Mechanisms of direct and TiO2-photocatalysed UV degradation of phenylurea herbicides.

Phenylurea herbicides undergo low-yield (phi(PI) <15 %) monophotonic photoionisation upon 193-nm laser flash excitation. The so-formed radical cations (phenylurea.+) are highly acidic (-1.5 < pKa <0.5) and deprotonate readily to yield the corresponding neutral radical (phenylurea.). Pulse radiolysis experiments allowed limitation of the reduction potential of phenylurea.+ within 2.22 V versus the normal hydrogen electrode (NHE) < E degrees (phenylurea.+/phenylurea) < 2.43 V versus NHE. The main photoproducts of UVC (lambda=193 nm) photodegradation of phenylureas correspond to a photo-Fries rearrangement. One-electron reduction with e-(aq) yields the corresponding radical anions (phenylurea.-), for which 4.3< pKa < 5.33. The rate constants for reaction with e-(aq) show that in photocatalysis the generation of phenylurea.- and O2.- on the surface of the photocatalyst may be competitive. High reactivity toward e-(aq) is predicted from linear free-energy relationships (LFER) for phenylureas bearing electron-withdrawing groups. Reaction with HO. takes place mainly via addition to the aromatic ring and/or H. abstraction from a saturated carbon atom (98 %), rather than one-electron oxidation (2 %). High reactivity toward oxidation by HO. is predicted from LFER for phenylureas bearing electron-donating groups. Adsorption studies for TiO2 in its polymorphic forms of rutile and anatase, as well as with the commercial mixture Degussa P-25, show photocatalysis is independent of the specific area of the catalyst. A variety of compounds are generated during the photocatalytic degradation of Diuron, while only two hydroxychloro derivatives are observed upon prolonged direct 365 nm irradiation. The photocatalytic degradation proceeds mainly by oxidation of the Me group of the side chain, hydroxylation of the aromatic ring, and dechlorination. The photoproducts of photocatalytic degradation differ from one polymorphic form of TiO2 to another.     

Electrochemical Reduction of Pyridinic Herbicides Picloram and Clopyralid on a Mercury Pool Electrode

This paper presents the identification by GC/MS of the products obtained after the total reduction of picloram and clopyralid on a mercury pool electrode. The products found in the strongly acidic media reduction of picloram are 4‐amino‐3,5,6‐trichloro‐2‐pyridinecarboxaldehyde, 4‐amino‐3,5,6‐trichloro‐2‐pyridinecarbinol and 4‐amino‐3,5‐dichloro‐2‐pyridinecarboxylic acid; at pH 3–4 the first compound is substituted by 4‐amino‐3,5‐dichloro‐2‐pyridinecarboxaldehyde. For clopyralid 3,6‐dichloro‐2‐pyridinecarbinol was detected. Under the light of such products the overall reduction processes are discussed showing the partial reductive cleavage of chlorine atoms in both cases.     

新型N-取代苯基-9-烷基-3-咔唑磺酰脲类化合物的合成及其抗肿瘤活性

以9-烷基咔唑为原料,经磺化、氯化和氨化反应制得9-烷基咔唑-3-磺酰胺(4a和4o);取代苯胺与三光气反应制得取代苯基异氰酸酯(6a~6n,6s,6Ⅳ);4分别与6经缩合反应合成了30个新型的N-取代苯基-9-烷基-3-咔唑磺酰脲类化合物(7a~7Ⅳ),其结构经1H NMR,IR和ESI-MS表征。对7进行了Cdc25B抑制活性筛选。结果表明,在用药浓度为20μg·m L-1时,其中12个化合物对Cdc25B具有良好的抑制活性,抑制率大于90%。     

Extraction of acetanilide herbicides in naked oat (Avena nuda L.) by using ionic‐liquid‐based matrix solid‐phase dispersion‐foam flotation solid‐phase extraction

The herbicides in naked oat (Avena nuda L.) samples were extracted, separated, and determined by using ionic‐liquid‐based matrix solid‐phase dispersion‐solvent flotation coupled with high‐performance liquid chromatography. The experimental parameters were optimized and evaluated by a univariate method and orthogonal experiment. A good linear relationship was obtained in the range of 5–5000 µg/kg, and the linear correlation coefficient are between 0.9989～0.9993. The quantification limits for alachlor, metazachlor, propanil, acetochlor, pretilachlor, metolachlor, and butachlor are 5.03, 2.62, 2.73, 4.58, 7.28, 5.05, 5.78 µg/kg, respectively. The average recoveries of the acetanilide herbicides at spiked concentrations of 10, 100, and 500 µg/kg ranged from 92.1 to 104.7%, and relative standard deviations were equal to or lower than 2.9%.     

