1050 



gations. Evidenllj lie assumes that well crystallised storaxcinnamic 

 acid ') can contain not even minimal amounts of impurities. Here, 

 however, it is a question of traces of impurity, seeing that so small 

 a quantity as 1 7^ of p-chlorocinnamic acid can so influence the 

 crystallisation of storaxcinnamic acid that it shows a perfect resem- 

 blance to the synthetic acid, ') while only 0.3 •/„ of o-nilrocinnamic 

 acid was necessary to produce the same etfect. ') If the impurity 

 occurs in smaller amount, it is possible that its effect on the 

 crystalline form is not observed. The reason why Eri,enmeyrr was 

 always able to prepare so-called synthetic cinnamic acid from 

 cinnaniic acid derived from various sources must thus be looked for 

 in the impurity of the materials used. Whether or not this impurity 

 was the same in all cases may for the present be left out of 

 consideiation. It must, however, have been a substance which on 

 oxidation gives an aldehyde from which by the Perkin reaction a 

 substituted cinnamic acid is formed. In the oxidation with permanganate 

 the benzaldehyde has relatively the better cliance of being oxidised 

 to benzoic acid than the aldehyde impui-ity, which occurs only in 

 traces, since, the vapour present being generally unsaturated with 

 respect to the latter, the impurity is more quickly removed from 

 the liquid reaction mixture. The amount of the impurity in the 

 benzaldehyde will thus be greater than in the cinnamic acid originally 

 used. In the Perkin synthesis, according to the researches of 

 Eri.enmeyer himself, the aldehyde impurity is more completely 

 transformed into the substituted cinnamic acid than the benzaldehyde, 

 since the cinnamic acid obtained was the so-called synthetic acid, 

 while fine crystals of storaxcinnamic acid were deposited from the 

 residual benzaldehyde. The cumulative result of these circumstances 

 should be that the amount of the impurity is increased, and its effect 

 in modifying the crystalline form rendered perceptible. 



It seemed to me thus necessary to ascertain whether synthetic 

 cinnamic acid can in fact be prepared from pure cinnamic acid in 

 the way indicated by Erlenmeyer, and if the product has the 

 properties observed by him. 



Preparation of pure cinnamic acid. 



As raw material the ethereal oil extracted from the roots of 

 Alpinia malaccensis was used. This consists, according to the researches 



1) Ber. 43, 957. He speaks here of "25 gr. der als einheitlich anerkannten 

 Stor axzimtsaure" . 



^) Ruber and Goldschmidt Ber. 43, 460 and Biochem. Zeitschr. 34, 406. 

 >) Ber. 43, 461. 



