王 鈺,夏婷婷,陳景文,蔡喜運(yùn) (大連理工大學(xué)環(huán)境學(xué)院,工業(yè)生態(tài)與環(huán)境工程教育部重點(diǎn)實(shí)驗(yàn)室,遼寧 大連116024)

丁烯氟蟲腈光降解反應(yīng)過程及機(jī)理

王 鈺,夏婷婷,陳景文,蔡喜運(yùn)*(大連理工大學(xué)環(huán)境學(xué)院,工業(yè)生態(tài)與環(huán)境工程教育部重點(diǎn)實(shí)驗(yàn)室,遼寧 大連116024)

考察了乙腈/水混合溶液中丁烯氟蟲腈的光解速率及水體中主要溶解性物質(zhì)對其光解的影響,通過產(chǎn)物鑒定及模擬計(jì)算判定了丁烯氟蟲腈光降解反應(yīng)機(jī)理.結(jié)果表明,模擬日光下丁烯氟蟲腈快速發(fā)生光降解,純水中反應(yīng)半衰期為 17.34 min.腐殖酸通過競爭光吸收來抑制丁烯氟蟲腈的光解,NO3-和 Cl-對其光解無影響.丁烯氟蟲腈光解反應(yīng)位點(diǎn)位為亞砜基團(tuán)上的硫原子,主要產(chǎn)物為脫硫化物(MW 442.0),砜化物(MW 506.0)及2種硫化物(MW 473.9和405.8).鍵級(jí)和鍵長分析也證實(shí)丁烯氟蟲腈硫原子連接的化學(xué)鍵不穩(wěn)定,易發(fā)生斷裂重排反應(yīng),生成上述轉(zhuǎn)化產(chǎn)物.

丁烯氟蟲腈；光降解；溶解性物質(zhì)；反應(yīng)機(jī)理

氟蟲腈為苯基吡唑類廣譜型殺蟲劑,具有殺蟲活性高,應(yīng)用范圍廣,與已有農(nóng)藥無交互抗性的特點(diǎn).因其在水和土壤中降解緩慢[1-3],2009年10月 1日起我國境內(nèi)停止銷售和使用含有氟蟲腈成分的農(nóng)藥制劑(衛(wèi)生用及旱田種子包衣劑除外).氟蟲腈 5位氨基的差異性取代,可能生成具有不同生物毒性的活性結(jié)構(gòu)[4].采用甲代烯丙基取代氟蟲腈的5位氨基氫原子,可合成一種新型殺蟲劑丁烯氟蟲腈[5].該農(nóng)藥可用于鱗翅目,蠅類和鞘翅目害蟲等有害生物防治,在水稻與蔬菜等作物上具有與氟蟲腈相當(dāng)?shù)臍⑾x活性,但對家蠶低毒,對鳥類中低毒,對魚類的毒性是氟蟲腈的千分之一.

研究表明,光解是氟蟲腈及氟乙腈等苯基吡唑類殺蟲劑重要的降解途徑,水中溶解性物質(zhì)對其光解產(chǎn)生影響[6-7].目前,關(guān)于丁烯氟蟲腈光降解的研究尚未見報(bào)道.研究丁烯氟蟲腈在環(huán)境中的光解降解行為,將有助于評估其環(huán)境歸趨及環(huán)境風(fēng)險(xiǎn).本研究選取模擬太陽光為光源,研究丁烯氟蟲腈在乙腈/水溶液中的光降解行為;考察了溶解性物質(zhì)(HA,NO3-,Cl-)對其光解反應(yīng)速率的影響;進(jìn)行了產(chǎn)物鑒定并利用模擬計(jì)算的方法研究了丁烯氟蟲腈的光解反應(yīng)機(jī)理.

1 材料與方法

1.1 材料

丁烯氟蟲腈(純度98.1%)由大連瑞澤農(nóng)藥股份有限公司提供;腐殖酸(HA,Fluka NO.53680)購于Sigma-Aldrich公司;乙腈、甲醇、石油醚、乙酸乙酯及正己烷均為色譜純.

