|Preferred IUPAC name
|Systematic IUPAC name
|Molar mass||160.86 g·mol−1|
|Melting point||−55 °C (−67 °F; 218 K)|
|Boiling point||133 °C (271 °F; 406 K)|
|Main hazards||Highly toxic, Irritant|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Methyldichloroarsine, sometimes abbreviated "MD", is an organoarsenic compound with the formula CH3AsCl2. This colourless volatile liquid is a highly toxic vesicant that has been used in chemical warfare.
Structure, synthesis, reactivity
Focusing on the arsenic center, the molecule is pyramidal with the Cl-As-Cl and C-As-Cl angles approaching 90° (see image). Virtually all related arsenic(III) compounds adopt similar structures.
- AsCl3 + CH3MgCl → CH3AsCl2 + MgCl2
Typically such syntheses are conducted in ether or THF solutions and typically the product is isolated by distillation. Use of larger amounts of the magnesium reagent affords greater amounts of dimethylchloroarsine ((CH3)2AsCl) and trimethylarsine ((CH3)3As).
- 2 Na3AsO3 + (CH3O)2SO2 → 2 CH3AsO(ONa)2 + Na2SO4,
- CH3AsO(ONa)2 + SO2 → CH3AsO + Na2SO4,
- CH3AsO + 2 HCl → CH3AsCl2 + H2O
The As-Cl bonds in MD are susceptible toward nucleophilic attack. Reduction of MD with sodium metal affords the polymer [CH3As]n.
Use as a weapon
Symptoms of poisoning
Although some of its symptoms resemble those from poison ivy, other symptoms include irritation to the eyes and to the nose, although blistering may be delayed for hours. Other symptoms include: dermal burns with vesicle formation; blepharospasm and photophobia. Convulsions, abdominal pain, coughing, and shortness of breath with damage to the respiratory system can be delayed for about three to five days; hemolysis can also occur.
Besides avoiding situations in which it might be used, an activated charcoal filter and a protective mask can help protect against MD. It should, however, be noted that MD can penetrate rubber, so some masks and clothing are ineffective. Other protective clothing, such as full body protection, are useful as well. Among the agents useful for decontamination of MD are bleach and caustic soda.
- Fitzgerald, G. M.; Vollmer, T. (2006-06-19). "CBRNE - Vesicants, Organic Arsenicals: L, ED, MD, PD, HL". WebMD. Retrieved 2008-12-23.
- Ledgard, J. (2006). The Laboratory History of Chemical Warfare Agents. Lulu.com. p. 117. ISBN 9781411694323.
- Lohs, K. H. (1974). Synthetische Gifte (in German) (4th ed.). Berlin (East), GDR: Militärverlag der Deutschen Demokratischen Republik.
- Cashman, J. R. (2008). Emergency Response Handbook for Chemical and Biological Agents and Weapons (2nd ed.). CRC Press. p. 216. ISBN 9781420052664.