Pyruvic acid, hydration

Lubineau and coworkers [18] have shown that glyoxal 8 (Ri = R2 = H), glyoxylic acid 8 (Ri = H, R2 = OH), pyruvic acid 8 (Ri = Me, R2 = OH) and pyruvaldehyde 8 (Ri = H, R2 = Me) give Diels-Alder reactions in water with poor reactive dienes, although these dienophiles are, for the most part, in the hydrated form. Scheme 6.6 illustrates the reactions with (E)-1,3-dimethyl-butadiene. The reaction yields are generally good and the ratio of adducts 9 and 10 reflects the thermodynamic control of the reaction. In organic solvent, the reaction is kinetically controlled and the diastereoselectivity is reversed. 

Methyl-1,2-benzenediamine (215, R = Me) with the hydrate of 3,3,3-trifluoro-pyruvic acid gave a mixture of isomers (216, R = Me) and (217, R = Me) (dioxane, reflux, 30 min 98%) from which neither appears to have been isolated in a pure state in contrast, 4-nitro-1,2-benzenediamine (215, R = NO2) and the same synthon gave a mixture of 6-nitro- (216, R = NO2) and 7-nitro-3-trifluoromethyl-2(l//)-quinoxalinone (217, R = NO2) (dioxane, reflux, 4 h 95%), from which both isomers were isolable, albeit with... 

This explanation is supported by nmr rate data for the dehydration of hydrated pyruvic acid, which is similar to glyoxalate. For this at 25 °C... 

An aqueous solution of glyoxylic acid reacts with cyclopentadiene to provide a-hydroxy-y-lactones the more acidic the solution, the faster the reaction (Scheme 13) [68]. Thus at pH 0.9 (2.25 M glyoxylic acid solution in water) the reaction is complete after 90 min at 40 °C providing a 83 % yield of a-hydroxy-y-lactones. In the case of cyclohexadiene, the reaction is complete after 2 days at 90 °C in water, compared to 21 h at 120 °C for the reaction with butyl glyoxylate in neat conditions (Scheme 13). These results show that it is possible to exploit the die-nophilic character of a carbonyl group in water in spite of its quasi total hydration. Pyruvaldehyde, glyoxal, and even ketones like pyruvic acid, also react with dienes in water [69]. 

Non-specific solute-solvent interactions are reviewed elsewhere in this Volume (p. 83). However certain interactions that are chemical in nature and can be studied by n.m.r. will be mentioned. These include the hydration of pyruvic acid and hydration and hemiacetal formation from carbonyl compounds. 

The first action is probably the hydration of cellulose and its breakdown to pyruvic acid and hydrogen. This is endothermic, so that pyruvic acid is not likely to be found as an end product. 

Materials Catalysts (5% metal content, pre-reduced in Ha at 3(XM(X) °C before use) and solvents were of commercial migin. Substrates and modifiers were either commercially available or prepared according to literature procedures. Benzylidenepyruvic acid was obtained by condensation of benzaldehyde and pyruvic acid in presence of KOH, the acid hydrate was isolated by pouring a warm, saturated solution of the K-salt into excess 2N aqueous HCl [4a]. 

T>-Lactose hydrate HCOCOOH Pyruvic acid, Levulinic acid Acetals (NH,kCOs... 

A stirred slurry of 2.93 g 0-(5-benzyloxy-3-indolyl)-Qf-sulfhydrylacrylic acid (9 mmol) in 10 mL absolute ethanol was treated with 2.4 mL 99-100% hydrazine hydrate (0.048 mol), and the mixture was heated under nitrogen. Reaction occurred at 60" C, accompanied by vigorous evolution of H2S. After the mixture was refluxed for 2 h, the liberation of H2S had ceased (no black precipitate when a stream of nitrogen was passed through the reaction solution and exited into aqueous lead acetate), and the flask was allowed to cool to room temperature. The crystalline product, the hydrazine salt of j0-(5-benzyloxy-3-indolyl)pyruvic acid hydrazone, was filtered, washed with cold ethanol (3x8 mL), and then dried. It weighed 2.35 g and was found to be analytically pure. 

Benzoy lace tone Quinones, p-Benzoquinone, Anthraquinone Diphenoquinones Ketenes, CH2— CO, (CsH,)2C CO Monosaccharides T>-Lactose hydrate HCOCOOH Pyruvic acid, Levulinic acid Acetals (NHJ2COS... 

Step 6 is the final step in the cellulose-to-lactic acid cascade, involving the isomerization of the 2-keto-hemi-acetal (here pyruvic aldehyde hydrate) into a 2-hydroxy-carboxyhc acid. This reaction is known to proceed in basic media following a Cannizzaro reaction with 1,2-hydride shift [111], Under mild conditions, Lewis acids are able to catalyze this vital step, which can also be seen as an Meerwein-Ponndorf-Verley reduction reaction mechanism. The 1,2-hydride shift has been demonstrated with deuterium labeled solvents [110, 112], Attack of the solvent molecule (water or alcohol) on pymvic aldehyde (step 5) and the hydride shift (step 6) might occur in a concerted mechanism, but the presence of the hemiacetal in ethanol has been demonstrated for pyruvic aldehyde with chromatography by Li et al. [113] andfor4-methoxyethylglyoxal with in situ CNMRby Dusselier et al. (see Sect. 7) [114]. 

The enzyme Is capable of catalysing other reactions such as hydrolysis of some carboxylic, sulfonic and carbonic esters (2-4) and the reversible hydration of aldehydes (5-7) and pyruvic acid (8), although with much smaller rates as compared with the hydration of CO2. 

There is a paradox with hetero Diels Alder reactions. In water the carbonyl group of the dienophile is mostly under the hydrate form, making the cycloaddition difficult, owing to the relatively low concentration of the reactive form of the carbonyl group. However different carbonyl compounds were tested with success by Lubineau, such as pyruvic acid, pyruvaldehyde and glyoxal (Scheme 4). ... 

D-Lactose hydrate Pyruvic acid, Leuulinic acid Acetals (NHJ2CO3... 

In an earUer paper (1958) the authors described an enzyme system from another Pseudomonas species, which catalyzed the formation of p3nmvic from acetylene dicarboxyUc acid. They reason that the jS-addition of the negative ion to yield malonic semialdehyde which occurred with propioUc acid is expected and that pyruvic acid would not be the expected product of hydration of propioUc acid. Accordingly, even aUowing for the fact that a different enzyme is involved, the production of p3nmvic acid from acetylene dicarboxyUc acid indicates that hydration precedes decarboxylation. This is in agreement with Eimhjellen s findings. In the Pseudomonas system, however, oxaloacetic acid was not found as a free intermediate. 

Even when a-ketoacids play an important role as a link between the metabolism of carbohydrates and proteins and their solution chemistry should be of general interest, quantitative information regarding positions of acid-base, keto-enol, and hydration-dehydration equilibria established in their dilute aqueous solutions is rather limited. Only properties of pyruvic acid were studied extensively, but those of a-ketoglutaric acid received only limited attention 2, jj ost... 

Hydrazinium metal pyruvates [N2H5]2M[CH3COCOO]4, where M = Co or Ni, are prepared from aqueous solution containing a mixture of the respective salts, pyruvic acid, and hydrazine hydrate [11]. The magnetic moments and electronic spectra of the complexes suggest a high-spin... 

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