Quantitative Determination of Oxalic Acid Using Victoria Blue B Based on a Catalytic Kinetic Spectrophotometric Method

A sensitive catalytic method is developed for the spectrophotometric determination of oxalic acid. The procedure is based on the effect of oxalate on the oxidation of Victoria blue B by dichromate in dilute sulfuric acid medium. The reaction is quantitatively estimated by measuring the decrease in absorbance of Victoria blue B at the maximum wavelength of 610nm after quenching the reaction with tap water. The factors effecting the sensitivity and reproducibility of the reaction were studied. The method is not interfered with by foreign species generally associated with oxalate and oxalic acid. The described method is simple, specific, inexpensive and suitable for oxalic acid concentrations of between 0.06 and 9.0µgmL^–1. It was validated with satisfactory results by determining oxalic acid content in water extracts from plant materials such as spinach and Lathyrus sativus.     

The question of the oxidation of α-hydroxypyridine and nicotinic acid by Fenton's reagent

The oxidation of nicotinic acid and -hydroxypyridine by Fenton's reagent (H₂O₂ + Fe⁺⁺) takes place with the decomposition of the pyridine ring to form oxalic acid. In this process, half the label from the -hydroxypyridine passes into one of the oxygen atoms of the oxalic acid and the other oxygen atoms are derived from the hydrogen peroxide. The oxalic acid isolated from the oxidation of the nicotinic acid contains oxygen from the oxidizing agent. The results obtained show that the hydroxylation of the pyridine ring, apparently preceding its decomposition, takes place with the addition of an OH group containing oxygen from the oxidizing agent to the nucleus.     

Radiolytic Gas Formation in Dilute Oxalic Acid Aqueous Solutions

The radiolytic gas formation in aqueous oxalic acid solutions was studied. The concentrations of ₂ and ₂, the gas phase constituents, were measured. It was found that gas evolution is mainly due to the degradation of both oxalic acid and its radiolysis products.     

Effect of medium pH on chemical selectivity of oxalic acid biosynthesis by <Emphasis Type="Italic">Aspergillus niger</Emphasis> W78C in submerged batch cultures with sucrose as a carbon source

The pH of the medium is the key environmental parameter of chemical selectivity of oxalic acid biosynthesis by Aspergillus niger. The activity of the enzyme oxaloacetate hydrolase, which is responsible for decomposition of oxaloacetate to oxalate and acetate inside the cell of the fungus, is highest at pH 6. In the present study, the influence of pH in the range of 3–7 on oxalic acid secretion by A. niger W78C from sucrose was investigated. The highest oxalic acid concentration, 64.3 g dm^?3, was reached in the medium with pH 6. The chemical selectivity of the process was 58.6% because of the presence of citric and gluconic acids in the cultivation broth in the amount of 15.3 and 30.2 g dm^?3, respectively. Both an increase and a decrease of medium pH caused a decrease of oxalic acid concentration. The obtained results confirm that pH 6 of the carbohydrate medium is appropriate for oxalic acid synthesis by A. niger, but the chemical selectivity of the process described in this paper was high in comparison to values reported previously in the literature.     

草酸电还原反应机理的研究

以硫酸钠溶液作底液,用快速循环伏安和电势阶跃法研究了草酸在铅电极上的电还原机理,测定了草酸电还原第一步反应的动力学参数,并根据循环伏安图比较相同条件下草酸,乙醛酸和乙醇酸的还原峰峰电势,推断出草酸还原的中间产物.研究结果表明,草酸电还原遵从不可逆2电子EE反应机理.     

Conversion of solid amorphous zirconium and hafnium phosphates into alpha crystalline form via molten oxalic acid

Solid amorphous zirconium phosphate /ZPa/ and hafnium phosphate /HPa/ are mixed with an excess of solid oxalic acid dihydrate and are digested in molten oxalic acid. Then oxalic acid is removed by extraction or by heating. The residue is washed with dilute HCl /0.01M/ and redistilled water. By this method -ZP and -HP is formed from amorphous ones.     

Determination of peroxydiphosphate in acid medium with oxalate (i) with silver(I) as catalyst and (ii) in the presence of excess of manganese(II)

Peroxydiphosphate can be determined with oxalate in acid medium in the presence of silver(I). Excess of oxalic acid along with the sample and silver (I) is heated to boiling and the excess of oxalic acid is titrated against standard permanganate. Another method involves boiling for 2 min a mixture consisting of the sample and excess of manganese(II), followed by titration of the resulting Mn(III) or MnO(2) with standard oxalic acid solution.     

