656 



the theoretical quantity of sulphuric acid and its rotatory power 

 was then determined. 



For c = 0.645 was found [«] = + 31°.6 and [M] = -}-4.S°.7. 



In another preparation was found for c = l.S5, [«] i= -[- 32°.0 

 and [J/] = + •49°.2. 



Therefore, it is the de.vtrorotatori/ acid, whose neutral barium salt 

 is laevorotatory . 



It was now tried to obtain also this dextrorotatory acid in the 

 solid condition. The solution was, therefore, concentrated in vacuo 

 first over sulphuric acid and then over PjOg. The viscous mass did 

 not crystallize on cooling, but did so slowly after a trace of the racemic 

 compound had been introduced. The crystals are exceedingly 

 hygroscopic, melt between 81° and 82° and contain one mol. of water. 



As the neutral barium salt of the dextro «-sulphopropionic acid 

 rotates in the opposite direction of the free acid, it became of 

 importance to investigate also the acid salt. For this was found 

 at c = 0.776 



[«] ^ _|- 18°.0 and [J/] = + 79^8 or r= 2 X 39°.9 '). 



The acid potassium salt gave at c = 0.516 the values: 



[«] = + 23°.8. [M] = + 45°.7. 



The acid metallic salts of dextro «-sulphopropionic acid are, there- 

 fore, dextrorotatory like the acid itself. The racemisation of dextro 

 «-sulphopropionic acid and its salts was also tried. 



The aqueous solution, at c = 0.645, when heated for six hours 

 at 100, suffered no appreciable racemisation, the rotation remaining 

 unchanged. 



A solution of the barium salt at c==:1.28 after being heated for 

 eight hours at 150° was racemised to the extent of 807o- 



A solution of the potassium salt at c = 0.64, which also contained 

 2 7o of free potassium hydroxide, was completely racemised after being 

 heated for eight hours at 180\ An excess of free base thus seems to 

 accelerate the racemisation ^), althougli also the temperature, the 



1) As the molecule of the acid barium salt contains two groups of the sulpho- 

 propionic acid, it may for the sake of comparison with the other rotations be 

 written more conveniently [itf ] = 2 X 39°.9. 



~) This would agree with the rule given by Rothe Ber. d. D. cli. G. 46. p. 845. 

 (1914), that active carboxylic acids, the ^.-carbon atom of which is asymmetric and 

 carries a hydrogen atom, are readily racemised under the influence of alkalies. He 

 tries to explain this by assuming that, owing to the base, enol formation takes 

 place in the molecule, thus causing the asymmetric carbon atom to disappear 

 temporarily. 



