Kinetics and mechanism of Ag(I) - promoted substitution of cyanide ion from hexacyanoferrate(II) by-nitrosobenzene

Abstract

The Ag(I)-promoted abstraction of CN^- from Fe(CN) &nbsp;- by nitrosobenzene leads to the formation of the violet complex, Fe(CN)₅C₆H₅NO^3-. The pseudo-first order rate constants of Fe(CN)₅C₆H₅NO^3- formation increase with increase in [Fe(CN)<img src='http://www.niscair.res.in/jinfo/equation29.gif' border=0>] and reach limiting value for [Fe(CN)<img src='http://www.niscair.res.in/jinfo/equation29.gif' border=0>]/[AgNO₃] &ge; 30. This indicates the formation of a strong adduct between Fe(CN)<img src='http://www.niscair.res.in/jinfo/equation29.gif' border=0> and AgN03 prior to the abstraction of CN^-. Activation parameters for the reaction <em>are</em>: <img src='http://www.niscair.res.in/jinfo/delta.gif' border=0> <em>H ^&ne; </em>= 139 &plusmn; 14 kJ mol^-1; and <img src='http://www.niscair.res.in/jinfo/delta.gif' border=0> <em>S ^&ne;</em> = 145 &plusmn;21 J K^-1 mol^-1. Positive entropy of activation suggests on S_N1 type of dissociation of the intermediate.