,5,8-tetraazaful-valenes of type 85 it must be mentioned that the bis-vinylogous compounds 94 can be easily prepared by reaction of acetamidine with bisimidoylchlo-rides derived from oxalic acid (96S1302). In the course of a complex reaction a cyclic ketene aminal was produced it immediately underwent an oxidative dimerization to yield deeply colored TAFs. Tlieir high chemical stability can be compared with that of indigoid dyes and manifests itself, for example, by the fact that they are soluble in hot concentrated sulfuric acid without decomposition. Tire same type of fulvalene is also available by cy-... 

Ruthenium, iridium and osmium Baths based on the complex anion (NRu2Clg(H20)2) are best for ruthenium electrodeposition. Being strongly acid, however, they attack the Ni-Fe or Co-Fe-V alloys used in reed switches. Reacting the complex with oxalic acid gives a solution from which ruthenium can be deposited at neutral pH. To maintain stability, it is necessary to operate the bath with an ion-selective membrane between the electrodes . 

The oxidation by Mn(lII) chloride involves three complexes and the kinetic data of Taube " are summarised in Table 15. The greater thermal stability of the /m-complex is considered to result from the lowering of the free energy relative to the transition state as compared with bis- and mono-complexes. The study of MnC204 was based on the Mn(III)-catalysed chlorine oxidation of oxalic acid. ... 

The protonated acridine must therefore provide special stabilization to the conjugate bases of small dicarboxylic acids. Evidence for the nature of this special stabilization was provided by some of the receptors which are not constrained to convergent conformations. Figure 2 shows the ambient temperature spectrum of 33 and its simple salts such as the picrate. At low temperature, complex spectra are observed as interconversion between the three possible conformations become slow. In the presence of appropriate diacids such as oxalic acid the spectra are sharpened and are no longer temperature dependent22c). 

Alfalfa, clover High yield, useful for animal vaccines, clonal propagation, homogenous N-glycans (alfalfa) Low protein stability in harvested material, presence of oxalic acid... 

Aliphatic carboxylic acids are difficult to reduce electroehemically. Reduction of a 10% oxalic acid in 10% H2SO4. at 15 °C at a mercury cathode (Refs. [494, 532] in Ref. [29]), a lead or amalgamated lead cathode (Ref. [495] in Ref. [29]) or at a sodium amalgam (Na(Hg) cathode (Ref. [497] in Ref. [29]) produces glyoxylic acid with a material yield of 88% and a current efficiency of 70%. The glyoxylic acid formed is stabilized by hydration [29]. 

Except for phthalic acid, all other carboxylic acids studied induce considerable increases in the light compared to the dark values (the relatively high rate of iron oxide dissolution induced by oxalic acid has been extensively studied (5,8). Phthalic acid actually appears to stabilize the iron oxide against photodissolution despite the solution phase complex exhibiting some photoactivity. 

Mitrovic and Knezic (1979) also prepared ultrafiltration and reverse osmosis membranes by this technique. Their membranes were etched in 5% oxalic acid. The membranes had pores of the order of 100 nm, but only about 1.5 nm in the residual barrier layer (layer AB in Figure 2.15). The pores in the barrier layer were unstable in water and the permeability decreased during the experiments. Complete dehydration of alumina or phase transformation to a-alumina was necessary to stabilize the pore structure. The resulting membranes were found unsuitable for reverse osmosis but suitable for ultrafiltration after removing the barrier layer. Beside reverse osmosis and ultrafiltration measurements, some gas permeability data have also been reported on this type of membranes (Itaya et al. 1984). The water flux through a 50/im thick membrane is about 0.2mL/cm -h with a N2 flow about 6cmVcm -min-bar. The gas transport through the membrane was due to Knudsen diffusion mechanism, which is inversely proportional to the square root of molecular mass. 

One-Step Activation Process. In a one-step activation process, the sensitizing and nucleating solutions are combined into one solution. It is assumed that when this solution is made up, it contains various Sn-Pd chloride complexes (24). These complexes may subsequently transform into colloidal particles of metallic Pd or a metallic alloy (Sn/Pd) to form a colloidal dispersion (19,28). This dispersion is unstable. It may be stabilized by addition of an excess of Sn ions. In this case, Pd particles adsorbed on the nonconductor surface are surrounded by Sn ions. The latter must be removed by solubilizing before electroless plating so that the catalytic Pd on the surface will become exposed, freely available, to subsequent plating. An example of such a solubilizing solution is a mixture of fluoroboric and oxalic acids in a dilute solution, or just plain NaOH or HCl. 

