1,2,4-Tributylphosphorotrithioate

Description

DEF is a cholinesterase-inhibiting organophosphorus pesticide compound used as a cotton defoliant that was registered in 1960.DEF is a colorless to pale-yellow transparent liquid with a skunk-like odor.It is completely miscible with n-hexane, dichloromethane, toluene, and 2-propanol and has an octanol–water partition coefficient of 3.31×10⁵ at 25°C. DEF toxicity is primarily attributed to inhibition of various esterases, including acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), neuropathic target esterase (NTE), and carboxylesterase, resulting in increased accumulation of endogenous acetylcholine (ACh) in cholinergic nerve terminals and related effector organs.

Chemical properties

Tribufos is a colorless to yellow liquid. Tribufos is relatively stable to acids and heat and is hydrolyzed slowly under alkaline conditions. Tribufos has a mercaptan or skunk-like odor. Tribufos has a mercaptan or skunk-like odor. Practically insoluble in water (2.3×10^-4 g/ 100 mL); completely miscible in dichloromethane, n-hexane, 2-propanol, toluene.

The Uses of 1,2,4-Tributylphosphorotrithioate

1,2,4-Tributylphosphorotrithioate is a defoliant for cotton.

The Uses of 1,2,4-Tributylphosphorotrithioate

Defoliant.

The Uses of 1,2,4-Tributylphosphorotrithioate

DEF is an organophosphate chemical used as a cotton defoliant to facilitate mechanical harvesting. Recommended application rate is ～1–2.5 pints per acre per year applied as a diluted spray. Two products containing DEF as their active ingredient include DEF 6, manufactured by Bayer Corporation, and Folex 6 DC, manufactured by Amvac Chemical Co. Used for pest control in industrial agriculture (tends to be more toxic agents), organophosphates of low to intermediate toxicity are used to control ectoparasites on farm and companion animals and humans (head lice), and for home and garden pest control.

Definition

ChEBI: Tribufos is an organic thiophosphate. It has a role as a defoliant.

General Description

Colorless to pale yellow liquid with mercaptan-like odor. Insoluble in water; soluble in aliphatic, aromatic, and chlorinated hydrocarbons.. Used as a growth regulator.

Air & Water Reactions

Insoluble in water. Hydrolyzed slowly by alkaline conditions.

Reactivity Profile

An organophosphate derivative. Organophosphates are susceptible to formation of highly toxic and flammable phosphine gas in the presence of strong reducing agents such as hydrides. Partial oxidation by oxidizing agents may result in the release of toxic phosphorus oxides.

Hazard

Cholinesterase inhibitor.

Agricultural Uses

Herbicide, Defoliant, Plant growth regulator: Tribufos is an organophosphate defoliant used for cotton crops. It is specifically used to defoliate cotton in preparation for machine harvesting. It was first registered in the United States in 1961. Not approved for use in EU countries . Registered for use in the U.S.

Agricultural Uses

Defoliants are substances that induce premature shedding of leaves and facilitate harvesting. Defoliants and desiccants are both harvesting aids, and are used as herbicides, as many are toxic in nature. They may be organic or inorganic.
Tribufos is a very effective defoliant for cotton and one of the many harvesting aids in use, for various kinds of crops.

Trade name

B-1776®; BUTIFOS®; BUTIPHOS®[C]; CHEMAGRO® 1776; CHEMAGRO® B-1776; DE- GREEN®; DEF®; DEF DEFOLIANT®; DELEAFDEFOLIANT®; EASY OFF®-D; E-Z-OFF® D; FOLEX® 6EC FOS-FALL® A; ORTHO® phosphate defoliant

Safety Profile

A poison by ingestion, skin contact, and intraperitoneal routes. Experimental reproductive effects. Animal experiments show an anti-cholinesterase effect. When heated to decomposition it emits toxic fumes of PO, and SO,. See also PARATHION, PHOSPHATES, ESTERS, and SULFATES.

