2.6.5.5.1 General Methods of Isolation
Mostly phenols are weak acids. Hence, they react with dilute alkali solutions (3-5% w/v) to result into the formation of corresponding water-soluble salts known as ‘phenolates’. This specific characteristic property usually offers, a convenient method for carrying out the separation of phenolic components from the non-phenolic ones. To affect the separation, therefore, the volatile oils or fractions are subjected to treatment with dilute alkaline solutions with vigorous shaking. Once the two layers get separated, the water-soluble salts are decomposed by acidification carefully and the phenols thus generated (or liberated) are isolated either by means of steam-distillation or by extraction with ether.Note
1. Thymol and carvacrol may be steam-distilled from alkaline solution without previous acidification.
2. Several phenols may be isolated by chilling the oil as such or its fraction to a very low temperature (–20 to –30°C) whereby these compounds normally separate in crystalline form.
