SV\1II1".SIS (II" DI'.l'SIDKS. 



147 



l)Ossil)le owin.i; to their proiiortics. in conscciucncc nf wliicli the 

 synthetic method was aclojjted. No free carhoxyl heinj^r present, 

 as the above experiments showed, the method of combination of 

 the glucose with the gallic acid was indicated as being in the form 

 of an ester, and these conditions are satisfied if tannin be consi- 

 dered as a compound formed by the union of i mol glucose with 

 5 mols digallic acid, similar to pentacetvl glucose. Digallic acid 

 C..H,(OH),CO.OQH,(OH),a)()H. i's a didei)side. which was 

 synthetically prepared in a pure condition, first bv Fischer in the 

 manner indicated above, but as it is extremelv difficult to work 

 with, an attempt was first made with gallic acid in order to obtain 

 l>entagalloyl glucose QH.D.JOC.QH.i OH ).,],, and test its 

 ])roperties. 



The methods hitherto used for the complete acylation of 

 glucose were found to be unavailable for the preparation of 

 jienta galloyl glucose, and a new method had to be worked out. 

 This was done, and consisted in bringing together the glucose and 

 the chloride of the acid dissolved in dry chloroform, together 

 with quinoline. Tn this manner penta trimethvl-carbonato gallovl 

 glucose (mol. wt. 1810.5) QiH„,0,,i or, 'C,H,0, [OC. QH, 

 ( OCOOCH;J;,]-, was obtained as a granular colourless amor- 

 phous powder sintering about 90° [a] i,'^ -f 34.34° (io.4°). 

 By careful saponification with excess alkali, in aqueous acetone 

 solution at ordinary temperature, this yielded pentagalloyl glu- 

 cose C4iH32(^2(i (Mol. wt. 940.26). as a yellow amorphous 

 powder, softening about 150°, and beginning to decom])ose at 



160^ [ar+3i° to 35°. 

 I) 



This substance shows a startling similarity to tannin, the 

 -chief differences being the optical rotation and the amount of 

 gallic acid obtained on hydrolysis with sulphuric acid. It pos- 

 sesses a strong astringent, and bitter, but not aci^. taste. It is 

 soluble in most of the organic solvents, gives coloration with 

 ferric chloride (inks) and is ])recipitated by the same reagents. 

 Analysis gave — 



Carbon. ])er cent.. . 52.49 Hydrogen 3-79 



Theoretically ... 52 . 33 3 . 43 



The benzoylation of glucose was also carried out, and in this 

 case two stereoisomers were obtained, which could be separated 

 hy crystallisation, according as a or /? glucose was used, but in 

 the case of the corresponding galloyl compounds, owing to their 

 amorphous nature, this was impossible. From analogy and other 

 considerations Professor Fischer does not consider that the 

 pentagalloyl glucose is a single uniform substance, but probably 

 a mixture of isomers. 



In spite of this, he states that with its preparation the chapter 

 of the principal synthesis seems to be concluded, though not yet 



