﻿22 CLOVER. 



about 10 per cent was found to have polymerized. The distillate when dried 

 showed the same boiling point a.s before. .The rotation had decreased a little: 



a g= +97°. 



(3) Twenty grams of pure limonene, together with 2 drops of water, were 

 heated in a sealed tube at 200° for ten hours. The amount of polymerization was 

 small. The boiling point was unchanged as well as the refractive index, 

 although the rotation had decreased 0°.5. 



(4) Twenty grams of pure limonene together with 1 gram of benzoic acid 

 were heated in a sealed tube at 250° for seven hours. The product was extracted 

 with a small amount of potassium hydroxide solution and all of the benzoic acid 

 recovered, it was distilled with steam, only a small amount of residue remaining. 

 After drying, the oil was redistilled and the boiling point found to be practically 

 unaltered, although the rotation had decreased from +110°. 1 to -+-98°. 



(5) Twenty grams of practically pure limonene together with 1 gram of 

 acetone were heated at 300° for six hours. The product was colorless. There 

 was considerable polymerization. The boiling point of the oil was unchanged 

 but the rotation has decreased from +98° to +96°. 5. 



(0) About 20 grams of pure limonene with 2 grams aniline were heated 

 at 280° for seven hours. The product was extracted with very cold, dilute 

 hydrochloric acid and distilled with steam. It then boiled completely from 

 176° to 177°. The rotation had decreased from + 100°.2 to +99°.4. 



(7) A few grams more of the pure substance were added to the limonene 

 obtained from the last experiment and it was heated at 380° for six hours. The 

 product was colorless. Approximately 15 per cent of the total had been poly- 

 merized. The boiling point of the distillate was unchanged, although the rotation 

 had decreased to +93°. 



It will be seen from the above experiments that if dipentene is formed 

 from dextro-limonene at elevated temperatures, the change is an ex- 

 tremely slow one. Even at 380° it would take many hours for the forma- 

 tion of a sufficient amount of dipentene to allow of detection. Moreover, 

 it does not follow that a decrease in the rotation implies the formation 

 of dipentene, although from the unchanged boiling point, this seems 

 probable. It will also be noted that the degree of polymerization is 

 more than double that of inversion. From these experiments limonene 

 is seen to be a very stable substance and almost indifferent to the influence 

 of foreign reagents even with respect to its optical activity. It may 

 repeatedly be distilled at ordinary pressure without any fear of its 

 suffering alteration. It was found that after heating for eight hours in a 

 tightly stoppered distilling bulb, placed in an oil-bath which was kept 

 at a temperature of 180° to 220°, the distillate was identical in all 

 respects with the original except that its rotation had decreased by about 

 0°.2. 



The behavior of dilute mineral acids toward limonene does not appear 

 to have been studied. Limonene is almost completely polymerized by 

 the action of dilute sulphuric acid in glacial acetic acid ; the same reagent 

 in absolute alcohol converts it into optically inactive terpenes which have 



