龐素艷,楊 悅,姜成春,周 揚(yáng),江 進(jìn),馬 軍

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KMnO4降解2-溴酚的氧化產(chǎn)物與反應(yīng)路徑

龐素艷1,2*,楊 悅2,姜成春3,周 揚(yáng)4,江 進(jìn)4,馬 軍4

(1.吉林建筑大學(xué)市政與環(huán)境工程學(xué)院,吉林長春130118；2.哈爾濱理工大學(xué)化學(xué)與環(huán)境工程學(xué)院,黑龍江哈爾濱150040；3.深圳職業(yè)技術(shù)學(xué)院建筑與環(huán)境工程學(xué)院,廣東深圳 518055；4.哈爾濱工業(yè)大學(xué)城市水資源與水環(huán)境國家重點實驗室,黑龍江哈爾濱 150090)

為了探討KMnO4氧化降解溴酚過程中溴代聚合產(chǎn)物的生成機(jī)理,利用三重四級桿串聯(lián)線性離子阱液相-質(zhì)譜聯(lián)用儀(LC-MS/MS)對KMnO4氧化降解2-溴酚的產(chǎn)物進(jìn)行檢測分析.結(jié)果表明,根據(jù)溴的天然同位素特性,建立了LC-MS/MS-PIS(79和81)子找母質(zhì)譜掃描方法測定溴代有機(jī)物,測得KMnO4氧化降解2-溴酚的主要產(chǎn)物為4個質(zhì)量數(shù)相同,341/343(79)和343/345(81),且分子結(jié)構(gòu)中含有2個溴的氧化耦合產(chǎn)物,同位素豐度比為1:1.推測4個溴代聚合產(chǎn)物為同分異構(gòu)體,由2-溴酚氧自由基通過C-C和C-O耦合產(chǎn)生,其中,C-C耦合的聚合產(chǎn)物先出峰,C-O耦合的聚合產(chǎn)物后出峰.2-溴酚氧自由基發(fā)生氧化耦合反應(yīng),理論上產(chǎn)生的8個溴代聚合產(chǎn)物并沒有全部被檢測到,主要是由于酚氧自由基的氧化耦合速率不同,導(dǎo)致聚合產(chǎn)物的形成產(chǎn)率不同.

KMnO4；2-溴酚；聚合產(chǎn)物；氧化耦合；反應(yīng)路徑

溴酚類有機(jī)物被廣泛應(yīng)用于助燃劑、木材防腐劑、聚合物等產(chǎn)品的生產(chǎn)過程中,導(dǎo)致地表水中溴代污染物含量增加[1-2].溴酚類污染物自身毒性高且能夠危害人類身體健康和水生生態(tài)環(huán)境[3-6].同時,溴酚也能夠引起飲用水的嗅味問題,而且嗅閾值非常低,只有ng/L范圍[7].目前,溴酚的處理技術(shù)主要有二氧化錳氧化[8]、光催化氧化[9-13]、過硫酸鹽催化氧化[14]等,同時,這些研究的產(chǎn)物分析結(jié)果證實溴酚的氧化降解產(chǎn)物是一些聚合物,如羥基化多溴聯(lián)苯醚(OH-PBDEs)和羥基化多溴聯(lián)苯(OH-PBBs).

高錳酸鉀(KMnO4)作為綠色氧化劑,運(yùn)輸、儲存、使用方便,且氧化后不易產(chǎn)生有毒有害副產(chǎn)物,能夠在水處理過程中進(jìn)行大規(guī)模應(yīng)用. Jiang等[15]研究了KMnO4降解2,4-二溴酚的氧化產(chǎn)物和反應(yīng)路徑,LC-MS/MS質(zhì)譜測定結(jié)果表明,2,4-二溴酚氧化后產(chǎn)生2個含有4個溴的聚合產(chǎn)物,一個為多溴聯(lián)苯醚,由2個2,4-二溴酚氧自由基通過鄰位C與O耦合產(chǎn)生,另一個是由2個2,4-二溴酚氧自由基通過鄰位C與鄰位C耦合產(chǎn)生,結(jié)構(gòu)中含有2個羥基,且每個苯環(huán)中都含有1個.到目前為止,還沒有關(guān)于KMnO4氧化降解2-溴酚氧化產(chǎn)物與反應(yīng)路徑的研究.

