﻿THE TERPEN E OILS OF MANILA ELEMI. 21 



Product, VIII, A, purified, showed: n ^=1.4705 and n ^=1.4728. 

 An average difference of 0.0071 was found between specific gravity ( ®) 

 and specific gravity ( 4 ) for three samples. The molecular refraction 



of limonene at 20° may therefore be calculated. 



The value of the rotation given corresponds very closely to that noted 

 by Kremers. 10 The latter states that the rotatory power of limonene 

 changes considerably on standing, giving as an instance a sample the 

 rotation of which had changed from +121°. 3 to +103°.23. He also 

 notes a corresponding increase in the specific gravity. I have found 

 that a sample of pure limonene, sealed up in a nearly filled flask, suffered 

 no noticeable change after standing four months, but several samples of 

 pure limonene which were kept in glass-stoppered bottles were found 

 to decrease gradually in rotatory power ; the same is true of phellandrene. 

 This change is undoubtedly caused by oxidation of the terpene. One 

 sample of limonene which originally had a rotation of -|-100 o .6 stood 

 for about a year in a partly filled, glass-stoppered bottle. It was then 

 redistilled with steam. A considerable amount of non-volatile matter 

 remained behind and the distillate had taken on a "menthol" odor. The 

 oil was redistilled in vacuo and then showed a rotation of -)-100 o .2. It 

 boiled completely from 176°.5tol77°.5. 



The behavior of limonene at elevated temperatures was also studied, 

 the question being considered of considerable importance because of the 

 readiness with which so many of the substances of the composition 

 C 10 H ie change into isomeric bodies. Wallach 20 states that hesperidene 

 (dextro-limonene obtained from oil of orange) is changed into dipenteno 

 by "mehrstundiges" heating at 250° to 270° and a similar statement, 

 probably derived from this source, appears in many of the books dealing 

 with this subject. 



(1) Twenty-five grams of pure limonene (a -p.= 100°.7) were heated in a 



sealed tube at 275° to 290° for five hours. The product was then distilled with 

 steam and a small amount of non-volatile matter, about % 5 per cent of the 

 original, remained behind. The polymerized product is only slightly soluble 

 in alcohol. The distillate after having been dried over solid potassium hydroxide, 

 showed exactly the same boiling point as the original. Its rotation was +99°. 8 

 and its refractive index was practically unchanged. A tetrabromide was pre- 

 pared in acetic acid and after recrystallizing once from acetic ester melted 

 at 104°-105°, this being the melting point of pure limonene-tetrabromide. 



(2) The limonene obtained from the last experiment was heated, together 

 with 2 or 3 drops of water, in a sealed tube at 290° for ten hours, the temperature 

 rising to 360° for a short time. On examining the contents of the tube the 

 water still appeared and the product was colorless. After distilling with steam, 



19 Loc. cit. 



20 Ann. Chem. (IAebig) (1885), 227, 289. 



