Anodic Chlorination of Olefins

Vinyl chloride and chloroprene (2-chlorobuta- 1,3-diene) are among the major intermediates which are produced industrially on the 100,000 tonnes/year scale by thermal chlorination or oxychlorination of ethylene or butadiene. 

The electrochemical halogenation of ethylene or butadiene permits substantially milder reaction conditions. Russian studies 83 8S) have shown that ethylene can be converted to 1,2-diehloroethane (intermediate of vinyl chloride) in high yields at graphite anodes using aqueous HC1 in the presence of small amounts of FeCl3 as electrolyte. 

Toya Soda 86 -88) has studied the anodic chlorination of butadiene in aprotic electrolytes (e.g. CHjCN and Fe, Ce, and Ca chlorides). 

This yields a 1 1 mixture of 3,4-dichlorobut-l-ene and l,4-dichlorobut-2-ene with a current efficiency of just under 80 %. In the presence of H20, dichlorobutanediols are formed 89), Since electrochemical halogenation did hot appear to have any substantial advantages over the established thermal processes, no efforts have been made so far to scale up these reactions. 

Here again are fairly good prospects for the industrial use of this method in the area of the area of fine chemicals. For example, Torii et al. (Otsuka Patents 90 92 ) have used electrochemical allyl halogenation for the synthesis of intermediates for P-lactam antibiotics. 

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