Formaldehyde, also known as methanal or formalin, is the simplest aldehyde with the formula CH2O.  It used to be found in most biology labs used as a preservative for dissection specimens, but this use has fallen into disfavor due to its carcinogenic nature.



Formaldehyde is a good electrophile. It is relatively easily oxidized into formic acid and thus formic acid is often a contaminant in fomaldehyde solutions.


Formaldehyde is a gas at STP and is usually supplied in a 37% aqueous solution.  Formaldehyde has an extremely characteristic and pungent odor.


A 37% solution of formaldehyde is cheaply available from suppliers such as Elemental Scientific. It can also be purchased from agricultural and veterinary stores, as a disinfectant.


Formaldehyde can be prepared by placing red hot copper into methanol, however this method is not economically viable for the amateur and produces lower quality formaldehyde.


Formaldehyde can be used along with ammonia to produce hexamine, a solid fuel used for camping and a precursor to many explosives including RDX. The mixture of concentrated sulfuric acid and concentrated (37%) formaldehyde is known as Marquis reagent, a versatile drug testing reagent.



Formaldehyde is toxic, with a LD50 of 100mg/kg and is carcinogenic. It will damage the optic nerves and cause blindness (methanol, being metabolized to formaldehyde, will also do this). Pure gaseous formaldehyde is highly flammable. Care must be taken to ensure formaldehyde is not mixed and heated with acetaldehyde as this will produce the dangerous substance acrolein


In closed bottles, away from any heat source.


Formaldehyde can be neutralized with sodium hydroxide, reaction that generates sodium formate and methanol.


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