Preparation of formaldehyde from formic acid, contributed by BASF

Formic acid can be bought as disinfectant for brewing barrels and as drain cleaner, for example.

1) formic acid(any concentration) is added to an excess of chalk(this means, when the vigorous, fizzling reaction is finished, undissolved chalk is still left) to yield an aqueous solution of calcium formate Attention: use safety goggles and -gloves!

2) the calcium formate solution is then filtered from the rests of unreacted chalk and then very carefully cooked down to nearly dryness, the crystals still moist.

3) a bigger quantity of the calcium formate is then filled into a 500ml florence flask and the flask is then fit with a stopper and a 2-angle-glass pipe which leads first through a two-hole-stoppered safety bottle and then with a second 2-angle-glass pipe the gas is led into an open 200ml flask, where it is dissolved in water, acetone or diethyl ether.

4) then the 500ml flask is heated sufficiently until the calcium formate got dry and begins to decompose under the evolution of formaldehyde gas

5) The process is stopped when no gas bubbles through the solvent and the white residue is mainly calcium carbonate

6) The formaldehyde solution can be polymerized to paraformaldehyde by adding to an excess of concentrated sulfuric acid, or just by boiling.

Attention: formaldehyde sol. is very harmful to the skin(causes the so-called "leather skin"), very poisonous and a carcinogen. It has an intensive smell.