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VII. — Electrolytic Synthesis of Dibasic Acids. By Professor Alexander Crum Brown 



and Dr James Walker. 



(Read 17th February, 19th May, 16th June, and 7th July 1890 ; revised 11th November 1890.) 



Part I. 



Forty years ago Kolbe * showed that a strong aqueous solution of potassium acetate, 

 when subjected to the influence of the electric current, is decomposed with formation of the 

 following products. At the anode a gaseous mixture is evolved which consists chiefly of 

 carbonic acid and ethan ; while at the cathode hydrogen escapes, and potassium hydrate 

 is formed in the solution. When dilute solutions of the same substance are electrolysed 

 under similar conditions, the decomposition products at the cathode are the same as in 

 the previous case, but at the anode the gas evolved is now oxygen, and free acetic acid 

 makes its appearance in the solution. The difference between the two cases must, on 

 modern views of electrolysis, be attributed to the occurrence of secondary reactions. The 

 primary process is in all cases the transference of the electrically-charged submolecules 

 or ions to the corresponding poles, where they lose their charges, and thereby become 

 capable of reacting with one another or with neighbouring molecules. As a general rule 

 they are, when discharged, themselves incapable of independent existence. 



The ions in a solution of potassium acetate are K and CH 3 COO, of which the former 

 travels to the cathode, the latter to the anode. On discharge, the potassium atom 

 immediately attacks the water in which the salt is dissolved, with formation of potassium 

 hydrate and liberation of hydrogen. The acetion, on the other hand, can either react 

 with the water or with another acetion molecule, according to circumstances. Should 

 the solution be dilute, the conditions evidently favour interaction with the water, which 

 will then take place according to the equations 



CH3COO + HOH = CH3COOH + OH 

 or 2CH 3 COO + H 2 = 2CH 3 COOH + 



But if the solution is concentrated, the reaction will rather take place between the acetions, 

 and that in either (or both) of two ways, viz. — 



I. 2CH 3 C0 2 = CH3CH3+ 2C0 2 

 II. 2CH 3 C0 2 = CH 3 C0 2 CH 3 +C0 2 



The secondary products in this case are therefore carbonic acid, ethan, and methyl acetate. 

 As KoLBEt proved, the quantity of methyl acetate formed is extremely small ; indeed, he 

 only succeeded in showing its existence in an indirect manner. The decomposition thus 



* Kolbe, Chem. Soc. Quart. Jour., ii. 157, 1850. t Kolbe, loc. tit., 177. 



VOL. XXXVI. PART I. (NO. 7). 2 I . 



