Katalysierte Dehalogenierungen mit Natriumborhydrid

Sodium tetrahydroborate has a poor reduction capacity for the elimination of aromatic halogens. The addition of metal catalysts (in particular Pd, Co, Ni, Cu) accelerates this reaction to such an extent that even the rather stable aromatic chlorine can be exchanged by hydrogen at room temperature. An activity order of catalysts (the best is palladium on charcoal), a reactivity comparison of iodine, bromine and chlorine, and the influence of ortho, meta or para position in halogenobenzoic acids in relation to halogenobenzenes and to several other halogen compounds are given. Two preparative examples are described.