88 



THE ALUMNI JOURNAL. 



2. 



atives of protocatecehuic alde- 

 hyde. 

 Isovanillin is formed, that is when 

 the methyl group replaces in the 

 hydroxyl occupying the vieta posi- 

 tion : 



a) in methylating mono-metallic salts 

 of protocatechuic aldehyde, 

 in methylating di-acetyl com- 

 pounds of protocatechuic alde- 

 hyde. 



COH 



b) 



COH 



COH 



JOCH, 



OH 



Vanillin. 



OH 



O. CH3 



Isovanillin. 



Homologues of vanillin may be pre- 

 pared after this process, in which an ethyl 

 group is introduced in place of a methyl. 



Another class of vanillin syntheses 

 start from the mono-methyl ether of pyro- 

 catechin (guaiacol), which on treatment 

 with chloroform and alcoholic potassa, 

 yields vanillin direct. 



COH 



/\ 



OCH, 



OH 



Guaiacol 



OH 



Vanillin. 



O. CH3 



In this process a side product is form- 

 ed, in which the aldehyde group enters 

 the ortho instead of the para position, this 

 product being methoxysalicylic aldehyde. 



COH' 'O. CH3 

 OH 



This feature has been avoided by von 

 Heyden, in which guaiacol-carboxylic 

 acid (produced in his synthetic salicylic 

 acid process) it treated with chloroform 

 and alcoholic potassa, yielding vanillic 

 acid, from which vanillin is obtained up- 

 on the removal of CO. group ; 



coohI J0CH3 



COOH' JOCH 



OH 



Guaiacol carboxylic acid. 



OH 



Vanillic acid. 



Lately Fajans devised a process in 

 which by the action of CO., on guaiacol 

 sodium at 180° C, aguaicol-di-carboxylic 

 acid is formed, thus : 



COH 



COOH' 'OCH, 

 OH 



Then on treatment with chloroform 

 and potassa, the carboxyl group (para) 

 is replaced by the aldehyde group, yield- 

 ing vanillic acid which is converted into 

 vanillin by heating. 



Summing up the various processes,, 

 they may be classified as follows : 



1. Through oxidation of an aliphatic 

 side chain, vanillin may be obtained 

 from 



a) coniferin, glucovanillin, olivil, 

 acetoferulic acid ; 



U) eugenol, isoeugenol, aceteugenol, 

 eugenol acetic acid, aceto-iso- 

 eugenol, benzyl-iso-eugenol, me- 

 thylen-iso-eugenol, iso-eugenol- 

 toluic acid, 



2. The following compounds are capable 

 of being converted into— ^-nitro-?«- 

 methoxybenzaldehyde, which is readi- 

 ly converted into vanillin : 



Toluol (as /'-nitro-;?z-chlorotoluol), 

 cinnamic acid (as 7«-methoxycinnamic 

 ester), benzaldehyde (as w-amido- 

 benzaldehyde). 



3. Through introduction of a methyl 

 group in protocatechuic aldehyde 

 yielding vanillin : 



The di-metallic salts, the mono- 

 acetyl, the benzyl and the benzol- 

 sulpho compounds of protocatechuic 

 aldehyde. 



