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Decomposition of dimethyl polysulfides under solar irradiation in oxic aqueous solutions

Decomposition of dimethyl polysulfides under solar irradiation in oxic aqueous solutions Environmental contextThe quality of drinking water can be greatly compromised by the presence of dimethyl polysulfides. We studied the rate and mechanism of decomposition of dimethyl polysulfides in aqueous solution under solar irradiation, and found that they decompose photochemically in seconds to minutes, i.e. much faster than under dark conditions. These results suggest that photochemical pathways of dimethyl polysulfide decomposition may prevail in euphotic zones of natural aquatic systems.AbstractThe presence of malodorous dimethyl polysulfides (DMPSs) has been documented in marine and limnic systems as well as in tap water distribution systems. These compounds compromise the quality of drinking water. Under oxic conditions and in the absence of radiation, DMPSs with n 3 sulfur atoms disproportionate into DMPSs with n1 and n1 sulfur atoms, and, finally, to dimethyl disulfide (DMDS) and S8. DMDS, in turn, decomposes to methyl mercaptan (MT) and methanesulfinic acid. Under these conditions, the half-lives of DMPSs vary from months for dimethyl pentasulfide (DM5S) to hundreds of thousands of years for DMDS. In this work, we studied the kinetics and mechanisms of the decomposition reactions of DMPSs with 25 sulfur atoms in aqueous solutions in the presence of oxygen and under exposure to solar radiation. The quantum yields of decomposition of DMPSs with 2, 3, 4 and 5 sulfur atoms do not depend on either the concentration of DMPSs or pH, and are 4010, 2.00.2, 3510 and 104 respectively. The quantum yields, which are higher than unity, suggest that under exposure to solar radiation the photochemical decomposition of DMPSs proceeds by a radical chain reaction mechanism. Half-lives of DMPSs in oxic aquatic solutions exposed to solar radiation under a very clear atmosphere and a solar elevation angle of 90 were calculated from the quantum yields and were found to be as low as 4313s for DMDS, 404s for dimethyl trisulfide (DMTS), 2.10.6s for dimethyl tetrasulfide (DM4S) and 4.21.7s for DM5S. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Environmental Chemistry CSIRO Publishing

Decomposition of dimethyl polysulfides under solar irradiation in oxic aqueous solutions

Buchshtav, Tamir; Kamyshny, Alexey
Environmental Chemistry , Volume 17 (5): 8 – Jan 31, 2020
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References (35)

Publisher
CSIRO Publishing
Copyright
Copyright © The Author(s). Published by CSIRO Publishing
ISSN
1448-2517
eISSN
1449-8979
DOI
10.1071/EN19252
Publisher site
See Article on Publisher Site

Abstract

Environmental contextThe quality of drinking water can be greatly compromised by the presence of dimethyl polysulfides. We studied the rate and mechanism of decomposition of dimethyl polysulfides in aqueous solution under solar irradiation, and found that they decompose photochemically in seconds to minutes, i.e. much faster than under dark conditions. These results suggest that photochemical pathways of dimethyl polysulfide decomposition may prevail in euphotic zones of natural aquatic systems.AbstractThe presence of malodorous dimethyl polysulfides (DMPSs) has been documented in marine and limnic systems as well as in tap water distribution systems. These compounds compromise the quality of drinking water. Under oxic conditions and in the absence of radiation, DMPSs with n 3 sulfur atoms disproportionate into DMPSs with n1 and n1 sulfur atoms, and, finally, to dimethyl disulfide (DMDS) and S8. DMDS, in turn, decomposes to methyl mercaptan (MT) and methanesulfinic acid. Under these conditions, the half-lives of DMPSs vary from months for dimethyl pentasulfide (DM5S) to hundreds of thousands of years for DMDS. In this work, we studied the kinetics and mechanisms of the decomposition reactions of DMPSs with 25 sulfur atoms in aqueous solutions in the presence of oxygen and under exposure to solar radiation. The quantum yields of decomposition of DMPSs with 2, 3, 4 and 5 sulfur atoms do not depend on either the concentration of DMPSs or pH, and are 4010, 2.00.2, 3510 and 104 respectively. The quantum yields, which are higher than unity, suggest that under exposure to solar radiation the photochemical decomposition of DMPSs proceeds by a radical chain reaction mechanism. Half-lives of DMPSs in oxic aquatic solutions exposed to solar radiation under a very clear atmosphere and a solar elevation angle of 90 were calculated from the quantum yields and were found to be as low as 4313s for DMDS, 404s for dimethyl trisulfide (DMTS), 2.10.6s for dimethyl tetrasulfide (DM4S) and 4.21.7s for DM5S.

Journal

Environmental Chemistry – CSIRO Publishing

Published: Jan 31, 2020

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