Glyceric acid

Abstract: The oxidation of aqueous solutions of glycerol is described and discussed for Pd, Pt and Au nanoparticles supported on graphite and activated carbon. The oxidation in a batch reactor at 60 °C and 1 bar pressure using air as oxidant was initially investigated. Under these conditions, supported Pd and Pt catalysts give some selectivity to glyceric acid, but the main reaction products are considered to be non-desired C1 by-products, e.g. CO2, HCHO and HCOOH. In addition, under these conditions, supported Au catalysts were totally inactive. Using an autoclave with pure oxygen at 3 bar pressure gave a significant improvement in reactivity and, for Pt and Au catalysts, the formation of C1 by-products was eliminated when NaOH was added. In particular, it was noted that, in the absence of NaOH, the Au/C catalyst was inactive. For 1 wt.% Au/graphite or activated carbon, 100% selectivity to glyceric acid at high conversion was readily achieved. The role of the base is discussed and it is proposed that the base aids the initial dehydrogenation via H-abstraction of one of the primary OH groups of glycerol and, in this way, the rate limiting step in the oxidation process is overcome.

Abstract: Eegriwe (1) introduced 1,3-dihydroxynaphthalene (naphthoresorcinol) as a spot test reagent for glycerate, and Rapoport (2) adapted the reaction for quantitative assay. In the present study it was found that, in addition to the naphthoresorcinol, 2,7-dihydroxynaphthalene and 4,5-dihydroxy-2,7-naphthalenedisulfonic acid (chromotropic acid) when heated with free or phosphorylated glycerates in concentrated sulfuric acid, produced distinctive colors which could be used to advantage for the identification of these compounds in column chromatographic eluates. The chromotropic acid reaction displayed the highest sensitivity and selectivity and was preferentially used for the quantitative analysis of glycerates.

Abstract: This paper addresses the oxidation mechanism of glycerol on Au and Pt electrodes under different pH conditions. Intermediates and/or reaction products were detected by using an online high-performance liquid chromatography technique (for soluble products) and online electrochemical mass spectrometry (for CO2). In alkaline media, the main product of glycerol oxidation on the Pt electrode is glyceric acid produced via glyceraldehyde. Glyceric acid is the primary oxidation product on the Au electrode, which is further oxidized to glycolic acid and formic acid at high potentials (≥0.8 V), yielding high current densities. As the pH of the solution is lowered, the glycerol oxidation becomes significantly more sluggish on both Au and Pt electrodes, which results in glyceraldehyde being the main oxidation product under neutral conditions, especially on gold. In acidic solutions, only the Pt electrode shows catalytic activity with a relatively low conversion rate, mainly to glyceraldehyde. At positive potentials corresponding to the formation of a Pt surface oxide, the PtOx surface oxide catalyzes the conversion of glyceraldehyde finally to formic acid and CO2, but only under acidic conditions. Gold catalyzes glycerol oxidation only under alkaline conditions, in contrast to a “real catalyst,” that is, platinum, which catalyzes glycerol oxidation over the entire pH range.