Formic acid

Earth Week molecule!
April 18, 2022
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Formic acid is the simplest carboxylic acid. Its discovery in the distillation products of ants is usually attributed to English scientist John Gray in 1671, although there is evidence that a Samuel Fisher made the discovery the year before. The name “formic” comes from formica1, the Latin word for ant and the name of the genus to which many ants belong.

Although ants and other insects produce significant amounts of formic acid, the large worldwide production of the chemical (870 kt in 2021) is made industrially. Most of it is made from carbon monoxide, either by heating it with sodium hydroxide to produce sodium formate, which is then acidified, or via the base-catalyzed reaction of CO and methanol to make methyl formate, which is hydrolyzed to the acid. Formic acid is also a major byproduct of acetic acid manufacture.

Formic acid has a wide range of uses: in leather tanning, as a decalcifier and cleaning product, as a chemical reducing agent, as a preservative in animal feeds, and for manufacturing its salts and esters. Its synthetic method can also be reversed to liberate CO.

This is Earth Week, and this year chemists and students are celebrating it by learning about insect chemistry. Foremost among insect-produced chemicals, formic acid is produced by ants in the subfamily Formicinae (almost 300 species) and some bee species as a venom against predators and as a pheromone to warn fellow insects of danger. Ants in the Formica genus emit formic acid when they bite or spray, causing skin irritation or worse in humans. Fire ants (Solenopsis spp.) cause even more damage because their venom contains toxic alkaloids.

1. This term should not be confused with the commercial plastic laminate Formica, which was so named because it was invented as a substitute for mica in electrical insulation. Formica laminate is not made from formic acid or any of its derivatives.

Formic acid hazard information

Hazard class* GHS code and hazard statement

Flammable liquids, category 3

H226—Flammable liquid and vapor Chemical Safety Warning
Acute toxicity, oral, category 4 H302—Harmful if swallowed Chemical Safety Warning
Skin corrosion/irritation, category 1A H314—Causes severe skin burns and eye damage Chemical Safety Warning
Serious eye damage/eye irritation, category 1 H318—Causes serious eye damage Chemical Safety Warning
Acute toxicity, inhalation, category 3 H331—Toxic if inhaled Chemical Safety Warning

*Compilation of multiple safety data sheets. 
**Globally Harmonized System (GHS) of Classification and Labeling of Chemicals. 
Explanation of pictograms.

Molecule of the future

Triphosphatetrahedrane1 (HCP3) is one of the more unusual compounds to come along in the past year. In October 2021, Martin-Louis Y. Riu, Mengshan Ye, and Christopher C. Cummins* at MIT (Cambridge, MA) reported the synthesis of this tetrahedral molecule, which is isostructural with former Molecule of the Week white phosphorus (P4) and the yet-to-be-synthesized C4H4 hydrocarbon tetrahedrane2.

Molecule of  the Future

The Cummins team prepared HCP3 via the reaction of bromodichloromethane3 (CHBrCl2) and a triphosphaniobium complex with the help of another niobium complex that strips the halogen atoms from CHBrCl2. HCP3 is stable in dilute tetrahydrofuran solution, but concentrating the solution releases a black precipitate that the authors believe is an HCP3 polymer.

The relative stability of HCP3 is not too surprising considering that its P4 cousin is stable under ambient conditions. According to the authors, the strain energy of the tetrahedral cage is reduced by “the more diffuse frontier orbitals of heavier p-block elements [such as phosphorus] and the propensity for lone pairs to accumulate s orbital character”.

1. CAS Reg. No. 1338340-47-8.
2. CAS Reg. No. 157-39-1.
3. CAS Reg. No. 75-27-4.

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Formic acid fast facts

CAS Reg. No. 64-18-6
SciFinder
nomenclature
Formic acid
Empirical formula CH2O2
Molar mass 46.03 g/mol
Appearance Colorless liquid
Melting point 8 °C
Boiling point 101 °C
Water solubility Miscible
Chemical Abstract Service - a division of ACS

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