Reduction of alkaline aqueous disodium pentacyanonitrosylferrate(2–)(sodium nitroprusside) and kinetic features of its colour reaction with thiols

Abstract

The products of each one-electron step in the reduction of the anion [(NC)₅Fe^IINO]^2–, (I), to pentacyano-(hydroxylamine)ferrate(3–) ion, [(NC)₅Fe^II(NH₂OH)]^3–, have been characterised spectroscopically. The anions [(NC)₅Fe–ṄO]^3– and [(NC)₅Fe–N(H)Ȯ]^4– have characteristic e.s.r. spectra; the anions [(NC)₅Fe–O]^4– and [(NC)₅Fe(NH₂OH)]^3– have broadish optical absorption maxima at 347 and 436 nm respectively and hydrolyse slowly to the aquapentacyanoferrate(3–) anion, [(NC)₅Fe^IIOH₂]^3–. The reduction processes resemble those of the stepwise reversible reduction of nitrobenzene to phenylhydroxylamine in alkali. Reversible reactions between (I) and thiolate anions give pink products, [(NC)₅Fe^II(NO)SR]^3–, which decompose irreversibly yielding [(NC)₅Fe–ṄO]^3– anions. The reactions (i) and (ii) may both be involved in these decompositions. [(NC)₅Fe(NO)SR]^3–→[(NC)₅Fe–ṄO]^3–+ RS·(i), [(NC)₅Fe(NO)SR]^3–+ RS^–→[(NC)₅Fe–NO]^4–+ RS·SR (ii)