On oxidative decarboxylations with periodic acid.

The behavior of hydroxypyruvic acid, CHzOH. CO. COOH, and some of its transformation products toward periodic acid, treated in detail in the preceding paper (I), suggested an orienting study of the action of this oxidant on glyoxylic acid, CHO. COOH, and other a-keto acids or on compounds giving rise to such keto acids, following oxidation by periodate. While cr-glycols, a-ketols, a-diketones, and cY-keto aldehydes are oxidized by periodic acid, q-keto acids are assumed to be inert to this reagent under the conditions commonly applied. (Compare the survey of the literature in (2).) Tartaric acid is reported to consume only 1 mole of periodic acid (3, 4); the further oxidation of the resulting 2 moles of glyoxylic acid to formic acid and carbon dioxide is claimed to require 36 to 48 hours for completion at room temperature (5). The very slow development of carbon dioxide (within 1 to 4 days) in the course of the oxidation of keto sugars by periodic acid has been attributed to the gradual breakdown of the glyoxylic acid arising as a primary product of the oxidation (6). Similarly, glyoxylic acid originating from the action of periodate on P-hydroxya-amino acids has been reported to be slowly attacked by the oxidant (7), though this action was shown to proceed at a faster rate in the presence of weak alkali (8). Pyruvic acid likewise is degraded slowly (9). The following discussion will attempt to illustrate the extent to which the oxidative decarboxylation by periodate of a-keto acids and compounds giving rise to them may be useful as a diagnostic method. Tartaric acid, as the most thoroughly investigated example of a polyhydroxy acid, will be taken up first, followed in turn by various cu-keto acids, hydroxyamino acids, polyhydroxy acids, keto sugars, polycarbonyl compounds, and malonic and tartronic acids.