Methylphosphonyl dichloride explained

Methylphosphonyl dichloride (DC) or dichloro is an organophosphorus compound. It has commercial application in oligonucleotide synthesis,^[1] 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.^[2]

Synthesis and reactions

Methylphosphonyl dichloride is produced by oxidation of methyldichlorophosphine, with sulfuryl chloride:^[3]

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.^[4] With hydrogen fluoride or sodium fluoride, it can be used to produce methylphosphonyl difluoride. With alcohols, it converts to the dialkoxide:^[5]

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. p. 871. As cited in HSDB.
2. Web site: June 26, 2020 . SAFETY DATA SHEET Methylphosphonic dichloride . April 27, 2022 . SAFETY DATA SHEET Methylphosphonic dichloride . MilliporeSigma.
3. Svara, J.; Weferling, N.; Hofmann, T. "Phosphorus Compounds, Organic," In 'Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2008. .
4. 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.
5. 10.15227/orgsyn.073.0152. Bis(Trifluoroethyl) (carboethoxymethyl)phosphonate. Organic Syntheses. 1996. 73. 152. Carl Patois, Philippe Savignac, Elie About-Jaudet, Noël Collignon.