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Polyoxyethylene tallow amine (POE-T) is a member of the polyoxyethylene alkylamine (POEA) class of nonionic surfactants and is a component of some glyphosate-based formulations. The presence of POE-T improves foliar uptake of glyphosate in weeds, thereby reducing the amount of glyphosate needed for weed control. To further characterize the environmental fate of POE-T, aerobic soil degradation, hydrolysis, adsorption/desorption, and aerobic aquatic degradation studies were conducted according to U.S. EPA and OECD pesticide regulatory testing guidelines. POE-T labeled with carbon-14 was used in the studies to aid in analysis, assess mineralization to CO

The fate and toxicity of a polyethoxylated tallowamine (POEA) surfactant system, MON 0818, was evaluated in water–sediment microcosms during a 4-d laboratory study. A surfactant solution of 8 mg l−1 nominal concentration was added to each of nine 72-l aquaria with or without a 3-cm layer of one of two natural sediments (total organic carbon (TOC) 1.5% or 3.0%). Control well water was added to each of nine additional 72-l aquaria with or without sediment. Water samples were collected from the microcosms after 2, 6, 24, 48, 72, and 96 h of aging to conduct 48-h toxicity tests with Daphnia magna and to determine surfactant concentrations. Elevated mortality of D. magna (43–83%) was observed in overlying water sampled from water-only microcosms throughout the 96-h aging period, whereas elevated mortality (23–97%) was only observed in overlying water sampled from water–sediment microcosms during the first 24 h of aging. Measured concentrations of MON 0818 in water-only microcosms remained relatively constant (4–6 mg l−1) during the 96-h period, whereas the concentrations in overlying water from microcosms containing either of the two types of sediment dissipated rapidly, with half-lives of 13 h in the 3.0% TOC sediment and 18 h in the 1.5% TOC sediment. Both toxicity and the concentration of MON 0818 in overlying water decreased more rapidly in microcosms containing sediment with the higher percent TOC and clay and with a higher microbial biomass. Mortality of D. magna was significantly correlated with surfactant concentrations in the overlying water. These results indicate that the toxicity of the POEA surfactant in water rapidly declines in the presence of sediment due to a reduction in the surfactant concentration in the overlying water above the sediment.

The geometry about oxygen in the transition-state structures for oxygen transfers from a nitrone to phosphorous, from a percarboxylic acid to a carbon-carbon double bond, and from an N-sulfonyl oxaziridine to a carbon-carbon double bond have been evaluated by the endocyclic restriction test. The former can proceed at an oblique angle, while the latter two require a large angle between the entering and leaving groups on oxygen. This informa- tion is used to determine the mechanism of the aldehyde-dependent oxygen transfer from molecular oxygen to a carbon-carbon double bond. Many chemical reactions, when broken down to their elementary steps, are atom transfer processes. Proper descriptions of the pathways of these reactions require experimental determinations of the arrangement of atoms in transition-state structures. With this information in hand, an informed choice between alternative pathways may be made, and understanding of the mechanism can be developed. The endocyclic restriction test is based on work by Eschenmoser, who investigated nucleophilic substitution of carbon and Hogg and Vipond who investigated nucleophilic displacements at sulfur (1-3). We have used this approach to evaluate the orientation of atoms in transition-state structures for reactions in which the atom Y is transferred from the leaving group L to a nucleophile N. The test deter- mines whether the transfer of Y from L to N can occur in an endocyclic ring. The size of the ring restricts the bond angles available in a transition-state structure (2) (1). Experimentally, the approach involves determination of whether reaction (2) is intramolecular or intermolecular.

The geometries allowed for formal transfers of oxygen to the phosphorus(III) of a phosphine from a nitrone, an O-acetylhydroxylamine, and a sulfoxide have been evaluated by the endocyclic restriction test. Investigations of the conversions of 1 to 2, 16 to 17, and 28 to 29, by isotopic labeling, substituent effect, and kinetic and spectroscopic experiments, reveal the operation of different mechanisms for each of these transfers. For 1, oxygen addition to phosphorus is the preferred mechanism. In the case of 16, the mechanism involves nucleophilic displacement of oxygen from nitrogen by phosphorus to give 26 followed by oxygen addition to phosphorus. In acetic acid, the oxygen is added to 26 from water in the workup whereas in toluene the oxygen is provided by the acetate produced by the displacement. For 28, either addition by oxygen of the sulfoxide to activated phosphorus or addition by phosphorus to sulfur of the sulfoxide precedes oxygen transfer.

