103-104 C.] 



TIGLIC ALDEHYDE 



191 



of the aldehyde (Herzig and Schiff, 

 Monats. 18, 714)- 



SYNTHETICAL PROCESS. 



[A.] From acetic aldehyde [92] and 

 propionic aldehyde (see under hexoic 

 aldehyde [2-methylpentanal ; 96,111; 

 A., C, &c.]) by heating 1 a mixture with 

 sodium acetate solution at 100 (Lieben 

 and Zeisel, Monats. 1, 54 : see also 

 Schmalzhofer, Monats. 21, 671). 



104. Citral ; Geranial ; 



Rliodiiial ; Licareal ; 

 2 : G-Dimetliyl-2 : G-Octaclieiial-8. 



CH 3 .C :CH.CH 2 .CH 2 .C:CH.CHO 

 CH 3 CH 3 



NATURAL SOURCES. 



In oil of lemon-grass from Andro- 

 pogcn citratus from India, Ceylon, 

 Singapore, and Jamaica (SchimmePs 

 Ber. Oct. 1888; Dodge, Am. Ch. , 

 Journ. 12, 553; Ber. 24, 90; Ch. 

 Centr. 1891, 1, 88); in oils of lemon, 

 Citrus limonum (Schimmel's Ber. Oct. 

 1888, p. 17); of C. medica (Ibid. 

 Oct. 1895; Burgess, 'Analyst/ 26, 

 260) ; of Eucalyptus staiaeriana or 

 ' lemon-scented iron-bark'' of Queens- 

 land (Schimmel's Ber. April, 1888); 

 of Baekkouna citriodora, Queensland 

 (Ibid, and Oct. 1888); of Tetranthera 

 citrata, Java (Ibid. Oct. 1888); and of 

 Xanthoxylonpiperitiim, Japan (Ibid. Oct. 

 1890). 



Citral occurs also in oil of Lippia 

 (Aloysia) citriodora or ( lemon-scented 

 verbena ' (Umney, Imperial Inst. Journ. 

 1896, p. 302; Journ. Soc. Ch. Ind. 15, 

 739 ; Pharm. Journ. 57, 2.57 > Barbier, 

 Bull. Soc. [3] 21, 635), in oil of man- 

 darin orange from Citrus nolilis or C. 

 madurensis (Semmler, Ber. 24, 202 ; 

 Schimmers Ber. April, 1897 ; Journ. 

 Soc. Ch. Ind. 16, 556 ; Flatau andLabbe, 

 Bull. Soc. [3] 19, 364), and in oil of 

 sassafras leaf from S. officinalis (Power 

 and Kleber, Pharm. Rev. 14, 103 ; Ch. 

 Centr. 1897, 2, 42). 



Citronella oil from Andropogon nardus, 



according to Flatau (Bull. Soc. [3] 21, 

 158), contains 2-5 per cent, citral. This 

 aldehyde is contained also in the oils of 

 Eucalyptus patentinervis and E. vitrea 

 (Smith, Proc. Roy. Soc., N. S. Wales, 

 1900; 'Nature/ 62, 384; SchimmeFs 

 Ber. Oct. 1901), in oil of sweet orange 

 (Semmler, Ber. 24, 202 ; Parry, ' Chemist 

 and Druggist/ 66,462; 722; Fabris, 

 Journ. Soc. Ch. Ind. 19, 771), in oil of 

 W. Indian bay from Pimento, acris 

 (Power and Kleber, Pharm. Rund. 13, 

 60), in oil of Pimenta leaf from a 

 Trinidad sp. (Schimmer's Ber. Oct. 

 1896), and in German oil of rose (Wal- 

 baum and Stephan, Ber. 33, 2305). 



NOTE: Citral, according to Doebner (Ber. 31, 

 1888 ; also Tiemann, Ibid. 2313), is the chief 

 unsaturated open-chain aldehyde present in 

 lemon-grass oil. According to Stiehl (Journ. 

 pr. Ch. 58, 51 ; 59, 497 ; Ch. Zeit. 22, 1086) 

 two other aldehydes are present, but these 

 have not been found by Semmler (Ber. 31, 

 3001), by Doebner (Ibid. 3195), nor by Tiemann 

 (Ibid. 3336; 32, 827). The citral from lemon- 

 grass oil and from ' verbena ' (Lippia citriodora} 

 consists of a mixture of two stereo-isomerides 

 (Tiemann, Ber. 33, 877 ; Kerschbaum, Ibid. 

 885). 



For bibliographical history of citral see Tie- 

 mann, Ber. 31, 3278 ; 32, 831, foot-note. 



SYNTHETICAL PROCESSES. 



[A.] From acetic acid [Vol. II], alcohol 

 [14], and methylheptenone [111]. Brom- 

 acetic ester (Perkin and Duppa, Ann. 

 108, 106; Hell and Miihlhauser, Ber.ll, 

 241 ; 12, 735 ; Michael, Am. Ch. Journ. 

 5, 202) and methylheptenone are heated 

 with zinc, and the product (hydroxy- 

 dihydrogeranic ester) hydrolysed by 

 dilute alcoholic potash so as to give the 

 acid (hydroxydihydrogeranic = 2 : 6-di- 

 methyl-2-octene-6-olic-8-acid). The lat- 

 ter, on heating with acetic anhydride and 

 sodium acetate, gives geranic = 2:6- 

 dimethyl-2 : 6-octadiene-8-acid, and this, 

 on distilling the calcium salt with cal- 

 cium formate [Vol. II], yields citral 

 (Tiemann, Ber. 31, 827). 



[B.] Geraniol [36] gives citral on 

 oxidation with chromic acid mixture 

 (Barbier, Bull. Soc. [3] 9, 803 ; Semm- 

 ler, Ber. 23, 2966; 24, 201 ; Tiemann, 

 Ber. 31, 3311). 



[C.] Linalool [37] gives citral on 

 oxidation as above (Tiemann and Semm- 