因此,本文利用液相色譜質(zhì)譜聯(lián)用儀(LC-MS/MS)測定KMnO4降解2-溴酚過程中的氧化產(chǎn)物,研究溴代氧化產(chǎn)物的質(zhì)譜特點及反應(yīng)路徑.

1 實驗部分

1.1 材料

2-溴酚(2-BrP)為分析純,購買于Sigma公司.乙腈為色譜醇,購買于Merck公司,甲酸為色譜純,購買于Sigma公司.實驗中所用其他試劑均為分析純,購買于國藥集團(tuán)上?；瘜W(xué)試劑有限公司.

1.2 試驗方法

一系列含10μmol/L 2-溴酚的純水中(含10%乙腈),加入不同濃度KMnO4起始反應(yīng)(5~20μmol/L),反應(yīng)完全后(即KMnO4完全被消耗),用0.45μm的玻璃纖維膜過濾,利用液相色譜質(zhì)譜聯(lián)用儀(LC-MS/MS)對過濾后樣品進(jìn)行產(chǎn)物分析測定.

1.3 分析方法

KMnO4降解2-溴酚的氧化產(chǎn)物采用AB SCIEX QTRAP 5500三重四級桿串聯(lián)線性離子阱質(zhì)譜與Agilent 1260高效液相聯(lián)用(LC-MS/ MS)進(jìn)行分析測定.色譜柱為Agilent Poroshell 120EC-C18(4.6mm×150mm,2.7μm),流動相為乙腈(A)和含1‰甲酸的超純水(B),流動相梯度為A先從5%開始,保持5min,然后在30min內(nèi)從5%線性升到50%,保持10min,再在0.1min內(nèi)降到5%,保持5min,流速為200μL/min,進(jìn)樣量為10μL,柱溫為35℃.采用電噴霧離子源負(fù)離子模式(ESI-)進(jìn)行檢測,測定方法選擇子找母掃描模式(PIS),即在四級桿Q3設(shè)定特殊質(zhì)量數(shù)的子離子,然后在四級桿Q1設(shè)定質(zhì)量數(shù)掃描范圍,尋找能夠產(chǎn)生該子離子的母離子.Q1設(shè)定掃描范圍為50~500Da, Q3設(shè)定子離子質(zhì)量數(shù)為79或81Da,掃描速度為1000Da/s,離子源電壓和溫度分別為-4500V和500℃,氮氣(N2)作為氣簾氣,流速為35L/min,去簇電壓(DP)和入口電壓(EP)分別為-70V和-10V,碰撞電壓(CE)為-30V~-100V.

2 結(jié)果與討論

2.1 溴代有機(jī)物質(zhì)譜測定方法的建立

天然環(huán)境中溴(Br)的同位素主要有2個,質(zhì)量數(shù)為79和81(Br79和Br81),且豐度比為1:1.研究中根據(jù)溴的這一同位素特性,建立了一種簡便、快速,可以選擇性檢測溴代有機(jī)物的質(zhì)譜檢測方法,其原理主要是利用溴代有機(jī)物在ESI源負(fù)電(ESI-)模式下,通過溴離子的同位素信息,進(jìn)行三重四級桿的質(zhì)譜掃描追蹤母離子測定,即子找母質(zhì)譜掃描模式[16-17].

研究中計算了溴代有機(jī)物中含溴元素個數(shù)與質(zhì)譜測定信息的關(guān)系,見表1[16,18-22].例如,2-溴酚分子結(jié)構(gòu)中含有1個溴,進(jìn)行質(zhì)譜全掃描模式測定時,會產(chǎn)生2個1:1的質(zhì)譜峰,采用79或81子找母質(zhì)譜掃描模式(79和81)進(jìn)行測定時,會各產(chǎn)生1個質(zhì)譜峰.

