Lewisite hydrolysis

Hazardous Decomposition Products Reasonably stable however, in presence of moisture, it hydrolyses rapidly, losing its vesicant property. It also hydrolyses in acidic medium to form HC1 and non-volatile (solid) chlorovinylarsenious oxide, which is less vesicant than Lewisite. Hydrolysis in alkaline medium, as in decontamination with alcoholic caustic or carbonate solution or DS2, produces acetylene and trisodium arsenate (Na3 As 04). Therefore, decontaminated solution would contain toxic arsenic. 

The dependence of the rate of P-chlorovinylarsineoxide (a lewisite hydrolysis product) degradation on the pH of aqueous solutions was studied. Buffer solutions and deionised water with pH 6.4 were used. The content of P-chlorovinylarsineoxide was determined by an HLEC method. Experimental results are presented in Table 4. 

An especially useful final product is arsenic. Conceptually the process of metallic arsenic production consists of two stages Lewisite hydrolysis, and electrolysis of arsenious acid in aqueous sodium chloride solution. This method is reliable for Lewisite destruction, and has the virtue of producing arsenic, which is valuable, and suitable for longterm storage. 

Rapid for vapor and dissolved Lewisite-1. Low solubility in water limits the hydrolysis. 

Rapid hydrolysis aids in lowering the duration of effectiveness of toxic chemical agents. For example, in the presence of water or water vapor, lewisite (L) rapidly hydrolyzes. Therefore, it has a shorter duration of effectiveness than distilled mustard (HD). 

New substances (hydrolysis products) form when an agent or compound reacts with water. In certain cases hydrolysis does not completely destroy the toxicity of an agent or compound. The resulting hydrolysis products may also be toxic. Examples include lewisite and other agents containing arsenic. 

Regardless of the method of lewisite degradation (combustion, hydrolysis, or other environmental degradation), the arsenic component will not be eliminated and, therefore, at least some combustion product or other degradation products may be some form of arsenical. The recognized degradation products of lewisite are listed in Table 1. 

Althongh no data on its fate in the atmosphere are available, UV absorption spectrum of lewisite at 200 to 350 nm indicates that some photodegradation may take place. Rapid hydrolysis may occur in the gas phase (MacNanghton and Brewer, 1994). 

Althongh lewisite is only slightly soluble in water, 0.5 g/L (Rosenblatt et al., 1975), hydrolysis, resulting in the formation of lewisite oxide and HCl is rapid. Qi-Lewisite mnst be heated to over 40°C to react with NaOH to yield vinyl chloride, sodium arsenite, and acetylene (Rosenblatt et al., 1975). In aqneons solution, the cis isomer nndergoes a photoconversion to the trans isomer (Rosenblatt et al., 1975). Upon standing in water, the toxic trivalent arsenic of lewisite oxide is converted to the less toxic pentavalent arsenic (Epstein, 1956). 

Lewisite in soil may rapidly volatilize or may be converted to lewisite oxide due to moisture in the soil (Rosenblatt et al, 1975). The low water solubility suggests intermediate persistence in moist soil (Watson and Griffin, 1992). Both lewisite and lewisite oxide may be slowly oxidized to 2-chlorovinylarsonic acid (Rosenblatt et al, 1975). Possible pathways of microbial degradation in soil include epoxidation of the C=C bond and reductive deha-logenation and dehydrohalogenation (Morrill et al, 1985). Due to the epoxy bond and arsine group, toxic metabolites may result. Additionally, residual hydrolysis may result in arsenic compounds. Lewisite is not likely to bioaccumulate. However, the arsenic degradation products may bioaccumulate (Rosenblatt et al, 1975). 

CWAs have been widely eondemned since they were first used on a massive scale during World War I. However, they are still stockpiled and used in many countries as they are cheap and relatively easy to produee, and can cause mass casualties. Although the blood agent CK is extremely volatile and undergoes rapid hydrolysis, the degradation of three types of vesicant CWAs, the sulfur mustards, nitrogen mustards, and Lewisite, results in persistent products. For... 

The reactions with thiol groups (e.g., those that are found in proteins) form an alkylarsine sulfide. Mustard gas, at the same LCtso, induces vesication, whereas Lewisite does not. Apparently, Lewisite is more irritating initially to the pulmonary systems than mustard. The hydrolysis products are more persistent in soil in comparison with mustard. In ambient air. Lewisite is about 10 times more volatile than mustard. 

