Transport of Pesticides Under Aquifer Conditions

Abstract

Pesticide transport was determined in a quarternary coarse grained aquifer which was characterized by low organic carbon content. Water spiked with the pesticides atrazine, chlortoluron, isoproturon, simazine and terbuthylazine and chloride salt as conservative tracer, was injected in the aquifer. Mean residence times (MRT) of pesticides were generally 1.5 to 3 times higher than the MRT of the tracer. Sediment retention capacity calculated from experimental data yielded generally small values below 250 ng/kg sediment. Retardation characteristics were in the order of magnitude expected from literature data on organic carbon/water partition coefficients. Transport of pesticides was due to convection and dispersion whereas adsorption and degradation was low.     

A One Pot Synthesis of 5-Phenyl-1,3-Dioxane-4,6-Dione Derivatives

A general procedure for synthesis of 5-phenyl-1,3-dioxane-4,6-dione derivatives is described. The synthesis involves the cycloaddition of (α-chlorocarbonyl)phenyl ketene with carbonyl compounds to generate the corresponding substituted 2-oxetanone's which is readily transformed to the final products in one step. The 1,3-dioxane-4,6-dione is a rigid cyclic structure, and can undergo easy hydrolysis.     

A Rapid and Efficient Synthesis of Diaryl Thioureas via Solvent-Free Reaction Using Microwave

The application of microwave techniques for chemical synthesis has attracted considerable interest in recent years1-5. The reason is that technology can enhance the selectivity and reactivity6,7, increase the chemical yields and shorten the reaction time8,9. In order to provide a method that is economic, without pollution, easy to carry out, we coupled the solvent-free reaction with microwave.As we know, thiourea compounds are associated with a serious biological activities such as antiviral10…     

原子经济反应:氢氧化铯催化下二硒醚与端炔反应合成炔硒醚

氢氧化铯是无机超强碱,它能夺去端炔上的氢而产生稳定炔负离子,这种炔负离子与亲电的酮、醛反应生成相应的炔醇,但是与亲电的杂原子反应形成碳杂键的研究尚未见报道,碳杂键的形成是合成杂原子有机化合物的主要途径,所以研究无机超强碱催化下的碳杂键形成反应,有可能开辟-个合成杂原子有机化合物的新领域,不论在理论上还是在应用上都具有重要意义。     

A Multiresidue Method for the Analysis of Carbamate and Urea Pesticides from Soils by Microwave-Assisted Extraction and Liquid Chromatography with Photodiode Array Detection

Abstract

A multiresidue approach using microwave-assisted extraction and liquid chromatography with photodiode array detection was investigated for the determination of butylate, carbaryl, carbofuran, chlorpropham, ethiofencarb, linuron, metobromuron, and monolinuron in soils. The critical parameters of the developed methodology were studied. Method validation was performed by analyzing freshly and aged spiked soil samples. The recoveries and relative standard deviations reached using the optimized conditions were between 77.0±0.46% and 120±2.9% except for ethiofencarb (46.4±4.4% to 105±1.6%) and butylate (22.1±7.6% to 49.2±11%). Soil samples from five locations of Portugal were analysed.     

Cation‐Tuned Stimuli‐Responsive and Optical Properties of Supramolecular Hydrogels

Hierarchical self‐assembly of an amphiphilic tris‐urea in aqueous media is shown. A mixture of the amphiphilic tris‐urea and an alkaline solution gave a viscous solution composed of fibrous aggregates. This viscous solution transformed into supramolecular hydrogels, which are capable of hierarchically organizing into higher‐order aggregates in response to several cationic triggers. The resulting supramolecular hydrogels were relatively stiff and their storage moduli attained over 10³ Pa. The stimuli‐responsive and optical properties of the resulting hydrogels were influenced by the cationic trigger. Proton and calcium ion triggers gave pH‐ and chemical stimuli‐responsive hydrogels, respectively. A terbium ion trigger also provided a highly luminescent hydrogel through energy transfer from the tris‐urea to terbium.     

Synthesis of 2-(arylthio)benzoates by [3+3] cyclocondensations of 3-arylthio-1-silyloxy-1,3-butadienes with 3-oxo-orthoesters, 1,1,3,3-tetramethoxypropane and 1,1-bis(methylthio)-1-en-3-ones

A variety of 2-arylthio-4-methoxybenzoates are regioselectively prepared by TiCl₄-mediated [3+3] cyclocondensations of 3-arylthio-1-trimethylsilyloxy-1,3-butadienes with 3-oxo-orthoesters. Unsubstituted 2-(arylthio)benzoates were prepared by Me₃SiOTf-catalyzed cyclization of 3-arylthio-1-trimethylsilyloxy-1,3-butadienes with 1,1,3,3-tetramethoxypropane. The TiCl₄-mediated cyclization of 3-arylthio-1-trimethylsilyloxy-1,3-butadienes with 1,1-bis(methylthio)-1-en-3-ones results in regioselective formation of 2-arylthio-6-(methylthio)benzoates.     

Considerations for analytical supercritical fluid extraction of sulfonyl ureas employing a modified fluid

Important considerations are discussed for analytical SFE method development employing methanol–modified carbon dioxide and solid-phase trapping. The focus of this study was to break the method development procedure into distinct steps so that the origins of low recoveries could be determined conclusively. Sulfonyl urea herbicides were used as probe analytes. Analyte solubility, analyte trapping, analyte trap removal (solid-phase), and extract analysis were all shown to be equally important in achieving quantitative SFE recoveries.     

Unexpected copper mediated benzyl O→O migration during an Ullmann ether coupling

The synthesis of a highly functionalized phenolic diaryl ether 5,5′-oxybis(4-hydroxy-3-methoxybenzaldehyde) (1) potentially interesting as a new scaffold for drug design, has been carried out using Ullmann coupling conditions. An unusual benzyl migration in o-benzyloxyphenol moiety occurred during this reaction leading to an unexpected compound identified as 4-(benzyloxy)-3-(2-(benzyloxy)-4-formyl-6-methoxyphenoxy)-5-methoxy benzaldehyde (7). A rationale for this migration process is proposed.