Highly reactive catalysts for aerobic thioether oxidation

Rapid Oxidative Detoxification of Mustard Simulant by the Multisite Synergistic Catalytic Action of {PMoVI11MoVO40CuI8} Units

Under hydrothermal and solvent-thermal conditions, we synthesized two novel polyoxometalate (POM)-based hybrids: [CuI4(Pz)2(H2O)8(PMoVI11MoVO40)]·3.5H2O (1, Pz = pyrazine) and [(C2H8N)5(HPMoVI9MoV3O40)]·DMF·4H2O (2). Single-crystal X-ray diffraction indicates that compound 1 is a three-dimensional structure consisting of Cu (I), {PMo12} anions, Pz, and water, where Cu (I) can be considered as Lewis acid sites. Furthermore, both compounds 1 and 2 possess favorable catalysis activity in catalyzing the conversion of chemical warfare agent simulant 2-chloroethylethyl sulfide (CEES) to nontoxic production of 2-chloroethylethyl sulfoxide (CEESO) under ambient temperature. Significantly, 1 could realize 98% conversion and 100% selectivity of CEES owing to the multisite synergy in the {PMoVI11MoVO40CuI8} units in which the tricoordinated Cu (I) could interact with S and O atoms from CEES and H2O2, respectively. This interaction not only decreases the distance of CEES from peroxomolybdenum species formed by H2O2 but also activates CEES.

Highly Reactive Heterogeneous Nanofibers Catalyst Based on [Mo154] Clusters for Green Aerobic Oxidation of Sulfur Mustard Analogues under Ambient Conditions

BACKGROUND

Due to the increasing chemical and biological threats posed by terrorist attacks, there is a need to design and prepare nanofibers (NFs) with the ability to neutralize CWAs. For this purpose polyacrylonitrile NFs and polyoxomolybdate [Mo154] (abbreviated as PAN NFs/[Mo154]) as a heterogeneous catalyst was prepared by electrospinning method with a diameter of about 100nm.

OBJECTIVE

The PAN NFs/[Mo154] catalyze the selective aerobic oxidation of sulfur mustard stimulants, such as 2-chloroethyl ethyl sulfide (2-CEES) and 2-chloroethyl phenyl sulfide (2-CEPS) under green and "ambient" conditions (25◦C, 1atm O2) in presence of ethanol with high efficiency and selectivity. 2-CEES was selected as a model reaction to optimize the parameters of the reaction.

METHOD

The progress of the reaction was evaluated after different times using GC-FID, GC-MS and TLC. The reaction product was also confirmed by 1H-NMR spectroscopy.

RESULT

The aerobic oxidation results of 2-CEES showed that PAN NFs/[Mo154] have a conversion of 98% to produce only a nontoxic product, 2-CEESO with selectivity of 100% after 45min. The results were performed using [Mo154] without any PAN NFs for comparison. Whereas [Mo154] converts only 52% of 2-CEES under the identical conditions.

CONCLUSION

Heterogeneous PAN NFs/[Mo154] catalyst was reused after washing with solvent up to 5 steps without leaching of [Mo154] from PAN NFs and without any loss in efficiency due to the morphology of NFs. In addition to the recovery of PAN NFs/[Mo154] in different cycles, the use of FT-IR, UV-Vis and TEM techniques confirms the stability and morphology of PAN NFs/[Mo154] after the fifth cycle, 2-CEES oxidation. According to our information, this report is the first use of PAN NFs enriched with [Mo154] for aerobic oxidation of sulfur mustard simulants.

Materials for the Simultaneous Entrapment and Catalytic Aerobic Oxidative Removal of Sulfur Mustard Simulants

Materials that both sequester chemical warfare agents (CWAs) and then catalytically decontaminate the entrapped CWAs are highly sought. This article reports such a system for air-based catalytic removal of the sulfur mustard (HD) simulant, 2-chloroethyl ethyl sulfide (CEES). Hypercrosslinked polymers (HCPs) sequester CEES, and an HCP-embedded oxidation system comprising tribromide, nitrate, and acid (NO_xBr_xH⁺) simultaneously catalyzes the aerobic and selective, oxidative conversion of the entrapped CEES to the desired far less-toxic sulfoxide under ambient conditions (air and temperature). (NO_xBr_xH⁺) has been incorporated into three HCPs, a fluorobenzene HCP (HCP-F), a methylated HCP (HCP-M), and an HCP with acidic moieties (HCP-A). HCP-A acts as both an absorbing material and a catalytic component due to its acidic side chains. All three HCP/NO_xBr_xH⁺ systems work rapidly under these optimally mild conditions. No light or added oxidants are required. The HCP/NO_xBr_xH⁺ systems are recyclable.

