THE CHEMICAL HISTORY OF THE TERPENES 53 



A. CMe CMe 



CH, 



CH, 



CH 

 Me 2 C.OH 



Terpineol. 



OCMe 



CH 



CH a 



CH 



o pinonic acid. 



OCMe 



CH, 



CH 2 



Methyl ketone of homoterpenylic 

 acid. 



a pinonic acid is converted by heating with 50 per cent, 

 sulphuric acid into the ketone, which was first obtained by 

 Wallach as a product of the oxidation of terpineol. 



The dimethylated tetramethylene ring in the formula for 

 pinene has been called by Baeyer " picean," and he has directed 

 special attention to its peculiarities. While it is readily 

 ruptured by the hydrolysing action of dilute acids, it resists the 

 attack of neutral oxidising agents in a remarkable manner. 



Among the products of the oxidation of pinene by perman- 

 ganate is found not only a pinonic acid C 10 H 16 O 3 but a dibasic 

 pinoyl-formic acid C 10 H 16 O 5 . Both these compounds contain 

 the same stable nucleus of four carbon atoms, which is capable 

 of hydrolytic rupture much as in the case of pinene itself. Both 

 acids when further oxidised yield the same pinic acid, C9H14O4, 

 which, however, is not similarly changeable by hydrolysis. 

 Pinic acid when brominated and then treated with baryta gives 

 a hydroxypinic acid, from which by further oxidation norpic 

 acid, C 8 H 12 4 , is obtained. Norpic acid has the constitution 

 shown below, retaining the picean ring : 



co,H . CH 



\ 



CMe, 



CH . C0 2 H 



CH a 



Norpic acid is extremely stable and resists further oxidation. 

 Finally, the view of the constitution of terpineol set forth 



