The complete conservation
of the carbon, hydrogen, and oxygen atoms
of cellulose and starch can theoretically be achieved by their conversion
to levulinic and formic acids. Similarly, hemicellulose can be converted
to furfural and water with 100% atom economy. The valorization of
carbohydrates of agricultural residues (banana-, orange-, and potato-peels,
corn leaf and root, and rice husk), potential components of raw food
wastes (corn, rice, potato, lettuce, onion, leek, vegetable, bean,
and tomato), and cooked food wastes (rice noodle, spaghetti, risotto,
noodle, bread, and biscuit) was demonstrated in the presence of sulfuric
acid at 130 °C in γ-valerolactone as the green solvent
to yield levulinic and formic acids as the two main products. Levulinic
acid was also produced from furfural by its transfer hydrogenation
with formic acid to furfuryl alcohol in the presence of Shvo’s
catalyst followed by its acid catalyzed conversion to levulinic acid.
Neutralization of the sulfuric acid in the reaction mixture with ammonium
hydroxide resulted in an aqueous ammonium sulfate phase and a γ-valerolactone
rich organic phase. Due to the salting out effect of the ammonium
sulfate in the aqueous phase, levulinic acid and formic acid partitioned
to the γ-valerolactone rich organic phase at >99.8% and >97.1%,
respectively. The transfer hydrogenation of levulinic acid with formic
acid in the presence of the Shvo’s catalyst resulted in the
formation of 4-hydroxyvaleric acid, which readily underwent dehydration
to yield γ-valerolactone, a green and sustainable liquid. The
possibility of converting C5- and C6-carbohydrates
to levulinic acid or γ-valerolactone is a great opportunity
for carbon conservation with a carbon-economy higher than that for
butanol or ethanol.
