Mild selective photochemical oxidation of an organic sulfide using OxP-polyimide porous polymers as singlet oxygen generators

Abstract

A series of porous organic polymers based on a singlet oxygen generating oxoporphyinogen (‘ OxP ’) has been successfully prepared from a pseudotetrahedral OxP -tetraamine precursor ( OxP(4-NH 2 Bn) 4 ) by its reaction with tetracarboxylic acid dianhydrides under suitable conditions. Of the compounds studied, those containing naphthalene ( OxP-N ) and perylene ( OxP-P ) spacers, respectively, have large surface areas (~530 m 2 g −1 ). On the other hand, the derivative with a simple benzene spacer ( OxP-B ) exhibits the best 1 O 2 generating capability. Although the starting OxP -tetraamine precursor is a poor 1 O 2 generator, its incorporation into OxP POPs leads to a significant enhancement of 1 O 2 productivity, which is largely due to the transformation of NH 2 groups to electron-withdrawing diimides. Overall 1 O 2 production efficacy of OxP-POP s under irradiation by visible light is significantly improved over the common reference material PCN-222 . All the materials OxP-B , OxP-N and OxP-P promote oxidation of thioanisole involving conversion of ambient triplet state oxygen to singlet oxygen under visible light irradiation and its reaction with the sulfide. Although the reaction rate of the oxidation promoted by OxP POPs is generally lower than for conventional materials (such as PCN-222 ) or previously studied OxP derivatives, undesired overoxidation of the substrate to methyl phenyl sulfone is suppressed. For organic sulfides, selectivity of oxidation is especially important for detoxification of mustard gas (bis(2-chloroethyl)sulfide) or similarly toxic compounds since controlled oxidation leads to the low toxicity bis(2-chloroethyl)sulfoxide while overoxidation leads to intoxification (since bis(2-chloroethyl)sulfone presents greater toxicity to humans than the sulfide substrate). Therefore, OxP POPs capable of promoting selective oxidation of sulfides to sulfoxides have excellent potential to be used as mild and selective detoxification agents.