Studies on technetium and some carboxylic and hydroxamic acids

Interactions between technetium and salicylic acid, oxalic acid, gentisic acid, dipicolinic acid, pyridine-2,5-dicarboxylic acid, salicylhydroxamic acid, dipicolindihydroxamic acid and 5-methoxycarbonyl-2-pyridinehydroxamic acid are described. The complexation reactions have been investigated (pH, , stability, stoichiometry) and the results obtained have been comparatively evaluated.     

496—Cyclic voltammetric studies on the application of carbon elctrodes in the determination of oxalic acid

The application of carbon paste and glassy carbon electrodes in the analysis of oxalic acid was investigated by comparing the characteristics of cyclic voltammograms of oxalic acid obtained in various supporting electrolytes (acetate, borate, citrate, phosphate, etc.). When a semi-micro carbon paste electrode (area 0.49 cm²) was used, the oxalic acid was oxidized at +1.0 to +1.2 V vs Ag|AgCl yielding current in the μA range (scan rate 50 mV/s) for oxalic acid concentration of approximately 10^?4M. Oxalic acid oxidation was observed under both acidic and alkaline conditions. The presence of chloride ions or oxygen did not have any deleterious effect on the electrode response. The peak current was reproducible for repeated scans obtained with the same electrode after brief stirring. The glassy carbon electrode was found to be less suitable for oxalic acid oxidation studies because the peaks in the voltammograms were poorly defined and the current response was markedly reduced. These investigations suggest that carbon paste electrodes are sensitive and stable for oxalic acid oxidation studies. A plot of the peak currents obtained with carbon paste electrode for different concentrations of oxalic acid between 1×10^?4M to 1×10^?3M was linear and reproducible. It is suggested that a flow through carbon paste electrode coupled to a chromatographic column can be used in the development of a sensitive method for oxalic acid analysis in biological samples.     

草酸对丙烯酸酯-胺体系稳定作用研究

研究了草酸对TEGMA-DMT,TEGA-DMT,HPMA-DMT体系的氧化和聚合的影响。表明微量草酸对丙烯酸酯-胺体系的稳定作用非常突出,比对苯二酚大得多,是此体系有效的稳定剂。认为草酸的稳定作用首先是它抑制丙烯酸酯-胺体系氧化,使体系中不能生成过氧化合物,从而使体系稳定不聚合。     

The role of salicylic acid, L-ascorbic acid and oxalic acid in promoting the oxidation of alkenes with H2O2 catalysed by [MnIV2(O)3(tmtacn)2]2+

The role played by the additives salicylic acid, L-ascorbic acid and oxalic acid in promoting the catalytic activity of [MnIV2(O)3(tmtacn)2](PF6)2 (1(PF6)2, where tmtacn = N,N',N'-trimethyl-1,4,7-triazacyclononane) in the epoxidation and cis-dihydroxylation of alkenes with H2O2 and in suppressing the catalysed decomposition of H2O2 is examined. Whereas aliphatic and aromatic carboxylic acids effect enhancement of the catalytic activity of 1 through the in situ formation dinuclear carboxylato bridged complexes of the type [MnIII2(mu-O)(mu-RCO2)2(tmtacn)2]2+, for L-ascorbic acid and oxalic acid notable differences in reactivity are observed. Although for L-ascorbic acid key differences in the spectroscopic properties of the reaction mixtures are observed compared with carboxylic acids, the involvement of carboxylic acids formed in situ is apparent. For oxalic acid the situation is more complex with two distinct catalyst systems in operation; the first, which engages in epoxidation only, is dominant until the oxalic acid additive is consumed completely at which point carboxylic acids formed in situ take on the role of additives to form a second distinct catalyst system, i.e. that which was observed for alkyl and aromatic carboxylic acids, which yield both cis-diol and epoxide products.     

