Singlet oxygen is key to the environmental fate and transformation of toxins and pollutants. The reactions of singlet oxygen have been extensively studied in organic solvents, but fundamental mechanistic information in aqueous media is relatively limited. We are studying the reactions of 1O2 with a series of dienes (a) (2E,4E)-hexa-2,4-dienoate (S-COO2-), (b) (2E,4E)-hexa-2,4-dien-1-ol (S-OH) and (c) Domoic acid (DA), a problematic natural occurring toxin. Product studies of these diene systems allow us monitor the [4+2], [2+2], and ene completing reaction pathways. The analysis of the different geometric isomers can distinguish between concerted and non-concerted reaction mechanisms. The 1O2 reaction with S-OH in methanol-d4 results in the formation of the [4+2] product (endoperoxide) as the only product. Whereas, singlet oxygenation of S-COO2- in deuterated water and methanol, d4, yields a pair of isomers or conformers of the corresponding endoperoxide(s). When deuterated water was used as the solvent for the 1O2 reaction with S-COO2-, three additional minor products were observed. The first product had trans coupling constant of the olefinic region of the 1H NMR and COSY NMR spectrum that agreed with the structure of a solvent trapped intermediate and accounted for about 20% of the transformed compound. The other two minor products (&gt;2%) were consistent with the [2+2] reaction products. Ongoing studies for the 1O2 reaction with DA indicate the major pathways are [4+2] and ene. The results of ongoing studies of the singlet oxygenation of the geometric isomers (EE, EZ, ZE, and ZZ) of S-OH and S-COO2- will be discussed. The results of these experiments illustrate the importance of establishing the reaction mechanisms and products of the reactions of 1O2 in aqueous media for specific compounds in order to make accurate predictions in regards to the implications and applications of 1O2 in field of environmental chemistry.

Singlet oxygenation of dienes in water and methanol: Domoic acid, sorbate, and sorbic alcohol

253rd National Meeting (2017)

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