Main Group Chemistry

The rates, products, and mechanisms of the degradation of the chemical warfare agents GD, thickened GD, HD and VX on environmental substrates were determined using Solid State Magic Angle Spinning Nuclear Magnetic Resonance (SSMAS NMR). Increases in temperature were found to increase the rates of the reactions. The addition of water affected both the rate of the reactions and the products formed. The alkalinity or acidity of the substrate was also observed to affect the products formed and the mechanism of the reaction.

O-ethyl S-(2-diisopropylaminoethyl)phosphonothiolate (VX) is among the most toxic of chemical warfare agents. VX is an oily liquid that is relatively involatile and is slow to hydrolyze, and thus may persist for weeks or longer in the environment, creating long term contamination of the territory. Concern over prolonged risk from VX exposure is exacerbated because it poses a dermal contact hazard -lethal dose on bare skin is about 10 mg/70 kg and it is readily absorbed through the skin. Therefore, a detailed understanding of its volatilization behavior and degradation pathways and rates is necessary. Volatilization has not been considered to be an important depletion mechanism, however, recent studies have shown a significant fraction of VX may volatilize. VX degradation reactions and their rates have been difficult to measure in many environmental media. For this reason, VX persistence has generally been described in terms of half lives. In this review, rates of VX degradation are compared on the basis of pseudo-first order rate constants in order to provide a basis for assessing VX persistence in a given environment. An issue of concern is that one VX degradation pathway produces S-2-(diisopropylaminoethyl) methylphosphonothioic acid (known as EA2192), a degradation product that is almost as toxic as VX. Consequently degradation pathways and rates for EA2192 are also discussed.

Many laboratories are studying the reactions of Chemical Warfare Agents (CWA) and simulants with various sorbent materials, fabrics, and decontamination solutions, in an effort to develop commercial or military CW remediation methods. In order to facilitate the comparisons of the results between various laboratories, it is helpful to have a standard, well-characterized analytical method. The method should not require specialized instrumentation, if possible. It should be standardized to allow simulant reaction studies to be compared directly to CWA reactions that are done at specialized laboratories. High Resolution (Solid State) Magic Angle Spinning (HRMAS) NMR studies have been used to study reactions on solids, since it can detect volatile CW agents as well as nonvolatile decontamination products. A headspace gas chromatography/mass spectrometry (GC/MS) method was also tested for this application, since it can be used to study reactivity and permeation. An approach is described for measuring permeation through films as vapor or liquid by using a two vial (vial within a vial) approach. Reactions on treated fabrics with the CWA HD [bis(chloroethyl) sulfide], GD (pinacolyl methylphosphonofluoridate), and VX [S,2-(diisopropylamino)ethyl methylphosphonothioate], and some simulants for these agents, are discussed.

Chemical warfare agents (CWA) are rapidly decontaminated using a hydrogen peroxide-based decontamination solution. In the weakly-basic decontaminant (pH 8) – activated and buffered with bicarbonate, molybdate, and citrate – nerve agents such as VX and GD undergo perhydrolysis (OOH $^{-}$ ) whereas the blister agent HD is catalytically oxidized, primarily, by tetraperoxomolybdate [Mo(OO) $_{4}^{2-}$ ] to the non-vesicant sulfoxide. The decontaminant, once mixed, exhibits remarkable stability, maintaining efficacy (pot-life) for at least 12 h. On non-sorptive, non-porous surfaces such as aluminum, the decontaminant decontaminates VX, GD, and HD to below acceptable levels (i.e., < 0.078, 1.67, and 10.0 μg/cm $^{2}$ , respectively).

Metal-catalyzed alcoholysis has proven to be an effective strategy for the rapid decomposition of neutral organophosphate triesters, phosphonates, phosphorothioates and phosphorothionates, as well as several organophosphate chemical weapons of the G and V-agent classes. This article reviews the development of the chemical methodology starting from early studies with phosphate triesters up to the most recent studies dealing with the testing for decontamination of live chemical agents.

We present an overview of the phosphonothioate hydrolytic chemistry promoted by molybdenum organometallics as well as new results on solvent effects. The metallocene bis(η $ ^{5}$ -cyclopentadienyl) molybdenum(IV) dichloride (Cp $_{2}$ MoCl $_{2}$ C=η $^{5}$ -C $_{5}$ H $_{5}$ ) and the methylated analog, (CH $_{3}$ Cp) $_{2}$ MoCl $_{2}$ hydrolyzes the compound O,S-diethyl phenylphosphonothioate (DEPP) whose core functional group mimics the neurotoxin VX. This is one of the few examples of phosphonothioate degradation yielding exclusively the desired P-S bond scission under mild aqueous conditions (pH 7, 25°C). The solvent composition affects the monomer-dimer equilibrium of aquated molybdocenes which in turn dictates the rate of DEPP hydrolysis. Kinetic and equilibrium results are presented to show that the monomer is the active species. Moreover, photoelectron spectroscopy data indicate that while the methylated (CH $_{3}$ Cp) $_{2}$ MoCl $_{2}$ has a higher monomer concentration compared to Cp $_{2}$ MoCl $_{2}$ , the former has a diminished electrophilic molybdenum center that is key in phosphonothioate hydrolysis.

