RECENT ADVANCES IN SCIENCE 35 



ORGANIC CHEMISTRY. By P. Haas, D.Sc, Ph.D., St. Mary's 

 Hospital Medical School, London. 



The synthesis of two pentadigalloyl glucoses by Fischer and 

 Bergmann {Berichte, 191 8, 51, 1760) marks a most important 

 advance towards the elucidation of the constitution of the 

 tannins. Previous to the year 191 2, ordinary oak bark tannin 

 had been regarded as being merely the anhydride formed 

 by the abstraction of one molecule of water from two mole- 

 cules of gallic acid : 



2 C 6 H 2 (OH) 3 COOH - H,0 = C 14 H 10 O 9 . 



Nobody seemed to doubt the accuracy of this assumption, 

 and all investigations concerning the chemistry of tannic acid 

 were directed towards (a) establishing the exact mode of union 

 between the two molecules and (b) suggesting a formula which 

 would account for the optical activity of the compound. The 

 fact, however, that natural tannin was always associated with a 

 certain small percentage of glucose led Fischer to suggest that 

 tannin was not merely the simple anhydride of gallic acid, but 

 that it was in reality some kind of compound of this substance 

 with glucose. With the object of testing this view he syn- 

 thesised (Fischer and Frendenberg, Berichte, 1912, 45, 915) a 

 pentagalloyl glucose which, although a derivative of gallic acid, 

 exhibited a remarkable similarity with natural tannic in its 

 physical and chemical properties. Since then Fischer has 

 made repeated attempts to synthesise the two isomeric m 

 and p digallic acids (I) and (II) 



OH OH OH OH 



Ho(T}-CO-0-^) H0(^}-C0.0-{[3 C00H 



OH COOH OH 



(I) (II) 



with the object of combining them with glucose, but found 

 that, no matter what method was employed for synthesising 

 these two acids, only the meta acid was obtained ; owing to 

 the fact that molecular rearrangement took place whenever 

 the acyl derivatives of the para acid were hydrolysed. Thus, 

 for example (Fischer, Bergmann and Lipschitz, Berichte, 191 8, 

 51, 45), 4 benzoyl 3 : 5 diacetylgallic acid (III) on hydrolysis 

 yielded 3 benzoyl protocatechuic acid (IV), in other words, the 