1.2 光解實(shí)驗(yàn)

光解實(shí)驗(yàn)在 XPA-1旋轉(zhuǎn)光化學(xué)反應(yīng)儀(南京胥江機(jī)電廠)中進(jìn)行,光源為模擬太陽光(300W 汞燈+290nm濾光片,λ>290nm),反應(yīng)液置于石英管中.丁烯氟蟲腈濃度為1mg/L.鑒于丁烯氟蟲腈在純水中溶解度較低,添加乙腈作為助溶劑,溶液中乙腈體積比例 20%,30%,40%,50%.水體中主要溶解性物質(zhì)的濃度設(shè)定參照其常見環(huán)境水平[8-9]. HA 濃度設(shè)置為2,4,8,12,15mg/L;NO3-濃度設(shè)置為5,10,15, 20,30mg/L;Cl-濃度設(shè)置為 10,20,30,40,60mg/L.光解實(shí)驗(yàn)過程中設(shè)置暗對照,每組實(shí)驗(yàn)重復(fù)2次.

采用準(zhǔn)一級(jí)反應(yīng)動(dòng)力學(xué)描述光解反應(yīng),并使用 ln(Ct/C0)-t線性擬合得到準(zhǔn)一級(jí)反應(yīng)速率常數(shù)(k).半衰期使用公式t1/2=ln2/k計(jì)算.

1.3 樣品分析

采用 Techcomp UV-2003型紫外可見分光光度計(jì)測定樣品紫外可見吸收光譜;使用Hitachi L2000型高效液相色譜(Hitachi)測定丁烯氟蟲腈濃度,色譜條件如下:色譜柱為大連依利特 YWG C18(10μm,250nm×4.6mm);流動(dòng)相為甲醇:乙腈:水=35:40:25(體積比);流速為 1.0mL/min;檢測波長為215nm;進(jìn)樣量10μL.

1.4 產(chǎn)物鑒定

將100mL含10mg/L丁烯氟蟲腈的反應(yīng)液置于光解實(shí)驗(yàn)條件下連續(xù)光照 10h.反應(yīng)液用石油醚:乙酸乙酯(V: V) = 50:50萃取3次,有機(jī)相經(jīng)無水硫酸鈉脫水后于旋轉(zhuǎn)蒸發(fā)器中濃縮至近干,用甲醇定容至1mL待測.

采用Agilent 1100 LC/MS/MS(Agilent)進(jìn)行產(chǎn)物分析鑒定.分析條件如下:色譜柱為 Zorbax SB-C18(1.5μm,2.1mm×50mm);流動(dòng)相為甲醇:乙腈:水=35:40:25(體積比);流速為 0.2mL/min;進(jìn)樣量為5μL;離子源為ESI,負(fù)離子掃描模式;質(zhì)量掃描范圍100~600m/z[10].

1.5 鍵長鍵級(jí)的計(jì)算

使用Gaussian 09軟件對丁烯氟蟲腈及氟蟲腈的分子結(jié)構(gòu)進(jìn)行優(yōu)化并對其鍵長、鍵級(jí)進(jìn)行計(jì)算.使用 PM3算法預(yù)優(yōu)化目標(biāo)化合物,利用密度泛函理論(DFT)中B3LYP泛函在6-31G(d,p)基組水平優(yōu)化獲得穩(wěn)定構(gòu)型,并對穩(wěn)定構(gòu)型進(jìn)行頻率分析[11-12];采用Natural Bond Orbital (NBO)方法進(jìn)行鍵級(jí)計(jì)算[13].

2 結(jié)果與討論

2.1 丁烯氟蟲腈在不同比例乙腈溶液中的光解

由圖1可知,實(shí)驗(yàn)條件下丁烯氟蟲腈迅速光解,遵循準(zhǔn)一級(jí)反應(yīng)動(dòng)力學(xué)方程(R2> 0.95).乙腈對光解過程產(chǎn)生抑制作用,作用效果隨其體積百分比的增加而增強(qiáng).乙腈的加入一方面降低了溶劑極性,一方面可能增強(qiáng)了體系的紫外可見光吸收強(qiáng)度,起到光掩蔽作用[14-15].

