ELECTROLYTIC SYNTHESIS OF DIBASIC ACIDS. 377 



is easily prepared by half-saponifying the corresponding ether. The concentrated solu- 

 tion at once began to colour, when the electrolysis was started, and only traces of a 

 substance soluble in ether were formed. 



We may therefore conclude that unsaturated acids do not, by the electrolysis of their 

 alkyl-potassium salts, yield synthetic products. The hydrocarbons of the acetylene and 

 ethylene series which are formed by the electrolysis of the normal salts of unsaturated 

 acids are, of course, not synthetic products, but decomposition products of the anion, 

 which owe their escape from oxidation to their volatility. 



In this connection it seemed of interest to examine the behaviour of the dibasic 

 aromatic acids. 



Ethyl-hydrogen phthalate can be easily prepared by boiling phthalic anhydride with 

 alcohol. The crude product was neutralised with baryta, and the pretty soluble barium 

 salt purified by recrystallisation from water. From the barium salt we prepared the pure 

 ethyl-hydrogen phthalate, and neutralised it with potash. On subjecting a colourless 

 concentrated solution to electrolysis it at once became yellow, then red, and ultimately 

 dark brown. Scarcely perceptible traces of a black viscid substance were extracted by 

 ether from the aqueous solution. An experiment was made with ethyl-potassium benzyl- 

 malonate, a substance in which the phenyl is not directly united to carboxyl. Here also 

 the result was the same. The solution rapidly darkened, and no ethereal substance was 

 produced. The aromatic acids thus behave like unsaturated acids, in undergoing practi- 

 cally complete oxidation at the anode. 



The solution of ethyl-potassium tartrate remains colourless and clear when electro- 

 lysed, but thorough oxidation takes place at the anode, and no ethereal products are 

 formed. The same is the case with the corresponding salt of dibromosuccinic acid. Here 

 free bromine makes its appearance in large quantity at the anode.* 



Behaviour of Oxalic Acid. — CLAiSENt has recently observed that oxalic ether, 

 oxalacetic ether, and acetoneoxalic ether, are half-saponified by boiling with an aqueous 

 solution of potassium acetate, so that, for instance, ethyl-potassium oxalate is formed from 

 oxalic ether, C 2 H 5 OCOCOOC 2 H 5 + CH s -COOK = C 2 H 5 OC(>COOK = CH 3 -COOC 2 H 5 . This 

 reaction is, in fact, a very satisfactory method for preparing ethyl-potassium oxalate, and 

 Claisen has suggested that it might be also applicable for the preparation of other ethyl- 

 potassium salts of dibasic acids. We have therefore tried this method on succinic acid 

 and on some of the alkylrnalonic acids. 



We added to the ether to be experimented on, potassium acetate dissolved 

 in its own weight of water, in molecular proportion, that is, in the proportion 

 R" (COOC 2 H 5 ) 2 to CH 3 "COOK, and boiled the mixture, with vigorous shaking, on an 

 inverted condenser. But the ether did not permanently mix with the aqueous solution, 

 and after several hours' boiling the ether was scarcely at all attacked. On heating the 

 two liquids at higher temperatures — up to 180° — in sealed tubes, decomposition indeed 

 occurred, but with the formation of dipotassium salts, and, in the case of the malonic 



* Michael, American Chemical Journal 1, 413. t Berichte der deutschen chemischen Gesellschaft 24, 127. 



VOL. XXXVII. PART II. (NO. 17). 3 I 



