— 170 — 



of potassium has now been investigated more closely. It is formed 

 by oxidising a-pinolene, and by analysis and the determination of 

 bases it was identified as racemic camphoric acid. Regenerated 

 from the anhydride, the acid melts at 20 2° 



Pure isopinene has the following constants: b. p. 154,5 to 155,5°, 

 d^° 0,8658, « D -(-2,6i , n D 1,470253, mol. refr. calc. 43,53, found 

 43,48. After heating for 8 hours with permanganate of potassium in 

 1,5 per cent, aqueous solution at 60 to 70 , the constants of the un- 

 attacked isopinene had remained almost unchanged. In the process 

 of oxidation two acids were obtained, the first (A), crystallising from 

 water in small, thickish flakes or prisms, m. p. 126 to 12 8°; the other 

 (B), easily soluble in water and melting at 200 . Acid A had the 

 formula C 10 H 16 O 3 ; it is a keto-acid, as is shown by the phenyl hydra- 

 zone (although this is unstable), and the semicarbazone. Acid B was 

 identified as m-apocamphoric acid by its constitution (C 9 H 14 4 ), its 

 inactivity and the forming of an anhydride melting at 178 to 179°. 

 From these facts, Aschan concludes that only one of the formulae I 

 and II applies to isopinene: — 



CH 9 CH C=CH„ CH 2 CH C • CHg 



C H„ — C — CH„ 



CH 



I 

 CH CH 



II. 



CH,-C-CH, 



CH 



I 

 -CH CH 



The first of these has been considered by Wallach for D-l-fen- 

 chene or L-d-fenchene. As fenchene, when oxidised, yields hydroxy 

 fenchenic acid (m. p. 153°) it follows that formula I. cannot apply to 

 isopinene. 



The keto-acid, m. p. 126 to 12 8° (called fenchenonic acid by 

 Aschan), gives, when oxidised with bromine and alkali, apocamphoric 

 acid. Hence the oxidation of isopinene proceeds in the manner 

 subjoined: 



CH CH C • CH Q CH 9 CH CO • CH a 



CH 2 — CH CH 



Isopinene 



CH 3 -C-CH 3 



3 i 



CH 2 CH C0 2 H 



Fenchenonic acid 



CH 2 CH C0 2 H 



CH3-C-CH3 



CH 2 CH C0 2 H 



Apocamphoric acid 



Limonene. On the use of limonene in the preservation of phos- 

 phorated oil, see Orange oil, p. 66. 



Terpinolene. Oxidation of terpinene obtained by the customary 

 methods yielded as its principal product a, a'-dihydroxymethyl-z^propyl- 

 adipic acid, and the erythritol C 10 H 16 (OH) 4 m. p. 23 7 . The acid 

 is no doubt formed from a-terpinene (zJi 3 3-dihydrocymene), while the 

 erythritol most probably is derived from y-terpinene (zJi 3 4-dihydrocymene). 