丁烯氟蟲腈光反應(yīng)速率與溶液中乙腈比例線性負(fù)相關(guān),擬合得方程,Y=-0.0327X+3.9952(R2= 0.85,P<0.001),外推得到丁烯氟蟲腈在純水中光解反應(yīng)速率為3.99×10-2min-1,半衰期17.35min.

圖1 乙腈對丁烯氟蟲腈光解的影響Fig.1 Effect of the acetonitrile concentration on the butylene fipronil photolysis rate constants

2.2 溶解性物質(zhì)對丁烯氟蟲腈光降解的影響

由表 1可知,加入腐殖酸(2~15mg/L)顯著抑制丁烯氟蟲腈的光解,抑制效應(yīng)與腐植酸濃度表現(xiàn)出明顯的線性相關(guān)(R2>0.95,P<0.05).溶液中乙腈比例為20%時(shí), 2,4,8,12,15mg/L腐殖酸的光解反應(yīng)抑制率分別為 8.9%,17.8%,34.6%,42.7%, 51.6%.腐殖酸的加入增強(qiáng)了體系 190~300nm的紫外可見光吸收(圖 2),產(chǎn)生強(qiáng)烈光掩蔽效應(yīng),進(jìn)而對丁烯氟蟲腈的光降解產(chǎn)生抑制作用.這與Walse等[16]對氟蟲腈光解的研究結(jié)果一致,腐殖酸等可溶性有機(jī)質(zhì)可通過競爭光吸收及淬滅激發(fā)態(tài)來影響氟蟲腈的光解反應(yīng)速率.

表1 溶解性物質(zhì)對丁烯氟蟲腈光解反應(yīng)速率的影響(×10-2min-1)Table 1 Values of k calculated from photolysis data (×10-2min-1)

圖2 腐殖酸對體系紫外可見吸光光譜的影響Fig.2 UV-vis absorption spectra of butylene fipronil in the presence of HA

NO3-(5~30mg/L)對丁烯氟蟲腈光解無影響.有研究表明,NO3-主要通過光屏蔽作用及產(chǎn)生活性氧物種(ROS)來影響化合物光降解過程[8,17-18].本研究中NO3-顯著增強(qiáng)體系190~250nm的紫外可見光吸收強(qiáng)度,但模擬日光照射下化合物實(shí)際接受λ>290nm范圍內(nèi)的光照,NO3-與丁烯氟蟲腈不存在競爭光吸收關(guān)系.而反應(yīng)中產(chǎn)生的ROS一方面促進(jìn)化合物的光降解,另一方面可通過競爭吸收對光解產(chǎn)生抑制作用.

研究表明,Cl-可捕獲·OH轉(zhuǎn)化成 Cl2,影響化合物的間接光解,而其對光解的雙重作用機(jī)理仍有待于研究[9,19].添加 3%的 NaCl可提高氟蟲腈光解反應(yīng)速率 20%[16].在本研究中 10~60mg/L Cl-對丁烯氟蟲腈光解反應(yīng)速率未產(chǎn)生顯著影響,對體系紫外可見吸收光譜亦無影響.可能原因是丁烯氟蟲腈未發(fā)生間接光解,此外,Cl-雙重作用機(jī)理相互抵消,表觀上呈現(xiàn)出無影響.

環(huán)境水體中,HA,NO3-及 Cl-等光活性物質(zhì)共存,單獨(dú)和交互的影響化合物的光化學(xué)行為,致使化合物的環(huán)境光化學(xué)行為更趨復(fù)雜[16].

