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CLOVER. 



LBIONE'NH. 



Limonene is one of the most widely distributed terpenes. It occurs 

 generally in the dextro-rotatory form, as the chief component of a number 

 of the most important essential oils of commerce. From some of these 

 it has been obtained in a fair degree of purity by fractional distillation, 

 but the physical properties of the substance as given in the literature 

 vary somewhat, depending upon the degree of purity with which it is 

 possible to isolate it from the other constituents of those oils by the 

 process mentioned. From caraway oil Schimmel and Co. 13 have isolated 



dextro-limonene which showed a notation of [a] jy= +123°. 6 while 

 Kremers 16 obtained [a] ^ = -j-120°.46 for the carefully fractionated por- 

 tion of commercial carvene boiling at 174°. 5 to 175°, and presumably 

 from the same source. For the lsevo-limonene of pine-needle oil, Wallach 

 found [a] D = — 106°. Godlewsky and Robhanowitsch 17 for the purpose 



of obtaining accurate data as to its physical constants, have succeeded 

 in preparing what appears to be almost, if not quite pure, limonene 

 by reduction of the pure tetrabromide. Their product which is described 



as constant-boiling, showed:— sp. gr. ( 2 4 °) = 0.8425; [a] p = -f 125°. 6; 



boiling point, 177°. 5 at 759 millimeters. Considering the small variation 

 which I have found in the optical activity of the many constant-boiling 

 samples of dextro-limonene obtained from different samples of elemi, 

 this property appears to serve well as a check upon the purity of the 

 limonene. 



The following table of physical constants for dextro-limonene is taken 

 from some of the samples which have a rotation close to the average : 



Designation of 

 product. 



Boiling 



point 

 complete. 



„ 30 

 a D 



+ 



n 30 

 n D 



Sp. gr. 

 ( 3 4°) 



Boiling point at reduced 

 pressure. 



VIII. A, purified 



XII, A, purified 



XIII, A, purified 



IX,A, purified 



VI, A. purified _ 

 II,A, purified 



o o 

 176 -176.7 

 176 -176.7 

 176. 5-177. 5 

 176. 5-177. 5 

 176 -176.7 

 176 -177 



o 

 100.8 

 100.3 

 100.1 

 100.3 

 99.9 

 100.0 



1. 4679 



1. 4682 



1. 4683 



1. 4680 



0. 8353 



.8;50 



' . 8364 



18 . 8371 



95°.3-96°.5, 60.5 millimeters. 



93°-94°, 55 millimeters. 

 82°.5-S3°.5, 36.5 millimeters. 











15 Gildemeister und Hoffman, Die Aertherischen Oele (1899), 172. 



10 Am. Chem. Jour. (1895), 17, 694. 



"Ghem. Central. (1899), 70, I, 1241. 



18 The high number probably has its cause in the age of the resin ; the product 

 was notably more difficult to purify than any of the others. Unfortunately, 

 several of the samples of pure limonene were used up before their physical 

 constants had been accurately determined. 



