Reaction with preformed trialkyl oxonium salts

Reaction with preformed trialkyl oxonium salts. 

Reaction with preformed trialkyl oxonium salts. The easiest mode of initiation to interpret involves transfer of an alkyl group from a preformed trialkyl oxonium ion salt to a THF molecule  

Like the propagation reaction, this probably occurs by a nucleophilic attack by the THF oxygen atom on a carbon alpha to the oxygen of the trialkyl oxonium ion salt. Commonly the triethyl-oxonium ion with a tetrafluoroborate gegenion has been used (3, 24, 32). Meerwein (3) has also used the hexachlorantimonate, tetrachloroferrate, and tetra-chloroaluminate gegenions. 

In situ formation of oxonium ion. Because of the disadvantages of the trialkyl oxonium salts a number of workers have found it expedient to prepare the trialkyl oxonium ion or the THF oxonium ion directly in the polymerization charge. Instead of adding the preformed trialkyl oxonium salt, the reactants which will form the salt are charged. 

The reaction used to prepare the trialkyl oxonium salts is that originally used by Meerwein (33). The reaction is carried out at dry ice temperatures. The intermediate product, which Meerwein calls an inner oxonium ion salt is not isolated. The preparation of Et30+BF4 is illustrated in equation 6. 

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