THE ALUMNI JOURNAL. 



57 



past decade the study of the group of 

 terpenes has been a very productive field, 

 yielding us such odorous and valuable 

 principles as geraniol, ionon iron, isobo- 

 rneol, carvocrol, eucalyptol, camphor, 

 vanillin, etc Among these artificial 

 aromatics, the rapid progress in the 

 various synthetic processes for the pro- 

 duction of vanillin demands particular 

 attention. Vanillin was first produced 

 synthetically by Messrs. Tiemann & 

 Haarmann, from coniferin, a glucoside 

 discovered by the latter in the cambial 

 juice of the Coniferae. This glucoside 

 consists of one molecule of dextrose com- 

 bined with one of coniferyl alcohol, thus: 



CH^CH— CH.OH 



JOCH3 +CbHiA 



OH Coniferin, 



By means of an oxidizing agent, the 

 aliphatic side chain in this coniferyl 

 alcohol is oxidized into an aldehyde 

 group resulting in vanillin, 



COH 



l^/''0CH3 

 OH 



which is the methyl ether of protocatech- 

 uic aldehyde 



COH 



OH 

 This process was patented by Haar- 

 mann in 1877, according to which the 

 hot aqueous solution of coniferin (obtain- 

 ed by exhausting the wood with water) 

 was oxidized with chromic acid, then ex- 

 tracted with ether, the residue remaining 

 after the evaporation of the solvent was 

 vanillin, which was purified by recrystal- 

 lization. 



The knowledge that vanillin was a 

 comparatively simple benzole derivative 

 led to a large number of experiments in 

 view to its direct synthesis. The first 

 attempts were to oxidize bodies of a like 

 constitution to coniferin, such as olivil, a 

 gummy exudation from the olive tree, 

 further from the acetyl derivatives of 

 homovanillic acid and ferulicacid, which 

 are to a certain extent intermediate pro- 

 ducts of the oxidation of coniferyl al- 

 cohol. 



CH=CH— CH.OH 



OCH. 



CHoCOOH 



OH 



Coniferyl Alcohol. 



I 'OCH, 

 OH 



Homovanillic Acid. 



CH=CH— COOH 



OCH, 



OH 



Ferulic Acid. 



By complete oxidation vanillic acid 



/COOH 

 C^H^ — OCH3 

 \0H 



is prodced, from which vanillin may be 

 obtained by the action of chloroform and 

 potassium hydrate, the carboxyl being 

 replaced by an aldehyde group. 



Of greater practical interest is the con- 

 version of eugenol into vanillin. Eugenol, 

 as is well known, occurs as the main 

 constituent of clove oil, hence can be 

 readily obtained ; in constitution it is an 

 allyl guaiacol 



/CH,— CH^CH, (i) 



CSH3-OCH3 (3) 



\0H (4) 



The allyl group (CH — CH=CH,), like 

 the aliphatic side chains, is converted by 

 oxidation into an aldehyde group, thus 

 eugenol is converted into vanillin. An 



