The Reimer-Tiemann synthesis. Salicylaldehyde from phenol and chloroform

THE REIMER-TIEMANN SYNTHESIS SALICYLALDEHYDE FROM PHENOL AND CHLOROFORM 1 

In a round-bottomed flask (capacity 1 1.) sodium hydroxide (80 g.) is dissolved by heating in water (80 c.c.), pure phenol (25 g.) is added to the hot solution, and the mixture is cooled to 60°-65° by dipping the flask in cold water, without shaking, however, so that separation of crystalline sodium phenoxide is avoided. By means of a two-holed cork the flask is then fitted with an efficient reflux condenser and a thermometer, the bulb of which dips into the liquid. Chloroform (20 g.) is next poured in through the condenser, and the contents of the flask are gently shaken a transient fuchsine-red colour is developed in the liquid. After a period of about ten minutes, during which the temperature of the mixture is maintained 

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 whi( 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, p -hydro xybenzaldehyde, 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 p-compound 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. 

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