Insight Into the Formation Paths of Methyl Bromide From Syringic Acid in Aqueous Bromide Solutions Under Simulated Sunlight Irradiation

Hui Liu, Tong Tong, Yingying Pu, Bing Sun, Xiaomei Zhu and Zhiyu Yan
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Hui Liu: College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China
Tong Tong: College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China
Yingying Pu: College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China
Bing Sun: College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China
Xiaomei Zhu: College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China
Zhiyu Yan: College of Environmental Science and Engineering, Dalian Maritime University, Dalian 116026, China

IJERPH, 2020, vol. 17, issue 6, 1-12

Abstract: Methyl bromide (CH 3 Br) is one of the largest natural sources of bromine in the stratosphere, where it leads to ozone depletion. This paper reported the photochemical production of CH 3 Br from syringic acid (SA) that has been used as an environmentally relevant model compound for terrestrially-derived dissolved organic matter. The formation of CH 3 Br increased with the increase of bromide ion concentration ranging from 0.8 to 80 mmol L −1 . Ferric ions (Fe(III)) enhanced CH 3 Br production, while chloride inhibited it, with or without Fe(III). Meanwhile, methyl chloride (CH 3 Cl) was generated in the presence of chloride and was inhibited by Fe(III). The different effects of Fe(III) on the formation of CH 3 Cl and CH 3 Br indicate their diverse formation paths. Based on the intermediates identified by liquid chromatography-mass spectrometry and the confirmation of the formation of Fe(III)-SA complexes, it was proposed that there were two formation paths of CH 3 Br from SA in the bromide-enriched water under simulated sunlight irradiation. One path was via nucleophilic attack of Br − on the excited state protonation of SA; the other was via the combination of methyl radical and bromine radical when Fe(III) was present. This work suggests that the photochemical formation of CH 3 Br may act as a potential natural source of CH 3 Br in the bromide-enriched environmental matrix, and helps in better understanding the formation mechanism of CH 3 Br.

Keywords: methyl bromide; syringic acid; photochemical production; reaction paths (search for similar items in EconPapers)
JEL-codes: I I1 I3 Q Q5 (search for similar items in EconPapers)
Date: 2020
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