KMnO4降解2-溴酚的氧化產物與反應路徑

龐素艷,楊 悅,姜成春,周 揚,江 進,馬 軍

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KMnO4降解2-溴酚的氧化產物與反應路徑

龐素艷1,2*,楊 悅2,姜成春3,周 揚4,江 進4,馬 軍4

(1.吉林建筑大學市政與環境工程學院,吉林長春130118；2.哈爾濱理工大學化學與環境工程學院,黑龍江哈爾濱150040；3.深圳職業技術學院建筑與環境工程學院,廣東深圳 518055；4.哈爾濱工業大學城市水資源與水環境國家重點實驗室,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物的生成機理,利用三重四級桿串聯線性離子阱液相-質譜聯用儀(LC-MS/MS)對KMnO4氧化降解2-溴酚的產物進行檢測分析.結果表明,根據溴的天然同位素特性,建立了LC-MS/MS-PIS(79和81)子找母質譜掃描方法測定溴代有機物,測得KMnO4氧化降解2-溴酚的主要產物為4個質量數相同,341/343(79)和343/345(81),且分子結構中含有2個溴的氧化耦合產物,同位素豐度比為1:1.推測4個溴代聚合產物為同分異構體,由2-溴酚氧自由基通過C-C和C-O耦合產生,其中,C-C耦合的聚合產物先出峰,C-O耦合的聚合產物后出峰.2-溴酚氧自由基發生氧化耦合反應,理論上產生的8個溴代聚合產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,導致聚合產物的形成產率不同.

KMnO4；2-溴酚；聚合產物；氧化耦合；反應路徑

溴酚類有機物被廣泛應用于助燃劑、木材防腐劑、聚合物等產品的生產過程中,導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環境[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,這些研究的產物分析結果證實溴酚的氧化降解產物是一些聚合物,如羥基化多溴聯苯醚(OH-PBDEs)和羥基化多溴聯苯(OH-PBBs).

高錳酸鉀(KMnO4)作為綠色氧化劑,運輸、儲存、使用方便,且氧化后不易產生有毒有害副產物,能夠在水處理過程中進行大規模應用. Jiang等[15]研究了KMnO4降解2,4-二溴酚的氧化產物和反應路徑,LC-MS/MS質譜測定結果表明,2,4-二溴酚氧化后產生2個含有4個溴的聚合產物,一個為多溴聯苯醚,由2個2,4-二溴酚氧自由基通過鄰位C與O耦合產生,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耦合產生,結構中含有2個羥基,且每個苯環中都含有1個.到目前為止,還沒有關于KMnO4氧化降解2-溴酚氧化產物與反應路徑的研究.

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

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,購買于國藥集團上海化學試劑有限公司.

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(5~20μmol/L),反應完全后(即KMnO4完全被消耗),用0.45μm的玻璃纖維膜過濾,利用液相色譜質譜聯用儀(LC-MS/MS)對過濾后樣品進行產物分析測定.

1.3 分析方法

KMnO4降解2-溴酚的氧化產物采用AB SCIEX QTRAP 5500三重四級桿串聯線性離子阱質譜與Agilent 1260高效液相聯用(LC-MS/ MS)進行分析測定.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內從5%線性升到50%,保持10min,再在0.1min內降到5%,保持5min,流速為200μL/min,進樣量為10μL,柱溫為35℃.采用電噴霧離子源負離子模式(ESI-)進行檢測,測定方法選擇子找母掃描模式(PIS),即在四級桿Q3設定特殊質量數的子離子,然后在四級桿Q1設定質量數掃描范圍,尋找能夠產生該子離子的母離子.Q1設定掃描范圍為50~500Da, Q3設定子離子質量數為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 結果與討論

2.1 溴代有機物質譜測定方法的建立

天然環境中溴(Br)的同位素主要有2個,質量數為79和81(Br79和Br81),且豐度比為1:1.研究中根據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物的質譜檢測方法,其原理主要是利用溴代有機物在ESI源負電(ESI-)模式下,通過溴離子的同位素信息,進行三重四級桿的質譜掃描追蹤母離子測定,即子找母質譜掃描模式[16-17].

研究中計算了溴代有機物中含溴元素個數與質譜測定信息的關系,見表1[16,18-22].例如,2-溴酚分子結構中含有1個溴,進行質譜全掃描模式測定時,會產生2個1:1的質譜峰,采用79或81子找母質譜掃描模式(79和81)進行測定時,會各產生1個質譜峰.

2.2 KMnO4降解2-溴酚的氧化產物與反應路徑

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值很高的色譜峰.因此,與全掃描質譜模式相比,子找母質譜掃描模式對溴代有機物的測定更靈敏,響應值更高.2-溴酚的保留時間為24.8min,在嵌入的質譜圖中,子找母掃描時質量數為171(79)和173(81),全掃描時質量數為171/173,且質譜峰的溴同位素豐度比為1:1,與表1中含1個溴的總結相一致.

圖1 2-溴酚標準樣品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

表1 溴代有機物在LC-MS/MS全掃描和子找母掃描中理論同位素豐度規律

注:為被檢測物質的最小質量數.

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-溴酚氧化產物的色譜峰更清晰、更靈敏、更全面.與2-溴酚標準色譜圖相比,通過子找母質譜掃描模式檢測到KMnO4降解2-溴酚產生4個主要產物,分別標記為I、II、III、IV,而在全掃描模式下只測到產物I和II,并且色譜峰非常小.從質譜圖可以看出,4個產物進行子找母掃描時質量數相同,為341/343(79)和343/345(81),且2個質譜峰的同位素豐度比為1:1,應該是同分異構體.在全掃描時質量數為341/343/345,且豐度比為1:2:1.根據表1的計算結果,推測產物I-IV中含有2個Br,可能是目標物2-溴酚氧自由基的聚合物.這一測定結果,與Jiang等[15]研究中KMnO4氧化降解2,4-二溴酚的LC-MS/MS質譜檢測結果相似.2,4-二溴酚氧化后產生2個含有4個溴的聚合產物,而2-溴酚氧化后產生4個含有2個Br的聚合產物.溴酚中溴離子的個數和位置直接導致其氧化產物和反應路徑不同,從而導致LC-MS/MS質譜測定結果不同.

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

圖3中質量數為263/265的3個聚合產物是2-溴酚氧自由基通過脫1個溴產生,但是在LC-MS/MS-PIS測定過程中并未檢測到質量數為263/265的產物.2-溴酚氧自由基發生耦合反應理論上產生的聚合產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,從而導致聚合產物的產率有所不同[15,23].

3 結論

3.1 根據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)子找母質譜掃描測定方法.

3.2 LC-MS/MS-PIS子找母質譜掃描方法測得KMnO4氧化2-溴酚的主要產物為4個不脫溴的氧化耦合產物,分子結構中含有2個溴,質量數為341/343(79)和343/345(81),豐度比為1:1.

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

3.4 2-溴酚氧自由基發生耦合反應理論上產生的8個溴代聚合產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,導致耦合產物的形成產率不同.

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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,主要從事水質物化處理技術與理論.發表論文30余篇.

2017-05-03

國家自然科學基金資助項目(51578203, 51378316)

* 責任作者, 教授, psyhit@126.com