Rearrangement products in aqueous photolysis of thifensulfuron methyl

• Published in: Journal of photochemistry and photobiology. A, Chemistry. Chemistry., 2017-09, Vol.346, p.401-410
• Main Authors: Sharma, Ashok K., Ryan, David L., Marr, Nina L., Wadsley, Michael P., Cheatham, Steve F.
• Format: Article
• Language: English
• Subjects: Chemical synthesis; Contraction; Degradation; Degradation products; Ipso-contraction; Light sources; Photochemistry; Photodegradation; Photolysis; Sulfonylurea; Thifensulfuron methyl; Thiophene rearrangement; Triazine; Ultraviolet radiation
• ISSN: 1010-6030; 1873-2666
• DOI: 10.1016/j.jphotochem.2017.06.028

[Display omitted] •Photochemical rearrangement of thiophene ring during thifensulfuron photolysis leading to interchange of the substituent locations.•Formation of an unexpected thiophene amine and unambiguous evidence of its structure.•Differentiating isomeric amine structures using independent synthesis and then by comparing the NMR and UV spectra Photo-degradation of [14C]-thifensulfuron methyl has been investigated in aqueous media using a light source which simulates sunlight. Degradation of thifensulfuron methyl proceeds predominantly via sulfonylurea bridge ipso-contraction, and via cleavage of the bridge structure, to yield products in which the thiophene and the triazine rings have disconnected. One significant degradation product, which accounts for nearly 10%, retained both rings with truncated bridge moiety. Surprisingly, this product had thiophene ring substituents rearranged from their original locations. Other laboratories have reported photodegradation of thifensulfuron-methyl, and identified similar degradation products as well. The structure of the rearrangement product has been misidentified in previous reports because the rearrangement of the thiophene ring is not widely recognized. An unambiguous identification of this product and potential rearrangement mechanisms are presented in this report.