— 132 — 



present in such quantity as to influence the boiling point of inactive 

 limonene to such an extent. Wallach considers it probable that the 

 increase in the boiling point is due to another hydrocarbon which is 

 difficult to separate from dipentene even by repeated fractionating. For 

 practical purposes it is in any case clear that in searching for dipentene 

 in mixtures of hydrocarbons, now as before the fractions boiling some- 

 what higher than limonene must be taken into consideration. 



J. W. Bruhl 1 ) reports on the relations between the physical constants 

 of d- and 1- and also i-limonene, which he compares with the constants 

 of Perkin's and Kay's 2 ) zl 3) 8(9)-menthadiene. The limonenes had been 

 produced by us from caraway oil and templin oil respectively. The 

 1-limonene had a somewhat lower rotation than the d-limonene, but 

 could not be purified further by fractional distillation. 



The constants given by Bruhl are: — 





Boiling point 



(763 mm. press., 



corr.) 



d 



«D 



n D 



M D/2~ 



m d/T 



calculated 



d-limonene 



175,5 to 176,5° 



0,8402 

 21° 



0,8407 

 20,5° 



+ io 4 °i5' 

 at i 9 ,5° 



1,47428 

 at 21° 



45,51 



45, 2 4 



1-limonene 



175,5 to 176,5° 



— ioi°3o' 

 at 19,5° 



1,47468 

 at 20,5° 



45,52 



45,24 



d- and 1-limonene 

 in equal parts 



175,5 to 176,5° 



0,8409 

 20,7° 



+ I°2 9 ' 



at 19° 



1,47448 

 at 20,7° 



45,49 



45, 2 4 



d- and so much 

 1-limonene that 



175,5 to 176,5° 



0,8402 

 .♦ 2 °> 8 5° 



±o° 

 at 20° 



1,47 443 

 at 20,85° 



45,53 



45,24 



the mixture was 





at 

 4 











inactive 













As d- and (d-(-l)-zl3 j 8(9)-p-menthadienes of Kay and Perkin show 

 considerable differences in these constants, they cannot stand in the 

 same relation to each other, as d- and 1-limonene on the one side 

 to dipentene on the other. For it will be seen from the table that 

 these bodies correspond completely in their properties. It is more 

 probable that (d-|-l)-zl3 j 8(9)-p-menthadiene is a racemic body. 



Our view (which we communicated to Mr. Bruhl), that the 

 1-limonene was not absolutely pure, is based upon the lower rotation 

 as compared with d-limonene. Now if Bruhl finds a further proof 

 for the impurity in this, that a mixture of equal parts of d-limonene 

 («d4-io4°I5 / ) and 1-limonene (« D — ioi°3o') only rotates -f-i 2o/, 



*) Journ. chem. Soc. 91 (1907), 120. 



2 ) Journ. chem. Soc. 89 (1906), 839; Report October 1906, 107. 