2.3 丁烯氟蟲腈光降解產(chǎn)物鑒定

由圖4可知,丁烯氟蟲腈光解后生成一系列產(chǎn)物.使用 ESI負(fù)離子模式掃描光解產(chǎn)物,得到M,M-1,M+Cl及M+62離子碎片.其中分子離子失去H形成的M—H及獲得COO-和H2O形成的M+62碎片離子表現(xiàn)為強(qiáng)峰,用于定性分析.離子碎片解析結(jié)果表明,丁烯氟蟲腈(MW 489.9)光解主要生成4種產(chǎn)物.脫硫化物(MW 442.0, 5-甲代烯丙基氨基-1-(2,6-二氯-4-三氟甲基苯基)-4-三氟甲基-3-氰基吡唑),砜化物(MW 506.0, 5-甲代烯丙基氨基-1-(2,6-二氯-4-三氟甲基苯基)-4-三氟甲基磺酰基-3-氰基吡唑)及兩種硫化物(MW 473.9, 5-甲代烯丙基氨基-1-(2,6-二氯-4-三氟甲基苯基)-4-三氟甲基硫基-3-氰基吡唑; MW 405.8, 5-甲代烯丙基氨基-1-(2,6-二氯-4-三氟甲基苯基)-4-巰基-3-氰基吡唑).該結(jié)果與文獻(xiàn)中報(bào)道的氟蟲腈光降解產(chǎn)物質(zhì)譜分析結(jié)果相一致[10,23].

以往研究表明,氟蟲腈在水環(huán)境中迅速光解.光解主產(chǎn)物為脫硫化物氟甲腈,并有伴微量砜化物,硫化物,脫三氟甲基亞硫?；盎撬嵫苌锷蒣20-23].綜上,丁烯氟蟲腈與氟蟲腈具有相似的產(chǎn)物構(gòu)成,其光解途徑可能與氟蟲腈相似.

圖3 丁烯氟蟲腈光解產(chǎn)物的總離子色譜Fig.3 Total ion chromatogram of photoproduct

2.4 丁烯氟蟲腈的理論計(jì)算及光解反應(yīng)機(jī)理

圖4 氟蟲腈(a,c)及丁烯氟蟲腈(b,d)的鍵長鍵級(jí)Fig.4 Bond order and length of fipronil and butylene fipronil

理論上,化學(xué)鍵越穩(wěn)固,鍵能越大,鍵長越短,鍵級(jí)則越大[24].丁烯氟蟲腈C4—S8,S8=O9及S8—C10的鍵長(或鍵級(jí))分別為1.7806 (0.9355), 1.5095 (1.2465)及 1.9099 (0.7631);氟蟲腈 C4—S8,S8=O9及 S8—C10的鍵長(或鍵級(jí))分別為1.7714(0.9440),1.2283 (1.2283)及 1.9119(0.7620).2種化合物的C4—S8, S8—C10鍵鍵長較長,鍵級(jí)較小,表現(xiàn)出不穩(wěn)定性,光降解過程中較易發(fā)生斷裂(圖4).該結(jié)果與產(chǎn)物鑒定中得到的丁烯氟蟲腈及氟蟲腈[20-21]主要光解產(chǎn)物相一致,表明該化學(xué)鍵易于斷裂,發(fā)生轉(zhuǎn)化反應(yīng).

苯基吡唑類農(nóng)藥因結(jié)構(gòu)相似性,可能具有相似的光解反應(yīng)路徑.產(chǎn)物鑒定及鍵長鍵級(jí)計(jì)算證實(shí)了氟乙腈和氟蟲腈具有相同的光解反應(yīng)活性中心,光照后均發(fā)生氧化,還原及脫亞磺酸基反應(yīng)[7].甲代烯丙基取代氟蟲腈 5位氨基氫而形成的丁烯氟蟲腈,其S8原子周邊化學(xué)鍵性能與氟蟲腈相比未發(fā)生顯著變化,加之光降解產(chǎn)物構(gòu)成相似,判斷丁烯氟蟲腈與氟蟲腈具有相同的光解反應(yīng)機(jī)理(圖5).光解反應(yīng)中,丁烯氟蟲腈C4—S8鍵斷裂生成脫硫化物,質(zhì)譜解析 MW=442.0; S8=O9斷裂生成硫化物,質(zhì)譜解析 MW=473.9; S8=O9及 S8—C10同時(shí)斷裂生成硫化物,質(zhì)譜解析MW=405.8; S8=O9氧化加氧生成砜化物質(zhì)譜解析MW=506.0.

