Tartronate

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 hydroxylated compound thus formed would be hydroxymalonaldehyde —i.e. tartronic dialdehyde (8). This compound has never been obtained or studied, but its enol form, which is the so-called triose reductone (11) (14), is well known, and it is generally agreed that, in solution, the equilibrium... 

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.

In the presence of Au/C catalyst, the reaction pathway was studied concluding that glycerate/tartronate amounts represents the probe of path a and glycolate of path b [41c] (Scheme 1). The overall selectivity of the reaction is dictated by the balance of path a and b and represents the most valuable parameter to be considered for evaluating the effectiveness of a catalyst. 

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. 

The reaction described is of considerable general utility for the preparation of benzoyloxy derivatives of /8-carbonyl compounds. Thus 0-benzoyl tartronates have been prepared, from which routes to diethyl tartronates and tartronic acids have been developed. Ethyl benzoyloxy cyanoacetates have similarly been prepared and are of potential interest in connection with the chemistry of amino acid precursors. Similarly the benzoyloxy... 

This enzyme [EC 4.1.1.54] catalyzes the conversion of dihydroxyfumarate to tartronate semialdehyde and carbon dioxide. 

This enzyme [EC 1.1.1.60], also referred to as tartronate semialdehyde reductase, catalyzes the reversible reaction of (i )-glycerate with NAD(P)" to produce 2-hy-droxy-3-oxopropanoate and NAD(P)H. 

A second atom of oxalyl has not been produced in glycerin, so as to convert the latter into a dibasie acid but there can be little doubt that tartronic add, which is formed by the spontaneous decomposition of nitrotartoric add, is the acid in question, and that it has the following constitution —... 

Onl two acids belonging to this series are known, viz. tartronic acid and. malic acid. Like lactic acid, thejr both contain an atom of fwnhom Uo hydroxyl —... 

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