128 A-129 D.] 



PULEGONE 



227 



Tiemann, Ber. 32, 825 ; Harries and 

 Boeder, Ibid. 3357). 



NOTE : Isopulegol is formed (with mentho- 

 glycol) by agitating citronellal with 5 per cent, 

 sulphuric acid (Barbier and Leser, Comp. 

 Rend. 124, 1308). 



[B.] From isopulegol [42] as above. 



129. Meiithoiie ; 

 Methylisopropyl-ketohexamethylene. 



CH 3 



CH 



SYNTHETICAL PROCESSES. 



H. 2 C CH 2 



H.C C : O 



CH 



CH(CH 3 ) 2 



NATURAL SOURCES. 



With menthol [4l] in oil of pepper- 

 mint from Mentka piperita and vars. 

 (Moriya, Trans. Ch. Soc. 39, 82; 

 Andres and Andre jeff, Journ. Buss. 

 Soc. 23, 26; Ber. 25, 617; Wallach, 

 Ber. 28, 1955; Power and Kleber, 

 Arch. Pharm. 232, 639 ; Charabot, 

 Bull. Soc. [3] 19, 117 : see also 

 SchimmePs Ber. April, 1895 : for 

 occurrence in essence of Mentha pule- 

 ffium see Tetry, Bull. Soc. [3] 27, 186; 

 in Italian oil of peppermint, SchimmeFs 

 Ber. Oct. 1902). 



In Bourbon geranium oil (Flatau and 

 Labbe, Bull. Soc. [3] 19, 788). In oil 

 of Eiicalyptus Jiamastoma (SchimmeFs 

 Ber. April, 1888), and in the oil of 

 Bystropogon origanifolius, Teneriffe 

 {Ibid, Oct. 1902; Ch. Centr. 1902, 2, 

 1208). Possibly occurs in oil from 

 ' bucco-leaves ' from S. African species 

 of Barosma (Gildemeister and Hoff- 

 mann, p. 599 ; also Kondakoff and 

 Bachtschieff, Journ. pr. Ch. [2] 63, 49 : 

 see also under dipentene [9, p. 3/]). 



The natural product is 1-menthone. 

 According to Charabot (Ann. Chim. 

 [7] 21, 207 ; 279), menthone is probably 

 formed in plants from the oxidation of 

 citronellol. 



[A.] From menthol [41] by oxidation 

 with sulphuric acid and potassium di- 

 chromate (Moriya, loc. cit. 77 ; Atkin- 

 son and Yoshida, Trans. Ch. Soc. 41, 

 49; Beckmann, Ann. 25O, 325; 289, 

 362). 



1-Menthone, on treatment with strong 

 acids or alkalis at ordinary tempera- 

 tures, or by keeping per se, is trans- 

 formed into d-menthone (Beckmann, 

 Ann. 250, 334). 



[B.] Citronellol [38] is said to give 

 menthone among the products of its 

 oxidation ( Barbier and Bouveault, Comp. 

 Rend. 122,673; 737; 795). 



NOTE : The citronellol referred to is the 

 ' rhodinol ' of Barbier and Bouveault. Ac- 

 cording to Bouveault rhodinal is transformed 

 into menthone by the same process as that by 

 which citronellal is transformed into pulegone 

 (see above). Tiemann and Schmidt on the 

 other hand consider rhodinol and citronellol to 

 be the same compound and the corresponding 

 aldehydes to be also identical (Tiemann and 

 Schmidt, Ber. 29, 925 ; Harries and Roeder, 

 Ber. 32, 355 : compare Bouveault, Bull. Soc. 



[ 3 ] 23, 458 ; 463). 



[C.] From metacresol [62] through 

 m-(y)-cresotic acid (m-homosalicylic 

 = m-hydroxy-p-toluic acid) by the 

 action of sodium and carbon dioxide 

 (Engelhardt and Latschinoff, Zeit. [2] 

 5, 623 ; Biedermann and Pike, Ber. 6, 

 324). Dibrom-m-cresotic acid, on heat- 

 ing with sodium in amyl alcohol and 

 oxidation of the product with alkaline 

 permanganate, gives /3-methylpimelic 

 acid (Einhorn and Ehret, Ann. 295, 

 173). The diethyl ester of the latter 

 condenses under the influence of sodium 

 with the formation of methyl-/3-keto- 

 hexamethylenecarboxylic ester, and this 

 on treatment with sodium and isopropyl 

 iodide [16] gives the isopropyl methyl 

 derivative. The latter on heating with 

 strong alcoholic potash yields a ketone, 

 which is probably methylisopropylketo- 

 hexamethylene = i-menthone (Einhorn 

 and Klages, Ber. 34, 3793). 



[D.] Thymol [67] on distillation with 

 phosphorus pentasulphide gives thio- 

 thymol (Fittica, Ber. 6, 938 ; Ann. 

 172, 325), and this on oxidation with 

 nitric acid yields 3-sulpho-p-toluic acid 

 (IL-uL Ann. 172, 329). The latter on 



Q2 



