Lewisite isomers

The forward reaction is favored because lewisite oxide and polymerized lewisite oxide are insoluble. In a basic solution, the trauj-lewisite isomer is cleaved by the hydroxyl ion to give acetylene and sodium arsenite this reaction may occur even at low temperatures (Rosenblatt et al, 1975 Clark, 1989). C/5-lewisite heated to over 40° C reacts with sodium hydroxide to yield vinyl chloride, sodium arsenite, and acetylene (Rosenblatt et al, 1975). In aqueous solution, the cA-isomer imdergoes a photoconversion to the trans-isomer (Rosenblatt et ah, 1975). Epstein (1956) reported that the toxic trivalent arsenic of lewisite oxide in standing water is converted to the less toxic pentavalent arsenic. 

Smith et al. (34) studied three isomers (els-, trans-and, geminal) of a lewisite using GC/MS, GC/FTIR, and NMR. 

Lewisite [dichloro(2-chlorovinyl)arsine] is an organic arsenical known for its vesicant properties (Rosenblatt et al., 1975). It has a molecular weight of 207.32, vapor pressure of 0.58 mm HG at 25°C, a liquid density of 1,89 g/cm at 25°C, freezing point of -18°C, boiling point of 190°C, and is negligibly soluble in water (DA, 1974). The chemical structure of lewisite is shown below. Lewisite may occur as a trans-isomer and as a cis-isomer. In aqueous solutions, the cis-isomer undergoes photoconversion to the trans-isomer (Clark, 1989). hi the presence of moisture, lewisite is rapidly converted to the more stable but highly toxic lewisite oxide (2-chlorovinylarsenous acid) (Cameron et al., 1946). 

Lewisite [L or L-1 dichloro(2-chlorovinyl) arsine] is an arsenical vesicant developed early in the 20th century. Lewisite occurs as cis- and tranx-isomers the typical ratio being 10 90. Several impiuities including 6w(2-chlorovinyl) chloroarsine (L-2) and tnY(2-chlorovinyl)arsine (L-3) are typically present. The chemical and physical properties of the cis- and tranj-isomers are similar. 

P-chlorovinyldichloroarsine. (l-chloro-2-di-chloroarsinoethane dichloro[2-chlorovinyl] arsine chlorovinylarsinedichloride Lewisite). Two isomers, probably cis and trans, are known. CICIfCIIAsCL... 

FIGURE 19.6 Published analytical approaches for the analysis of CVAA in urine (a) reaction of lewisite (trans isomer shown) with water to form CVAA, (b) reactions of CVAA with various thiols, and (c) derivatization using HFBI. 

Smith JR, Logan TP, Szafraniec LL, Jakubowski EM. Spectroscopic characterization of the geminal isomer of lewisite. Anal Lett, 1995 28 1541-1554. 

Environmental Fate. When manufactured by normal processes, commercial lewisite is composed of cis and trans isomers in the ratio of 10 90 and several impurities including bis(2- chlorovinyl)chloroarsine and tris(2-chlorovinyl)ar-sine (Rosenblatt et al. 1975). The chemical and physical properties of the two isomers are similar. 

The main product is j8-chIorovinyldichloroarsine with the trans isomer predominating. The proportion of the ds isomer is increased when other catal)rsts such as mercuric and cuprous chloride are used 180, 181, 182), though this is never very great. The Lewisite phase usually separates from the reaction mixture and this is believed to be the reason for the predominant formation of the dichloroarsine. If acetone is added to the reaction mixture separation of the Lewisite layer does not take place, and the main product is tris- -chlorovinylarsine 181). Mercuric-chloride-catalyzed addition appears to proceed through a mercurial intermediate 181). 

The correct structure of the isomers present in Lewisite was first proposed as a result of dipole moment studies (438). The moment of the main component, trawj-CHCl=CHAsCl2, was found to be 2.21 x 10 esu in benzene at 25° and that of iso-Lewisite, the cis compound, to be 2.61 x 10 esu. The greater value for the cis compound is perhaps the most reliable criterion of structure although in the original paper calculations of moments based on assumed structures were offered as evidence. Because of the uncertainty in these calculations and the small difference in the experimental moments the structure of Lewisite was redetermined, and verified, by electron diffraction (434) as mentioned above. 

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