Efficient Decontamination of HD by an Electrophilic Iodine/Carboxylate Composite as an Active Sorbent

Abstract

The development of new and efficient decontamination methods has become more relevant in recent years, especially with regard to solid-based decontamination and detoxification systems. The majority of powders used today are dealing with the physical adsorption of chemical warfare agents (CWAs) and their removal from sites without actively destroying them. In this work, we have designed and developed an active solid composite matrix combining organic carboxylate salts and N-iodosuccinimide (NIS) for HD decontamination via oxidation. All the reactions and mechanistic studies for the sorption and degradation of CWAs were conducted using direct polarization and cross polarization solid-state magic-angle spinning nuclear magnetic resonance techniques. Performance toward the sorption and detoxification of HD was tested, exhibiting oxidation within minutes in a mild and selective manner to the nontoxic sulfoxide derivative followed by visible formation of iodine. The results indicate that carboxylate moieties in the matrix are important for stabilizing the positively charged sulfonium ion intermediate and for supplying oxygen for hydrolysis in a water-deficient environment. The NaOBz/NIS composite was shown to be the most efficient in sorbing and converting the water-insoluble agent HD to its nontoxic, water-soluble sulfoxide, which could then be removed from the site with mere water, resulting in less environmental damage and quick remediation.

Figure 1

HD and common oxidation products.

Figure 2

SEM images of the NIS-free support vs the NaSalt/NIS composites (scale bar of 100 μm). (A1) Neat NaPA salt; (A2) NaPA/NIS composite; (B1) neat NaOAc salt; (B2) NaOAc/NIS composite; (C1) neat NaOBz salt; (C2) NaOBz/NIS composite.

Figure 3

¹³C MAS NMR spectra (DP/CP) of HD on different salt/NIS composites over time. (A1) DP NMR of the NaPA composite; (A2) CP NMR of the NaPA composite; (B1) DP NMR of the NaOAc composite; (B2) CP NMR of the NaOAc composite; (C1) DP NMR of the NaOBz composite; (C2) CP NMR of the NaOBz composite; (D1) DP NMR of the NaTFA composite; (D2) CP NMR of the NaTFA composite.

Scheme 1. Postulated Oxidation Pathway of HD with NIS on a Carboxylate Solid Support

Figure 4

Left to right: NaOBz/NIS (no HD); NaOBz/NIS+HD (15 min); NaOBz/NIS+HD (45 min).

Figure 5

¹³C NMR spectra of dibutylsulfide (Bu₂S) oxidation with NIS under dry and hydrolytic conditions (in ACN-d₃). (A) Neat Bu₂S; (B) control: Bu₂S with NIS under dry conditions; (C) control experiment (B) with added water; (D) Bu₂S with NaOBz and NIS under dry conditions.

Scheme 2. (A–C) The Role of Carboxylates in the Oxidation Mechanism of Sulfoxides with Electrophilic Iodine

(A) General reaction of sulfonium with carboxylates in aqueous solutions. (B) General reaction of sulfonium with dicarboxylate in aqueous solutions. (C) Suggested sulfonium reaction mechanism on a carboxylate solid support (this work). Adapted with permission from ref (48). Copyright 1982 American Chemical Society.Adapted with permission from ref (42). Copyright 1968 American Chemical Society.