Methyldichlorophosphine (alternatively known as dichloro(methyl)phosphane, SW and methylphosphonous dichloride) is an organophosphorus compound with the chemical formula CH3PCl2.

Methyldichlorophosphine is produced by alkylation of phosphorus trichloride with methyl iodide followed by reduction of the resulting phosphonium salt with iron powder:[2][3] The compound is an intermediate for the synthesis of other chemicals for instance dimethylphenylphosphine.

Methyldichlorophosphine belongs to the group of halophosphines, some of which are used as intermediates in the production of plant protection agents, stabilizers for plastics, and catalysts.

[4] Due to the recycling problem of phosphoryl chloride, SW was adopted in step three of the DMHP process in the preparation of Sarin.

[6] It is also toxic if inhaled, can cause burns upon contact with the skin and eyes, and releases fumes of hydrochloric acid in moist environments.