2.2 KMnO4降解2-溴酚的氧化產(chǎn)物與反應(yīng)路徑

由圖1可見,全掃描色譜圖中觀察不到明顯的2-溴酚色譜峰,而在子找母掃描色譜圖中能夠觀察到響應(yīng)值很高的色譜峰.因此,與全掃描質(zhì)譜模式相比,子找母質(zhì)譜掃描模式對溴代有機(jī)物的測定更靈敏,響應(yīng)值更高.2-溴酚的保留時間為24.8min,在嵌入的質(zhì)譜圖中,子找母掃描時質(zhì)量數(shù)為171(79)和173(81),全掃描時質(zhì)量數(shù)為171/173,且質(zhì)譜峰的溴同位素豐度比為1:1,與表1中含1個溴的總結(jié)相一致.

圖1 2-溴酚標(biāo)準(zhǔn)樣品LC-MS/MS色譜圖

(a) PIS79, (b) PIS81, (c) 全掃描

圖2 KMnO4氧化2-溴酚的LC-MS/MS色譜圖

(a) PIS79, (b) PIS81, (c) 全掃描

圖3 2-溴酚氧自由基的所有C-C和C-O耦合反應(yīng)

表1 溴代有機(jī)物在LC-MS/MS全掃描和子找母掃描中理論同位素豐度規(guī)律

注:為被檢測物質(zhì)的最小質(zhì)量數(shù).

從圖2可見,與全掃描色譜圖相比,采用子找母掃描模式測定KMnO4降解2-溴酚氧化產(chǎn)物的色譜峰更清晰、更靈敏、更全面.與2-溴酚標(biāo)準(zhǔn)色譜圖相比,通過子找母質(zhì)譜掃描模式檢測到KMnO4降解2-溴酚產(chǎn)生4個主要產(chǎn)物,分別標(biāo)記為I、II、III、IV,而在全掃描模式下只測到產(chǎn)物I和II,并且色譜峰非常小.從質(zhì)譜圖可以看出,4個產(chǎn)物進(jìn)行子找母掃描時質(zhì)量數(shù)相同,為341/343(79)和343/345(81),且2個質(zhì)譜峰的同位素豐度比為1:1,應(yīng)該是同分異構(gòu)體.在全掃描時質(zhì)量數(shù)為341/343/345,且豐度比為1:2:1.根據(jù)表1的計算結(jié)果,推測產(chǎn)物I-IV中含有2個Br,可能是目標(biāo)物2-溴酚氧自由基的聚合物.這一測定結(jié)果,與Jiang等[15]研究中KMnO4氧化降解2,4-二溴酚的LC-MS/MS質(zhì)譜檢測結(jié)果相似.2,4-二溴酚氧化后產(chǎn)生2個含有4個溴的聚合產(chǎn)物,而2-溴酚氧化后產(chǎn)生4個含有2個Br的聚合產(chǎn)物.溴酚中溴離子的個數(shù)和位置直接導(dǎo)致其氧化產(chǎn)物和反應(yīng)路徑不同,從而導(dǎo)致LC-MS/MS質(zhì)譜測定結(jié)果不同.

酚氧自由基易發(fā)生氧化耦合反應(yīng),在耦合過程中會產(chǎn)生各種聚合產(chǎn)物[23-28].理論上,2-溴酚的4個酚氧自由基如果全部參與反應(yīng),通過C-O和C-C耦合可能產(chǎn)生8個含溴聚合產(chǎn)物,見圖3.這8個溴代聚合產(chǎn)物中有5個聚合產(chǎn)物的質(zhì)量數(shù)為341/343/345,含有2個溴,其中有2個聚合產(chǎn)物是通過C-O耦合生成,另外3個聚合產(chǎn)物是通過C-C耦合生成.但利用LC-MS/MS-PIS測定只檢測到4個聚合產(chǎn)物(圖2),同時也不能確定這4個產(chǎn)物是5個聚合產(chǎn)物中的哪一個.根據(jù)Jiang等[15]的研究結(jié)果,只能確定通過C-C耦合,含有2個羥基的聚合產(chǎn)物先出峰,通過C-O耦合,含有1個羥基的聚合產(chǎn)物后出峰.

