Kinetic and mechanistic analysis of the reactions in the aqueous system pentacyanoferrate(II)–ammonia–nitrite

Abstract

The pentacyanoferrate()-ammonia-nitrite system was subjected to a kinetic and mechanistic study as a function of NH 3 and NO 2 Ϫ concentration, pH, temperature and pressure. A detailed study was performed on the formation of [Fe II (CN) 5 (NO)] 2Ϫ in the system consisting of NO 2Ϫ and [Fe II (CN) 5 L] 3Ϫ (L = H 2 O or NH 3 ). Two equilibria were taken into consideration, viz. the pH dependent aquation of the ammine complex, and the transformation of the nitro into the nitrosyl complex. Based on the reported activation parameters, the substitution of water or ammonia in [Fe II (CN) 5 L] 3Ϫ (L = H 2 O or NH 3 ) by nitrite follows a limiting dissociative mechanism. The reaction of [Fe II (CN) 5 -(NO)] 2Ϫ with ammonia leading to the formation of dinitrogen was investigated in a more qualitative way, and found to depend strongly on pH with a maximum nitrogen yield at a pH of ca. 10.5. The trend was accounted for on the basis that the process involves nucleophilic attack of NH 3 on the N (NO) atom in [Fe II (CN) 5 (NO)] 2Ϫ . This reaction was found to be the rate-limiting step in the catalytic cycle occurring in this system and leading to the overall reduction of NO x to dinitrogen.

The Mercury(II) Catalyzed Ligand Exchange Between Hexacyanoferrate(II) and Pyrazine in Aqueous Medium

“…In this direction, much attention has been paid towards the studies concerning the ligand exchange reactions of low spin pentacyano(ligand)ferrate(II) complexes with a variety of ligands [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. In recent years, the mechanistic importances of such reactions have attracted considerable attention of some researchers towards their studies in micellar [13,17,18] and electrolyte [14,19] media.…”

Synthesis of Isotope Enriched (CN 3 H 6 ) 2 [ 57 Fe(CN) 5 NO] starting from 57 Fe

“…The complex pentacyanonitrosylferrate(II) or nitroprusside anion [Fe(CN) 5 NO] 2± (1) is a species of high academic [1,2] and pharmaceutical [3] interest. The sodium salt, Na 2 [Fe(CN) 5 NO]´2 H 2 O (sodium nitroprusside) is given as a medicine to lower the blood pressure e. g. during operations or heart attacks [3,4].…”

Mechanistic Studies on the Activation of NO by Iron and Cobalt Complexes

“…[24] On the basis of these discrepancies, we propose that reaction (7) [6,7] The rate constant k H + is also reported to be very fast under the selected conditions. [25] According to this information, the reduction by NO must be rate determining in the overall reaction (7), and k f = k NO . Although NO reduction of the [Fe(CN) 5 …”