Laboratory Methods of Organic Chemistry - Sciencemadness Dot Org

236 THE KBIMBK-TIBMANN SYNTHESIS
between 65° and 70° by dipping the flask in cold or hot water, a
second 20 g. portion of chloroform is added and once again, after an
interval of fifteen minutes, a third portion of 20 g. At this stage
the flask should frequently be shaken. To complete the reaction
the flask is heated on the water bath for one hour and steam is then
blown through the reaction product until chloroform ceases to pass
over. The reaction mixture is now allowed to cool somewhat, and
dilute sulphuric acid is carefully added until the orange-coloured
alkaline liquid becomes acid and almost colourless. Steam is then
passed through again until no more drops of oil come over with the
water.
The distillate is at once extracted with ether and the extract,
after having been separated from the water, is heated on the water
bath until most of the ether has distilled. The residue, which contains
unchanged phenol as well as the salicylaldehyde, is now vigorously
shaken in a small glass-stoppered bottle with two volumes of
concentrated commercial sodium bisulphite solution. A thick paste
of the bisulphite compound of the aldehyde is formed. After this
paste has stood for from half an hour to one hour the bisulphite compound
is separated by filtration at the pump, pressed well on the
filter funnel, and washed several times, first with alcohol and
finally with ether, until completely free from adherent phenol. The
crystals (small plates, iridescent like mother-of-pearl) are then decomposed
with dilute sulphuric acid in a small round-bottomed flask
whic,h is fitted with an air condenser and gently warmed on the
water bath. After the liquid thus produced has cooled, the aldehyde
which separates is extracted with ether and the ethereal solution
is dried with anhydrous sodium sulphate. The pure aldehyde
which remains when the ether is evaporated distils at 196°. The
yield amounts to 10-12 g.
From the residue after the steam distillation, filtered while hot
and saturated with sodium chloride, ^-hydroxybenzaldehyde, which
is not volatile with steam, crystallises, often only after long standing.
If the filtrate, obtained when the crystalline material is separated
by filtration, be extracted with ether, a further amount of the pcompound
is obtained. By recrystallisation from water, to which
some aqueous sulphurous acid is added, both portions can be purified
together. Melting point 116°. Yield 2-3 g.
If the sodium phenoxide separates at the beginning, the synthesis
fails.