Mechanistic Insight into the Conversion of Tetrose Sugars to Novel α‐Hydroxy Acid Platform Molecules

Abstract

α‐Hydroxy acids (AHAs) such as lactic acid are considered platform molecules in the biorefinery concept and have high‐end applications in solvents and biodegradable polyester plastics. The synthesis of AHAs with a four‐carbon backbone structure is a recently emerging field. New biomass‐related routes towards their production could stimulate their practical use in new polyester plastics. Herein, we report the unique catalytic activity of soluble tin metal salts for converting tetroses, namely erythrulose and erythrose, into new four‐carbon‐backbone AHAs such as methyl vinylglycolate and methyl‐4‐methoxy‐2‐hydroxybutanoate. An in situ NMR study together with deuterium labeling experiments and control experiments with intermediates allowed us to propose a detailed reaction pathway.

Advances in the Conversion of Short-Chain Carbohydrates: A Mechanistic Insight

“…In alcoholic media, the tetroses seemed to degrade rapidly, preserving only a limited total tetrose yield (27 %) after 1 h at 80 °C in methanol. This is in correspondence with our earlier work [ 39 ] which showed the rapid conversion of tetroses in alcoholic media after 1 h at 90 °C in the presence of Brønsted and Lewis acids, both sites that are also present in the H-USY zeolites used in Saravanamurugan's work.…”

“…On the other hand, as discussed above, the retro-aldol reaction of fructose leads to the two trioses, DHA and GLY, which can subsequently be converted to lactic acid or lactates. Interested by this fi nding, Dusselier et al were the fi rst to explore the mechanism of the formation of MVG and MMHB by the conversion of erythrulose (ERU) and erythrose (ERO), the keto-and aldotetroses, respectively, with soluble Lewis acid catalysts [ 39 ]. In analogy with Hayashi's work on trioses, Sn salts, viz., SnCl 4 .5H 2 O, were the most active catalysts, yielding up to 83 % MMHB in methanol after 1 h at 80 °C.…”

Tandem catalysis for the production of alkyl lactates from ketohexoses at moderate temperatures

“…Additionally, the use of equimolar DHA and GLA mixture as starting substrate does not result in significantly higher yields of ethyl lactate when MoO 3 is used by itself, further illustrating the rapidity of side reactions of trioses when a catalytic path to the thermodynamically stable lactate products is not present. As discussed above, other Mo-containing 1,2-CS catalysts, e.g., MoO 2 4 , and CaMoO 4 , were also able to accelerate alkyl lactate production from fructose when paired with Sn-MFI (reactions 15-17 in Table 1, and SI Appendix, Fig. S13, for the first three).…”

“…retro-aldol reactions | alkyl lactates | heterogeneous catalysis C hemocatalytic routes for the production of α-hydroxy carboxylic acids, e.g., glycolic acid, lactic acid, 2-hydroxy-3-butenoic acid, and 2,4-dihydroxybutanoic acid, from biomassderived sugars have been extensively investigated in the recent years, as these acids, as well as their esters and lactones, have been recognized to have a large potential to function as renewable, platform chemicals for a number of applications such as polymers, solvents, and fine chemicals (1)(2)(3)(4)(5)(6)(7). Considerable progress has been achieved with the production of lactic acid and alkyl lactates from trioses [glyceraldehyde (GLA) and dihydroxyacetone (DHA)], with nearly quantitative yields obtained with state-of-the-art catalysts, e.g., tin-containing zeotypes Sn-Beta and Sn-MFI, which are known for their capacity to catalyze 1,2-intramolecular hydride shift (1,2-HS) reactions, at moderate temperatures (around 100°C) (8).…”

“…Considerable progress has been achieved with the production of lactic acid and alkyl lactates from trioses [glyceraldehyde (GLA) and dihydroxyacetone (DHA)], with nearly quantitative yields obtained with state-of-the-art catalysts, e.g., tin-containing zeotypes Sn-Beta and Sn-MFI, which are known for their capacity to catalyze 1,2-intramolecular hydride shift (1,2-HS) reactions, at moderate temperatures (around 100°C) (8). Similarly, the C 2 and C 4 products (glycolic acid, 2-hydroxy-3-butenoic acid, 2,4-dihydroxybutanoic acid, and esters thereof) can be produced in good yields when glycolaldehyde, glyoxal, or tetroses (erythrose, threose, and erythrulose) are used as substrates (4,6). However, the substrates required for these reactions are not easily obtained or isolated from biomass, as the majority of terrestrial biomass comprises cellulose and hemicellulose (polymers of hexoses and pentoses) (5).…”