ELECTROLYTIC SYNTHESIS OF DIBASIC ACIDS. 215 



in the case of sebacic acid, we obtain a salt, two parts of which dissolve in one part of cold 

 water, being thus much more soluble than the dipotassium salt. If the concentration 

 exceeds the above limit, the resistance of the solution becomes very high, and the 

 electrolysis proceeds slowly ; at the same time the viscosity of the liquid occasions exces- 

 sive and inconvenient frothing. The quantity and appearance of the froth gives indeed 

 a very good notion as to whether the electrolysis is proceeding properly or not. At first 

 the froth is small in quantity and creamy in appearance. Afterwards it increases in 

 amount and becomes coarser. When the electrolysis is near an end, the froth disappears 

 almost entirely from the middle of the crucible, so that one can see an oily liquid on the 

 surface, and masses of a solid in the aqueous layer below. The solid is potassium car- 

 bonate, or bicarbonate. On completion of the electrolysis the two layers are separated, 

 and the aqueous one extracted with ether. The ethereal extract is then added to the 

 oily layer, the mixture dried with fused calcium chloride, and the ether and alcohol 

 distilled off on the water-bath. The alcohol is a secondary product arising from the partial 

 saponification of the ethyl-potassium salt by the potash formed during the electrolysis. 

 What remains in the distilling-flask as a colourless or slightly yellow oil is pure diethyl 

 succinate. 



In the above way it is easy to work up 25 grams of ethyl -potassium malonate in an 

 hour. The yield is in this case very satisfactory. Thirty grams of ethyl-potassium 

 malonate dissolved in 20 grams of water gave 9 '2 grams of succinic ether, or 60 

 per cent, of the calculated quantity. In the case of the higher acids the yield is much 

 smaller, falling at once to 35 per cent, at the next step, and scarcely reaching 20 percent, 

 in the electrolysis of ethyl-potassium sebate. 



We have confined ourselves to the preparation and study of the esters which are 

 formed according to equation I. Other ethereal products of the electrolysis are met 

 with in any quantity only in the case of acids well up in the series. These may form 

 the subject of a future investigation. From the aqueous solution considerable quantities 

 of the original acid may be recovered on acidification. 



The replacement of the hydrogen atom of one carboxyl group in the dibasic acids by 

 ethyl is not the only mode of rendering this group electrolytically inactive. We have 

 found that the electrolysis of a methyl-potassium salt yields almost as favourable 

 results. It might be possible to effect the same synthesis by electrolysing solutions of 



the potassium salts of the amic acids R\pf>OK *' °^ *^ e acid potassium salts 



^ \OOOK' or even m some cases of the acids R' \pr)fkrr themselves ; for it has been 



proved indirectly that w T eak dibasic acids split off only one hydrogen atom as cation, so 



<COO 

 roOTT' wn i° n would, according to equation I., give 



COOH'R'^R'^COOH and carbonic acid. Experiments made by us in this direction 

 with malonic acid have not as yet led to the desired result. With the acid potassium 

 salts the same reaction ought to take place, but these salts are by no means so convenient, 



