8 BULLETIlSr 372, U. S. DEPABTMEXT OF AGEICULTURE. 



EXTRACTION OF THE THYMOL. 



The oil of liorsemint distilled from plants grown in Florida con- 

 sists of phenols to the extent of 70 to 80 per cent, and these phenols 

 consist almost entirely of thymol, there being present also very small 

 quantities of carvacrol. The nonphenol portion of the oil consists 

 largely of cymene, which acts as a solvent for the thymol and pre- 

 vents complete crystallization. It is therefore necessary to separate 

 these two compomids as a preliminary step in the extraction of the 

 thymol. 



Since the two main constituents have a widely different boiUng 

 point, cymene boiling at 175° to 176° C. and thymol at 232° C. under 

 normal pressure, ahnost complete separation can be secured by frac- 

 tional distillation. The method devised for the separation is as fol- 

 lows: The crude oil is distilled in a proper retort of copper, which is 

 fitted with an efficient fractionation column, the one used in these 

 experiments with the best results being the Hempel form. Dis- 

 tillation is carried on slowly and the portion of the oil coming over 

 below 215° C. is set aside. The temperature is then raised slightly 

 and the fraction distilling over between 215° and 240° C. is secured. 

 The residue in the retort is a thick, tarlike mass and so far as known 

 is of no value. 



Practically all the thymol is now contained in the second fraction, 

 which consists of a rather heavy, slightly yellow liquid. The quan- 

 tity of thymol contained in the first fraction should not be large if the 

 process has been carried on carefully, but may rmi as high as 25 to 

 30 per cent. This fraction is now redistilled under the same condi- 

 tions as before, and the second fraction secured between 215° and 

 240° C. is placed with the first one secured at this temperature and 

 the residue discarded. 



The total fractions secured between 215° and 240° C. are allowed 

 to cool in a shallow container and a small crystal of thymol is added 

 to start crystallization. Withm a few minutes a heavy crop of 

 crystals will be secured. After standing over night the crystals 

 are separated from the mother hquor by means of a centrifuge, 

 and the crystals are washed with water while the centrifuge is run- 

 ning at full speed and then dried by continued running of the cen- 

 trifuge for three to five minutes. 



If cooled in a freezing mixture or by setting in a cold place, the 

 mother Hquor will deposit another crop of crystals, but if a very large 

 quantity of mother hquor is present it indicates that a considerable 

 portion of the lower boiling fractions was not removed. It should, 

 therefore, again be distilled in the same manner as before and the 

 fraction secured between 215° and 240° C. should be treated in the 

 manner previously described. 



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