22. U. Burger, P. Müller, L. Zuidema,
    “1-Fluoro-benzocyclopropenium Ion from 1,1-difluoro-benzocyclopropene”
    Helv. Chim. Acta 1974, 57, 1881-1883.

1,1-Difluoro-benzocyclopropene (1) ionizes in fluorosulphonic acid to yield the cation 2, which is stable at − 50° for several hours. Upon quenching with water 2 affords benzoic acid.

DOI : 10.1002/hlca.19740570641 

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