Separation of Monovalent and Divalent Cations on a Pure Silica Gel Column with Dilute Oxalic Acid Containing 18-Crown-6 as Mobile Phase

Summary Pure silica gel (Pia Seed 5S-60-SIL) has been investigated as a cation-exchange stationary phase for ion chromatography of common monovalent and divalent cations (Li⁺, Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) with conductimetric detection; dilute oxalic acid (0.05 mm oxalic acid, pH 4.1, to 1 mm oxalic acid, pH 3.0) was used as mobile phase. The Pia Seed 5S-60-SIL silica gel acted as a cation-exchange stationary phase for these cations when 0.2 mm oxalic acid at pH 3.6 was used as the mobile phase. Excellent simultaneous separation and highly sensitive indirect conductimetric detection of these cations were achieved in 20 min on a 150 mm × 4.6 mm i.d. Pia Seed 5S-60-SIL silica gel column with 0.2 mm oxalic acid containing 4 mm 18-crown-6 (1,4,7,10,13,16-hexaoxacycloctadecane), pH 3.7, as mobile phase (detection limits (signal-to-noise ratio, 3, injection volume, 20 L), were 0.15 m for Li⁺, 0.16 m for Na⁺, 0.21 m for NH₄⁺, 1.0 m for K⁺, 0.17 m for Mg²⁺, and 0.25 m for Ca²⁺). The proposed IC–CD method was successfully applied to the separation and detection of major cations (Na⁺, NH₄⁺, K⁺, Mg²⁺, and Ca²⁺) in rain and river water samples.     

Volumetric estimation of potassium permanganate and potassium dichromate in mixtures with oxalic acid

1. A simple method has now been developed for the volumetric estimation of potassium permanganate and potassium dichromate in mixtures The method consists in taking an aliquot volume of the mixture in an Erlenmeyer flask, adding sufficient quantities of sulphuric acid and manganous sulphate (catalyst) and titrating with a standard solution of sodium oxalate or oxalic acid run in from the burette, until the colour changes from orange-red to yellow. The oxalic acid run ingives a measure of the permanganate present in the mixture Then the mixture in the flask is titrated with a standard solution of Mohr's salt using diphenylbenzidine as indicator. The volume of Fe⁺² solution run in the second stage gives a measure of the dichromate present in the original mixture. 2. The reverse titration does not give accurate results, because it is affected by the induced reaction between oxalic acid and dichromate which is induced by the reaction between oxalic acid and permanganate during the first stage of the reaction. This induced reaction has been studied in some detail.     

Extraction of Am(III) from different acid media by di-2-ethyl hexyl phosphoric acid containing phosphorous pentoxide

The extraction of Am(III) from nitric, hydrochloric, oxalic, phosphoric and hydrofluoric acids was studied using 0.4F di-2-ethyl hexyl phosphoric acid (HDEHP) containing 0.1M phosphorous pentoxide (P₂O₅) in dodecane/xylene. The extraction with pure 0.4F HDEHP was found to be negligible from all the media studied. However, the presence of a small amount of P₂O₅ in it increased the extraction substantially. The distribution ratios of Am(III) obtained for HDEHP - P₂O₅ mixture 3M nitric acid containing different concentrations of oxalic acid/phosphoric acid/hydrofluoric acid are in the order of 200-250. The same for 3M hydrochloric acid is very high (800). These distribution ratios are sufficiently high for the quantitative extraction of Am(III) from all the acid media studied. Different reagents such as ammonium oxalate, sodium oxalate, oxalic acid, hydrofluoric acid, sodium carbonate and potassium sulphate were explored for the back extraction of Am(III) from 0.4F HDEHP + 0.1M P₂O₅ in dodecane/xylene. Of these, 0.35M ammonium oxalate and 1M sodium carbonate were found to be most suitable. The back extraction of Am(III) was also attempted with water and 1M H₂SO₄, HNO₃, HClO₄ and HCl solutions after allowing the extracted organics to degrade on its own. It was found that more than 90% of Am could be back extracted with these acids. Using this method more than 90% of Am(III) was recovered from nitric acid solutions containing calcium and fluoride ions.     

