352 Sir James Walker [April 22, 



two discharged hydrogen ions combining with each other to form a 

 molecule of hydrogen gas. If the positive electrode is of copper we 

 have the reaction 



S0 4 + Cu = CuS0 4 . . . (2) 



the discharged iron acting on the material of the electrode and form- 

 ing copper sulphate. If, on the other hand, the positive electrode 

 consists of the resistant metal platinum, the discharged ion acts on 

 the solvent water according to the equation 



2 SO, + 2 H 2 = 2 H 2 S0 4 + 0, . (3) 



sulphuric acid being regenerated and oxygen gas evolved. 



Equation (1) expresses a kind of synthesis, two atoms originally 

 separate uniting to form a single molecule. In organic chemistry 

 synthesis in the strict sense is held to mean the union of carbon 

 atoms originally belonging to separate molecules. The first electro- 

 synthesis was effected in 1849 by Kolbe, who, to take a simple, 

 example, electrolysed potassium acetate solution with platinum 

 electrodes, and at the anode obtained the hydrocarbon ethane. 

 The negative ion of the acetates is represented by the formula 

 CH 3 'COO-, and under appropriate conditions two of these when 

 discharged at the anode interact in accordance with the equation 



2CH 3 -COO = CH 3 -CH 3 + 2 C0 2 . (4) 



Here an organic synthesis in the strict sense has been effected, two 

 CH 3 groups originally contained in different molecules being now 

 joined together by their carbon atoms to form a molecule of the 

 hydrocarbon ethane CH 3 'CH 3 . This method of synthesis was for 

 long neglected, but attention was again drawn to it in 1890 by a 

 suggestion of Professor Crum Brown, which was worked out in 

 detail in conjunction with the lecturer. If the sodium ethyl salt of a 

 dibasic acid, e.g. malonic acid COOH'CH 2 'COOH, is electrolysed, 

 the anion COOEt , CH 2 *COO - reacts according to equation (4) as 

 follows : — 



2 COOEt-CH 2 -COO - COOEt-CH 2 -CH,-COOEt + 2 C0 2 . 



The product, diethyl succinate, contains two CH 2 groups instead of 

 the single CH 2 group present in malonic acid, and may readily 

 be converted into sodium ethyl succinate, which yields the anion 

 COOEt-CH 2 -CH 2 'COO-. This on electrolysis reacts as before, 

 thus : — 



2 COOEfCH 2 -CH 2 -COO = 

 COOEfCH 2 -CH 2 -CH 2 -CH 2 -COOEt + 2 C0 2 



giving diethyl adigate, which now contains four CH 2 groups. This 

 may be again converted into a sodium ethyl salt, and the process 

 continued. 



