Pyruvic acid Quantum

Photolytic. Dalapon (free acid) is subject to photodegradation. When an aqueous solution (0.25 M) was irradiated with UV light at 253.7 nm at 49 °C, 70% degraded in 7 h. Pyruvic acid is formed which is subsequently decarboxylated to acetaldehyde, carbon dioxide, and small quantities of 1,1-dichloroethane (2-4%) and a water-insoluble polymer (Kenaga, 1974). The photolysis of an aqueous solution of dalapon (free acid) by UV light (X = 2537 A) yielded chloride ions, carbon dioxide, carbon monoxide, and methyl chloride at quantum yields of 0.29, 0.10, 0.02, and 0.02, respectively (Baxter and Johnston, 1968). 

The mechanism of the photoinduced decarboxylation of pyruvic acid has been reinvestigated and accounted for via electron transfer from an excited to a ground state molecule. Quantum yields of triplet production at 295 K in deoxygenated benzene, acetonitrile, and water are 0.65, 0.88, and 0.22, respectively. ... 

Photo-oxidation studies of pyruvic acid, a product found in the photo-oxidation of methylglyoxal, have been carried out (Warneck). Quantum yields of the primary reaction steps are given in Table 15. 

Product quantum yields for the 350 nm photo-decomposition of pyruvic acid in air, Ber. Bunsenges. Phys.Chem. 96 (1992) 413-416. 

Product quantum yields for the photolysis of pyruvic acid under atmospheric conditions, (in German),... 

Berges and Warneck (1992) determined the quantum yields of products formed in the photolysis of pyruvic acid in air at 1 atm. using a band of radiation centered at 350 nm. They reported 4>co2 = 1-27 0.18 d>cH3CHO = 0.48 0.01 4>ch3C02H = 0.14. They found also that with added NO2 in the pyruvic acid-air mixture, peroxyacetyl nitrate was formed with a quanmm yield of 0.15 0.02 while 4>ch3Cho was reduced to 0.30 0.04. This latter result suggests that acetyl radicals are formed in a primary... 

Theoretical studies aimed at rationalizing the interaction between the chiral modifier and the pyruvate have been undertaken using quantum chemistry techniques, at both ab initio and semi-empirical levels, and molecular mechanics. The studies were based on the experimental observation that the quinuclidine nitrogen is the main interaction center between cinchonidine and the reactant pyruvate. This center can either act as a nucleophile or after protonation (protic solvent) as an electrophile. In a first step, NH3 and NH4 have been used as models of this reaction center, and the optimal structures and complexation energies of the pyruvate with NH3 and NHa, respectively, were calculated [40]. The pyruvate—NHa complex was found to be much more stable (by 25 kcal/mol) due to favorable electrostatic interaction, indicating that in acidic solvents the protonated cinchonidine will interact with the pyruvate. 

Photodecarboxylation of the dissociated form of a-hydroxy-substituted arylacetic acids and related substrates occurs from the singlet excited state (SJ and leads to the corresponding benzyl alcohols with high quantum yields (O = 0.2 to 0.7) via a heterolytic mechanism (Scheme 2). Photodecarboxylation of some diarylacetic acids (Scheme 2) also proceeds from Sj via heterolytic mechanism. It is remarkable that these compounds show dramatic differences in their relative photodecarboxylation efhciency (O = 0.04 to 0.6). The reaction is enhanced when a cyclic delocalized carbanion with 4n electrons is formed. By contrast, photodecarboxylation of m- and p-nitrophenylacetic acids in aqueous solutions occurs via a heterolytic mechanism from Tj." The photodecarboxylation of pyruvic and benzoylformic acids takes place with high quantum yields ( 5 > 0.6) in aqueous solutions, to give acetaldehyde and benzaldehyde, respectively as the primary photoproducts. On the other hand, 2-, 3-, and 4-pyridinylacetic acids undergo photodecarboxylation in aqueous solutions via a heterolytic mechanism from their zwitterionic forms. 

---