655 



An acid strychnine salt was obtained by evaporating an aqueous 

 solution of the acid with the equimolecular quanlily of strychnine 

 on a steam-bath until crystallisation set in. The Uirge crystals that 

 had separated were purified by repeated crystallisation from water; 

 their composition then was CjHgOsS -|- C^iH^jOaN^ -{- E^O. They, 

 however, proved to be not the acid strychnine salt of the inactive 

 (racemic) f.- ulphojn-opionic acid, but of the dextrorotatory acid. On 

 heating, they are decomposed at about 250° with evolution of gas 

 and formation of a brown liquid. 



As in the case of all other compounds described here, tlie rotating 

 power was determined in aqueous solution with sodium light at 20°. 

 B}' concentration c is meant the number of grams of anhydrous 

 active substance per 100 cc. solution. The specitic rotation [«] is 

 likewise calculated on the anhydrous substance. The molecular 

 rotation has, of course, the same value for the anhydrous and the 

 hydrated crystalline substance. 



For the acid strychnine salt was found at c = J. 938, 

 [«]^o ^ _ 140 (5 and [MY^ = — 71°.4. 



By way of comparing, strychnine hydrochloride was also investiga- 

 ted and at cirr 1.297 was found: [«] == - 30^.2 and [JYJ = — 112° ^). 



The acid strychnine salt of «-sulphopropionic acid investigated is, 

 therefore, presumably that of the dextrorotatory acid. 



In order to obtain this acid, the acid strychnine salt was first 

 decomposed with the theoretical quantity of barium hydroxide ^). 

 After complete separation of the strychnine by extracting the drained 

 off liquid witii chloroform, the neutral barium salt was precipitated 

 by addition of alcohol. This salt is laevorotatory. 

 *For c=: 1.764 was found [«] = — 4°.96 and' [J/] = — 14°.4. 



From this salt the active «-sulphopropionic acid was liberated by 



1) This value agrees fairly well with the constant [ilf ] = — 114° found by Pope 

 and Read for a somewhat different concentration. J. Chem. Soc. 105, p. 8:20 (1914). 



2) The acid strychnine a-sulphopropionate can be titrated with baryta water and 

 a suitable indicator such as methyl-red which is sensitive to feeble bases. It may 

 also be titrated with litmus to violet-blue. If however, phenolphthalein is used which 

 is but little sensitive to weak bases such as strychnine, the colour does not appear 

 until also the second acid group combined to the strychnine has been neutralised 

 by the inorganic base. As the change in colour is fairly sharp, both with methyl- 

 red and phenolphthalein, the titration forms an interesting application of the 

 theory of indicators. Still more remarkable becomes the experiment, when 

 both indicators are used simultaneously. The methyl-red passes into yellow after 

 addition of a semi-molecule of barium hydroxide, the phenolphthalein then being 

 still colourless; so soon, however, one mol has been added, the violet colour of the 

 phenolphthalein salt appears, unaffected by the pale yellow colour of the naethyl-red. 



