EPR investigation into the kinetics and mechanism of the one-electron reduction of benzenediazonium ions by Fe^II–EDTA and other iron(II) complexes

Abstract

A n EPR approach has been developed and applied t o the determination of the rate constants for the decomposition of some arenediazonium ions b y Fell complexes to give aryl radicals. In continuousf l o w experiments, steady-state concentrations have been measured both for the aryl radical-adducts to the fumarate anion and for ' CH,CO,-(obtained b y reaction of Ar' with the iodoacetate anion): analysis of the dependence of these upon [Fe"] and [ArN,'] leads to values of the rate constants for electron transfer.For the reaction between Fell-EDTA and a series of diazonium ions, for which values of k are in the range 2 x 1 04-4 x 1 O5 dm3 mo1-l s-l, it is shown that there is a good dual-parameter Hammett-Taft correlation (involving 0, and oR+, and with p = 1.74), consistent with the occurrence of an outer-sphere electron-transfer process.

Mechanism of Hydroxyl Radical‐Induced Breakdown of the Herbicide 2,4‐Dichlorophenoxyacetic Acid (2,4‐D)

“…ESR studies and other theoretical studies have shown that the radical character of phenoxyl radicals is well dispersed in the aromatic ring, giving relatively high stability to the radical 68–71. The spin densities obtained from our calculations confirm this radical dispersion.…”

Sandmeyer reactions. Part 6.1 A mechanistic investigation into the reduction and ligand transfer steps of Sandmeyer cyanation

“…copper-free) conditions, Scheme 3 2 PERKIN outer-sphere reductions of diazonium ions by ferrocyanide in aqueous solution and by decamethylferrocene in MeCN have been reported by Doyle and co-workers 22 and we have previously inferred comparable behaviour in their reduction by Fe 2ϩ ligated by EDTA in aqueous solution at pH 9. 23 No kinetic study of Sandmeyer cyanation has been carried out, perhaps because of the formation of the intermediate solid or oily phases which have been reported for the reaction in aqueous solution. 24 Nevertheless, cyanide being a 'pseudohalide', the reaction is believed to occur in a manner comparable to that of the copper() halides and there may well be more than one active cyanocuprate species.…”

Understanding and eliminating iron interference in colorimetric nitrate and nitrite analysis

“…Since EDTA is only a hexadentate ligand (two tertiary amines with lone electron pairs and four carboxylic acid groups), iron has two orbitals free to interact with the diazonium ion. Not only this, but EDTA lowers the reduction potential of iron from 0.77 to 0.14 and thereby makes it a better reductant and increases the favorability of reduction of diazonium (Gilbert et al 1992). Thus, EDTA appears to selectively create the interference with NO − 3 and NO − 2 analyses.…”

“…Reducing agents (Vollhardt and Schore 1994). In fact, Gilbert et al (1992) showed that Fe(II)EDTA at pH 9 causes the loss of azide from several very similar benzene diazonium ions. Thus, we hypothesize that Fe(II)EDTA reduces the diazonium ion (see Fig.…”