Mono- and Di-Sc-Substituted Keggin Polyoxometalates: Effective Lewis Acid Catalysts for Nerve Agent Simulant Hydrolysis and Mechanistic Insights

Recently, the hydrolysis of nerve agents by Lewis acid catalysts has attracted considerable attention. The development of molecular catalysts, such as polyoxometalates (POMs) with Lewis acidic sites, is helpful to improve degradation efficiency and understand the catalytic mechanism at a molecular level. Herein, two novel Keggin-type POMs, namely, mono-Sc-substituted K₄[Sc(H₂O)PW₁₁O₃₉]·22H₂O·2(CH₃COOK) (1) and di-Sc-substituted Na₇[Sc₂(CH₃COO)₂PW₁₀O₃₈]·10H₂O·2CH₃COONa (2), have been successfully synthesized and thoroughly characterized by routine techniques. To our knowledge, 1 and 2 represent the first example of discrete Sc-substituted Keggin clusters. Compared with the reported Sc-containing POMs, 1 and 2 exhibit relatively good solubility and stability in aqueous solution, as evidenced by ³¹P nuclear magnetic resonance spectroscopy and Fourier-transform infrared spectroscopy. The two Sc-substituted POMs can effectively catalyze the hydrolytic decontamination of dimethyl 4-nitrophenyl phosphate (DMNP), a nerve agent simulant, at near-neutral pH. Notably, the catalytic performance of 2 (conversion: 97%) is much better than that of 1 (conversion: 28%). It is found that the different coordination environment of Sc is the key factor to impact their activity. Mechanistic studies including the control experiments and spectroscopy analysis (¹³C nuclear magnetic resonance spectroscopy and electrospray ionization mass spectrometry) show that under the turnover conditions the coordinated acetate dissociates from 2 and the exposed coordinatively unsaturated Sc center is more active than the water-coordinated Sc in 1 for binding with DMNP.

A dual-function all-inorganic intercluster salt comprising the polycation ε-[Al13O4(OH)24(H2O)12]7+ and polyanion α-[PMo10V2O40]5- for detoxifying sulfur mustard and soman

ε-[Al13O4(OH)24(H2O)12]7+, which shares similarity with the phosphotriesterase active site ZnII-OH-ZnII, was specially chosen to interact with the cluster α-PMo10V2O405- to form a new three-dimensional intercluster, which crystallized in the monoclinic space group P21/m with Z = 2, for the decontamination of chemical warfare agents. The experimental results showed that 50 mg of the compound decontaminated 96.4% (within 120 min) and 99.5% (within 40 min) of sulfur mustard (HD) (4 μL) and soman (GD) (4 μL), respectively, in ambient conditions. The decontamination processes followed first-order reaction kinetics with a rate constant and half-life of 0.01234 min-1 and 56.15 min for HD and 0.1198 min-1 and 5.78 min for GD, respectively. It was concluded that the α-PMo10V2O405- moiety was responsible for the catalytic oxidation of HD into non-toxic sulfoxide, while the ε-[Al13O4(OH)24(H2O)12]7+ moiety was responsible for the catalytic hydrolysis of HD and GD into nontoxic hydrolysates. Besides, the compound showed notable efficacy for the decontamination of HD on guinea pig skin and of GD on Kunming mouse skin, indicating high potential for use in human skin protection and treatment.

