1049 



die synthefische Saure bei 132—133°, die Sforaxsanre bei 134—135°.^)" 

 It was shown by Riibek and Goldschmidt ') that the differences 

 between the synthetic and sloraxcinnainic acid observed by Erlenmeyer, 

 can easily be atlribnted to iinpni-ities in tlie synthetic 'acid, since 

 the mode of crystallisation of cinnamic acid is strongly intlnenced 

 by traces of other acids snch as chlor- or nitro-cinnamic acids. They 

 found tliat commercial synthetic cinnan)ic acid contained chlor- 

 cinnamic acid as an impurity. 



To this Erlknmkykr ') answered that even synthetic cinnamic acid 

 prepared from pure, well crystallised storaxciiinamic acid by dis- 

 solving in alkali, oxidising with permanganate to benzaldehyde, and 

 then from this preparing the acid by the Perkin synthesis, exiiibifs 

 the same peculiar crystalline form. 



In spite of this answer, a study of Erlenmkykr's papers leads to 

 the conclusion that heterocinnamic acid is not a pure substance, and 

 that the difference from ordinary cinnamic acid found by him must 

 be referred to some impurity. 



According to Erlenmkyer') both synthetic and heterocinnamic acids 

 can be tiansformed, although with a lO"/, loss, into stoiaxcinnamic 

 acid by heating their colourless aqueous solutions with animal char- 

 coal. Also repeated sublimation °) brings about the transformation of 

 heterocinnamic into storaxciiinamic acid. He also succeeded by frac- 

 tional preci|)itatiou'') of the sodium salt of synthetic cinnamic acid in 

 easily se|)arating 90 7o as storaxcinnamic acid, whereas synthetic 

 cinnamic acid should consist of storaxcinnamic acid to the amount 

 of 50 7o. ') He says then : «) 



"Da die Heterozimtsaure, trotz der Gewinnung von Storaxzimt- 

 stiure aus ilir, in ihren Eigenschaften unverandert bleibt, kann man 

 nicht anders annehmen, als dass bei dem fortgesetzten Fraktionier- 

 ungsverfahien ein allmahlicher iTebergang von Hetero- in Storax- 

 zimtsaure stattfindet'. 



In his detailed papers no indication is given of the method which 

 he used for the preparation of pure cinnamic acid for his investi- 



1) Further particulars of the crystalline forms are given in Biocliem. Zeitschr. 

 34, 366 and in Ber. 42, 507. 



2) Ber. 43, 453. 



3) Ber. 43, 955. 

 *) Ber. 43. f076. 



5) Ber. 42, 2658. 



6) Bioch. Zeitschr. 34, 423. 



7) Bioch. Zeitsclir. 34. 4'25. 



8) Ibidem 424. 



68* 



