Negative production of acetoin in the photochemistry of aqueous pyruvic acid

Abstract

Recently, Griffith et al. reported that acetoin is a major product of the photolysis of aqueous pyruvic acid (PA), and proposed that its mechanism of formation involves the thermal decarboxylation of α-acetolactic acid (AL) intermediate (1). This finding is in contrast with a previous study by Guzman et al., based on experiments performed under similar conditions, which reported the formation of two major products: 2,3-dimethyl tartaric acid ( A ) and 2-(3-oxobutan-2-yloxy)-2-hydroxypropanoic acid ( B ) (2⇓–4). Both A and B result after triplet radical pairs are formed via long-range (proton-coupled) electron transfer between carbonyl groups (5). Product B can thermally decompose into acetoin, but its carbonyl chromophore absorbs at λmax ∼ 285 nm vs. 276 nm for acetoin (2). In fact, Guzman et al. had shown … [↵][1]1To whom correspondence should be addressed. E-mail: marcelo.guzman{at}uky.edu. [1]: #xref-corresp-1-1