Imazamethabenz (Ref: AC 263840)

Imazamethabenz (Ref: AC 263840)	Last updated: 17/09/2025
(Also known as: CL 263840; imazamethabenz acid)

SUMMARY

Hazard alerts

The following alerts are based on the data in the tables below. An absence of an alert does not imply the substance has no implications for human health, biodiversity or the environment but just that we do not have the data to form a judgement. These hazard alerts do not take account of usage patterns or exposure, thus do not represent risk.

Environmental fate	Ecotoxicity	Human health
Environmental fate Moderate alert: GUS: Transition state; Drainflow: Moderately mobile Warning: Significant data are missing	Ecotoxicity Moderate alert: Earthworms acute ecotoxicity: Moderate	Human health Moderate alert: Reproduction/development effects

GENERAL INFORMATION

Description

A post-emergence herbicide, usually used as the methyl ester, to control grasses and some dicotyledonous weeds. Also pesticide transformation product

Example pests controlled

Grasses and some dicotyledonous weeds

Example applications

Sunflowers; Wheat; Barley

Efficacy & activity

GB regulatory status

GB COPR regulatory status

Not approved

Date COPR inclusion expires

Expired

GB LERAP status

No UK approval for use as a plant protection agent

EC Regulation 1107/2009 (repealing 91/414)

EC Regulation 1107/2009 status

Not approved

Dossier rapporteur/co-rapporteur

Date EC 1107/2009 inclusion expires

Expired

EU Candidate for substitution (CfS)

Not applicable

Listed in EU database

Yes

Approved for use (✓) under EC 1107/2009 in the following EU Member States

ATAustria	BEBelgium	BGBulgaria	CYCyprus	CZCzech Republic	DEGermany	DKDenmark	EEEstonia	ELGreece

ESSpain	FIFinland	FRFrance	HRCroatia	HUHungary	IEIreland	ITItaly	LTLithuania	LULuxembourg

LVLatvia	MTMalta	NLNetherlands	PLPoland	PTPortugal	RORomania	SESweden	SISlovenia	SKSlovakia

Approved for use (✓) under EC 1107/2009 by Mutual Recognition of Authorisation and/or national regulations in the following EEA countries

ISIceland	NONorway

Additional information

Also used in

Chemical structure

Isomerism

Imazamethabenz is a chiral molecule. The technical material is a reaction mixture of the 5-methyl- and 2-methyl- isomers in the ratio 3:2.

Chemical formula

C₁₅H₁₈N₂O₃

Canonical SMILES

CC1=CC(=C(C=C1)C(=O)O)C2=NC(C(=O)N2)(C)C(C)C

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

KFEFNHNXZQYTEW-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C15H18N2O3/c1-8(2)15(4)14(20)16-12(17-15)11-7-9(3)5-6-10(11)13(18)19/h5-8H,1-4H3,(H,18,19)(H,16,17,20)

2D structure diagram/image available?

Yes

General status

Pesticide type

Herbicide; Metabolite

Metabolite Type

Soil; Plant

Substance groups

Imidazolinone herbicide

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Selective, systemic absorbed through roots and leaves. Inhibits plant amino acid synthesis - acetohydroxyacid synthase AHAS.

CAS RN

100728-84-5

EC number

600-126-1

CIPAC number

529

US EPA chemical code

128842

PubChem CID

3034382

CLP index number

No data found

Molecular mass

274.32

PIN (Preferred Identification Name)

reaction mixture of rac-5-methyl-2-[(4R)-4-methyl-5-oxo-4-(propan-2-yl)-4,5-dihydro-1H-imidazol-2-yl]benzoic acid and rac-4-methyl-2-[(4R)-4-methyl-5-oxo-4-(propan-2-yl)-4,5-dihydro-1H-imidazol-2-yl]benzoic acid in the ratio 3:2

IUPAC name

reaction mixture of 6-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-m-toluic acid and 2-[(RS)-4-isopropyl-4-methyl-5-oxo-2-imidazolin-2-yl]-p-toluic acid

CAS name

2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-4(or 5)-methylbenzoic acid

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

Herbicide Resistance Class (HRAC MoA class)

Herbicide Resistance Class (WSSA MoA class)

Insecticide Resistance Class (IRAC MoA class)

Not applicable

Fungicide Resistance Class (FRAC MOA class)

Not applicable

Examples of recorded resistance

Physical state

Off white powder

Related substances & organisms

imazamethabenz-methyl

Can be a metabolite of:

Parent

Formation medium

Estimated maximum occurrence fraction

1107/2009 relevancy

imazamethabenz-methyl

Soil

Commercial

Property

Value

Availability status

Introduction & key dates

1998, introduced

Example manufacturers & suppliers of products using this active now or historically

BASF

Example products using this active

Assert 300

Formulation and application details

Commercial production

Imazamethabenz is synthesised through a multi-step process that builds its imidazolinone core and attaches functional groups for herbicidal activity. The synthesis typically begins with the formation of a substituted imidazolinone ring, often derived from the condensation of methyl isobutyraldehyde with cyanamide and acetic acid derivatives under controlled conditions. This intermediate is then coupled with a benzoic acid derivative, such as 2-methylbenzoic acid, through an acylation or esterification reaction to form the final active compound. The product is usually formulated as a toluate ester, which enhances its solubility and uptake in plants.

