Formic acid, from hexoses

On oxidation with periodate, one mole of the arabinogalactan A consumes 1.01 mole of oxidant, with liberation of 0.45 mole of formic acid per hexose residue. The terminal n-galactopyranose, 6-0-substituted D-galactopyranose, and L-arabinopyranose residues will each consume 2.0 molecules of periodate, with concomitant formation of 1.0 molecule of formic acid, whereas the terminal n-arabinofuranose residues will consume 1.0 molecule of oxidant, without formation of formic acid. The relative proportion of the latter residues will thus be equivalent to the difference between the total consumption of periodate and the amount consumed by those residues which give rise to formic acid. The figure obtained in the present example was 11%, in good agreement with the value of 12% approximated from the methylation data. 

Bevington and coworkers have suggested a scheme for determining the distribution of radioactive carbon in labeled n-glucose, using the degradation of D-arabino-hexose phenylosotriazole. The scheme is based on the periodate oxidation of n-ambmo-hexose phenylosotriazole and d-arabino-hexose phenylosotriazole 6-benzoate. The former gives formaldehyde from C-6, formic acid from C-4 and C-5, and 4-formyl-2-phenyl-1,2,3-triazole from C-1, C-2, and C-3. This latter aldehyde can be further... 

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]. 

Owing to the possibility of tuning (1) their acidic and basic properties, (2) their surface hydrophilicity, and (3) their adsorption and shape-selectivity properties, catalytic activity of zeolites was investigated in the production of HMF from carbohydrates. Whatever the hexose used as starting material, acidic pillared montmorillonites and faujasite were poorly selective towards HMF, yielding levu-linic and formic acids as the main products [81-83]. 

The polymer from 2-deoxy-D-ara6mo-hexose was found to be fairly soluble in alcohol and very sensitive to hydrolysis by acid. There was no significant amount of formic acid liberated on periodate oxidation, since internal residues do not contain three adjacent hydroxyl groups the formic acid obtained arose, probably, from overoxidation at the reducing end of the polymer molecule. A positive precipitation reaction1 with concanavalin A (see Section IV,6) suggests the presence of at least a few terminal, nonreducing 2-deoxy-a-n-arabmo-hexopyranosyl residues. 

Isbell and co-workers (51) have tried to minimize the oxygen reaction and to maximize the peroxide reaction. When a large excess of peroxide and a low temperature were maintained, they found that the monosaccharides are converted almost quantitatively to formic and two-carbon acids. Table II presents results for the peroxide oxidation of 14 sugars. The total acid produced from aldo-hexoses under favorable conditions is about six moles, consisting almost entirely of formic acid. Aldopentoses react more rapidly than aldo-hexoses and yield about five moles of formic acid per mole of pentose. Fructose and sorbose yield approximately five moles of total acid of which four moles are formic acid. Glycolic acid was identified qualitatively but not determined quantitatively. L-Rham-nose and L-fucose yield about five moles of acid, including four moles of formic acid. Acetic acid was identified only qualitatively. 

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-... 

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). 

At American University, Harriet Frush and Horace Isbell worked on the mechanism of oxidation of carbohydrates by peroxides. They discovered that, in aqueous alkaline hydrogen peroxide, aldoses are quantitatively degraded to formic acid, so that hexoses produce six moles of this acid and pentoses produce five moles. A detailed study of the mechanism of the reaction revealed that degradation takes place by several pathways, the most rapid one involving the formation of peroxy radicals and hydroxy radicals. Thus, when a hydroperoxide-aldose adduct reacts with hydrogen peroxide, a peroxy radical is formed, which decomposes to a hydroxy radical, formic acid, and the next lower aldose. It was also found that, under basic conditions, hydroxy radicals oxidize alditols and aldonic acids to carbonyl compounds in much the same way they do with Fe2+ in the Fenton reaction. During the years she spent at American University, Dr. Frush was able to publish 10 papers without help from any research assistant or laboratory technician. This brought her total to more than 70 papers. 

Four major carboxylic acids, acetic, formic, glyceric, and lactic, are formed under mild alkaline oxidation conditions from xylose (Rahardja et al, 1994). At 40-60°C, lactic acid is formed from dilute aqueous solutions of xylose in the largest mass yield, about 50%, under continuous oxidation conditions. This is about 83% of the maximum theoretical yield of 60%. Under batch conditions, the yield of lactic acid from xylose is about 23%, while the yield from glucose is about 41%. These data indicate a commercial alkaline oxidation process for lactic acid from pentoses and hexoses is feasible, but it should be realized that the recovery of carboxylic acids having high water solubilities from dilute aqueous solutions can add signihcantly to production cost (Busche, 1984). 

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). 

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). 

---