In a
5-l. flask fitted with a
reflux condenser, a solution containing
200 g. (1.8 moles) of resorcinol,
1 kg. (9.9 moles) of potassium acid carbonate (Note
1), and 2 l. of water (Note
2) is heated slowly on a
steam bath for four hours. The flask is then placed over a flame and refluxed vigorously for thirty minutes; a rapid stream of
carbon dioxide is passed through the solution during this heating process.
While still hot the solution is acidified by adding
900 cc. of concentrated hydrochloric acid (sp. gr. 1.19) from a
separatory funnel with a tube delivering the acid to the bottom of the flask; this prevents the formation of a layer of acid over the unneutralized solution. The flask is allowed to cool to room temperature and is then chilled in an
ice bath. The
resorcyclic acid crystallizes in prisms which are almost colorless but which, on exposure to air, turn pink owing to contamination with a small amount of
resorcinol. The yield of crude acid is
225 g. By extracting the mother liquor with
ether several times,
35 g. of
resorcylic acid and some unchanged
resorcinol can be recovered. The
resorcylic acid is extracted from the
ether by shaking with an aqueous solution of
sodium bicarbonate. The aqueous solution is acidified with
hydrochloric acid and again extracted with
ether. The
ether is then evaporated, leaving the
resorcylic acid, which is usually highly colored and must be recrystallized several times from boiling water and charcoal to remove the color.
The combined yield of crude acid (
260–270 g.) is dissolved in 1 l. of water, boiled with about
25 g. of Norite, filtered through a
heated filter, and crystallized by placing in an ice-salt freezing mixture and stirring vigorously. A finely crystalline, colorless product is obtained in this way. If the acid is allowed to crystallize slowly the crystals are somewhat colored. The yield of pure
resorcylic acid melting at
216–217° is
160–170 g. (
57–60 per cent of the theoretical amount) (Note
3).