64 



SCIENCE 



[N. S. Vol. XLIV. No. 1124 



ous fruits but none that can be identified with 

 accuracy. 



A reference is also made in the manuscript 

 to worms around the roots of peach trees which 

 are said to cause an exudation of gum. This 

 probably refers to the larva? of some boring 

 insect. An attempt was made to get rid of 

 them by applying a handful of salt around the 

 roots once or twice a season with the only re- 

 sult, however, that the larvae were more nu- 

 merous after the application than before. 



P. L. RlCKER 



Bureau or Plant Industry 



SPECIAL ARTICLES 



THE INVERSION OF MENTHONE BY SODIUM, 



POTASSIUM AND LITHIUM ETHYLATES, 



AND A METHOD OF ANALYSIS FOR 



METHONE IN PINE OILS 



The work of Tubandt 1 has shown that the 

 reaction 



Z-menthone ^ d-menthone 



can be followed polarimetrically, is mono- 

 molecular and is catalyzed by acids and 

 bases. The present study has involved the 

 measurement of the velocity of the inversion 

 when brought about by sodium, potassium and 

 lithium ethylates in absolute ethyl alcohol at 

 25° ; a special constant temperature bath, hold- 

 ing silver-plated copper polarimeter tubes, has 

 been employed. 



The molar constant, Km, found for the ac- 

 tivity of the three ethylates at dilutions rang- 

 ing from N/32 to N/512, were substituted in 

 the equation K K =K 4 a -f- K m (l — a), derived 

 by one of us 2 to express the activity of both the 

 non-ionized molecules and the ions of a react- 

 ing electrolyte, and gave series of satisfactory 

 constants for the activity of both the ethylate 

 ions, K», and the non-ionized molecules Km, of 

 each ethylate. 



It was found that the constant expressing 

 the activity of the ethylate ion was the same, 

 whether calculated from the data for sodium, 

 potassium or lithium ethylate: for NaOCsIL, 

 Pi = 0.501; for KOCJ£ s , K 4 = 0.501, and 

 for LiOC„H 6 , K i = 0.496." The constants for 



i Ann., 339, 41, 1904. 



2 Am. Chem. Jour., 48, 359, 1912. 



the reactivity of the non-ionized ethylate were ' 

 found to be very nearly the same for sodium 

 and potassium ethylates, but somewhat lower 

 in the case of lithium ethylate, as has been 

 found to occur with other reactions. Thus, for 

 NaOCJEI,, K m = 0.693; for KOCJI 5 , K m = 

 0.701, and for LiOOH,, K„, = 0.478. 



The relative magnitudes of these constants 

 agree with the fact that the molar constant, 

 -K N , drops off with dilution for sodium and 

 potassium ethylates, but does not change with 

 dilution in the case of lithium ethylate; that 

 the molar constants for sodium and potassium 

 ethylates are close to one another in value, but 

 different from those for lithium ethylate ; and, 

 finally, that the reaction velocity constants be- 

 come practically the same for all three ethy- 

 lates in the very dilute solutions in which the 

 metallic ethylate is nearly completely ionized. 



Having shown above that sodium, potassium 

 and lithium ethylates cause the inversion of 

 menthone, it was thought important to use this 

 as an analytical method to determine the pres- 

 ence of menthone, and its amount, in certain 

 pine oils said to contain the levo form of this 

 material. Eight per cent, absolute alcoholic 

 solutions of pine oil and of several of its frac- 

 tions were made. These contained also N/64 

 sodium ethylate. These solutions showed no 

 appreciable change in optical rotation in about 

 three hours. In order to prove that no Z-men- 

 thone was present in the pine oil an alcoholic 

 solution containing 2 per cent, of partly in- 

 verted Z-menthone and 8 per cent, of the same 

 pine oil, or of its fractions, and iV/64 sodium 

 ethylate, was found to give the usual change in 

 rotation observed for alcoholic solutions of 

 Z-menthone. It is clear, then, that pine oils 

 have no appreciable influence on the change of 

 rotation of admixed Z-menthone and that the 

 amount and rapidity of change of rotation by 

 a given concentration of sodium, potassium or 

 lithium ethylate can be used as a measure of 

 the amount of d- or Z-menthone in pine oil in 

 excess of any amount of the equilibrium mix- 

 ture of d- and Z-menthone. If there is an ex- 

 cess of Z-menthone present its effect on the ro- 

 tation may be offset by other constituents hav- 



