INVOLVEMENT OF DICATIONIC SPECIES AS THE REACTIVE INTERMEDIATES IN GATTERMANN, HOUBEN-HOESCH, AND FRIEDEL-CRAFTS REACTIONS OF NONACTIVATED BENZENES

The active electrophile involved in the Gattermann reaction of benzene with cyanide is N,N-diprotonated hydrogen cyanide, HC+=N+H2. Similarly, Houben-Hoesch acylation by benzonitrile involves N,N-diprotonated nitrile as the active species. Participation of the second proton was demonstrated by kinetic measurement of the intramolecular cyclization of phenylpropionitrile. Acylation of benzene, toluene, and chlorobenzene by CH3COSbF6 or C6H5COSbF6 depends strongly on the acidity of the media. The major active species are the protonated acyl cations formed in the highly acidic media. The acyl cation itself contributes only to a minor extent even in the acylation of benzene and toluene. Dications (superelectrophiles or protosolvated cations) are proposed to be the real electrophiles in these reactions of benzene and nonactivated benzenes.