Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners

Monica E McFadden; Eric V Patterson; Keith P Reber; Ian W Gilbert; John D Sivey; Gregory H LeFevre; David M Cwiertny

doi:10.1021/acs.est.1c05958

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Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners

Journal article

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Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners

Monica E McFadden, Eric V Patterson, Keith P Reber, Ian W Gilbert, John D Sivey, Gregory H LeFevre and David M Cwiertny

Environmental science & technology, Vol.56(1), pp.325-334

12/17/2021

DOI: 10.1021/acs.est.1c05958

PMID: 34920670

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Abstract

Safeners are used extensively in commercial herbicide formulations. Although safeners are regulated as inert ingredients, some of their transformation products have enhanced biological activity. Here, to fill gaps in our understanding of safener environmental fate, we determined rate constants and transformation products associated with the acid- and base-mediated hydrolysis of dichloroacetamide safeners AD-67, benoxacor, dichlormid, and furilazole. Second-order rate constants for acid- (HCl) and base-mediated (NaOH) dichloroacetamide hydrolysis (2.8 × 10–3 to 0.46 and 0.3–500 M–1 h–1, respectively) were, in many cases (5 of 8), greater than those reported for their chloroacetamide herbicide co-formulants. In particular, the rate constant for base-mediated hydrolysis of benoxacor was 2 orders of magnitude greater than that of its active ingredient co-formulant, S-metolachlor. At circumneutral pH, only benoxacor underwent appreciable hydrolysis (5.3 × 10–4 h–1), and under high-pH conditions representative of lime-soda softening, benoxacor’s half-life was 13 h─a timescale consistent with partial transformation during water treatment. Based on Orbitrap LC–MS/MS analysis of dichloroacetamide hydrolysis product mixtures, we propose structures for major products and three distinct mechanistic pathways that depend on the system pH and compound structure. These include base-mediated amide cleavage, acid-mediated amide cleavage, and acid-mediated oxazolidine ring opening. Collectively, this work will help to identify systems in which hydrolysis contributes to the transformation of dichloroacetamides, while also highlighting important differences in the reactivity of dichloroacetamides and their active chloroacetamide co-formulants.

safeners

pest control

agrochemicals

hydrolysis

dichloroacetamide safeners

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Details

Title: Subtitle: Acid- and Base-Mediated Hydrolysis of Dichloroacetamide Herbicide Safeners
Creators: Monica E McFadden - University of Iowa
Eric V Patterson - Stony Brook University
Keith P Reber - Towson University
Ian W Gilbert - Towson University
John D Sivey - Towson University
Gregory H LeFevre - University of Iowa
David M Cwiertny - University of Iowa
Resource Type: Journal article
Publication Details: Environmental science & technology, Vol.56(1), pp.325-334
DOI: 10.1021/acs.est.1c05958
PMID: 34920670
NLM abbreviation: Environ Sci Technol
ISSN: 0013-936X
eISSN: 1520-5851
Publisher: American Chemical Society
Grant note: DOI: 10.13039/100000165, name: Division of Chemistry, award: CHE-191942; DOI: 10.13039/100000082, name: Division of Graduate Education, award: DGE-163309; DOI: 10.13039/100001082, name: Camille and Henry Dreyfus Foundation, award: TH-20-021; DOI: 10.13039/100000146, name: Division of Chemical, Bioengineering, Environmental, and Transport Systems, award: CBET-1702610, CBET-1703796
Language: English
Date published: 12/17/2021
Academic Unit: Center for Health Effects of Environmental Contamination; Civil and Environmental Engineering; IIHR--Hydroscience and Engineering; Public Policy Center (Archive); Chemistry; Chemical and Biochemical Engineering
Record Identifier: 9984202152102771

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