Methylphosphonyl dichloride explained

Methylphosphonyl dichloride (DC) or dichloro is an organophosphorus compound. It has a number of commercial uses but is most notable as being a precursor to several chemical weapons agents. It is a white crystalline solid that melts slightly above room temperature.^[1]

Synthesis and reactions

Methylphosphonyl dichloride is produced by oxidation of methyldichlorophosphine, with sulfuryl chloride:^[2]

CH₃PCl₂ + SO₂Cl₂ → CH₃P(O)Cl₂ + SOCl₂

It can also be produced from a range of methylphosphonates (e.g. dimethyl methylphosphonate) via chlorination with thionyl chloride. Various amines catalyse this process.^[3] With hydrogen fluoride or sodium fluoride, it can be used to produce methylphosphonyl difluoride. With alcohols, it converts to the dialkoxide:^[4]

CH₃P(O)Cl₂ + 2HOR → CH₃P(O)(OR)₂ + HCl

Safety

Methylphosphonyl dichloride is very toxic and reacts vigorously with water to release hydrochloric acid. It is also listed under Schedule 2 of the Chemical Weapons Convention as it is used in the production of organophosphorus nerve agents such as sarin and soman.

Notes and References

1. Web site: June 26, 2020 . SAFETY DATA SHEET Methylphosphonic dichloride . April 27, 2022 . SAFETY DATA SHEET Methylphosphonic dichloride . MilliporeSigma.
2. Svara, J.; Weferling, N.; Hofmann, T. "Phosphorus Compounds, Organic," In 'Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2008. .
3. Maier. Ludwig. Organic Phosphorus Compounds 90.l A Convenient, One-Step Synthesis of Alkyl- and Arylphosphonyl Dichlorides. Phosphorus, Sulfur, and Silicon and the Related Elements. 1990. 47. 3–4. 465–470. 10.1080/10426509008038002.
4. 10.15227/orgsyn.073.0152. Bis(Trifluoroethyl) (carboethoxymethyl)phosphonate. Organic Syntheses. 1996. 73. 152. Carl Patois, Philippe Savignac, Elie About-Jaudet, Noël Collignon.