圖5 丁烯氟蟲腈光解反應(yīng)路徑Fig.5 Photolysis reaction mechanism of butylene fipronil in aqueous solution

然而丁烯氟蟲腈與氟蟲腈的光解產(chǎn)物在分布上存在顯著差異.氟蟲腈光降解產(chǎn)生脫硫化物的比例大于 50%;丁烯氟蟲腈光解中未產(chǎn)生脫三氟甲基亞磺酰基產(chǎn)物,脫硫化物產(chǎn)率最高而2種硫化物產(chǎn)率相當(dāng),結(jié)合分子的立體結(jié)構(gòu)可以解釋該現(xiàn)象.氟蟲腈生成脫硫化物及脫三氟甲基亞磺?；a(chǎn)物需要鄰位氨基氫的參與[20].反應(yīng)時(shí),O9首先與氨基氫形成大環(huán)氫鍵過渡態(tài),而后生成產(chǎn)物.甲代烯丙基取代后,氧原子與氨基氫的空間位阻增加,氨基氫與氧原子的距離由2.0852增加至4.6201,不利于大環(huán)氫鍵過渡態(tài)的形成,進(jìn)而抑制脫硫化物的生成.

3 結(jié)論

3.1 丁烯氟蟲腈在模擬太陽光下可快速光解,半衰期為17.34min.

3.2 水體中腐殖酸可通過光掩蔽作用,抑制丁烯氟蟲腈的光解,NO3-及Cl-對其光解無影響.

3.3 丁烯氟蟲腈的光解反應(yīng)活性位點(diǎn)為亞砜基團(tuán)上的硫原子,該殺蟲劑發(fā)生脫硫,還原及氧化反應(yīng),生成脫硫化物,砜化物及硫化物.

[1] Gunasekara A S, Truong T, Goh K S, et al. Environmental fate and toxicology of fipronil [J]. Journal of Pesticide Science, 2007,32(3):189-199.

[2] Nillos M G, Lin K, Gan J, et al. Enantioselectivity in fipronil aquatic toxicity and degradation [J]. Environmental Toxicology and Chemistry, 2009,28(9):1825-1833.

[3] Aajoud A, Ravanel P, Tissut M. Fipronil metabolism and dissipation in a simplified aquatic ecosystem [J]. Journal of Agricultural and Food Chemistry, 2003,51(5):1347-1352.

[4] Huber S K. (S)-Enantiomer enriched fipronil composition: US, PCT/EP2000/004172 [P]. 2000.4-12.

[5] 丁烯氟蟲腈 [J]. 農(nóng)藥科學(xué)與管理, 2008,29(9):58.

[6] Ramesh A, Balasubramanian M. Kinetics and hydrolysis of fenamiphos, fipronil, and trifluralin in aqueous buffer solutions [J]. Journal of Agricultural and Food Chemistry, 1999,47(8): 3367-3371.

[7] Caboni P, Sammelson R E, Casida J E. Phenylpyrazole insecticide photochemistry, metabolism, and GABAergic action: Ethiprole compared with fipronil [J]. Journal of Agricultural and Food Chemistry, 2003,51(24):7055-7061.

[8] Fisher J M, Reese J G, Pellechia P J, et al. Role of Fe(III), phosphate, dissolved organic matter, and nitrate during the photodegradation of domoic acid in the marine environment [J]. Environmental Science and Technology, 2006,40(7):2200-2205.

[9] Chiron S, Minero C, Vione D. Photodegradation processes of the antiepileptic drug carbamazepine, relevant to estuarine waters [J]. Environmental Science and Technology, 2006,40(19):5977-5983.

[10] Lacroix M Z, Puel S, Toutain P L, et al. Quantification of fipronil and its metabolite fipronil sulfone in rat plasma over a wide range of concentrations by LC/UV/MS [J]. Journal of Chromatography B-Analytical Technologies in the Biomedical and Life Sciences, 2010,878(22):1934-1938.

[11] Becke A D, Johnson E R. A density-functional model of the dispersion interaction [J]. Journal of Chemical Physics, 2005, 123(15):154101.

[12] Chengteh L, Weitao Y, Par R G. Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density [J]. Physical Review B (Condensed Matter), 1988,37(2):785-9.

