Tartronic oxidation

Rea.ctlons, When free (R-R, R -tartaric acid (4) is heated above its melting point, amorphous anhydrides are formed which, on boiling with water, regenerate the acid. Further heating causes simultaneous formation of pymvic acid, CH COCOOH pyrotartaric acid, HOOCCH2CH(CH2)COOH and, finally, a black, charred residue. In the presence of a ferrous salt and hydrogen peroxide, dihydroxymaleic acid [526-84-1] (7) is formed. Nitrating the acid yields a dinitro ester which, on hydrolysis, is converted to dihydroxytartaric acid [617 8-1] (8), which upon further oxidation yields tartronic acid [80-69-3] (9). 

The appearance of free iodine during the periodate oxidation of compounds having an active hydrogen atom (27) or an ene-diol structure (1,39) has frequently been observed, and this implies that further reduction of iodate, formed from periodate during the main reaction, takes place. It has, in fact, been shown that, in acid solution, iodate is fairly readily reduced by such compounds as triose reductone (27), dihydfoxy-fumaric (39), and tartronic (32) acids. 

However, when we oxidized malonaldehyde (56) in the conditions just described for triose reductone, although formic acid and carbon dioxide were produced in high yields, the periodate consumption was erratic. Similar results were obtained with deoxy sugars. This discrepancy may be caused by the incomplete enolization of the first intermediate, hydroxy malonaldehyde —i.e. tartronic dialdehyde (5,22,32), to triose reductone, or may concern the hydroxylation step itself. 

As to the first point, tartronic dialdehyde (8) could, as has already been suggested (32), be oxidized by classical glycol cleavage to give three molar equivalents of formic acid (and no carbon dioxide) with the concomitant reduction of two (instead of three for the enol form) molar equivalents of periodate ... 

Crystalline triose reductone has been shown (56) by titration with strong base and with iodine, to exist in solution, for practical purposes, entirely as the enol form. In addition, the fact that it reduces exactly three molar equivalents of periodate to give quantitative yields of formic acid and of carbon dioxide indicates that it is also oxidized entirely in this form. However, nothing is known of the rate of enolization of tartronic dialdehyde and the possibility therefore remains that part of it may be oxidized in the dialdehydo form. If this were the case, the results of periodate oxidations would be dependent on the ratio of the rate of enolization of tartronic dialdehyde to the rate of its oxidation by periodate, since the oxidation of triose reductone is, again, for practical purposes, instantaneous. 

The readily oxidised intermediates are probably tartronic and glyoxylic acids in all the oxidations, viz. 

Calcium tartronate was precipitated and hence samples required acidification prior to the filtration step necessary to remove the catalyst. The chief product of over-oxidation was oxalic acid. However, conversion to oxalic acid proceeds at a relatively low rate and yields of the former are consequently high. This is probably partly due to the tartronate being precipitated, effectively hindering further oxidation. 

The reduced catalyst deactivation compared to the analogous oxidations of glycerol and tartronic acid was attributed to the use of the calcium salt rather than the free acid. A recent publication describes a similar observation for the oxidation of sodium gluconate [15]. Sodium ions were assumed to counter catalyst deactivation by neutralizing the acid species responsible. 

Tartronic acid was oxidised to mesoxalic acid on 6%Pt2%Bi/C, prepared by exchange/redox, under acidic conditions (reaction f, Scheme 1) (29% yield at 53% conversion, pH=1.5). Figure 10 shows that the conversion rate of tartronic acid is high at first but decreases as the reaction proceeds, probably because the formed mesoxalic acid is more strongly adsorbed on the surface than tartronic acid. The initial high selectivity tapers off due to over-oxidation. 

Figure 10. Product composition for the oxidation of tartronic acid, obtained at pH=1.5 on 6%Pt2%Bi/C, as a function of time.

From product distribution analysis it could be concluded that larger particles present higher selectivity to glycerate due to the reduction of consecutive reaction, i.e. oxidation of glycerate to tartronate, remaining glycolate amount being almost stable. 

