— 164 — 



Chemical. 



In the hydrogenation of certain unsaturated compounds of the terpene 

 series, Wallach 1 ) has employed Paal's method, by which is understood 

 a reduction carried out in neutral solvents by the aid of palladium and 

 hydrogen, similar to that according to the slightly modified method of 

 Skita 2 ), and of Vavon 3 ), which has already been described in our Reports. 

 Wallach regards Paal's reduction-process as one of the most valuable 

 modern aids in the research into unsaturated alicyclic compounds. It is an 

 inestimable advantage of the method that it is carried out without heat 

 and with neutral solvents, for which reason constitutional interchanges are 

 impossible. Moreover, with the palladium method it is possible, at ordinary 

 temperature, to dissolve by means of hydrogen absorption, hydrocarbon 

 compounds which resist other reducing agents. 



It is an important condition of succes in the experiment that the 

 bodies to be reduced should be as pure as possible, as otherwise trouble- 

 some by-products are formed which lower the activity of the catalysing agent. 



The reduction of i-a-terpineol (m. p. 35°) gave rise to p-menthanol-8 

 (b. p. 209 to 210°; d 20 o 0,905; n D20 o 1,4629) of which the phenylurethane 

 melts at 115 to 116°. These constants agree fairly well with those given 

 by Behal 4 ). 



From /?-terpineol (m. p. 32°), the author obtained p-menthanol-1 (tert. 

 carvomenthol) which had already previously been prepared by v. Baeyer 5 ) 

 in a roundabout manner. This body has the following constants: b. p. 

 208 to 209°, d 20 o 0,9000, n D20O 1,4619. Its phenylurethane melts at 100 to 

 101°. When p-menthanol-1 is heated with chloride of zinc, ^-tetrahydro- 

 p-cymene (carvomenthene) is formed; a hydrocarbon with a limonene-like 

 odour. The nitrosochloride of carvomenthene (m. p. 95 to 96°) yields 

 with piperidine a nitrolpiperidine, m. p. 159° which, when the hydrogen 

 chloride has been removed, forms a solid oxime. The ketone which is 

 regenerated from this oxime, and purified from the semicarbazone (m. p. 

 177 to 178°), is i-carvotanacetone (m. p. of the oxime 93 to 94°) which, 

 therefore, can be prepared synthetically by this method. 



The reduction of sylveterpineol 6 ) gives rise to dihydrosylveterpineol 

 (m-menthanol) a body with the following constants: b. p. 206 to 208°, 

 d 18 o 0,9090, n D180 1,4645, mol. refr. found 47,40, calc. as Ci H 19 OH 47,55. 

 The phenylurethane melts at 71 to 74°. When heated with chloride of zinc 

 there is formed an m-menthene, b. p. 168 to 169°, d 20 o 0,8180, n D20 o 1,4556, 

 probably admixed with a hydrocarbon with a semicyclic bond. 



*) Nachr. K. Ges. Wiss. Gottingen 1910, Meeting of October 29 th . 



2 ) Report October 1909, 186. 



3) Report April 1910, 166; October 1910, 174. 



4 ) Compt. rend. 150 (1910), 1762; Report October 1910, 189. 

 & ) Berl. Berichte 26 (1893), 2270. 



6 ) The product also contains fractions with a lower b. p. (about 75°). 