Carcinogenicity

No carcinogenic effects occurred when rats were given diets with 0, 4, 40, or 320 ppm tribufos (equivalent to 0.0, 0.2, 1.8, and 16.8 mg/kg/day in males and 0.0, 0.2, 2.3, and 21.1 mg/kg/day in females, respectively) for 2 years .
In a carcinogenicity study, mice were fed diets containing tribufos at doses of 0, 10, 50, or 250 ppm (equivalent to 0.0, 1.64, 8.28, or 48.02 mg/kg/day in males and 0.0, 2.08, 11.14, or 63.4 mg/kg/day in females) for 90 weeks . Carcinogenic effects were evident at 250 ppm (48.02 mg/kg/day in males and 63.4 mg/kg/day in females). Males exhibited a statistically significant increase in hemangiosarcomas and adenocarcinomas of the small intestines and females exhibited a statistically significant increase in alveolar/bronchiolar adenomas.

Environmental Fate

Soil. Hydrolyzes in soil to ethyl mercaptan, carbon dioxide and diisobutylamine (Hartley and Kidd, 1987). Butylate is probably subject to degradation of soil microorganisms. It was reported that butylate may degrade via hydrolysis of the ester linkage forming the corresponding mercaptan (ethyl mercaptan), alkylamine (diisobutylamine) and carbon dioxide. Transthiolation and oxidation of the mercaptan forms the alcohol which may further oxidize to afford a metabolic pool (Kaufman, 1967). Somasundaram and Coats (1991) reported butylate in soils is oxidized to the corresponding sulfoxide. The reported half-life in soil is approximately 1.5–10 weeks (Worthing and Hance, 1991). The reported half-life of butylate in a loam soil at 21–27°C was 3 weeks (Humburg et al., 1989). Residual activity in soil is limited to approximately 4 months (Hartley and Kidd, 1987).
Groundwater. According to the U.S. EPA (1986) butylate has a high potential to leach to groundwater.
Plant. In plants, butylate is metabolized to carbon dioxide, diisobutylamine, fatty acids, conjugates of amines and other compounds (Hartley and Kidd, 1987; Humburg et al., 1989).

Toxicity evaluation

DEF is relatively stable in aqueous solutions (pH 5 and 7) up to 32 days but slightly degraded at pH 9 with a half-life of 124 days. The hydrolytic breakdown product of DEF is known as desbutylthio tribufos. DEF is stable up to 30 days in sandy loam soil exposed to natural sunlight, but degrades in aqueous solution upon exposure to natural sunlight for 30 days, with an estimated half-life of 44 days. The estimated soil adsorption coefficient (K_d) for DEF ranges from 60.6 for sandy loam soil to 106 for clay loam. The estimated soil adsorption constant (K_oc) for DEF ranges from 4870 for silt loam to 12 684 for sand. DEF is highly persistent in soil with biodegradation half-lives of 745 and 389 days in sandy loam soil under aerobic and anaerobic conditions. Based on water solubility, high soil adsorption, hydrolysis, and aerobic soil metabolism data, DEF is not identified as a potential groundwater contaminant. However, DEF is likely to become airborne following aerial application or ground spraying. Also, while DEF itself is not significantly volatile, its degradation product, n-butyl mercaptan (nBM), is volatile and accounts for a skunk-like odor near areas where DEF has been applied. DEF is also formed via release of the defoliant merphos, which undergoes rapid oxidation under environmental conditions to tribufos. DEF has a vapor pressure of 5.3×10^-6 mm Hg at 25°C, suggesting its occurrence in both vapor and particulate phases in ambient atmosphere. Vaporphase DEF degrades by interacting with photochemically produced hydroxyl radicals; half-life for this reaction in air is estimated to be 5 h. Particulate-phase DEF gets removed from atmosphere by wet and dry deposition. Volatilization of DEF from water surfaces is not an important fate process based on its Henry’s Law constant of 2.9  107 atmm3 mol1 at 20°C.