Generation of Nucleophiles and Bases

Oxygen is reduced at the mercury cathode in a dipolar aprotic solvent containing a quaternary ammonium salt to form the superoxide ion, 02 , in a reversible one-electron transfer process 165 166 The reduction takes place at -0.8 V (SCE) and concentrations of tetraalkylammonium superoxide of at least 0.1 M can be obtained (the half life of the superoxide ion in dimethylformamide is about 40 min at room temperature). 

Superoxide ion is a strong base and can be used for initiation of the autoxida-tion of certain aromatic hydrocarbons. Thus, electrolysis of fluorene at -0.8 V (SCE) in DMF-tetrabutylammonium perchlorate solution continuously flushed with oxygen produces fluorenone with a current efficiency of about 5000 %. The reaction was demonstrated to be a base-catalyzed oxidation, in which superoxide ion acts as a base 16 6a  

Superoxide ion is also a powerful nucleophile, capable of reacting with alkyl halides to form dialkyl peroxides  

From butyl bromide, an 80 % yield of dibutyl peroxide was obtained. 

Electrochemical generation of strong base has been applied in an interesting modification of the Wittig reaction 161 A solution of azobenzene, benzaldehyde, benzyltriphenylphosphonium bromide, and lithium chloride in dimethylformamide was electrolyzed at a potential where only the easily reducible azobenzene was electroactive. The phosphonium ion then acts as a proton source, giving the ylide as an intermediate. Under these conditions a 98 % yield of a mixture of cis- and trans-stilbene was obtained, presumably via the following reactions  

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