Abstract
An easy 2-step method for the synthesis of the water-soluble singlet oxygen trap AES has been developed. The method is based on a novel Heck reaction with sodium vinylsulfonate followed by vinyl hydrogenation. It is shown that the Heck product AVS is also suitable as a water-soluble and colored singlet oxygen trap that allows singlet oxygen to be detected specifically and simply by visual inspection. The cumulative amount of 1 O2 generated into the solution can be determined unambiguously by measuring the concentration of the endoperoxides AVSO2 or AESO2 by HPLC or by 1 H NMR.
Key words
Heck reaction - hydrogenation - palladacycle - oxidation - catalysis
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trans -di(µ-acetato)- bis[o -(di-o -tolylphosphino)benzyl]dipalladium(II) (0.81 g, 0.9 mmol) in a mixed solvent system of DMF (330 mL) and NMP (330 mL) was heated at 100 °C until a clear solution was obtained. A 25% aqueous solution of sodium vinylsulfonate (110 mL, 248.6 mmol) was evaporated to a volume of ca. 80 mL. This concentrated solution was added to the hot reaction mixture in one portion, and the resulting solution was heated for 18 h under reflux (110 °C). The precipitate formed on cooling the reaction mixture to r.t. was filtered off. Insoluble metallic Pd residues were removed from the precipitate by hot filtration from a refluxing H2 O (300 mL) and EtOH (350 mL) mixture. Cooling of the hot filtrate to r.t. yielded, after filtration and drying, the product as yellow crystals (30.93 g, 70% yield). Anal. Calcd (%): C, 42.7; H, 4.0. Found: C, 43.0; H, 4.0. MS-FAB (negative ion mode): 389 [M - 2 Na + H], 411 [M - Na]. 1 H NMR (D2 O): δ = 7.74 (m, 4 H), 7.46 (m, 4 H), 7.29 (d, 2 H), 6.31 (d, 2 H).
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