Catalytic reaction system for rapid selective oxidation of alkyl sulphide

Highly efficient catalytic reaction systems are developed to rapidly and selectively oxidize 2-chloroethyl ethyl sulfide (CEES). In the systems, precursors containing bromide(s) and nitrate anions are chosen for the development of cyclic catalytic loop and the effect of acids on the selective oxidation of CEES are investigated by the addition of several homogeneous acid catalysts. The experimental results reveal that addition of acid results in a higher concentration of tribromide, which is reported as a key component for the observed activity in the catalytic solution. As a consequence, a dramatic improvement in catalytic activity is observed, especially when the molar amount of acid is controlled to be more than twice the initial concentration of tribromide. For the efficient design of a catalytic system, heterogeneous acid catalysts possessing different ratios of Brønsted to Lewis acid sites are also considered. Compared to reaction systems catalysed by homogeneous acids, similar reaction behaviour is observed for the reaction with Amerlyst-15, while those with other heterogeneous catalysts, containing Lewis or mixed acid sites in their structure, exhibits an adverse effect of selective sulfoxidation, mainly due to the adsorption of anions onto Lewis sites and consequential deconstruction of the catalytic loop.

Mechanistic reaction model for oxidation of sulfur mustard simulant by a catalytic system of nitrate and tribromide

A new metal-free catalytic reaction system is developed to selectively oxidize 2-chloroethyl ethyl sulfide (CEES), a surrogate of sulfur mustard. The combination of two catalytic precursors, tribromide and nitrate, allows a rapid sulfoxidation of CEES even at ambient conditions. The kinetic behaviours at various reaction conditions are investigated to identify the most probable reaction pathways of the development of catalytic loop and the overall reaction steps of CEES sulfoxidation. The mechanistic study demonstrates that the catalytic loop does not require an addition of mineral acid or water, which is common in most other reaction systems. Incomplete catalytic systems with one precursor are also examined to uncover the complex network of sulfoxidation in the catalytic reaction system. The results reveal that the complex between CEES and bromine is a reactive intermediate, bromosulfonium, which can be further catalysed and converted into sulfoxide by nitrate. Based on the proposed reaction mechanism, a predictive kinetic model fully describing most reaction behaviours is developed.

Mono-transition-metal-substituted polyoxometalate intercalated layered double hydroxides for the catalytic decontamination of sulfur mustard simulant

The mono-transition-metal-substituted polyoxometalate intercalated layered double hydroxides Zn₂Cr-LDH-PW₁₁M can effectively catalyze the oxidative decontamination of a sulfur mustard simulant.

Rapid Capture and Hydrolysis of a Sulfur Mustard Gas in Silver-Ion-Exchanged Zeolite Y

Sulfur mustard gas, also called HD, is one of the main chemical warfare agents and has claimed thousands of lives and left many more contaminated. The development of functional materials to promptly capture and detoxify sulfur mustard within a few minutes is extremely important to save the lives of the affected people. This has motivated us to explore excellent detoxification systems that can be deployed in the field to rapidly capture and hydrolyze mustard gas in a short time. To that end, we present a silver-ion-exchanged zeolite Y [(Ag⁺) _n@Y, n = 5, 13, 21, 32, 43, and 55] that can rapidly capture mustard gas and its simulant (2-chloroethyl ethyl sulfide, CEES) in ambient conditions to enable the prompt hydrolysis of the CEES captured in its nanopores. The capture and hydrolysis ability of Ag⁺@Y positively correlated with its number of Ag⁺ ions. In addition, 70% of CEES (2.5 μL in 1 mL) was captured by (Ag⁺)₅₅@Y within 20 min at 25 °C in ambient conditions. Moreover, 100% CEES (2.5 μL in 1 mL aqueous ethanol cosolvent) was hydrolyzed in 1 min at 25 °C. The efficiency of Ag⁺@Y in capturing and hydrolyzing CEES as well as mustard gas is thus a system with high detoxification efficiency for this dangerous chemical warfare agent.

Impact of ambient gases on the mechanism of [Cs8Nb6O19]-promoted nerve-agent decomposition

Polyoxoniobate catalyst, nerve agent decomposition, reaction mechanism, impact of ambient gases on the stability and reactivity of the polyoxoniobate.

