Methylidynephosphane

Methylidynephosphane (phosphaethyne) is a chemical compound with the chemical formula HC≡P. It was the first phosphaalkyne compound discovered, containing the unusual C≡P carbon-phosphorus triple bond. Although isolated samples of methylidynephosphane are impractical, other derivatives have been well studied such as tert-butylphosphaacetylene. The conjugate base of methylidynephosphane is cyaphide.

Methylidynephosphane is the phosphorus analogue of hydrogen cyanide, with the nitrile nitrogen replaced by phosphorus. Methylidynephosphane can be synthesized via the reaction of phosphine with carbon, but it is extremely reactive and polymerises readily at temperatures above −120 °C. However, several types of derivatives, with bulky groups, such as tert-butyl or trimethylsilyl, substituted for the hydrogen atom, are much more stable, and are useful reagents for the synthesis of various organophosphorus compounds. The [OCP]⁻ (cyaphate) and [SCP]⁻ (thiocyaphate) anions are also known.

HCP has been detected in the interstellar medium.

While the existence of the molecule had been discussed, and early attempts had been made to prepare it, methylidynephosphane was first successfully synthesised in 1961, by T.E. Gier of E. I. duPont de Nemours, Inc. Earlier reports of preparing its sodium salt were reported as unreproducible by Gier. Methylidynephosphane may have contributed to an explosion that killed Vera Bogdanovskaia, an early chemist pursuing it, one of the first female chemists in Russia, and perhaps the first woman to die from her own research.