>70 PROFESSOR A. CRUM BROWN AND DR JAMES WALKER ON THE 



Secondary Eeactions Accompanying the Electrolytic Synthesis of 



Dibasic Acids. 



In our former paper we showed that besides the synthesis of compound ethers of 

 dibasic acids, other reactions might be expected to result from the electrolysis of ethyl- 

 potassium salts of dicarboxyl-acids. Oxidation occurs, which we endeavoured to limit 

 by operating on concentrated solutions, at a low temperature, and with great current 

 density at the anode.* The products of oxidation are chiefly carbonic acid and water, so 

 that no complication arises from this source. The same is the case with the reaction by 

 which, in the electrolysis of potassium acetate, small quantities of methyl acetate are 

 produced. The corresponding products from the ethyl-potassium salts of the dibasic 

 acids would have the general formula C 2 H 5 -0-(CO)-R // -(CO)-0-R // -(CO)-0-C 2 H 5 , and 

 would be complicated compound ethers. It is possible that such substances are con- 

 tained in small quantity in the high boiling residues of the ethereal products, but as these 

 residues cannot be distilled without decomposition, we did not attempt to isolate them. 



In most cases there are formed non-saturated compound ethers, the formation of which 

 may be represented by the following equation, corresponding to equation III. of our 

 former paper, 2C 2 H 5 -0-(CO)-R // CH 2 -CH 2 -(CO)-0- = C 2 H 6 -0-(CO)-R"-CH : CH 2 + CO,+ 

 CJIz'0'(CQy~R" , C~H- 2 -CII 2 , (CO) 2 '0~H.. This general equation applies to the normal dibasic 

 acids, and similar schemes can easily be constructed for acids with side chains. The 

 compound ethers of non-saturated monobasic acids thus formed have a much lower 

 boiling-point than the compound ethers of the dibasic acids formed by electrolysis at the 

 same time, so that there is no difficulty in separating them from the latter. These 

 non-saturated ethers first make their appearance in quantity in the case of the higher 

 members of the normal oxalic acid series, and seem to be formed in greater proportion 

 in the case of acids with side chains than in that of normal acids. Thus from dimethyl- 

 malonic acid we have obtained quite considerable quantities of methylacrylic acid, and 

 a large yield of ethylcrotonic acid from diethylmalonic acid. 



Methylacrylic Acid. — About a quarter of the ethereal product obtained by the 

 electrolysis of 200 grammes of ethyl-potassium dimethylmalonate distilled between 115° 

 and 125°. This fraction was boiled for an hour and a half with 10 grammes of caustic 

 potash in alcoholic solution, and the acid was obtained in the usual way from the potas- 

 sium salt. The acid, in aqueous solution, was then neutralised by boiling with calcium 

 carbonate, the excess of the latter removed by filtration, and the solution concentrated. 

 After remaining for some time in an exhausted desiccator, the solution solidified to a 

 felt-like mass of brilliant flattish needles. The calcium salt is very soluble in water, 

 more soluble in cold than in hot water. The solution of the purified salt was decomposed 

 with hydrochloric acid and extracted with ether. The ethereal layer was separated and 

 washed with a little water to remove hydrochloric acid. 



* See Murray, Journal of tlie Chemical Society 61, 10. 



