Kinetics and mechanism of the oxidation of a cobaloxime by sodium hypochlorite in aqueous solution: Is it an outer-sphere mechanism?

Abstract

The kinetics and mechanism of the oxidation of [Co(dmgBF2)2(OH2)2] (where dmgBF2 = difluoroboryldimethylglyoximato) by sodium hypochlorite (NaOCl) were investigated by stopped-flow spectrophotometry at 450 nm over the temperature range of 10 °C ≤ θ ≤ 25 °C, pH range of 5.0 ≤ pH ≤ 7.8, and at an ionic strength of 0.60 M (NaCl). The pKa1 value for [Co(dmgBF2)2(H2O)2] was calculated as 5.27 ± 0.14 at I = 0.60 (NaCl). The redox process was dependent on pH and oxidant concentration in a complex manner, that is, kobs = ((k2[H+] + k1Ka)/([H+] + Ka))[OCl−]T, where at 25.3 °C, k1 was calculated as 3.54 × 104 M−1 s−1, and k2 as 2.51 × 104 M−1 cm−1. At a constant pH value, while varying the concentration of sodium hypochlorite two rate constants were calculated, viz., k′1 = 7.56 s−1 (which corresponded to a reaction pathway independent of the NaOCl concentration) and k′2 = 2.26 × 104 M−1 s−1, which was dependent on the concentration of NaOCl. From the variation in pH, ΔnormalH1≠,ΔnormalH2≠,ΔnormalS1≠, and ΔnormalS2≠ were calculated as 58 ± 16 kJ mol−1, 46 ± 1 kJ mol−1, 34 ± 55 J mol−1 K−1, and −6 ± 4 Jmol−1 K−1, respectively. The self-exchange rate constant, k11, for sodium hypochlorite (as ClO−) was calculated to be 1.2 × 103 M−1 s−1, where an outer-sphere electron transfer mechanism was assumed. A green product, [Co(dmgBF2)2(OH2)(OH)]·1.75NaOCl, which can react with DMSO, was isolated from the reaction at pH 8.04 with a yield of 13%.

Collagen-depletion strategies in dentin as alternatives to the hybrid layer concept and their effect on bond strength: a systematic review

“…What can be clearly seen from Table 5 , are the vast differences in the percentages and application times of NaOCl used. These aspects most likely influence not only the extent of the proteolytic activity—how much collagen is dissolved, but also the impact of the redox effect 61 , detrimental to resin-based materials dependent upon the generation of free-radicals for polymerization mechanisms. Furthermore, the rinsing protocol after the use of NaOCl will most likely also impact the detrimental effect of this agent since ineffective rinsing protocols will not get rid of the residual NaOCl.…”

Reversible detection of hypochlorite using the deprotonation–protonation strategy: a search for new building blocks

“…In continuation of this work and motivated by the merits of reversible probes, we were then interested in the development of a reversible 'turn on' fluorescent probe for the detection of ClO À . Keeping in mind the weak basic nature of hypochlorite (pK a = 7.40), 24 we planned to utilize the deprotonation-protonation strategy for detecting the hypochlorite induced emission changes. We envisaged that a probe having labile protons may have potential to exist in optically switchable protonated-deprotonated states in the presence of hypochlorite.…”