— 138 — 



Since then the same author has continued his investigations 1 ) and has 

 discovered that the hydrogenation of limonene takes place in two phases. 

 In the first stadium a hydrocarbon Ci Hi 8 is formed, and this body yields 

 the ultimate product Ci H 2 o. The last-named compound being inactive, 

 examination of the rotation shows how far the process of reduction has 

 proceeded. By this means it was easy to obtain the hydrocarbon C10H1& 

 in the pure state. Its constants are as follow: b. p. 175 to 177°, di 8 o 

 0,8246, [«] 578 +118°, n D180 1,4563. The dibromo derivative possessed the 

 following properties: b. p. 136 to 140° (16 mm.), d 2 ^ 1,459, [4> 7 8-|-49°, 

 nD2io 1,5236. The nitrosochloride ([«] 578 + 344°) melts between 95 and 96°. 

 This dihydrolimonene is probably pure d-carvomenthene, while the 

 product obtained by Wallach 2 ) was partly racemised. 



Dipentene. By treating dipentene nitrosochloride or nitrosate with 

 sodium azide, M. O. Forster and F. M. van Gelderen 3 ) have succeeded in 

 preparing dipentene nitrosoazide, Ci Hi 5 ( : NOH)N 3 , a compound with m. p. 

 between 72 and 73°, and consisting of colourless plates. With alcoholic 

 potash liquor hydrazoic acid is eliminated from the azide, ^-carvoxime 

 being produced. Reaction of hot aqueous oxalic acid with the nitroso- 

 azide yields d^-triazodihydrocarvone, Ci H 15 ON 3 , a colourless liquid with 

 an agreeable odour reminding of peppermint: b. p. 81 ° (0,4 mm.), d 20 o 1,0409. 

 The semicarbazone melts at 132 to 133°. 



The corresponding derivatives of d- and Z-limonene were obtained by 

 the same method, d- and Z-limonene nitrosoazide melt between 52 and 53°: 

 [«] D + 6,5° and — 3° respectively. Treatment of the azides with alcoholic 

 potash liquor gives rise to Z- and d-carvoxime respectively, d- or Z-triazo- 

 dihydrocarvone has the following constants: b. p. 93° (0,46 mm.) and 

 93 to 94° (0,48 mm.) respectively; d 20 o 1,0487 and 1,0472 respectively and 

 Md + 88,49° and —92,5° respectively. Both semicarbazones melt at 220°. 



According to A. H. Richard 4 ), the polymerisation of dimethylbutadiene 

 gives rise to a rubber-like mass from which by means of dry distillation 

 a yield of about 50% of a homologue of terpene, probably dimethyl- 

 dipentene, Ci 2 H 20 , may be obtained. This hydrocarbon possesses the 

 following constants: b. p. 97 to 98° (22 mm.), about 205° at ordinary 

 pressure, d o [0,872, d 2 ^ 0,85322, a + 0, n D25 o 1,47786. Reduction with 

 platinum black and hydrogen results in a hydrocarbon C i2 H 22 , possessing 

 the following constants: b. p. 93 to 95° (20 mm.), d 0O 0,860, df£ 0,842307, 

 "D250 1,46635. No crystalline tetrabromide or hydrochloride of dimethyl- 

 dipentene was obtained, but the author obtained a small yield of the 

 hydrochloride of a nitrosochloride (m. p. about 160°). 



x ) Compt. rend. 152 (1911), 1675. 



2 ) Liebigs Annalen 277 (1893), 132. 



3 ) Proceed, chem. Soc. 27 (1911), 195. 



4 ) Compt. rend. 153 (1911), 116. 





