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Performic acid (PFA) is an organic compound with the chemical formula CH2O3. It is an unstable colorless liquid which can be produced by mixing formic acid with hydrogen peroxide. Owing to its oxidizing and disinfecting action, it is used in the chemical, medical and food industries.
The popularity of performic acid as a sterilizer originates from the safe nature of its degradation products, mostly carbon dioxide, oxygen and water. The disinfecting action of performic acid is also faster than that of the related compounds peracetic acid and hydrogen peroxide. The major drawbacks of performic acid are handling dangers related to its high reactivity, as well as instability, especially upon heating, which means that the acid must be used within about 12 hours of it being synthesised.
Synthesis of pure performic acid has not been reported, but aqueous solutions up to about 48% can be formed by simply mixing equimolar amounts of concentrated aqueous reactant solutions. Using an excess of either reactant shifts the equilibrium towards the product side. The aqueous product solution can be distilled to increase the concentration of performic acid to about 90%.
This reaction is reversible and can be used for large scale industrial production if accelerated with a catalyst; however, its temperature must be kept below 80–85 °C to avoid an explosion.Elvers, B. et al. (ed.) (1991) Ullmann's Encyclopedia of Industrial Chemistry, 5th ed. Vol. A12, Wiley, p. 16 The catalyst can be nitric acid, hydrofluoric, phosphoric acid or sulfuric acid or their salts; it can also be an organic compound containing at least one ester group, such as carboxylic acid esterMatilla, T. and Aksela, R. 2000 Method for the Preparation of Aqueous Solutions Containing Performic Acid as Well as Their Use. , Issue date: April 11, 2000 or peracetic acid.Preuss, A., Fuchs, R., Huss, M. & Schneider, R. 2001 Aqueous Disinfecting Agent Containing Performic Acid and Peracetic Acid Process for Production and Process for Use Thereof , Issue date: April 3, 2001
Synthesis
Performic acid is synthesized by the reaction of formic acid and hydrogen peroxide by the following equilibrium reaction:
Safety
Performic acid is non-toxic; it does irritate the skin, but less so than peracetic acid. Concentrated acid (above 50%) is highly reactive; it readily decomposes upon heating, and explodes upon rapid heating to 80–85 °C. It may ignite or explode at room temperature when combined with flammable substances, such as formaldehyde, benzaldehyde, or aniline, and explodes violently upon addition of metal powders. For this reason, spilled performic acid is diluted with cold water and collected with neutral, non-flammable inorganic absorbents, such as vermiculite.
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