磁性石墨烯纳米粒子固相萃取与气相色谱-质谱相结合测定环境水样中的三嗪类除草剂

将磁性石墨烯作为磁性固相萃取的吸附剂与气相色谱-质谱(GC-MS)相结合建立了环境水样中7种三嗪类除草剂残留的测定新方法。对影响萃取效率的一些因素如吸附剂用量、萃取时间、样品溶液的pH值、离子强度和解吸条件等进行了优化。在优化的实验条件下,7种三嗪类除草剂的富集倍数在574~968之间。测定西玛津、扑灭津、嗪草酮、西草净、氰草津的线性范围为0.01~10.0 μg/L,莠去津的线性范围为0.05~10.0 μg/L,扑灭净的线性范围为0.01~8.0 μg/L。线性相关系数为0.9968~0.9998,检出限(S/N=3)为1.0~5.0 ng/L。将本方法应用于井水、自来水和湖水等实际水样的分析,在0.5 μg/L和2.0 μg/L下的加标回收率为79.8%~118.3%,相对标准偏差为3.6%~10.5%。该法操作简单、富集倍数高,可满足水样中三嗪类除草剂残留的检测要求。     

Magnetic solid-phase extraction of sulfonylurea herbicides in environmental water samples by Fe3O4@dioctadecyl dimethyl ammonium chloride@silica magnetic particles

A magnetic solid phase extraction (MSPE) method coupled with high-performance liquid chromatography (HPLC) was proposed for the determination of five sulfonylurea herbicides (bensulfuron-methyl, prosulfuron, pyrazosulfuron-ethyl, chlorimuron-ethyl and triflusulfuron-methyl) in environmental water samples. The magnetic adsorbent was prepared by incorporating Fe₃O₄ nanoparticles and surfactant into a silica matrix according to a sol–gel procedure, which can provide surfactant free extracts during the eluting step to avoid chromatographic interference. The prepared adsorbent was used to extract the sulfonylurea herbicides in several kinds of water samples. The main factors affecting the extraction efficiency, including desorption conditions, extraction time, sample volume, and sample solution pH were optimized. Under the optimum conditions, good linearity was obtained within the range of 0.2–50.0 μg L⁻¹ for all analytes, with correlation coefficients ranging from 0.9993 to 0.9999. The enrichment factors were between 1200 and 1410, and the limits of detection were between 0.078 and 0.10 μg L⁻¹. The proposed method was successfully applied in the analysis of sulfonylurea herbicides in environmental samples (tap, reservoir, river, and rice field). The recoveries of the method ranged between 80.4% and 107.1%. This study reported for the first time the use of MSPE procedure in the preconcentration of sulfonylurea herbicides in environmental samples. The procedure proved to be efficient, environmentally friendly, and fast.     

Catalytic Hydrolysis of Urea Herbicides Combined with Column Chromatography

Abstract

A method is described for the hydrolysis of urea herbicides on silica gel surfaces, making use of the acidic silanol groups. Only a heating step is needed without reagents being added and complete hydrolysis to the corresponding anilines can be achived in about 15 min at 165°C. Gas and liquid chromatographic techniques coupled with derivatization of the anilines before and after the column are then introduced as the actual analysis step. The potential of these analytical systems is demonstrated with a residue analysis in soil. The selectivity and sensitivity (detection limits, low nanogram to low picogram level) permit quantitation of urea herbicide traces with a minimum of sample clean-up.     

Preparation of Amides of Carboxylic Acid Herbicides for Gas Chromatographic Analysis

Abstract

Amides of 14 carboxylic acid herbicides were prepared by reacting the free acid with the amine in toluene for 1 hr at 80[ddot]C in the presence of PCl₃ or P₂I₄. The acids include phenoxyacetic acids, arylacetic acids, and benzoic acids. Aniline, o-toluidine, 3,5-bis(trifluoromethyl)aniline, piperidine, and tetrahydroquinoline were the amine components. Excess of reagents and by-products of the reaction were removed by partitioning into aqueous acid and base. Retention times relative to 2,4-D anilide on 1% OV-22 and FSOT RSL-150 columns are listed for the anilides and should be useful for confirmation purposes. The anilides of 2,4-D, silvex and 2,4,5-T were obtained in better than 90% yield.     

Fluorimetric Determination of Non-Fluorescent Dinitroaniline Derivative Herbicides,Using the Photoreduction of Anthraquinone - 2, 6-Disulfonate

Abstract

A photoreduction - fluorescence technique has been developed for the quantitative analysis of several dinitroaniline derivative herbicides. The photoreduction of anthraquinone - 2.6 - disulfonate by dinitroanilines generates highly fluorescent dihydroxyanthracene-2,6disulfonate, in a 20 : 80 vol/vol acetonitrile-water mixture at room temperature. Optimal irradiation times for obtaining a convenient, sensitized fluorescence signal are relatively short, ranging between 2 and 4 min.

Linear log-log calibration curves are established over several orders of magnitude in concentration units. The limits of detection range between 0.3 and 4.2 pg m1^?l. The photoreduction-fluorescence technique is shown to be very convenient, sensitive, and precise for the quantitation of dinitroaniline herbicides.