Formic acid (HCOOH) is the simplest carboxylic acid, produced industrially through a two-step process involving methanol and carbon monoxide. While large-scale manufacturing requires specialized equipment and high pressures, understanding the chemistry behind each method helps clarify why formic acid is made the way it is, and why some approaches are more practical than others.
The Standard Industrial Method
Nearly all commercial formic acid is made through a process called methyl formate hydrolysis. In the first step, methanol reacts with carbon monoxide under pressure to form methyl formate. In the second step, that methyl formate is split apart with water (hydrolysis) to yield formic acid and methanol, which gets recycled back into the first step.
The hydrolysis reaction typically runs at 80 to 110°C under about 20 bar of pressure. Interestingly, formic acid itself can serve as the catalyst for this reaction, though using it tends to slightly reduce the overall yield of the final product. The process is continuous in industrial settings, with methanol looping back through the system to keep costs down.
The Sodium Hydroxide Route
An older method produces formic acid by reacting carbon monoxide with a sodium hydroxide solution. Carbon monoxide is absorbed into a 25% sodium hydroxide solution at around 145°C, producing sodium formate crystals. Those crystals are then treated with a stronger acid (typically sulfuric acid) to release formic acid and leave behind a sodium sulfate byproduct.
This route is simpler in concept but less efficient than the methyl formate process. It consumes sodium hydroxide and sulfuric acid without recycling them, which makes it more expensive per kilogram of formic acid produced. It’s largely been replaced in modern manufacturing but still appears in smaller-scale or regional operations.
Making Formic Acid From CO2
A newer approach uses electricity to convert carbon dioxide directly into formic acid. Researchers have demonstrated an electrochemical reactor using a bismuth-based catalyst that achieves remarkable performance: conversion selectivity above 97%, meaning almost all the electrical energy goes toward making formic acid rather than unwanted byproducts. The system ran stably for over 100 hours in testing and produced nearly pure formic acid (up to 100% concentration) by condensing the output vapor.
This method is appealing because it turns a greenhouse gas into a useful chemical. It’s not yet widely commercialized, but the efficiency numbers suggest it could eventually compete with traditional manufacturing, especially in regions with cheap renewable electricity.
Why You Can’t Easily Make It at Home
Every practical synthesis of formic acid involves either high-pressure carbon monoxide, strong bases paired with strong acids, or specialized electrochemical equipment. None of these are safe or feasible in a home setting. Carbon monoxide is lethally toxic, and concentrated formic acid itself is a serious hazard.
OSHA limits workplace exposure to just 5 parts per million over an eight-hour shift, with a short-term ceiling of 10 ppm. At higher concentrations, formic acid causes severe burns to skin, eyes, and the respiratory tract. Even the vapors from a moderately concentrated solution can damage lung tissue with prolonged exposure.
Where Formic Acid Comes From in Nature
Formic acid gets its name from the Latin word for ant, “formica.” It’s a component of ant venom and was historically associated with the sting of nettles. Stinging nettles do contain formic acid in their needle-like hairs, though researchers now believe the concentration is too low to account for the lasting pain of a nettle sting. Other compounds in the plant’s trichomes are likely more responsible.
Some people assume you could extract meaningful quantities from ants or plants, but the concentrations involved are far too small for any practical collection. Industrial synthesis remains the only viable source.
Commercial Grades and Their Uses
Formic acid is sold at several concentrations depending on the application. The most common commercial grade is an 85% solution, though concentrations of 65%, 90%, and 99% are all available for different purposes.
The 65% solution is widely used in beekeeping to control tracheal mites. One study found 95% mite mortality in infested hives after three weekly treatments of 30 mL each. Solutions below 50% are preferred when there’s a risk of the vapors reaching nearby plants, since stronger concentrations can damage vegetation.
Other major uses include:
- Silage preservation: added to hay crops at up to 2.25% of dry weight to prevent spoilage
- Leather tanning: used for dehairing and plumping hides
- Textile processing: acts as a reducing and decalcifying agent in dyeing
- Rubber production: coagulates latex and helps regenerate old rubber
- Food flavoring: permitted at low concentrations in beverages, candy, baked goods, and processed cheese (typically 1 to 28 ppm depending on the product)
Storing Formic Acid Safely
If you purchase formic acid for legitimate use, storage material matters. High-density polyethylene (HDPE) containers are resistant to formic acid at both room temperature and elevated temperatures up to 60°C. Low-density polyethylene performs equally well. Polycarbonate containers hold up at room temperature but are vulnerable to stress cracking when warm, so they’re not suitable for storage in hot environments.
Formic acid corrodes most common metals, so glass or compatible plastics are the standard choices. Keep it sealed, stored in a cool and ventilated area, and away from strong oxidizers. Even at moderate concentrations, the vapor pressure is high enough to create irritating fumes in an enclosed space.