Hydroxypyruvic acid, oxidation

Dihydroxyacetone is not stable under the basic conditions preferred for oxidation of the primary function to give hydroxypyruvic acid (reaction e). Under acidic conditions the rate of oxidation of a 1 mol I l aqueous solution is veiy slow (5 mol h l mol i(Pt)). On platinum the initial rate of conversion for reduced concentrations of the starting material (0.3 mol whilst retaining the same amount of catalyst, was 42 mol h mol-i(Pt), as might be expected under non-favourable acidic conditions. Hydroxypyruvic acid is evolved with a selectivity of 82% at 40% conversion (see Figure 11). 

The Pt/C catalyst, compared with Pd/C, showed not only enhanced activity (vide supra) but also reduced selectivity for glyceric acid (only 55% at 90% conversion), favoring dihydroxyacetone formation up to 12%, compared with 8% for the Pd case [48]. The Pt/C catalyst promoted with Bi showed superior yields of dihydroxyacetone (up to 33%), at lower pHs. Glyceric and hydroxypyruvic acids, apparently, are formed as by-product and secondary product, respectively [48], The addition of Bi seems to switch the susceptibility of glycerol oxidation from the primary towards the secondary carbon atoms. 

Furthermore, a base-catalyzed transformation by OH from the reaction medium between glycerate and hydroxypyruvate aldehyde (or hydroxypyruvic acid) could be excluded, while hydroxyacetone and glyceraldehyde interconversion was possible (Scheme 11.11). The existence of two major routes, of which hydroxyacetone and glyceric aldehyde are the primary oxidation products and glycolic and oxalic acid are the end-members, respectively, is now firmly established. Clearly, rapid oxidation of glyceraldehydes favors glyceric acid rather than hydroxyacetone formation. 

As shown in Scheme 3.4, there are several reaction pathways of glycerol oxidation to form dihydroxyacetone, glyceric acid, hydroxypyruvic acid, mesoxalic acid, and so on. Dihydroxyacetone is formed by the oxidation of a secondary hydroxy group under... 

In a critical study of the periodate oxidation of raffinose and related oligosaccharides, Courtois and Wickstrom showed78 that 1 mole of raffinose reduces 5 moles of periodate, with the formation of 2 moles of formic acid plus a hexaldehyde. Conversion of the aldehyde to the hexa-carboxylic acid, followed by hydrolysis, gave the expected amounts of glyoxylic acid, glyceric acid, hydroxypyruvic acid, and glycolaldehyde (by decarboxylation of hydroxypyruvic acid). 

Figure 2.2.12 Reaction network of glycerol oxidation (GLY, glycerol DHA, dihydroxyace-tone GLA, glyceric aldehyde GLS, glyceric acid HBT, hydroxypyruvic acid MOS, mesoxalic acid TS, tartronic acid GOX, glyoxal GOS, glycolic acid GYS, glyoxylic acid OS, oxalic acid).

Sucrose was oxidized by Fleury and Courtois, who obtained a tetra-aldehyde (87) which was oxidized by bromine, in the presence of strontium or barium carbonate, to the corresponding tetracarboxylic acid salt the latter compound was hydrolyzed with acid to yield D-glyceronic acid, glyoxylic acid, and hydroxypyruvic acid, which spontaneously decomposed into carbon dioxide and glycolaldehyde. It was found that oxysucrose shows four aldehyde groups from hypoiodite estimation, but only two from mercurimetry the latter result was attributed to steric hindrance, but it would seem more likely that, under the conditions of the determination. 

Oxidation — Apart from C02 and H20, there are three series of products that result from the oxidation of saccharide. They are 2,3-dialdehydes (5.43 and 5.49) formed on the oxidative cleavage of saccharides (5.42 and 5.48) with periodates, the sole oxidants providing such course of oxidation. Such dialdehydes are considered toxic. Further oxidation of dialdehydes leads to glyceric acid (5.45), glyoxalic acid (5.47), hydroxypyruvic acid (5.46), and erythronic acid (5.51), as shown below for the oxidative cleavage of sucrose (5.42) and maltose (5.48). 

Selective oxidation with air of glyceric to hydroxypyruvic acid and tartronic to mesoxalic acid on PtBi/C catalysts... 

Figure 3 Product distribution for the oxidation of glyceric acid on Pt(4.3%)Bi(3.9%)/C at (a) pH 2, (b) pH 4, (c) pH 5 and (d) pH 6, as a function of time (A - glyceric acid, O -hydroxypyruvic acid, o- oxalic acid and - glycolic acid).

Activity and selectivity data for the oxidation of glyceric acid to hydroxypyruvic acid. 