The impact of ambient gas molecules (X), NO₂, CO₂ and SO₂ on the structure, stability and decontamination activity of Cs₈Nb₆O₁₉ polyoxometalate was studied computationally and experimentally. It was found that Cs₈Nb₆O₁₉ absorbs these molecules more strongly than it adsorbs water and Sarin (GB) and that these interactions hinder nerve agent decontamination. The impacts of diamagnetic CO₂ and SO₂ molecules on polyoxoniobate Cs₈Nb₆O₁₉ were fundamentally different from that of NO₂ radical. At ambient temperatures, weak coordination of the first NO₂ radical to Cs₈Nb₆O₁₉ conferred partial radical character on the polyoxoniobate and promoted stronger coordination of the second NO₂ adsorbent to form a stable diamagnetic Cs₈Nb₆O₁₉/(NO₂)₂ species. Moreover, at low temperatures, NO₂ radicals formed stable dinitrogen tetraoxide (N₂O₄) that weakly interacted with Cs₈Nb₆O₁₉. It was found that both in the absence and presence of ambient gas molecules, GB decontamination by the Cs₈Nb₆O₁₉ species proceeds via general base hydrolysis involving: (a) the adsorption of water and the nerve agent on Cs₈Nb₆O₁₉/(X), (b) concerted hydrolysis of a water molecule on a basic oxygen atom of the polyoxoniobate and nucleophilic addition of the nascent OH group to the phosphorus center of Sarin, and (c) rapid reorganization of the formed pentacoordinated-phosphorus intermediate, followed by dissociation of either HF or isopropanol and formation of POM-bound isopropyl methyl phosphonic acid (i-MPA) or methyl phosphonofluoridic acid (MPFA), respectively. The presence of the ambient gas molecules increases the energy of the intermediate stationary points relative to the asymptote of the reactants and slightly increases the hydrolysis barrier. These changes closely correlate with the Cs₈Nb₆O₁₉–X complexation energy. The most energetically stable intermediates of the GB hydrolysis and decontamination reaction were found to be Cs₈Nb₆O₁₉/X-MPFA-(i-POH) and Cs₈Nb₆O₁₉/X-(i-MPA)-HF both in the absence and presence of ambient gas molecules. The high stability of these intermediates is due to, in part, the strong hydrogen bonding between the adsorbates and the protonated [Cs₈Nb₆O₁₉/X/H]⁺-core. Desorption of HF or/and (i-POH) and regeneration of the catalyst required deprotonation of the [Cs₈Nb₆O₁₉/X/H]⁺-core and protonation of the phosphonic acids i-MPA and MPFA. This catalyst regeneration is shown to be a highly endothermic process, which is the rate-limiting step of the GB hydrolysis and decontamination reaction both in the absence and presence of ambient gas molecules.

H5PV2Mo10O40 encapsulated in MIL-101(Cr): facile synthesis and characterization of rationally designed composite materials for efficient decontamination of sulfur mustard

A newly synthesized composite H₅PV₂Mo₁₀O₄₀@MIL-101(Cr) can decontaminate HD quickly and efficiently owing to the synergetic combination of the components.

A Polyoxoniobate-Polyoxovanadate Double-Anion Catalyst for Simultaneous Oxidative and Hydrolytic Decontamination of Chemical Warfare Agent Simulants

A novel double-anion complex, H₁₃ [(CH₃ )₄ N]₁₂ [PNb₁₂ O₄₀ (V^V O)₂ ⋅(V^IV₄ O₁₂ )₂ ]⋅22 H₂ O (1), based on bicapped polyoxoniobate and tetranuclear polyoxovanadate was synthesized, characterized by routine techniques and used in the catalytic decontamination of chemical warfare agents. Under mild conditions, 1 catalyzes both hydrolysis of the nerve agent simulant, diethyl cyanophosphonate (DECP) and selective oxidation of the sulfur mustard simulant, 2-chloroethyl ethyl sulfide (CEES). In the oxidative decontamination system 100 % CEES was transformed selectively to nontoxic 2-chloroethyl ethyl sulfoxide and vinyl ethyl sulfoxide using nearly stoichiometric 3 % aqueous H₂ O₂ with a turnover frequency (TOF) of 16 000 h^-1 . Importantly, the catalytic activity is maintained even after ten recycles and CEES is completely decontaminated in 3 mins without formation of the highly toxic sulfone by-product. A three-step oxidative mechanism is proposed.

Tunable multilayer assemblies of nanofibrous composite mats as permeable protective materials against chemical warfare agents

The developed permeable materials consist of multilayer assemblies of inner and outer layers of composite nanofibers containing adsorbents. Controlled stacking of these inner and outer layers into assemblies allows their properties to be modulated.