With a vapor pressure of 0.58 mmHg at 25°C, lewisite is considered non-volatile. However, it is more volatile than HD and may be used as a moderate irritant vapor over greater distances than HD (Watson and Griffin, 1992). Based on its UV absorption band (Rewick et al., 1986), some photodegradation may take place in the atmosphere. Hydrolysis may also occur in the gas phase (MacNaughton and Brewer, 1994). 

Under environmental conditions, CWAs (vesicant agents, sulfur mustard (H, HD and HT) and lewisite (L) nerve agents, GA, GB, GD and VX) can undergo multiple-degradation processes such as hydrolysis, oxidation, dehydration and photolysis. These baseline degradation reactions can vary in rate and completeness, depending upon reaction temperature and pH, as well as the presence of free radicals and catalysts. Knowledge of these baseline reaction parameters has formed the basis for many modern decontamination procedures. 

Chlorovinyl arsonous acid (CVA) 2-Chlorovinyl arsenous acid 2-Chloroethenyl arsonous acid Dihydroxy(2-Chlorovinyl)arsine 2-Chloroethenyl dihydroxyarsine C2H4AsC102 85090-33-1 Hydrolysis of Lewisite... 

Chlorovinyl arsenous oxide 2-Chlorovinyl arsenic oxide 2-Chlorovinyl arsine oxide 2-Chloroethenyl arsinic oxide Lewisite oxide C2H2AsC10 3088-37-7 Hydrolysis or dehydration of 2-chlorovinyl arsonous acid... 

Figure 7. Hydrolysis of lewisite I to chlorovinylarsonous acid and its derivatization to 1,3-dithioarsenolines (10) with 1,2-dithiols...

Over 700 tons of mustard agent were destroyed by hydrolysis in Canada (Sutherland, 1997). The destruction was carried out at the Defence Research Establishment Suffield (DRES) in 1975-1976. Alkaline hydrolysis was employed and the products were incinerated. From 1989 to 1991, nerve agents (G and V classes) were removed from weapons using drill-and-drain methods and neutralized using 20 percent potassium hydroxide in methanol. The neutralization products were then incinerated. Lewisite was neutralized with an alkaline peroxide solution containing sodium or calcium chloride. The products included sodium or calcium arsenate, acetylene, and chloride salts. 

As an example we can look at the hydrolysis of Lewisite-1 (or 2-chlorovinylarseneous dichloride) according to equations 6 to 8 [56]. Subsequently, the adsorbed HCl will react with the copper ions of the impregnation according to reaction 9. The other hydrolysis products are all large molecules, some being solids, and are very well retained on the carbon physisorption. 

Fig. 4-2. Agent vaporization increases in proportion to energy sources such as heat from explosive charges or from ambient heat (as measured by air or surface temperatures). Vapor persistence is then determined by weather factors such as wind and humidity. Hydrolysis rates are affected by factors such as temperature and solubility. Agents show characteristic hydrolysis rates in water, and water vapor, as described by humidity, may cause significant hydrolysis of vaporized agent. The vesicant Lewisite, for example, shows relatively rapid hydrolysis in water vapor, while the nerve agent VX is more resistant to hydrolysis.

D. Agent decomposition (see also Table 11-57). Some warfare agents produce toxic by-products during attempts at decontamination or when exposed to acidic environments. GA may produce hydrogen cyanide and carbon monoxide. GB and GD produce hydrogen fluoride under acidic conditions. Lewisite is corrosive to steel and in nonalkaline conditions may decompose to trisodium arsenate. VX fonns the toxic product EA2192 when undergoing alkaline hydrolysis. 

Sulfur mustard can be considered environmentally persistent because it is chemically stable and of low volatility. When protected from weathering conditions, it may persist in soil for years. VX is moderately persistent because of low volatility and slow rate of hydrolysis. The G-agents can be considered non-persistent on the basis of volatility and hydrolysis rates. Depending on environmental conditions, their half-lives may be measured in hours to days. Lewisite is rapidly hydrolyzed but the insoluble oxide formed is stable in the environment. In addition, arsenical degradation products of lewisite persist in the environment. Because of its extreme volatility and relatively rapid hydrolysis, cyanogen chloride is not persistent in the environment. 

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