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Nucleophilic Addition Reactions of the Nitroprusside Ion – The Case of O ‐Methylhydroxylamine
Author(s) -
Gutiérrez María M.,
Olabe José A.,
Amorebieta Valentín T.
Publication year - 2012
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201200387
Subject(s) - chemistry , adduct , isonicotinamide , reaction rate constant , medicinal chemistry , aqueous solution , nucleophile , kinetics , spectroscopy , inorganic chemistry , analytical chemistry (journal) , catalysis , organic chemistry , molecule , hydrogen bond , physics , quantum mechanics
The kinetics of the reaction between aqueous solutions of [Fe(CN) 5 NO] 2– and NH 2 OCH 3 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), CH 3 OH, and [Fe II (CN) 5 H 2 O] 3– , characterized as the [Fe II (CN) 5 (pyCONH 2 )] 3– complex (pyCONH 2 = isonicotinamide). In excess NH 2 OCH 3 , the kinetic runs indicated pseudo‐first‐order behavior, with corresponding rate constants, k obs [s –1 ], that correlated linearly with the concentration of NH 2 OCH 3 . The rate law is: R = k exp [Fe(CN) 5 NO 2– ][NH 2 OCH 3 ], with k exp = (4.1 ± 0.4) × 10 –4 M –1 s –1 at 25 ± 0.2 °C, Δ H # = 27 ± 1 kJ mol –1 , and Δ S # = –220 ± 5 J K –1 mol –1 , at pH 7.1. The value of k exp is much lower than that for similar addition reactions of NH 2 OH 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) 5 NO] 2– .