Glyoxalic acid, determination

The extent of oxidation, when determined by the reaction of the product with phenylhydrazine, is 85%. Hydrolysis of the oxidized xylan should produce approximately equimolar quantities of D-glyceraldehyde and glyoxal. Experimental determination of glyceraldehyde indicates 67 % of the theoretical when the oxidized xylan is distilled with sulfuric acid and the evolved methylglyoxal measured as the phenylosazone. Glyoxal is isolated in 63% yield, when separated as the phenylosazone or as the dioxime. Aldehyde groups in the oxidized xylan may be further... 

Derr, W. Organic acids in Virginia tobacco Detection and determination of glyoxalic acid and a-ketoglutaric acid Tabak Eorschung 67 (1957) 53-60. 

Gilbert recently examined the ozonation of maleic and fumaric acids in aqueous solution. In a detailed study, he observed that the concentration of maleic and fumaric acids dropped linearly with time as determined spec-trophotometrically. However, at low concentrations of maleic acid (or toward the end of the reaction) further oxidation of the primary products occurred. Maleic acid consumed 1.28 equivalents of ozone in contrast to Noller s less than theoretical amount. The primary products of reaction, namely, glyoxalic acid and formic acid, reached a maxima (Fig. 3-3) after complete consumption... 

Derivatives of Formaldehyde and Acetaldehyde.—According to Tafel and Pfeffermann,1 the phenylhydrazones of aldehydes are readily converted into amines by reduction in sulphuric-acid solution at a lead cathode. Thus ethylidene phenyl-hydrazine yields about 60% of the theoretical percentage of pure ethylamine salt. The decomposition of glyoxime is more complicated. Besides ammonia and glyoxal and a small quantity of an acid (glyoxylic acid ) there is formed as the principal product the crystalline sulphate of a base, C2H802N2, the nature of which could not be determined with certainty. Ethylenediamine is not formed. Nor was a diamine obtained from methylglyoxime. 

Certain volatile aldehydes such as formaldehyde and methyl glyoxal have always presented some difficulties in the determination of their levels in foods and beverages. Formaldehyde is difficult to extract from an aqueous solution with an organic solvent because it is very water soluble or exists as a polymer in an aqueous media. Methyl glyoxal is also hard to recover from food samples because it exists as a copolymer with some amines such as amino acids and proteins. 

The solution frequently becomes warm,12 and its refractive index,1 viscosity,2 freezing point-composition curve,3 and ultraviolet absorption spectrum 36 are not those which would be expected if no reaction took place. Usually hydrates or hemiacetals of simple aldehydes are too unstable to be isolated, but a number of them are actually known and their physical properties have been determined.4 When the carbonyl group is attached to an electron-attracting group (making the carbonyl carbon atom abnormally positive), stable hydrates are frequently formed. Glyoxal, chloral, and ketomalonic acid are common examples. 

Figure 3.9 Typical capillary gas chromatogram of the derivatives of dicarboxylic acids (C2 Cg), ketocarboxylic acids ( C0C2, C0C4, pyruvic acid), and dicarbonyl (glyoxal) isolated from sea water (Sample collected in the Bay of Marseille (northwestern Mediterranean Sea) in September 2005. Reprinted with permission from Determination of low molecular weight dicarboxylic and ketocarboxylic acids in seawater sample) Tedetti, M, et ai, Analytical Chemistry (1 Sep 2006), 78 ( 7), 6012-6018. Copyright (2006) American Chemical Society).

Imino-Diels-Alder reaction [49] containing the coupling of imine and electron-rich alkene gradually became a powerful tool for the synthesis of quinazohne derivatives [50], In Povarov imino-Diels-Alder reaction, aniline and ethyl glyoxalate were chosen as substrates. And two molecules of a-iminoesters, which were obtained from the condensation of aniline and ethyl glyoxalate, were hypothesized to form the direct additive product. Cascade imino-Diels-Alder reaction conducted by Chenetal. [51] (Scheme 13.11) was extended from the Povarov imino-Diels-Alder reaction. In this research, researchers chose the same substrates as in the Povarov imino-Diels-Alder reaction, adopted various kinds of Lewis acids as catalysts, and finally produced quinazoline derivatives. Iron powder was determined as the optimized catalyst with highest yields. 

Complexometric titration with ethylenedioxy-bis-(ethylenenitrilo)tetraacetic acid (EGTA) has been used for the direct determination of calcium in seawater for several years. A very accurate and simple procedure by visual titration using glyoxal-bis(2-hydroxyanil) (GBHA) as metal indicator has been developed by Tsunogai et al. (1968) and will be described with slight modifications in this text. 

Based on that AA could inhibit the chemiluminescent reaction of glyoxal and potassium permanganate in hydrochloric acid Simultaneous determination of AA and rutin (RT) using partial least squares calibration. Method based on the fact that AA and RT can reduce Fe to Fe + at different reaction rates... 

Wang, S. M., X. M. Fan, X. W Cui, C. Zhang, Z. Yang, and X. W. Zheng. 2012. Potassium permanganate-glyoxal chemiluminescence system for determination of ascorbic acid. Fenxi Shiyanshi 31 23-26. 

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