Efficient and selective oxidation of sulfur mustard using singlet oxygen generated by a pyrene-based metal-organic framework

A pyrene-based metal-organic framework (MOF) NU-1000 was used as a heterogeneous photocatalyst for the degradation of a sulfur mustard simulant, 2-chloroethyl ethyl sulfide (CEES). Using irradiation from a commercially available and inexpensive ultraviolet (UV) light-emitting diode (LED), singlet oxygen (1O2) is generated by NU-1000 and selectively oxidizes CEES to the nontoxic product 2-chloroethyl ethyl sulfoxide (CEESO). More importantly, this method was tested on the warfare agent sulfur mustard (HD) for the first time using 1O2 and a MOF catalyst, and this method proved to be effective in oxidizing sulfur mustard to nontoxic products without forming the toxic sulfone by-product.

Alkaline niobates ANbO3 (A = Li, Na, K) as heterogeneous catalysts for dipropyl sulfide oxidation

Alkaline ANbO₃ (A = Li, Na, K) niobates with perovskite type structure were prepared by sol gel method, extensively characterized and evaluated as heterogeneous catalysts for selective oxidation of dipropyl sulfide to its corresponding sulfoxide.

Dual-Function Metal-Organic Framework as a Versatile Catalyst for Detoxifying Chemical Warfare Agent Simulants

The nanocrystals of a porphyrin-based zirconium(IV) metal-organic framework (MOF) are used as a dual-function catalyst for the simultaneous detoxification of two chemical warfare agent simulants at room temperature. Simulants of nerve agent (such as GD, VX) and mustard gas, dimethyl 4-nitrophenyl phosphate and 2-chloroethyl ethyl sulfide, have been hydrolyzed and oxidized, respectively, to nontoxic products via a pair of pathways catalyzed by the same MOF. Phosphotriesterase-like activity of the Zr6-containing node combined with photoactivity of the porphyrin linker gives rise to a versatile MOF catalyst. In addition, bringing the MOF crystals down to the nanoregime leads to acceleration of the catalysis.

Efficient and convenient oxidation of sulfides to sulfoxides with molecular oxygen catalyzed by Mn(OAc)2 in ionic liquid [C12mim][NO3]

A simple, efficient, and eco-friendly procedure for aerobic oxidation of sulfides catalyzed by Mn(OAc)₂/[C₁₂mim][NO₃] has been developed.

Sulfide Oxidation by O2: Synthesis, Structure and Reactivity of Novel Sulfide-Incorporated Fe(II) Bis(imino)pyridine Complexes

The unsymmetrical iron(II) bis(imino)pyridine complexes [FeII(LN3SMe)(H2O)3](OTf)2 (1), and [FeII(LN3SMe)Cl2] (2) were synthesized and their reactivity with O2 was examined. Complexes 1 and 2 were characterized by single crystal X-ray crystallography, LDI-MS, 1H-NMR and elemental analysis. The LN3SMe ligand was designed to incorporate a single sulfide donor and relies on the bis(imino)pyridine scaffold. This scaffold was selected for its ease of synthesis and its well-precedented ability to stabilize Fe(II) ions. Complexes 1 and 2 ware prepared via a metal-assisted template reaction from the unsymmetrical pyridyl ketone precursor 2-(O=CMe)-6-(2,6-(iPr2-C6H3N=CMe)-C5H3N. Reaction of 1 with O2 was shown to afford the S-oxygenated sulfoxide complex [Fe(LN3S(O)Me)(OTf)]2+(3), whereas compound 2, under the same reaction conditions, afforded the corresponding sulfone complex [Fe(LN3S(O2)Me)Cl]2+ (4).

Transition-metal-free highly efficient aerobic oxidation of sulfides to sulfoxides under mild conditions

A highly efficient transition-metal-free catalytic system Br₂/NaNO₂/H₂O has been developed for a robust and economic acid-free aerobic oxidation of sulfides. It is noteworthy that the sulfide function reacts under mild conditions without over-oxidation to sulfone. The role of NaNO₂ as an efficient NO equivalent for the activation of molecular oxygen was identified. Under the optimal conditions, a broad range of sulfide substrates were converted into their corresponding sulfoxides in high yields by molecular oxygen. The present catalytic system utilizes cheap and readily available agents as the catalysts, exhibits high selectivity for sulfoxide products and releases only innocuous water as the by-products.