Impact on climate of production and use

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C (mg l⁻¹)

1110

High

Solubility - In organic solvents at 20 °C (mg l⁻¹)

30900

Methanol

4500

Toluene

23000

Acetone

Melting point (°C)

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

Octanol-water partition coefficient at pH 7, 20 °C

4.90 X 10⁰¹

Calculated

Log P

1.69

Low

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

Dissociation constant pKa) at 25 °C

23.5

Vapour pressure at 20 °C (mPa)

Henry's law constant at 25 °C (Pa m³ mol⁻¹)

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

Maximum UV-vis absorption L mol⁻¹ cm⁻¹

Surface tension (mN m⁻¹)

Degradation

Property

Value

Source; quality score; and other information

Interpretation

General biodegradability

Soil degradation (days) (aerobic)

DT₅₀ (typical)

Moderately persistent

DT₅₀ (lab at 20 °C)

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

DT₅₀ modelling endpoint

Note

Literature values DT₅₀ 25-45 days

Dissipation rate RL₅₀ (days) on plant matrix

Value

Note

Dissipation rate RL₅₀ (days) on and in plant matrix

Value

Note

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Note

Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7

Value

Note

Water-sediment DT₅₀ (days)

Water phase only DT₅₀ (days)

Sediment phase only DT₅₀ (days)

Air degradation

As this parameter is not normally measured directly, a surrogate measure is used: ‘Photochemical oxidative DT₅₀’. Where data is available, this can be found in the Fate Indices section below.

Decay in stored produce DT₅₀

Soil adsorption and mobility

Property

Value

Source; quality score; and other information

Interpretation

Linear

K_d (mL g⁻¹)

K_oc (mL g⁻¹)

Notes and range

Freundlich

K_f (mL g⁻¹)

Moderately mobile

K_foc (mL g⁻¹)

320

¹/_n

Notes and range

Literature values K_oc range 55 to 584 mL g⁻¹

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

2.21

Calculated

Transition state

SCI-GROW groundwater index (μg l⁻¹) for a 1 kg ha⁻¹ or 1 l ha⁻¹ application rate

Value

9.52 X 10^-02

Calculated

Note

Potential for particle bound transport index

Low

Calculated

Potential for loss via drain flow

Moderately mobile

Calculated

Photochemical oxidative DT₅₀ (hrs) as indicator of long-range air transport risk

Bio-concentration factor

BCF (l kg⁻¹)

4.0

Low potential

CT₅₀ (days)

Known metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 5000

Rat

Low

Mammals - Short term dietary NOEL

(mg kg⁻¹)

(ppm diet)

Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)

Birds - Acute LD₅₀ (mg kg⁻¹)

> 2150

Anas platyrhynchos

Low

Birds - Short term dietary (LC₅₀/LD₅₀)

Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)

Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹ dw soil)

> 123

Eisenia foetida as methyl variant

Moderate

Earthworms - Chronic NOEC, reproduction (mg kg⁻¹ dw soil)

Soil micro-organisms

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

Vegetative vigour ER₅₀ (g ha⁻¹)

Seedling emergence ER₅₀ (g ha⁻¹)

Honeybees (Apis spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

> 100

Low

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Chronic

Notes

Bumblebees (Bombus spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Mason bees (Osmia spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Other bee species (1)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Other bee species (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Beneficial insects (Ladybirds)

Beneficial insects (Lacewings)

Beneficial insects (Parasitic wasps)

Beneficial insects (Predatory mites)

Beneficial insects (Ground beetles)

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Temperate Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

> 100

Oncorhynchus mykiss

Low

Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

> 100

Daphnia magna

Low

Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)

Aquatic Plants (free-floating, fonds growth, fresh) - 7 day (mg l⁻¹)

Aquatic plants (rooted, growth rate, fresh) - 14 day (mg l⁻¹)

Algae - Acute (growth rate, fresh; mg l⁻¹) (EC₅₀)

89.0

Raphidocelis subcapitata

Low

Algae - Chronic (growth rate, fresh; mg l⁻¹)

Mesocosm study data

NOEAEC mg l⁻¹

Marine bivalves

HUMAN HEALTH AND PROTECTION

General

Property

Value

Source; quality score; and other information

Interpretation

Threshold of Toxicological Concern (Cramer Class)

High (class III)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

> 5000

Rat

Low

Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)

2000

Rat

Mammals - Inhalation LC₅₀ (mg l⁻¹)

5.8

Rat 4 hr

Other Mammal toxicity endpoints

ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)

ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)

AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)

AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

Occupational

MRLs

European

EU MRL pesticide database

Great Britain

GB MRL Register

Notes

Drinking Water Standards

Drinking Water MAC (μg l⁻¹)

Mammalian dose elimination route and rate

Health issues

Specific human health issues (hazard-based)

Carcinogen

Genotoxic

Endocrine disruptor

; ; ; ;

No data found

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

May cause irreversible eye damage

Handling issues

Property

Value and interpretation

General

Prevent generation of mists
Corrosive

CLP classification 2013

Health: H319
Environment: H412

WHO Classification

U (Unlikely to present an acute hazard)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

imazamethabenz

French

German

Danish

Italian

Spanish

imazametabenz

Greek

Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	17/09/2025
Contact:	aeru@herts.ac.uk
Please cite as:	Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242