262 



SCIENCE 



[N. S. Vol. XXXVI. No. 922 



identical with the hemiterpene, isoprene." 

 Now, angelic and tiglic acids are compara- 

 tively common in the plant world and if, 

 as Kondakow states, these hydrocarbons are 

 readily obtained from the acids, then it is 

 possible that the hemiterpenes are formed 

 in this way and by the condensation of two 

 molecules of the hemiterpenes, a terpene in 

 this particular case, eamphene, is formed 

 according to the following simple equation : 

 2C„H8 = Ci„Hie. 

 In pursuing the work of the terpene 

 polymerization, practically all of the meth- 

 ods in the terpene literature were tried. 

 All of them, however, were unsatisfactory. 

 It was noticed in previous work on the 

 chlorhydrochlorides' of terpenes, that in the 

 preparation of the hydrochloride on a large 

 scale there was always left a considerable 

 portion of material of thick oil consistency 

 after the chloride had been removed. 

 Examination showed that this oil contained 

 a small quantity of resinous matter. After 

 unsatisfactory attempts to isolate the resin, 

 other agents were tried. Bromine and 

 iodine were tried and each was found to 

 produce resins more readily than chlorine. 

 As iodine gave best results, it was used in 

 the experimental work which follows. It 

 was found, first of all, that iodides some- 

 what similar to the chlorhydrochlorides 

 could be formed, especially if the reaction 

 took place in sunlight. These iodides were 

 first isolated and studied. The diiodide 

 proved to be of special interest. When 

 pure it is a heavy colorless oil with a slight 

 camphoraceous odor. When exposed to 

 sunlight it readily decomposes, liberating 

 iodine and resins, notwithstanding the fact 

 that sunlight seems to play an important 

 part in its formation. If exposed to sun- 



° It may be interesting to the reader to note that 

 isoprene has very recently been polymerized to 

 India rubber. 



' Jour. Am. Chem. Soc, 28, p. 1461. 



light for some time the iodine is all liber- 

 ated and there is left a resinous mass com- 

 posed chiefly of two substances. This res- 

 inous mass was subjected to distillation in 

 vacuo. The distillate obtained was a thick, 

 colorless, stable oil. Its molecular weight 

 indicated a dipinene. It contained no 

 iodine, and from its remarkable stability it 

 is probable that the pinene radicles are 

 doubly joined to each other. By oxidation 

 it forms an acid isomeric with abietic acid. 

 The residue left in the flask after the di- 

 pinene had been removed was also of un- 

 usual interest. It proved to be a solid of a 

 light amber color. It had exactly the same 

 melting point of ordinary rosin. Most of 

 its properties were also identical with those 

 of common rosin. It proved to be a tetra 

 pinene, and, owing to its close resemblance 

 to ordinary colophonium, it has been called 

 colophonene. 



These two condensed forms, the di- and the 

 tetra-pinene compounds, have been isolated 

 and carefully studied. Both are stable, 

 but may be oxidized to acids with many of 

 the characteristics of the resin acids. A 

 comparison of these synthetic compounds 

 with the natural resins is both interesting 

 and important. Those which have been 

 prepared and examined at the present time 

 do not agree in every respect with the nat- 

 ural resin acids. This fact is not sur- 

 prising, however, as any one of the differ- 

 ent groups, occurring in the molecule when 

 oxidized, would give a different acid. It 

 would, therefore, be mere chance if the 

 synthetic compounds should be identical 

 with the common resin acid. 



In summing up the experimental evi- 

 dence in connection with the theories of the 

 formation of the resins and terpenes and 

 their chemical relationship, the following 

 syntheses may, under different conditions, 

 represent what takes place in certain phases 

 of plant life: 



