Homogeneous Catalysis Under Ultradilute Conditions: TAML/NaClO Oxidation of Persistent Metaldehyde

Abstract

TAML activators enable homogeneous oxidation catalysis where the catalyst and substrate (S) are ultradilute (pM-low μM) and the oxidant is very dilute (high nM-low mM). Water contamination by exceptionally persistent micropollutants (MPs), including metaldehyde (Met), provides an ideal space for determining the characteristics and utilitarian limits of this ultradilute catalysis. The low MP concentrations decrease throughout catalysis with S oxidation (k) and catalyst inactivation (k) competing for the active catalyst. The percentage of substrate converted (%Cvn) can be increased by discovering methods to increase k/k. Here we show that NaClO extends catalyst lifetime to increase the Met turnover number (TON) 3-fold compared with HO, highlighting the importance of oxidant choice as a design tool in TAML systems. Met oxidation studies (pH 7, DO, 0.01 M phosphate, 25 °C) monitored by H NMR spectroscopy show benign acetic acid as the only significant product. Analysis of TAML/NaClO treated Met solutions employing successive identical catalyst doses revealed that the processes can be modeled by the recently published relationship between the initial and final [S] (S and S, respectively), the initial [catalyst] (Fe) and k/k. Consequently, this study establishes that ΔS is proportional to S and that the %Cvn is conserved across all catalyst doses in multicatalyst-dose processes because the rate of the k process depends on [S] while that of the k process does not. A general tool for determining the Fe required to effect a desired %Cvn is presented. Examination of the dependence of TON on k/k and Fe at a fixed S indicates that for any TAML process employing Fe < 1 × 10 M, small catalyst doses are not more efficient than one large dose.

Zero‐Order Catalysis in TAML‐Catalyzed Oxidation of Imidacloprid, a Neonicotinoid Pesticide

“…The equilibrium shown in Equation 4has been outlined as the most plausible reason for deviations from Equation (1). [11,[18][19] When [S t ] @ [Fe III t ], Equations (2)-(4)l ead to Equation (5), which shows that the effective rate constant( k I,eff ) for the catalysta ctivation by H 2 O 2 in this case equals…”

“…10 times the second-order rate constant for the oxidation of imidacloprid by ozone determined at pH 2. [21] The value of k II for imidacloprid should be compared with the recently reported value of k II for TAML 1 and metaldehyde (120 m À1 s À1 ), [5] which is exceptionally resistantt oo xidation. Note that 1 itself does not catalyze the oxidation of imidacloprid by H 2 O 2 and this emphasizes additionally the catalytic potential of the bis-sulfonamide TAML activator 2.…”

“…[2] The genesiso fT AML activators aimed at increasing their catalytic activity at neutral pH [3] madei tp ossible to degrade resistant-to-oxidation targets such as Safranin O [4] andm etaldehyde. [5] The most recentT AML specimens 2,c ontainingt wo sulfonamide units instead of two amide residues in the 'tail' part of the molecule [6] (see Figure 1), appeared to be exceptionally active under neutral reactionc onditions;t his openeda gate to detoxificationo fs uper resistant-to-oxidation targets such as imidacloprid (Figure 1), whichb elongs to the neonicotinoids-a new class of highly active, systemic insecticides. [7] Neonicotinoidsa re ar elatively new class of pesticides that have dominated the globalm arket since their development in the 1990s due to their broad activity in insects andl ow toxicity in humans.…”

A multidisciplinary investigation of the technical and environmental performances of TAML/peroxide elimination of Bisphenol A compounds from water

“…TAML catalysts and TAML/H 2 O 2 processes appear to be environmentally benign based on a diversity of evidence [307][308][309][310] and, as further shown here, are extremely simple to deploy. TAML/H 2 O 2 processes have been employed to oxidatively destroy numerous targets in water, [311][312][313][314][315] including bromo-, 310 chloro- 309 and nitro- 316 phenols, drugs, 317 thiophosphate pesticides, 318,319 molluscicides, 320,321 nitroaromatics, 316,322 the B. atrophaeus noninfectious surrogate for pathogenic B. anthracis and protozoa, 323 dyes, [324][325][326][327] coloured paper industry effluents, 328 and signature oestrogenic micropollutants. 4,329,330 Importantly, 2/H 2 O 2 chemistry is comprised exclusively of biochemically common elements as a foundational strategy for avoiding toxicity.…”

“…We have developed a mathematical tool for modelling TAML catalysis 345 which we have used to examine the comparative behaviour of 15 different catalysts in the oxidation of one substrate under one set of conditions 327 and, more recently, the oxidation of 5 different substrates by 2 different catalysts and 2 different oxidants at two different pHs. 321 We used the k II value for 2/H 2 O 2 oxidation of 1a and the 2 k i value of (7.7 ± 0.3) × 10 −5 s −1 determined in 2/H 2 O 2 oxidation of the azo dye Orange II at pH 11 and 25°C, 346 to estimate the percent removal of 1a by 150 nM 2 treatment. The predicted removal of ca.…”