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

Abstract

This chapter discusses recent insights in the conversion of short carbohydrates, viz., sugars containing four or less carbon atoms. Rather than summarizing product yields from such sugars and reported catalysts for the conversions, the focus lies on understanding the underlying mechanisms. These short carbohydrates can lead to a broad spectrum of products, ranging from platform chemicals such as lactic acid and ethylene glycol to high-value chemicals such as α-hydroxy-γ-butyrolactone and even fuels. Different synthesis strategies of these short carbohydrates include (1) a top -down approach from mono-or polysaccharides and (2) a selective bottom -up synthesis route from formaldehyde. Lewis acids play a major role in carbohydrate chemistry, and among these, Sn-based catalysts often show the highest activity. Whether dioses, trioses, or tetroses are used as substrate, Sn is able to convert them effi ciently into α-hydroxy acids or esters, which are useful building blocks for renewable polyesters. Other reaction types such as isomerization, hydrogenation, and cross couplings are discussed briefl y as well. Glycerol and glyoxal are no sugars, but their chemistry shows great resemblance to that of carbohydrates. Therefore, these compounds are also briefl y accounted for in this chapter.

Selective Degradation of End‐of‐Life Poly(lactide) via Alkali‐Metal‐Halide Catalysis

“…The EoL PLA ( 1 ) is degraded with the degradation reagent methanol and with the support of a catalyst to form as main chemical methyl lactate ( 2 ). Subsequently, methyl lactate ( 2 ) can be transformed to compound 3 (lactide), which is a fundamental compound in the industrial production chain of PLA (Scheme ) . As second product methanol is produced, which can be recycled for further degradation; therefore, reduced amounts of waste are generated and the whole process is made highly atom efficient.…”

Continuous Liquid-Phase Upgrading of Dihydroxyacetone to Lactic Acid over Metal Phosphate Catalysts

“…In the literature, it is reported that PVA is produced by GLA dehydration. 27 Some authors hypothesized the possibility to produce PVA directly by dehydrating DHA, which is unlikely based on common reactivity trends in organic chemistry. 27 However, none of these possibilities explain an apparent second-order reaction.…”

“…27 Some authors hypothesized the possibility to produce PVA directly by dehydrating DHA, which is unlikely based on common reactivity trends in organic chemistry. 27 However, none of these possibilities explain an apparent second-order reaction. DHA and GLA are in equilibrium with each other, although DHA seems to be always the most abundant species in solution.…”

“…On the contrary, when GLA is used as the substrate, its concentration rapidly drops in favor of DHA and PVA, and only at longer reaction times, the LA concentration starts to be significant. Triose dehydration can be catalyzed by mild Brønsted acids . The dehydration can be assisted even by Lewis acid sites, but it occurs more efficiently in the presence of Brønsted acidity. ,, Finally, PVA is converted into LA or alkyl lactate over Lewis acid sites via the Cannizzaro reaction, and the presence of strong Brønsted acid sites leads to the formation of PVA diacetal as a side product in alcoholic solvents .…”