Abstract
Sugar acids obtained by aldohexose oxidation of both the terminal aldehyde group and the hydroxy group at the other end to carboxyl groups are called hexaric acids (i.e., six-carbon aldaric acids). Because hexaric acids have four secondary hydroxy groups that are stereochemically diverse and two carboxyl groups, various applications of these acids have been studied. Conventionally, hexaric acids have been produced mainly by nitric acid oxidation of aldohexose, but full-scale commercialization has not been realized; there are many problems regarding yield, safety, environmental burden, etc. In recent years, therefore, improvements in hexaric acid production by nitric acid oxidation have been made, while new production methods, including biocatalytic methods, are actively being studied. In this paper, we summarize these production methods in addition to research on the application of hexaric acids.
Highlights
The International Energy Agency defines a biorefinery as “the sustainable processing of biomass into a spectrum of marketable products and energy”, which is the most comprehensive and commonly accepted definition [1]
Studies have used hexuronic acids derived from polysaccharides, which are not used as food, as the Mojzita et al reported the production of meso-galactaric acid from d-galacturonic acid using starting compounds for hexaric acids
Hexaric acids are sugar acids that can be produced from biomass
Summary
The International Energy Agency defines a biorefinery as “the sustainable processing of biomass into a spectrum of marketable products and energy”, which is the most comprehensive and commonly accepted definition [1]. Has selected twelve chemicals from more than three hundred biomass-derived chemicals, based on cooperative research with industry and academia, to be developed using biorefinery production methods [3]. More than half of the twelve selected chemicals are carboxylic acids. Aldaric acid (hexaric acid) is a dicarboxylic acid produced by oxidizing both groups (Figure 1). Because aldaric acids have been studied for numerous types of applications, improved methods for their production are urgently needed. D-Glucaric acid, the aldaric acid of d-glucose or l-gulose, was selected by the DOE as one of the twelve chemicals [3]. This article summarizes biorefinery methods relating to aldaric acids with six carbon atoms (hexaric acids; Figure 1), including d-glucaric acid. Sci. 2019, 20, biorefinery article summarizes methods relating to aldaric acids with six carbon atoms (hexaric acids; Figure 1), including ᴅ-glucaric acid
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