[13] Frank W, Clark R L. Natural bond orbitals and extensions of localized bonding concepts [J]. Chemistry Education: Research and Practice in Europe, 2001,2(2):91-104.

[14] Schick B, Moza P N, Hustert K, et al. Photochemistry of vinclozolin in water and methanol-water solution [J]. Pesticide Science, 1999,55(11):1116-1122.

[15] Choi J, Choi W, Mhin B J. Solvent-specific photolytic behavior of octachlorodibenzo-p-dioxin [J]. Environmental Science and Technology, 2004,38(7):2082-2088.

[16] Walse S S, Morgan S L, Kong L, et al. Role of dissolved organic matter, nitrate, and bicarbonate in the photolysis of aqueous fipronil [J]. Environmental Science and Technology, 2004,38(14): 3908-3915.

[17] Mack J, Bolton J R. Photochemistry of nitrite and nitrate in aqueous solution: a review [J]. Journal of Photochemistry and Photobiology A-Chemistry, 1999,128(1-3):1-13.

[18] 展漫軍,楊 曦,鮮啟鳴,等.雙酚A在硝酸根溶液中的光解研究[J]. 中國環(huán)境科學(xué), 2005,25(4):487-490.

[19] Liao C H, Kang S F, Wu F A. Hydroxyl radical scavenging role of chloride and bicarbonate ions in the H2O2/UV process [J]. Chemosphere, 2001,44(5):1193-1200.

[20] Bobe A, Meallier P, Cooper J F, et al. Kinetics and mechanisms of abiotic degradation of fipronil (hydrolysis and photolysis) [J]. Journal of Agricultural and Food Chemistry, 1998,46(7):2834-2839.

[21] Hainzl D, Casida J E. Fipronil insecticide: Novel photochemical desulfinylation with retention of neurotoxicity [J]. Proceedings of the National Academy of Sciences of the United States of America, 1996,93(23):12764-12767.

[22] Raveton M, Aajoud A, Willison J C, et al. Phototransformation of the insecticide fipronil: Identification of novel photoproducts and evidence for an alternative pathway of photodegradation [J]. Environmental Science and Technology, 2006,40(13):4151-4157.

[23] Ngim K K, Mabury S A, Crosby D G. Elucidation of fipronil photodegradation pathways [J]. Journal of Agricultural and Food Chemistry, 2000,48(10):4661-4665.

[24] Bruce A, Patricia E. Chemistry: Principles, Patterns, and Applications [M]. US:Pearson/Prentice Hall, 2007:409.

Kinetics and mechanism of photolysis of new insecticide butylene fipronil.

WANG Yu, XIA Ting-ting, CHEN Jing-wen, CAI Xi-yun*(Key Laboratory of Industrial Ecology and Environmental Engineering, Ministry of Education, School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China). China Environmental Science, 2012,32(1)：89~93

Photolysis of butylene fipronil was investigated, including reaction kinetics, transformation product identification and theoretical computation analysis. Photolysis of butylene fipronil under simulated sunlight was well fitted to first-order kinetic model with a half-life of 17.34min. Humic acids significantly reduced photoactivity of the insecticide, due to competitive light absorption, while NO3-and Cl-, didn’t affect its photolysis. Major transformation products were identified as desulfinyl derivative (MW 442.0), sulfone derivative (MW 506.0) and sulfide derivatives (MW 473.9 and 405.8). The proposed pathway of the insecticide was further confirmed by bond order and bond length analysis. The bonds round sulfur atom were easily broken and rearranged to form the transformation products.

butylene fipronil；photolysis；dissolved substances；mechanism

2011-03-19

國家自然科學(xué)基金資助項(xiàng)目(21077020);中國博士后科學(xué)基金資助項(xiàng)目(20090450103);中央高校基本科研業(yè)務(wù)費(fèi)專項(xiàng)資金資助(DUT10LK02)

* 責(zé)任作者, 副教授, xiyuncai@dlut.edu.cn

X592

A

1000-6923(2012)01-0089-05

王 鈺(1985-),女,遼寧大連人,大連理工大學(xué)環(huán)境學(xué)院碩士研究生,主要從事污染物環(huán)境光化學(xué)行為研究.