The transfers of oxygen from nitrogen to phosphorus in the conversions of 1 to 2 and 3 to 4 are shown by kinetic, solvent-labeling, and double-labeling criteria to be intramolecular reactions. This information in conjunction with the stabilities of 13 and 14 is taken to rule out the mechanisms of classic linear S N 2 substitutions at oxygen or nitrogen, biphilic insertion, or a radical chain reaction and to favor reactions via a 10-P-5 species (18). The results appear to providc the first experimental demonstration that oxygen can be transferred at an oblique angle

The geometry about oxygen in the transition-state structures for oxygen transfers from a nitrone to phosphorous, from a percarboxylic acid to a carbon-carbon double bond, and from an N-sulfonyl oxaziridine to a carbon-carbon double bond have been evaluated by the endocyclic restriction test. The former can proceed at an oblique angle, while the latter two require a large angle between the entering and leaving groups on oxygen. This informa- tion is used to determine the mechanism of the aldehyde-dependent oxygen transfer from molecular oxygen to a carbon-carbon double bond. Many chemical reactions, when broken down to their elementary steps, are atom transfer processes. Proper descriptions of the pathways of these reactions require experimental determinations of the arrangement of atoms in transition-state structures. With this information in hand, an informed choice between alternative pathways may be made, and understanding of the mechanism can be developed. The endocyclic restriction test is based on work by Eschenmoser, who investigated nucleophilic substitution of carbon and Hogg and Vipond who investigated nucleophilic displacements at sulfur (1-3). We have used this approach to evaluate the orientation of atoms in transition-state structures for reactions in which the atom Y is transferred from the leaving group L to a nucleophile N. The test deter- mines whether the transfer of Y from L to N can occur in an endocyclic ring. The size of the ring restricts the bond angles available in a transition-state structure (2) (1). Experimentally, the approach involves determination of whether reaction (2) is intramolecular or intermolecular.

Addition of monosubstituted alkylhydrazines to acetylenic esters with either electron-withdrawing or sterically bulky β-substituents afforded 1-alkyl-3-hydroxy-5-substituted-pyrazoles 1 as the major regioisomeric product. By comparison, the classical cyclocondensation of alkylhydrazines with β-keto esters gives the regioisomeric pyrazol-5-ones 2. The reaction solvent employed in these cyclocondensations can have a profound effect on regiosomeric product ratios. Addition of methylhydrazine to 5g in methylene chloride gave regiospecific formation of pyrazolinone 2o, whereas addition in water-methanol mixtures afforded hydroxypyrazole 1o as the major product

Biomonitoring was used to assess the combined dermal, oral, and inhalation exposure associated with the agricultural use of Harness Plus, an emulsifiable concentrate formulation of the herbicide acetochlor. Twenty Spanish farmers handled and applied acetochlor to maize in the spring of 2003, following the product label recommendations. Open- and closed-cabin applications were equally represented. Urine was collected during six consecutive days, starting the day prior to application. Daily composites were analyzed for 2-ethyl-6-methyl-aniline, a common chemophore representing the major urinary acetochlor metabolites. All applicators showed detectable concentrations in urine after application. Although, the open-cabin applicators treated fewer hectares, they showed significantly higher exposure compared to the closed-cabin applicators (average exposure: 0.004 and 0.002 mg/kg bw/day, respectively). Linear regression analysis suggested that untracked incidents had a significant impact on the total exposure. Other events that may have contributed to the observed exposure are repair of faulty equipment, accidental spillages, splashes, and inadequate use of protective gloves. The average margins of exposure (MOE) for farmers ranged from 23,000 (open cabin) to about 44,000 (closed cabin). For professional applicators the MOEs were 10-fold lower. These MOEs clearly indicate that no adverse health effects should be expected from agricultural acetochlor applications.