The importance of size control has been depicted for the selective oxidation of glycerol it was shown that by increasing particle size a high selectivity to glycerate has been reached at the expense of the consecutive oxidation of glycerate to tartronate. 

When applied to N-acylglycofuranosylamines, the periodate oxidation showed an abnormal uptake of oxidant ( overoxidation ). For example, when oxidized with lead tetraacetate12 and with periodate,1065 N-acetyl-a-D-glucofuranosylamine (15) afforded formaldehyde (indicating a furanose structure), and it consumed more than 5 moles of oxidant per mole. This result can be attributed to subsequent oxidation of the formic acid produced,69 or to the formation,10 by hydrolysis, of the intermediate 2-hydroxypropanedial (tartron-aldehyde) (77) that would then be oxidized. This tendency to undergo overoxidation has been found common for the furanoid N-acyl-gly cos y lam ines.24,25... 

Some bacteria use a "dicarboxylic acid cycle" to oxidize glyoxylate OHC-COO to C02. The regenerating substrate for this cycle is acetyl-CoA. It is synthesized from glyoxylate by a complex pathway that begins with conversion of two molecules of glyoxylate to tartronic semialdehyde ... 

The Au-catalyzed glycerol oxidation was influenced by the kind of support, the size of Au particles and the reaction conditions such as concentration of glycerol, p02 and molar ratio of NaOH to glycerol. As metal oxide supports showed inferior selectivity to glyceric acid compared to carbons, due to successive oxidation and C—C bond cleavage to form di-adds such as tartronic acid and glycolic acid, research has focused on Au NPs supported on carbon, as in the case of ethylene glycol oxidation [182]. Indeed, the catalytic activity was influenced by the kind of carbon support in terms of porous texture [183]. 

In the a approach by Mombarg et a/.,[59] oxidation of disaccharides, such as trehalose and sucrose (25 mmol), was performed in 25 ml of water at 70 °C, with 100 mg of Ti-MCM-41 (7.2 pmol of Ti) and 25 g of 35 wt% H2O2, at pH = 4. After 20 h of reaction, a deep oxidation is observed leading to C1-C4 mono- and dicarboxylic acids, formic acid, glycolic acid, tartronic acid and tartaric acid. The absence of selectivity is then a major drawback compared with other oxidation processes, but another drawback was identified with Ti leaching from the molecular sieve framework. 

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).

From Glycerol.—This synthesis shows tartronic acid to have the constitution given, i.e., mono-hydroxy malonic acid. It may also be obtained from glycerol by oxidation. In this reaction the two primary alcohol groups in glycerol are both oxidized to carboxyl while the secondary alcohol group remains unchanged. 

Scheme 1. Possible pathways for the oxidation of methyl a-D-glucopyranoside to tartronic acid. The identified products (1-0-methyl glucuronic acid and tartronic acid) are within the frames.

Figure 1. The Ti-MCM-41(100 mg) catalysed oxidation of methyl a-D-glucopyrano-side (5.0 g) with aqueous 35% hydrogen peroxide (25g). The concentration of the substrate and the oxidation products 1-O-methyl glucuronic (x), formic ( ), tartronic ( ) cuid glycolic ( ) acid vs. time (h).

Figure 3. The Ti-MCM-41 catalysed oxidation of a,a-trehalose with hydrogen peroxide. The concentration of the substrate ( ) and the identified oxidation products formic acid ( ), glycolic acid ( ), tartaric acid (x) and tartronic acid (a) vs. time (h).

In aqueous medium in the presence of hydrogen peroxide the titanium leaches easily out of Ti-MCM-41 synthesised by impregnation by bis-cyclopentadienyl titanium dichloride of an all silica MCM-41. The dissolved titanium eatalyses the oxidation of methyl a-D-glucopyranoside to 1-0-methyl glucuronic acid. This product is sensitive to further oxidation to formic, glycolic and tartronic acid. In the oxidation of sucrose and trehalose monocarboxylate are probably formed beside C - C4 mono-and dicarboxylates. 

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

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