Mechanism of the nitrous acid-catalysed aquation of aquochromium(III) complexes

Abstract

Nitrous acid, in perchloric acid, dramatically increases the rate of aquation of Cr(H₂O)₅X²⁺(X = Cl or Br), cis- and trans-Cr(H₂O)₄Cl₂⁺, and cis-Cr(NH₃)₄(OH₂)Cl²⁺, but has little effect upon the rate of hydrolysis of Cr(NH₃)₅Br²⁺ and trans-Cr(NH₃)₄(OH₂)Cl²⁺. The mechanism is believed to involve the formation of traces of nitrito-intermediates by O-nitrosation, with H₂NO₂⁺ or NO⁺ as the nitrosating agent. These preliminary results indicate that the catalysis may be stereospecifically restricted to complexes containing an aquo-ligand in a cis-position relative to the leaving group. Some new nitrito-chromium(III) compounds are reported.