Probably because of its conjugation with the cyclobutene moiety, the DPMA group in the protected amino acids 109 demonstrated an increased stability towards hydrolysis. Nevertheless, deprotection was achieved under acidic conditions [oxalic acid/water in methanol/ether or aluminum trichloride/water (1 2... 

Hydrogen peroxide is more stable in an acidic medium than in an alkaline one, and acids are therefore used as stabilizers. Apart from phosphoric acid, already mentioned, boric acid, oxalic acid etc. may also be used. 

If a powder which decomposes and forms acid products is mixed with a healthy" powder it causes the latter to decompose. The products of decompostion of smokeless powder were found to contain formic add, hydroxypyruvie acid CH2OH- CO COOH, hydroxyisobutyric acid (CH3)2C(OH)COOH and oxalic acid. All these acids except oxalic acid are hygroscopic, hence by increasing the moisture content in the powder, they hasten its decomposition. Acid products react with alkaline stabilizing components. 

This class of compound is represented by the dicyanoiodate(I) anion, involving a pseudohalide rather than an alkyl or aryl ligand. The linear ion, with I—C distance of 2.302 A, has been characterized in the compound K[I(CN)2]C6H12N202, resulting from reaction of an aqueous solution of KCN with an ethanolic solution of ICN. The diimino oxalic acid diethyl ester molecule apparently stabilizes the structure.56... 

Catalytic decarboxylation processes occur in aliphatic keto acids in which the keto group is in an a-position to one carboxyl group and in a P-relationship to another. Thus, the normal decarboxylation of a p-keto acid is facilitated by metal coordination to the a-keto acid moiety. The most-studied example is oxaloacetic acid and it has been shown that its decarboxylation is catalyzed by many metals following the general order Ca2+ < Mn2+ < Co2+ < Zn2+ < Ni2+ < Cu2+ < Fe3+ < Al3"1".66 67 The overall rate constants can be correlated with the stability constants of 1 1 complexes of oxalic acid rather than oxaloacetic acid, as the uncoordinated carboxylate anion is essential for the decarboxylation. The generally accepted mechanism is shown in Scheme 15. Catalysis can be increased by the introduction of x-bonding ligands, which not only increase the... 

L.A.Burrows et al, USP 2376474(1945) CA 39, 3556(1945)(Nitrourea stabilized by blending small amts of non-volatile acid materials, such as oxalic acid, etc) 21)L.A.Burrows, USP 2387742(1945XExplosive rivets) 22)L.A. 

A previously reviewed method was applied for OTC, TC, CTC, DXC, and DMC analysis in tissue and egg samples however, further optimization and improvement were necessary. The optimal recoveries from tissue were obtained using succinate buffer and MeOH as a depro-teinization agent. The eluate from the MCAC column was acidified and further purified on an Empore disk equipped with a poly(styrene-divinylbenzene)-RP sulphonated membrane previously activated with MeOH and hydrochloric acid (pH 1.0). The elution of TCs was done with methanolic ammonia solution. The extract was evaporated under vacuum and reconstituted in oxalic acid solution. Even though the stability of TCs is poor under alkaline conditions, no influence on the recovery was observed (59-76% with RSD < 6.5% for kidney samples) (26). 

Schoneweg, M. Patented in 1887 in Fr the concept of adding oxalic acid and oxalates to gelatinized NC or expl compns, in order to prevent the formation of hot flames as well as to improve their stability (Ref 1)... 

Other oxygen stabilized ethylene dications have been prepared and studied using stable ion conditions. For example, Olah and White were able to observe as early as 1967 diprotonated oxalic acid (74) in FSOsH-SbFs solutions.33 This species and related dications were also studied subsequently by theoretical methods. Diprotonated a-keto acids and esters have likewise been generated in superacidic media, such as 75-77 34... 

The tendency of theophylline to convert to its monohydrate crystal form when exposed to either high relative humidity or bulk water was investigated in its cocrystal products formed with oxalic, malonic, maleic, and glutaric acids [65]. It was found that the theophylline-oxalic acid cocrystal demonstrated superior humidity stability relative to theophylline anhydrate under the conditions studied, while the other cocrystal products appeared to offer comparable stability to that of theophylline anhydrate. These workers concluded that one could demonstrate the feasibility of... 

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