FISCHER'S SYNTHESIS OF DEPSIDES AND TANNING 



SUBSTANCES. 



By Prof. J. A. Wilkinson. M.A.. F.C.S. 



The work carried out by Professor luiiil Fischer and his 

 j)upils on the polypeptides, which has contributed so largely to 

 the extension of our knowledge of the ])roteins and their deriva- 

 tives, is well known, and led indirectly to the work outlined here, 

 culminating in the synthesis of a substance which possesses 

 practically all the j^roperties of tannic acid, and the preparation 

 of a large nunil)er of others, strictly allied both in properties and 

 composition. Whilst engaged on the synthesis of ])olype])tides of 

 tyrosin, he desired to prepare a chloride of chloracetyl tyrosin in 

 order to obtain glycyl tyrosyl glycin. On treating with phos- 

 phorus trichloride, it was found, that the free jihenol groups 

 present in the molecule caused trouble, and hence he conceived 

 the idea of fixing them, in the meanwhile, by means of a group, 

 which could afterwards be removed easily, and the original 

 phenol group restored. For this ])ur])ose the methyl ester of 

 chlor-carbonic acid, Cl.COOCH.^, was used, the hydrogen of the 

 phenolic hvdroxyl being replaced by the methyl carbonato' group 

 — CCJOCHg. The methyl carbonato-compoimds thus produced 

 were then treated with phosphorus chloride, yielding the methyl 

 carbonato-chlorides, which on subsequent treatment with sodium 

 hydroxide reintroduced the original phenol group. The success 

 of this procedure in the case mentioned led to its trial with the 

 phenol carboxylic acids, the results of which are detailed in a 

 series of brilliant papers, entitled "The Methyl Carbonato Deriva- 

 tives of Phenol Carboxylic Acids, and their use for synthetic 

 operations," the first of which api)eared in i»)o8. In these it was 

 shown, that the chlorides of these acids were unobtainable by the 

 ordinary methods of preparing acid chlorides, owing to the fact 

 that tiie ])hosphorus chlorides attack both the hydroxyl and car- 

 boxyl groups, and yield products of variable composition, as had 

 been shown previously by R. Anschutz. The reactions which 

 take place may be exemplil'ied thus: — 



Starting with para-hvdroxy-benzoic acid — 



/Oil I. 



(a) CJI, 



^COOII 4. 



By the action of CI.C( )( )CH, — 



y O.COOCH.. I. 



{h^ c,ji. 



"^ coon. 4. 



By the action- of PCI- — 



/ O.COOCH, I. 



(0 C,H, 



^COCl 4 