光-Fe3+-草酸体系中对氯苯酚的冰相光转化

本文利用室内低温反应装置研究了在模拟太阳光-Fe3+-草酸作用下冰相中对氯苯酚（4-CP）的光转化。结果表明,Fe3+-草酸存在条件对冰相中4-CP的光转化有促进作用。Fe3+和草酸初始浓度、Fe3+与草酸的初始浓度比以及初始pH值对体系中4-CP的转化率具有较大影响。当溶液初始pH值为6.50,Fe3+和草酸的初始浓度比是1/5,草酸初始浓度为0.80mmol/L时,4-CP光照7.5h转化率可达39.1%。在光转化过程中,TOC的转化率滞后于4-CP的光转化率。4-CP的光转化符合一级动力学模型。分别利用直接萃取法和衍生化法富集了反应中间产物,并采用GC-MS进行了分析,据此推断了冰相中模拟太阳光-Fe3+-草酸作用下4-CP光转化的反应机理。     

Enhanced degradation of 2,4-dinitrotoluene by ozonation in the presence of manganese(II) and oxalic acid

Manganese catalytic ozonation of 2,4-dinitrotoluene (DNT) in the presence of oxalic acid was studied. The addition of manganese ion (Mn²⁺) or oxalic acid alone in ozonation process did not enhance DNT degradation, but the addition of Mn²⁺ coupled with oxalic acid accelerated degradation of DNT. The DNT degradation efficiency was influenced by carbonate in the catalytic ozonation process. Kinetics study showed that Mn²⁺ catalytic ozonation significantly promoted the decomposition of ozone. Experimental results of electron spin resonance (ESR) demonstrated that addition of Mn²⁺ and oxalic acid produced much hydroxyl radicals in catalytic ozonation system than that in single ozonation system. These results suggested that catalytic ozonation followed hydroxyl radical-type mechanism. Mn²⁺ promoted decomposition of ozone to produce hydroxyl radical and it was oxidized into manganese oxide. Manganese oxide was reduced into Mn²⁺ by oxalic acid, which is the key step of catalytic process. Based on above results, a cycle catalytic mechanism of Mn²⁺ was proposed. Intermediates were determined by HPLC and GC–MS, and they mainly included aromatic organics and aliphatic carboxylic acids.     

反相高效液相色谱法测定植物组织及根分泌物中草酸

采用反相C1 8柱 ,2 2 0nm紫外检测 ,0 .5 %KH2 PO4 0 .5mmol L四丁基硫酸氢铵 (tetrabutylammoniumhydrogensulfate ,TBA) (pH 2 .0 )的水溶液体系 ,可使草酸及其它测试的 6种有机酸及硝酸有效分离。进一步研究了该方法测定植物组织及根分泌物中草酸的效果 ,结果表明其精确灵敏、回收率高、重复性好 ,并且成本低、操作简便 ,可应用于各种生物材料、食品、饮料等产品中的草酸含量检测。     

Spectrophotometric studies on oxidation of some primary alcohols by 2,2′-bipyridinium chromate. A kinetic study

Some primary alcohols were oxidized by 2,2-bipyridinium chromate (BPC) in the presence of oxalic acid and TsOH giving aldehyde as major product. The reactions were carried out in 80% MeCN-DMF (v/v) medium under varied experimental conditions. The rate depends on the first power of the concentration of BPC and fractional power on the concentrations of alcohol, oxalic acid and TsOH.     

草酸处理对丙烷氨氧化催化剂Sb-V-O结构和催化性能的影响

以不同量的草酸处理钒的起始原料,采用共沉淀法制备了VSb3混合氧化物催化剂,运用N2低温吸附、X射线衍射、X射线光电子能谱和H2程序升温还原等方法对催化剂进行了表征,并考察了其在丙烷氨氧化反应中的催化性能.结果表明,草酸的处理可使所得样品中V处于较低的价态,从而有利于活性相SbVO4的生成.当草酸/V(摩尔比)为3时,所制VSb3混合氧化物中存在较多的活性相SbVO4,且其表面具有适量Sb和V的分布,使催化剂具有良好的氧化/还原性能平衡,因而在丙烷氨氧化反应中表现出更高的活性和丙烯腈选择性.     

Use of complexing ligands in the determination of antimony and tin by atomic-absorption spectrometry

The atomic-absorption spectrophotometric determination of antimony is best achieved in the presence of either an ammonium fluoride, hydrochloric acid, nitric acid mixture, or one of the following complexing agents: tartaric acid, citric acid, oxalic acid, 2-mercaptopropanoic acid. The interference of the 29 metals tested is least in the ammonium fluoride-hydrochloric acid-nitric acid mixture and is similar in tartaric acid, citric acid and 2-mercaptopropanoic acid media. However, the interference is pronounced in oxalic acid. Tin can be determined if any of the complexing agents or 6M hydrochloric acid is present.