GALLOTANNIC ACID 29 1 



Similarly gallotannic acid is precipitated by many alkaloids 

 and basic substances which have no action on gallic acid. 



THE CONSTITUTION AND SYNTHESIS OF NATURAL 

 GALLOTANNIC ACID. C^gHsP^e- 



The close relationship subsisting between gallotannic and 

 gallic acids was first observed by Scheele, who, by allowing an 

 infusion of gall nuts to undergo fermentation, obtained gallic 

 acid. 



When, therefore, it was found by Schiff * that gallic acid 

 could be converted back into the anhydride by means of phos- 

 phorus oxychloride it was assumed that this substance, which 

 was called digallic acid, was identical with natural gallotannic 

 acid or " tannin." 



This view came to be generally accepted, although objections 

 were raised from time to time on the ground that the physical 

 constants, such as electrical conductivity and optical activity 

 of natural tannin and synthetic digallic acid were different.f 



Until 1912 there was considerable uncertainty as to whether 

 tannin occurred in the plant combined with glucose in the 

 form of a glucoside, or whether the sugar which is frequently 

 found associated with it was merely an impurity. | 



E. Fischer and Freudenberg, § on reinvestigating the ques- 

 tion, found that gallotannic acid obtained from Chinese galls, 

 even after repeated careful purification, yielded about 7-8 per 

 cent of glucose on hydrolysis with sulphuric acid ; from this it 

 was concluded that " tannin" or gallotannic acid as it occurs 

 in nature is not identical with synthetic digallic acid, since the 

 natural product contained glucose as an essential constituent. 



The role played by the glucose as a constituent of natural 

 gallotannic acid of Chinese oak galls was finally established 

 when Fischer and Freudenberg synthesized a pentadigalloyl 

 glucose which from all appearances was identical with the 

 natural gallotannic acid. 



* Schiff : " Ber. deut. chem. Gesells.," 1871, 4, 232. 



t Walden : id., 1897, 30, 3151 ; i8g8, 31, 3167. 



X Cf. Strecker : " Annalen," 1852, 81, 248 ; 1854, 90, 328 ; Pottevin : 

 " Compt. rend.," igoi, 132, 704. 



§ Fischer and Freudenberg : " Ber. deut. chem. Gesells.," 1912, 45, 

 915 and 2709. 



19* 



