ANHYDRIDES OF ORGANIC ACIDS 231 



results. Reaction takes place immediately, and proceeds 

 apparently as smoothly as with acids of other types. Silver 

 glycollate gave an intermediate compound which can be 

 isolated in the pure state, while similar derivatives of mandelic 

 and malic acids were obtained, but not pure. 



If to silver glycollate suspended in ether, an ethereal 

 solution of thionyl chloride be added, immediate reaction 

 occurs, and, after filtration, there is obtained, on addition of 

 light petroleum, a white crystalline substance, the composition 

 of which is in agreement with the formula [CH 2 (OH)COO] 2 SO. 

 It loses sulphur dioxide when allowed to stand, but only 

 slowly. When nearly all the sulphur dioxide has been evolved 

 there is left, after washing with ether, a white powder the 

 composition of which agrees with that required by the formula 

 [CH a (OH)CO] 2 0. It is inadvisable to hasten the decom- 

 position by the application of heat, as a syrup is then formed 

 which cannot be caused to crystallise, and elevation of tem- 

 perature favours the formation of anhydro-compounds other 

 than the normal anhydride. The anhydride melts at about 

 100, is almost but not completely soluble in water, and appears 

 to be different from the anhydride obtained by Fahlberg by the 

 action of sulphur trioxide on glycollic acid (J. Pract. Chem., 

 [2], 7, 336). The manner of formation of this compound would 

 point to its having the normal structure, were it not for the 

 comparative stability of the intermediate compound. It is 

 possible that in this reaction silver glycollate behaves in the 

 abnormal manner sometimes displayed by silver salts of 

 hydroxy-acids, and the participation of the hydroxyl group in 

 the reaction is therefore not excluded. 



With silver mandelate the tendency to form chlorinated 

 products is pronounced, and the consequent formation of 

 water has made it impossible to isolate the intermediate 

 compound free from admixture with acid. The chlorine- 

 containing impurities may be removed by repeated precipita- 

 tion of the substance from its ethereal solution by means of 



