^9^ TANNINS 



The constitution of this substance is represented by the 

 formula — 



— CH— O . Dg 



CH — O . Dg in which Dg stands for the m-di-galloyl group 



CH— O. 



OH 



O CH— O.Dg OH / \ ^Q 



OHO< )— CO— -CH 



—CO . O A / 



— CH OH 



CH,— O . Dg 



from which it will be seen that it is composed of a molecule , 

 of glucose in which each of the five hydroxl groups have^aeen" 

 esterified by a molecule of digallic acid. 



Actually two isomeric substances of this formula, C76H52O46, 

 with a molecular weight of 1700, were synthesized.* The 

 one derived from meta-digallic acid,t i.e. penta- (w-di-galloyl) 

 j3-glucose, has been found to be practically identical with 

 Chinese tannin, and to differ from it only in regard to its 

 specific rotation ; this difference is, however, of no great 

 significance considering the colloidal nature of the substance 

 concerned. 



Although not connected with the constitution of gallo- 

 tannic acid it is of interest to mention in connection with the 

 above synthesis that Fischer, Bergmann, and Lipschitz have 

 also synthesized a galloyl glucose of the formula — 



C«H„(OH)3 . CO . O . CH . (CHOH), . CH . CHOH . CHpH 



I o— I 



which is identical with glucogallin, a substance first isolated 

 from Chinese rhubarb by Gilson.J 



ELLAGITANNIC ACID. 



This tannin, which is commonly found together with 

 gallotannic acid, is important as being the mother substance 

 of ellagic acid, which is responsible for the bloom characteristic 



* Fischer, Bergmann, and Lipschitz : " Ber. deut. chem. Gesells.." 

 1918, 51, 45. 



t For formula, see p. 284. 



% Gilson : " Compt. rend.," 136, 385. For summary of work on syn- 

 thesis of tannins, see Fischer : " Ber. deut. chem. Gesells.," 1919. 52» 13. 809. 



