Nucleophilic Addition Reactions of the Nitroprusside Ion – The Case of O-Methylhydroxylamine

MARÍA M. GUTIÉRREZ, JOSÉ A. OLABE, VALENTÍN T. AMOREBIETA

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2012 p. 4433 - 4438

1434-1948

The kinetics of the reaction between aqueous solutions of [Fe(CN)5NO]2– and NH2OCH3 has been studied by means of UV/Vis spectroscopy and complementary solution techniques, FTIR/ATR spectroscopy, mass spectrometry, and isotopic labeling ([Fe(CN)5 (15)NO]2–), in the pH range 6.0–9.3, I = 1 M (NaCl). The main products were nitrous oxide (N(15)NO), CH3OH, and [FeII(CN)5H2O]3–, characterized as the [FeII- (CN)5(pyCONH2)]3– complex (pyCONH2 = isonicotinamide). In excess NH2OCH3, the kinetic runs indicated pseudo-firstorder behavior, with corresponding rate constants, kobs [s–1], that correlated linearly with the concentration of NH2OCH3. The rate law is: R = kexp[Fe(CN)5NO2–][NH2OCH3], with kexp= (4.1)10–4 M–1 s–1 at 25 °C, ΔH# = 27 kJmol–1,and ΔS# = –220 JK–1mol–1, at pH 7.1. The value of kexp is much lower than that for similar addition reactions of NH2OH and of the N-substituted methyl derivative. In addition, the latter reactions exhibit a third-order rate law with a linear dependence of R on the concentration of OH–. The reaction profile has been modeled by density functional theoretical methodologies, providing mechanistic evidence on the different reaction steps, namely, the adduct formation and subsequent decomposition processes, with valuable comparisons with the reactivity of other nucleophiles with [Fe(CN)5NO]2–.