Pyruvic acid [127-17-3] , 2-oxopropanoic acid, pyroracemic acid, a-ketopropionic acid, H3C–CO–COOH, Mr 88.06, is the most important a-oxocarboxylic acid. It plays a central role in energy metabolism in living organisms [8]. During exertion, pyruvic acid is formed from glycogen in the muscle and reduced to lactic acid [79-33-4]. In the liver, pyruvic acid can be converted into alanine [56-41-7] by reductive amination. Pyruvic acid was discovered and first described in 1835 by BERZELIUS [9].
Pyruvic acid is totally miscible with water, ethanol, and ether. Pyruvic acid exists in the keto form; the enol form cannot be detected [10].
Chemical Properties Pyruvic acid reacts as both an acid and a ketone. It forms, for example, oximes, hydrazones, and salts. 4,5-Dioxo-2-methyltetrahydrofuran-2-carboxylic acid [24891-71-2] is formed from pyruvic acid either slowly on standing or more quickly under acid catalysis [11].
On standing in aqueous solution, pyruvic acid polymerizes to higher molecular mass products via the dimeric ketoglutaric acid [19071-44-4] and the trimeric aldol product [12] , [13].
Like all 2-oxo acids, pyruvic acid eliminates carbon monoxide on treatment with concentrated sulfuric acid [14].
Oxidation of pyruvic acid gives acetic or oxalic acid [144-62-7] and carbon dioxide, depending on the conditions [15]. Lactic acid is obtained by reaction with reducing agents [1].
Reaction of a-amino acids with pyruvic acid gives, besides carbon dioxide, alanine [56-41-7] (transamination reaction) and the corresponding aldehyde with one carbon atom less [16]. Alanine is also obtained by reductive amination of pyruvic acid [1]. Phenylethylamines react with pyruvic acid to form the corresponding tetrahydroisoquinolines via the Bischler – Napieralski reaction [17]. Reaction with o-phenylenediamines gives quinoxalinols [18]. In a similar reaction the corresponding hydroxypteridines are obtained from 4,5-diaminopyrimidines and pyruvic acid [19].
Pyruvic acid reacts with aldehydes to form the corresponding a-keto-g-hydroxy acids, which then cyclize to butyrolactone derivatives [1] . Friedel – Crafts type reactions of aromatic compounds with pyruvic acid yield diarylpropionic acids. These compounds have achieved a certain degree of importance because they provide a good route to 1,1-diarylethylenes by dehydration and decarbonylation [15] , [20].
Production On an industrial scale, pyruvic acid is produced by dehydration and decarboxylation of tartaric acid [87-69-4] [21]. In this process, pyruvic acid is distilled from a mixture of tartaric acid and potassium and sodium hydrogen sulfates at 220 °C. The crude acid obtained (ca. 60 %) is then distilled in vacuum. The reaction temperature can be lowered to 160 °C by adding ethylene glycol [107-21-1] [22]. Pyruvic acid can also be obtained by the gas-phase oxidation of lactic acid [23] , but this process has not been successful industrially. In contrast, microbial oxidation of D-lactic acid by a new process results in high yields [24]. Microbial oxidation of 1,2-propanediol [57-55-6] to pyruvic acid has also been described [25]. Another process describes the hydrolysis of 2,2-dihalopropionic acids to pyruvic acid [26]. A process for the oxidation of methylglyoxal [78-98-8] with halogens has recently been published [27].
Uses Pyruvic acid is used mainly as an intermediate in the synthesis of pharmaceuticals. It is also employed in the production of crop protection agents, polymers, cosmetics, and foods.
Storage and Quality Specifications Pyruvic acid is stored and transported in tightly closed polyethylene containers. It can be kept for only a limited period and must therefore be stored in refrigerated areas at a maximum of 10 °C. At higher temperature, explosion can occur through spontaneous self-condensation [28]. The concentration of the commercial product is determined acidimetrically and decreases by ca. 1 % per month during storage.
Toxicology Pyruvic acid has a corrosive effect and irritates the eyes, skin, and respiratory passages.
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[28] Sichere Chemiearbeit 29 (1977) 87.