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

Abstract

Bis‐sulfonamide bis‐amide TAML activator [Fe{4‐NO2C6H3‐1,2‐(NCOCMe2NSO2)2CHMe}]− (2) catalyzes oxidative degradation of the oxidation‐resistant neonicotinoid insecticide, imidacloprid (IMI), by H2O2 at pH 7 and 25 °C, whereas the tetrakis‐amide TAML [Fe{4‐NO2C6H3‐1,2‐(NCOCMe2NCO)2CF2}]− (1), previously regarded as the most catalytically active TAML, is inactive under the same conditions. At ultra‐low concentrations of both imidacloprid and 2, 62 % of the insecticide was oxidized in 2 h, at which time the catalyst is inactivated; oxidation resumes on addition of a succeeding aliquot of 2. Acetate and oxamate were detected by ion chromatography, suggesting deep oxidation of imidacloprid. Explored at concentrations [2]≥[IMI], the reaction kinetics revealed unusually low kinetic order in 2 (0.164±0.006), which is observed alongside the first order in imidacloprid and an ascending hyperbolic dependence in [H2O2]. Actual independence of the reaction rate on the catalyst concentration is accounted for in terms of a reversible noncovalent binding between a substrate and a catalyst, which usually results in substrate inhibition when [catalyst]≪[substrate] but explains the zero order in the catalyst when [2]>[IMI]. A plausible mechanism of the TAML‐catalyzed oxidations of imidacloprid is briefly discussed. Similar zero‐order catalysis is presented for the oxidation of 3‐methyl‐4‐nitrophenol by H2O2, catalyzed by the TAML analogue of 1 without a NO2‐group in the aromatic ring.

Predicting Properties of Iron(III) TAML Activators of Peroxides from Their III/IV and IV/V Reduction Potentials or a Lost Battle to Peroxidase

“…Some TAML activators are inactive toward slow‐to‐oxidize substrates. In particular, 1 a does not catalyze the oxidation of propranolol by H 2 O 2 , but 1 b does; [20] 1 b is inactive toward imidacloprid, though 2 d is active [23] . Note that these four TAMLs catalyze the oxidation of fast‐to‐oxidize Orange II dye [17, 24] .…”

“…[21,22] Thec orresponding k II values ared ifferent as well.N eedlesst os ay,f or onep articular S, the k II values depend on thenatureofT AML,and this dependence is strong.S omeT AMLa ctivatorsa re inactivet oward slowto-oxidize substrates.I np articular, 1a does notc atalyzet he oxidation of propranololb yH 2 O 2 ,b ut 1b does; [20] 1b is inactive toward imidacloprid, though 2d is active. [23] Note that thesefour TAMLsc atalyzet he oxidationo ff ast-to-oxidize Orange II dye. [17,24] Reductionp otentialsp rovide ac onvenientt oolf or quantitative rationalizationo ft hisp ropertyo fT AMLa ctivators.…”

First thermal studies on visible-light-switchable negative T-type photochromes of a nitrile-rich series

“…Zero-order reactions are usually found for heterogeneous or enzyme catalyzed processes. [32][33][34][35][36] The presence of a rate-limiting step allowing only a small fraction of the reactant molecules to react is typical for such reactions. Thus, the reactant conversion occurs with constant rate and therefore the true reaction order is hidden.…”

TAML- and Buffer-Catalyzed Oxidation of Picric Acid by H2O2: Products, Kinetics, DFT, and the Mechanism of Dual Catalysis

“…6−9 TAMLs have provided the platform for resolving key issues of homogeneous metal-complex catalysis, including, most significantly, catalyst inactivation in functioning catalytic cycles, 10−12 substrate inhibition, 9 and zero-order in catalyst concentrations. 13 The general features of TAML catalysis can be summarized as follows: if a substrate S is oxidized catalytically by H 2 O 2 into a product P, the stoichiometric mechanism outlined in Scheme 1 usually holds. 5 The corresponding rate law (eq 1) predicts the first order in concentration of Fe III…”