圖3中質(zhì)量數(shù)為263/265的3個聚合產(chǎn)物是2-溴酚氧自由基通過脫1個溴產(chǎn)生,但是在LC-MS/MS-PIS測定過程中并未檢測到質(zhì)量數(shù)為263/265的產(chǎn)物.2-溴酚氧自由基發(fā)生耦合反應(yīng)理論上產(chǎn)生的聚合產(chǎn)物并沒有全部被檢測到,主要是由于酚氧自由基相互耦合的速率不同,從而導(dǎo)致聚合產(chǎn)物的產(chǎn)率有所不同[15,23].

3 結(jié)論

3.1 根據(jù)溴的天然同位素特性,建立了一種簡便、快速LC-MS/MS-PIS (79和81)子找母質(zhì)譜掃描測定方法.

3.2 LC-MS/MS-PIS子找母質(zhì)譜掃描方法測得KMnO4氧化2-溴酚的主要產(chǎn)物為4個不脫溴的氧化耦合產(chǎn)物,分子結(jié)構(gòu)中含有2個溴,質(zhì)量數(shù)為341/343(79)和343/345(81),豐度比為1:1.

3.3 KMnO4氧化2-溴酚產(chǎn)生的4個溴代聚合產(chǎn)物推測是由2-溴酚氧自由基通過C-C和C-O耦合產(chǎn)生,其中,C-C耦合的聚合產(chǎn)物先出峰,C-O耦合的聚合產(chǎn)物后出峰.

3.4 2-溴酚氧自由基發(fā)生耦合反應(yīng)理論上產(chǎn)生的8個溴代聚合產(chǎn)物并沒有全部被檢測到,主要是由于酚氧自由基的氧化耦合速率不同,導(dǎo)致耦合產(chǎn)物的形成產(chǎn)率不同.

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Products and pathways of 2-bromophenol oxidation by potassium permanganate.

PANG Su-yan1,2*, YANG Yue2, JIANG Cheng-chun3, ZHOU Yang4, JIANG Jin4, MA Jun4

(1.School of Municipal and Environmental Engineering, Jilin Jianzhu University, Changchun 130118, China；2.College of Chemical and Environmental Engineering, Harbin University of Science and Technology, Harbin 150040, China；3.School of Civil and Environmental Engineering, Shenzhen Polytechnic, Shenzhen 518055, China；4.State Key Laboratory of Urban Water Resource and Environment, Harbin Institute of Technology, Harbin 150090, China)., 2017,37(11)：4159~4165

The purpose of this article was to investigate the mechanism responsible for the formation of brominated polymeric products from oxidation of bromophenols by aqueous potassium permanganate. Experiments were conducted to determine brominated oxidation products of 2-bromophenol by aqueous potassium permanganate using liquid chromatography-triple quadrupole mass spectrometry (LC-MS/MS). The results showed that four polymeric products of341/343 (at79) and 343/345 (at81) containing two bromine atoms were detected by the precursor ion scan (PIS) approach at79 and 81, respectively, and their abundance was about 1:1, consistent with the natural isotope of bromine atom. The four polymeric products were isomers, and they were formed by the C-O and C-C coupling of 2-bromophenoxy radicals, where the C-C coupling products eluted faster than the C-O coupling ones in LC-MS/MS. According to phenolic coupling theory, there would be eight brominated polymeric products. However, they were partially detected, probably due to the difference in coupling rates of phenoxy radicals.

potassium permanganate；2-Bromophenol；polymeric product；oxidative coupling；reaction pathways

X703.5

A

1000-6923(2017)11-4159-07

龐素艷(1978-),女,吉林遼源人,教授,博士,主要從事水質(zhì)物化處理技術(shù)與理論.發(fā)表論文30余篇.

2017-05-03

國家自然科學(xué)基金資助項目(51578203, 51378316)

* 責(zé)任作者, 教授, psyhit@126.com