Reactions of aliphatic free radicals with copper cations in aqueous solution. Part 2.—Reactions with cupric ions: a pulse radiolysis study

Abstract

Reactions of CuiG with the aliphatic-free radicals *CH2CO;, CH3qHCO;, O;CCHCH(OH)CO;, *CC13, $'H2CH20H and -CH,C(CH,),OH in aqueous solutions were studied.In these reactions the formation of unstable intermediates absorbing in the U.V. range was observed. This absorption is attributed to compounds with copper-carbon u bonds. The kinetics of formation and decomposition of these intermediates are reported and discussed. No intermediates were observed when Cu& reacts with *CR,R,OH-free radicals. Cu:, is one of the final products in all systems studied.Copper salts have been shown to affect a variety of reactions involving aliphatic free radicals including many catalytic processes in aprotic and protic media.l The results indicated that aliphatic free radicals react with many Cu" complexes via a mechanism involving the formation of " short lived " intermediates having a coppercarbon bond R* + CU" + Cu"'-R.It was suggested2 that the lifetime of the CU~~I-R intermediate is too short to be physically observable. The mechanisms of decomposition of CuI1'-R differ depending on the nature of -R, though in all cases the reaction can be summed up bywhere R(-H) is an oxidized form of the radical which lost one proton. In systems having a " good bridging " ligand on the Cu" the reaction scheme is often better described byIn some systems the results suggest an outer sphere redox mechanism However, the latter mechanism seems to be limited to unusual cases.

Flash photolysis of phenylacetatopentaminecobalt(III) in aqueous solution. Generation of benzyl radicals and their reversible trapping by cupric ions in homogeneous and micellar solutions

“…Figure 1 shows the spectra obtained at two different times after laser excitation. The formation of a species with absorptions in this region is in line with similar observations for other carbon centered radicals (6,14) and is attributed to reaction [2].…”

“…The formation of complex intermediates by reaction of carbon centered radicals with cupric ions seem to be a rather general phenomenon; some representative examples studied by pulse radiolysis (14), flash photolysis (16), and laser photolysis have been summarized in Table 1. Judging from the similarity of spectral shape and A, , , , the bonding interactions in all these species must be essentially the same.…”

Metal Induced Decarboxylation of Aliphatic Free Radicals. I. Kinetics of the Reactions of Copper(I) and Copper(II) Ions with the 2‐Methyl‐2‐Carboxylicacid‐Propyl Free Radical in Aqueous Solutions. A Pulse Radiolysis Study

“…A small part of the hydrated electrons might in some solutions react via reaction (12), thus increasing slightly the initial concentration of Cuta . Some of the hydrogen atoms might react via reaction (8) whch is followed by reaction (9).…”

Reactions of NO2 and nitrite ion with organic radicals

“…rnol dm-' sodium nitrate, 0.1 rnol dm-3stert-butanol solution to see if the copper(1) ion could reduce NO, to NO,. The copper(1) ion is formed by the overall reaction [8] from the 2-hydroxyalkyl radical (28,29).…”