OXIDATION OF MANILA COPAL BY THE AIR. 221 



c 



Herty and Dickson 11 have recently confirmed Schwalbe's experiment on speci- 

 mens which had been exposed to the air, but find that resin which has not been 

 long in contact with the air or oxygen can be heated indefinitely at a temperature 

 of 140° without losing carbon dioxide, provided oxygen and moisture are excluded 

 from the flask in which the resin is heated. Turpentine which had been exposed 

 to the air gave off carbon dioxide when warmed. The authors state as follows: 

 "No question of the splitting off of a car boxy 1 -group could arise here." They 

 also prepared specimens of the resin acids from the oleoresin of Pinus heterophylla 

 (Ell.) Sudworth, in such a manner as to avoid heating. However, they make 

 no mention of having made any effort to exclude oxygen. The salts of the resin 

 acids were dissolved in water, the solutions acidified and the precipitated acids 

 washed and dried. I have found that, when the resin acids from Manila copal 

 or colophony are prepared in this manner, the fine powders obtained rapidly take 

 up oxygen when dried in air. On heating the resin acids in a current of dry 

 nitrogen, Herty and Dickson found that a small amount of carbon dioxide was 

 given off at 65° to 70°. 



It is evident from their work that the evolution of carbon dioxide at compara- 

 tively low temperatures from turpentine and resin requires previous exposure to 

 oxygen. Both of these substances are known to form organic peroxides when 

 oxidized by the air. According to Engler and Weissberg, 12 pinene forms a peroxide 





 of the formula C 10 H 10 <^ | , which on exposure to direct sunlight or warming to 





 80° to 100° decomposes and gives up its "active" oxygen to "inner oxidation." 

 Thus turpentine yields, in addition to carbon dioxide, acetic acid, formic acid, 

 a camphoric acid melting at 176°, and an acid isomeric with campholic acid. 1 " 



Fahrion found that the peroxides formed by the autoxidation of colophony 

 were quickly decomposed by heating to 100° and by long standing in strongly 

 alkaline solutions. 



Dunlap and Shenk u and Genthe 15 found that organic peroxides were formed 

 during the autoxidation of linseed oil, and according to Mulder 1G carbon dioxide, 

 formic acid, and acetic acid are formed at the same time. 



The evolution of carbon dioxide from linseed oil, turpentine, colophon)', 

 the resin acids studied by Herty and Dickson, and Manila copal occurs 

 simultaneously with the breaking down of the peroxides present. If 

 oxygen is excluded and no peroxides are formed, no evolution of the 

 gas occurs. The formation of carbon dioxide, under the conditions 

 described above, can not be accounted for by the decomposition of a 

 carboxyl-group in view of the nature of the substances from which it 

 is evolved, since Herty and Dickson have shown that the resin acids 

 in colophony are not decomposed at a temperature of 140°. Therefore, 

 the conclusion seems warranted that the breaking down of the organic 



"Jowra. Ind. & Eng. Ghem. (1909), 1, 68. 



"Ber. d. deutschen chem. Ges. (1898), 31, 3046; (1900), 33, 1090. Compare 

 Skraval, "Die induzierten Reaktionen," Samm. chem. u. chem.-tech. Vortrage. 

 (1908), 13, 338. 



"Semmler, F. W., Die Atherischen ole, Leipzig (1906), 2, 217. 



u Journ. Am. Ghem. Soc. (1903), 25, 826. 



"Ztschr. f. ang. Chem. (1906), 25, 2087. 



10 Chemie der austrocknenden Oele, Berlin (1867), 109. 



