Levulinic acid, from hexoses

Scheme 9.3.2 Formation of HMF levulinic acid from hexoses.

Sassenrath CP, Shilling WL (1966) Preparation of levulinic acid from hexose-containing material. US 3258481 A... 

Levulinic acid and formic acid are end products of the acidic and thermal decomposition of lignocellulosic material, their multistep formation from the hexoses contained therein proceeding through hydroxymethylfurfural (HMF) as the key intermediate, while the hemicellulosic part, mostly xylans, produces furfural.A commercially viable fractionation technology for the specific... 

Scheme 5). However, this reaction is not as easy as it looks since numerous side reactions may occur. Antal et al. showed that four different classes of reactions can take place from hexoses (1) their dehydration leading to the formation of HMF, (2) their fragmentation, (3) their isomerization, and (4) their condensation leading to the formation of insoluble polymers and humins [58, 69]. Later, Van Dam and Cottier showed that at least 37 products can be produced, thus showing the complexity of this reaction. In particular, they highlighted that HMF can react with water, leading to the formation of undesirable side products such as levulinic and formic acids [68, 70]. 

The major products formed from hexoses that react in aqueous acidic solution are 5-(hydroxymethyl)-2-furaldehyde, levulinic acid, and polymeric materials. In addition, many minor dehydration products are found. In a study41 of D-fructose, 2-(2-hydroxyacetyl)furan (13), 2-acetyl-3-hydroxyfuran (isomaltol 16), 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one, and 3,4,5-trihydroxy-3,5-hexadien-2-one (acetylformoin) were identified. Products not formed solely by dehydration mechanisms include acetone,56 formaldehyde, acetalde-... 

Blanksma5 continued the investigation of the formation of hydroxy-methylfurfural and confirmed Kiermayer s results that it was formed from hexoses by elimination of three molecules of water on acidic degradation and showed that ketoses reacted more readily than aldoses, a fact which was observed by Kiermayer when sucrose was treated with aqueous oxalic acid. Kiermayer had observed also that levulinic acid was obtained when hydroxymethylfurfural was treated with aqueous oxalic acid under pressure and this received further confirmation by Van Ekenstein and Blanksma.6 It was these authors who first pointed out that the complete degradation of hexoses to levulinic acid took place through the intermediate formation of hydroxymethylfurfural. 

Hydroxymethylfurfural is not volatile by steam. It is prepared from hexoses in the presence of an acid catalyst by short heat treatment to avoid further degradation to levulinic acid. After recovery by solvent extraction hydroxymethylfurfural is purified by distillation. Levulinic acid can be prepared in good yield from hexose-based polysaccharides by heating with acids. In this reaction formic acid is liberated and levulinic acid is easily lactonized to form a- and /3-angelica lactones (Fig. 2-31). 

The last compound is formed by abstraction of three molecules of water from the hexose and is transformed into levulinic acid and formic acid on acid treatment ... 

The hexoses can also be converted directly to levulinic acid and formic acid on acid treatment without isolation of 2-hydroxymethylfurfural. Note that levulinic acid can be synthesized from both pentoses and hexoses, but is usually manufactured from cane sugar or starch by boiling with hydrochloric acid. A process for the manufacture of levulinic acid has also been developed for paper-mill sludge feedstocks (Fitzpatrick and Jarnefeld, 1996). 

A wide range of carbohydrates is degraded by acids to furan compounds. For example, pentoses give 2-furaldehyde, and hexoses, 5-(hydroxymethyl)-2-furaldehyde (58), which may react further to yield levulinic acid. In 1910, Nef suggested the first mechanism, (55) to (58), for the formation of 5-(hydroxymethyl)-2-furaldehyde. His proposal was made at the end of his classical paper on the saccharinic acids, and was overlooked by subsequent workers and reviewers. In 1944, Haworth and Jones advanced an identical mechanism for the formation of 5-(hydroxymethyl)-2-furaldehyde from D-fructose. 

Pummerer R, Guyot O, Birkofer L (1935) Mechanism of levulinic acid formation from hexoses. II. A hydroxyl-free glucosan-like substance. Berichte 68B 480-493... 

Levulinic acid (LA) is a compound derived from 5-HMF and Usted among the top 12 most promising value-added chemicals from biomass. This platform molecule is formed by dehydration in acidic media of hexoses to 5-HMF and subsequent hydration produces LA, formic acid, along with other unwanted polymerized products (humins) (Mukherjee et al., 2015). Likewise, LA can also be obtained by the hydrolysis of furfuryl alcohol (see Fig. 13.1). 

The most important aspect of the chemistry of the furan ring in 5-hydroxymethylfurfural is its scission under the influence of acidic reagents. In the very earliest work on the acidic degradation of hexoses, levulinic and formic acids were obtained which were shown subsequently to have arisen from the decomposition of 5-hydroxymethylfurfural. This degradation was studied by Teunissen53 87 who measured its rate and showed it to be a unimolecular reaction. He proposed the scheme represented by XLIV-XLIX for the conversion of 5-hydroxymethyl-... 

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