Formaldehyde is the simplest member of the aldehyde family.
Preparation. It is manufactured
By dehydrogenation of ethanol. Methanol vapours are passed over heated silver catalyst at 300°C.
By air oxidation of methanol. Methanol vapours and limited amount of air are passed over heated silver catalyst at 450°C.
By air oxidation of methane in the presence of various metallic oxides.
Since formaldehyde is a gas, the product is marketed as 40% aqueous solution under the name Formalin.
Formaldehyde is a colourless gas, bp -21°C. It has an irritating odour. It is extremely soluble in water.
Reaction with Ammonia.
When treated with ammonia, it does not give an aldehyde ammonia, but forms hexamethylene tetramine.
hexamethylene tetramine is used a urinary antiseptic, and has been given the trade name of Urotropine.
Reaction with Sodium Hydroxide (Cannizzaro Reaction).
Reaction with Alcohols.
- As a general antiseptic.
- In the manufacture of urinary antiseptic Urotropine.
- In the present creation of biological specimens.
- In the manufacture of synthetic dyes like Pararosaniline and Indigo.
- In the manufacture of synthetic plastics such as Bakelite and Melmac.