The chronological progression to more and more effective solid decontamination agents is used as a prelude herein. An hypothesis or "goal" is set: it should be possible to create multi-purpose solid decontamination reagents that serve as (1) destructive adsorbents, photooxidation catalysts under visible and UV light, and decon agents for CWAs and BWAs. In order to achieve this goal, one must design non-toxic metal oxide nanomaterials with chemically active Lewis Acid/Base sites. These nanomaterials must possess chromophores that absorb visible light, and be composed mainly of a semiconductor material so that rapid energy transfer of electrons and holes to reactive sites can be achieved. In order to succeed, knowledge about photocatalysts and their structure must be combined with knowledge about solar cells, especially dye-sensitized solar cells based on nano-TiO $_{2}$ . In this way, a multifunctional decon agent of high surface area and low toxicity to humans and animals, whose activity/selectivity is boosted by light, will be achieved.

The destruction of phosphorus based chemical warfare agents using aqueous buffer mixtures of aluminum sulfate (alum) and sodium aluminate is pursued. The production of VX (O-ethyl-S-[2-(diisopropylamino)ethyl]-methylphos-phonothiolate) hydrolysis products ethyl methyl phosphonic acid (EMPA), an aluminum complex of EMPA, and S-[2-(diisopropylamino)ethyl]methylphosphonothiolate (EA-2192) is characterized in acidic and basic alum buffers. The study employs $^{31}$ P high resolution magic angle nuclear magnetic resonance spectroscopy (HRMAS NMR) for both quantitative and qualitative analysis. The acidic buffer results in a slower reaction rate and is less effective than the basic buffer.

Group 13 chelates incorporating boron and aluminum deactivated the chemical warfare agents (CWAs) VX, sarin (GB), soman (GD), and the pesticide, diazinon, under mild conditions. The deactivation occured through elimination of alkyl bromide resulting in solid products containing a robust Al-O-P or B-O-P linkage. The Group 13 chelate deactivation methodology produces non-toxic, easily disposable solid proudcts after combination with CWAs. In previous studies the group 13 chelates were found to be active for a wide range of organophosphates, organophosphonates, and organophosphinates (OPs). Thus, the compounds could be used as a deactivating agent for a wide range of problematic compounds possessing P-O-C linkages, including, CWAs, pesticides, and plasticizers. The majority of the chelate compounds are of the general formula: LBX, L(BX $_{2})_{2}$ and LAlX where L = an inexpensive, easily prepared Schiff base chelate and X = Cl and Br. This article will describe the range of compounds that can be used in the dealkylation reaction. The primary focus will be on chelates of the Salen class (Salen=N,N'- alkylene(or arylene)bis(salicylideneimine)), but a wider of range of chelates could be used for the reaction as this review will demonstrate.

The accumulation of organophosphorus neurotoxic compounds and biological warfare agents in the environment is a recognized ecological threat existing in the global scenario. Despite sustained research efforts, there remains a need for new, simple, effective, inexpensive, biodegradable and environmentally friendly method for detoxification of chemical warfare agents and pesticides. In the last few years, our laboratory has aimed at demonstrating on the rapid method of α-nucleophiles hydroxamate and oximates mediated catalysis of organophosphate, phosphonate, phosphinate, paraoxon, parathion, fenitrothion and other chemical warfare simulants in microorganized media like micelles and microemulsions. Different types of α-nucleophiles, metallosurfactants, acetylcholinesterase reactivators, nanoparticles and functionalized surfactants have been designed as potential hydrolytic micellar catalysts. In this lecture, an overview of detoxification chemistry and application of some novel monomeric, and functionalized surfactants on the reactivity of some toxic phosphate esters and carboxylic esters will be presented. Our contribution in the field is the development of catalysts capable of converting chemical warfare agents into non toxic products. The results provide new insight and direction towards the design of more effective chemical agent for detoxification.

Acetylcholinesterase (AChE) reactivators are crucial antidotes for the treatment of organophosphate (OP) intoxication. Since pralidoxime, there is still no AChE reactivator able to counteract the full spectrum of different organophosphorus compounds. Our effort has been concerned on development of novel AChE reactivators against tabun and OP pesticides. Hundreds of novel AChE reactivators were prepared. Several novel compounds were found to be potent reactivators both in vitro and in vivo. One compound (K203) was highlighted against tabun poisoning and one compound (K027) was highlighted against OP pesticide poisoning. Selected compounds are becoming promising candidates for replacement of former clinically used AChE reactivators.