title: 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 (kII) and catalyst inactivation (ki) competing for the active catalyst. The percentage of substrate converted (%Cvn) can be increased by discovering methods to increase kII/ki. Here we show that NaClO extends catalyst lifetime to increase the Met turnover number (TON) 3-fold compared with H2O2, highlighting the importance of oxidant choice as a design tool in TAML systems. Met oxidation studies (pH 7, D2O, 0.01 M phosphate, 25 °C) monitored by1H 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] (S0and S∞, respectively), the initial [catalyst] (FeTot) and kII/ki. Consequently, this study establishes that ΔS is proportional to S0and that the %Cvn is conserved across all catalyst doses in multicatalyst-dose processes because the rate of the kIIprocess depends on [S] while that of the kiprocess does not. A general tool for determining the FeTotrequired to effect a desired %Cvn is presented. Examination of the dependence of TON on kII/kiand FeTotat a fixed S0indicates that for any TAML process employing FeTot< 1 × 10-6M, small catalyst doses are not more efficient than one large dose.
authors.affiliation: Institute for Green Science, Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Liang L
authors.initials: LL
authors.lastname: Tang
authors.affiliation: Institute for Green Science, Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Matthew A
authors.initials: MA
authors.lastname: DeNardo
authors.affiliation: Institute for Green Science, Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Schuler
authors.affiliation: Institute for Green Science, Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Matthew R
authors.identifier: 0000-0001-8975-2855
authors.initials: MR
authors.lastname: Mills
authors.affiliation: Institute for Green Science, Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Chakicherla
authors.initials: C
authors.lastname: Gayathri
authors.affiliation: Institute for Green Science, Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Roberto R
authors.initials: RR
authors.lastname: Gil
authors.affiliation: Institute for the Environment, Brunel University , Halsbury Building (130), Kingston Lane, Uxbridge, Middlesex, UB8 3PH, United Kingdom.
authors.forename: Rakesh
authors.initials: R
authors.lastname: Kanda
authors.affiliation: Institute for Green Science, Department of Chemistry, Carnegie Mellon University , 4400 Fifth Avenue, Pittsburgh, Pennsylvania 15213, United States.
authors.forename: Terrence J
authors.initials: TJ
authors.lastname: Collins