— 100 — 



with great ease from menthenone. In analogy with the method given by 

 Bredt for carvenone we heated 30 g. menthenone with 36 g. phosphoric 

 anhydride to 180 to 190°, afterwards treating the reaction-product in the 

 usual manner. The cymene boiled at 174 to 176° and, when oxidised 

 with permanganate, yielded hydroxy-isopropyl benzoic acid, melting at 

 154 to 155°. 



Oxidation into thymol: In order to convert the ketone into the 

 phenol we boiled 60 g. menthenone with a solution of 175 g. ferric chloride 

 in 160 cc. glacial acetic acid and 600 cc. water. The ferric chloride was 

 reduced within an hour, and the thymol was separated from the unused 

 menthenone by steam distillation and treatment with soda liquor. It boiled 

 at 231 to 233° and was identified from the phenylurethane (prepared by 

 adding aluminium chloride), m. p. 104 to 105°. 



Reduction to menthol and menthene: Reduction with sodium 

 in ethereal solution yields a product of a menthol-like odour. We did 

 not, however, isolate this product, but with chromic acid in glacial acetic 

 solution we oxidised into the corresponding ketone the alcoholic portions 

 which had been separated by steam-distillation from the pinakone, of 

 which a considerable quantity had been formed. The ketone was not a 

 uniform compound but by all appearance a mixture of menthone and 

 unattacked menthenone. The former we were able to identify from the 

 semicarbazone (m. p. 212 to 213°) by the same method which was used 

 by Wallach 1 ) for i-menthone from synthetic menthenone. 



Conversion into terpinene monochloride (zl 1,3 -monochloro- 

 2-dihydrocymene) and reduction of the latter into a-terpinene 

 (A 1, 3 -dihydrocymene). 



In the course of the investigations into the constitution of terpinene, 

 or the preparations of a-terpinene in the pure form, a reaction assumed 

 prominence which is based upon the conversion of carvenone by phos- 

 phorus pentachloride into terpinene monochloride and the reduction of 

 the latter to a-terpinene. Auwers 2 ), and in particular Wallach 3 ), have 

 shown that it is most difficult to obtain uniform products by this reaction, 

 the course of which Semmler 4 ) assumes to be uniform. In any case, 

 however, it is possible to obtain a product which is rich in a-terpinene. 

 Auwers 5 ) has tried to apply this reaction also to pulegone, hoping by 

 this means to obtain the as yet unknown hydrocarbon m>terpinolene, but 

 in the place thereof he obtained a mixture of hydrocarbons consisting 

 principally of various menthenes. 



!) Liebigs Annalen 362 (1908), 272. 



2 ) Berl. Berichte 42 (1909), 2424; Report October 1909, 173. 



3 ) Liebigs Annalen 368 (1909), 13; Report October 1909, 175. 



4 ) Berl. Berichte 41 (1908), 4474; 42 (1909), 522, 4171; Report April 1909, 122; October 

 1909, 171 ; April 1910, 169. 



») Berl. Berichte 42 (1909), 4895; Report April 1910, 163. 