Over-oxidation of the hydroxypyruvic acid to oxalic and glycolic acids reduces the selectivity in all cases and there appears to be a dependence on pH since increasing quantities of these by-products are evolved at higher pH. This may be because the rate of decarboxylation of hydroxypyruvic acid increases with pH and/or that the rate of the main reaction decreases with an increase in pH. At pH 2, levels of these by-products are negligible. 

Although plants and bacteria do not have the ability to do so, most animals can convert phenylalanine to tyrosine (Haslam, 1974). C6-C2 compounds are probably formed by a-oxidation of ketoacids such as phenylp)nuvic (10) and p-hydroxypyruvic acid (11). One well-known example, phen-ylacetic acid (8), is common in plants (Gross, 1981). Mammals and some microorganisms convert phenylalanine and t5rrosine to another C6-C2 compound, homogentisic acid (9) (Fig. 8.3). 

It was observed some years ago that in vitamin C-deficient guinea pigs the hydroxylation of tyrosine is inhibited and hydroxypyruvic acid, the deamination product, is excreted. These observations are of little practical interest because the enzymatic block is not manifested unless large amounts of tyrosine are administered to the individual. Since this original observation was made, ascorbic acid has been thought to be involved in several other dehydroxylation reactions, but the mechanism by which it acts is not clear. It probably involves the oxidation of ascorbic acid in the presence of a suitable metal. However, several reducing substances (glucoascorbic acid, isoascorbic acid, dichlorophenylindophenol, and hydroquinone) are active. 

When kidney slices act on n-serine it is oxidatively deaminated to hydroxypyruvic acid. D-Amino acid oxidase is not believed to be involved because the purified enzyme attacks DL-serine very slowly or not at all. 

Beziat, J., Besson, M. and GaUezot, P. (1996). Liquid Phase Oxidation of Cyclohexanol to Adipic Acid with Molecular Oxygen on Metal Catalysts, Appl. Catal. A Gen., 135, L7—LI 1. Abbadi, A. and vanBekkum, H. (1996). Selective Chemo-Catalytic Routes for the Preparation of Beta-Hydroxypyruvic Acid, A/7/ Z. Catal. A Gen., 148, pp. 113-122. 

Human and animal metabolism oxidatively degrade (2R 3R)-tartaric and meso-tartaric acids into glyoxylic and hydroxypyruvic acids respectively ... 

The acceptor aldehyde can be glycolaldehyde, 3-p-glyceraldehyde, 5-p-ribose, or 5-p-desoxyribose. There are really two quite separate processes which are catalyzed by Racker s yeast enzyme first, a non-oxidative decarboxylation of hydroxypyruvic acid to active glycolaldehyde and CO2 second, a transketolation of active glycolaldehyde from the enzyme to the acceptor aldehyde. One must conceive of the enzyme as the bearer of a keto group (ECO) which reacts with hydroxy-pyruvate to form an acyloin, with CO2 being liberated in the process ... 

In addition, incomplete oxidation of polyols leads to production of higher valued chemicals, such as dihydroacetone, which is a valuable tanning agent, hydroxypyruvic acid, which is a flavor component and a possible starting material for DL-serine synthesis, and tartronic and mesoxalic acids, which are important intermediates for novel polymer and pharmaceutical synthesis. Therefore, research on cogeneration of electricity and higher valued chemicals from polyols... 

Aldehydes have been formed from alcohols by the use of other oxidizing agents. Dihydroxyacetone has been oxidized with excess cupric acetate to hydroxypyruvic aldehyde in 87% yield. p-Cyanobenzyl alcohol treated at 0° with a chloroform solution of nitrogen tetroxide gives practically pure p-cyanobenzaldehyde (90%). Aromatic alcohols containing nitro groups have been oxidized to the corresponding nitro aldehydes with concentrated nitric acid, e.g., o- and p-nitrobenzaldehydes (80-85%). m-Nitrobenzenesulfonic acid in basic media has been used for the oxidation of substituted benzyl alcohols, most satisfactorily for the water-soluble phenolic benzyl alcohols. Selenium dioxide, or less effectively tellurium dioxide, oxidizes benzyl alcohol slowly to benzaldehyde. ... 

PtBi/C catalysts were reported earlier to enable selective oxidation of the secondary hydroxy function of glyceric and tartronic acid to hydroxypyruvic and mesoxalic acid, respectively [13]. In the work reported here, these two reactions were studied in more detail to determine Ae influence of the following parameters on selectivity and reaction progress pH of the reaction medium, over-oxidation of targeted products, and leaching of catalyst components. 

Under acidic conditions, bismuth-promoted platinum catalysts selectively oxidise the secondary hydroxy function of glyceric and tartronic acids to their respective keto-acids hydroxypyruvic and mesoxalic acids. A complexing mechanism is proposed to increase the rate of oxidation of the secondary hydroxy function. 

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