Formic Acid (HCOOH) is a weak acid with a pKa of 3.76 and a pH of 2.52 for a 0.050 M solution and a pH of 2.38 for a 0.1 M solution. It is more acidic than acetic acid because the methyl group (-CH3) in acetic acid inductively donates electron density to COOH, so the O-H bond is less likely to break. Formic acid has no electron-donating group, so its O-H bond is slightly more polarized and more acidic.

Formic Acid occurs naturally in the stings of bees and ants, acting as a venom against predators and as a pheromone to warn fellow insects of danger. Formic ants of the genus Formic release formic acid when they bite or spray, causing skin irritation or worse in humans. Although ants and other insects produce large amounts of formic acid, it is mainly produced industrially. Most formic acid is made from carbon monoxide, either by heating it with sodium hydroxide to form sodium formate, which is then acidified, or by the base-catalyzed reaction of CO and methanol to form methyl formate, which is then hydrolyzed to the acid. Formic acid is also a major byproduct of acetic acid production.

A new process for the production of formic acid from corncob waste was constructed by using MnCeOx/Nb2O5 catalyst. Among pristine hemicellulose, cellulose or lignin in corncob, hemicellulose gave the maximum formic acid yield (61.2 %). Dilute hydrochloric acid (0.37 wt%) assisted-ball milling pretreatment of pristine cellulose reduced its crystallinity and increased formic acid yield from 2.6 % to 40.2 %, while lignin was hardly converted into formic acid (<7 %). In the assessment of Mn and Ce in MnCeOx/Nb2O5, a synergistic effect was observed in formic acid formation. Formic acid yield obtained over Mn6Ce4Ox/Nb2O5 was 1.5-fold higher that obtained over MnOx/Nb2O5. Formic acid yield as high as 0.56 g/g could be obtained directly from pretreated corncob, demonstrating potential for converting agro-waste biomass into formic acid over Mn6Ce4Ox/Nb2O5 catalyst. Mechanistic studies revealed that arabinose, glyceric acid and glycolic acid were main intermediates in the conversion of corncob to formic acid.

References:

[1] セルヒィハラディ, ミハイロスタルチェフスキー, ヤロスラフラストフヤク, et al. Preparation of formic acid[C]. 2000: 0. DOI:10.1080/14786443308648187.

[2] SIYU XU . Efficient one-pot conversion of corncob to formic acid using bi-functional MnCeOx/Nb2O5 catalyst[J]. Biomass & Bioenergy, 2024, 187: Article 107297. DOI:10.1016/j.biombioe.2024.107297.