Diboron tetrachloride explained

Diboron tetrachloride is a chemical compound with the formula B₂Cl₄. It is a colorless liquid.^[1]

Synthesis

The modern synthesis involves dechlorination of boron trichloride using copper.^[2]

It can also be formed by the electrical discharge procedure of boron trichloride at low temperatures:

BCl₃ → BCl₂ + Cl

Cl + Hg (electrode) → HgCl or HgCl₂

2 BCl₂ → B₂Cl₄The most efficient synthesis technique uses no dechlorinating metal, instead passing radio-frequency AC current through gaseous boron trichloride.^[3]

Reactions

The compound is used as a reagent for the synthesis of organoboron compounds. For instance, diboron tetrachloride adds to ethylene:^[4]

CH₂=CH₂ + B₂Cl₄ → Cl₂B–CH₂–CH₂–BCl₂

Diboron tetrachloride absorbs hydrogen quickly at room temperature:^[5]

3 B₂Cl₄ + 3 H₂ → B₂H₆ + 4 BCl₃With boranes, it replaces a hydrogen to form dichloroborane(3) and a polyhedral dichloroborane. Heat induces disproportionation back to boron trichloride and a polyhedral boron(I) chloride.

Notes and References

1. Book: Advances in Inorganic Chemistry and Radiochemistry. Low Temperature Condensation. P. L. Timms. 143. 1972. Academic Press . 0-12-023614-1.
2. Book: 10.1002/9780470132500.ch14. Tetrachlorodiborane(4) (Diboron Tetrachloride). 74–78. 1979. 19. Timms. Peter L.. Inorganic Syntheses. 9780470132500.
3. Morrison . John A. . 1991-01-01 . Chemistry of the polyhedral boron halides and the diboron tetrahalides . Chemical Reviews . en . 91 . 1 . 35–48 . 10.1021/cr00001a003 . 0009-2665.
4. Urry. Grant. Kerrigan. James. Parsons. Theran D.. Schlesinger. H. I.. Diboron Tetrachloride, B₂Cl₄, as a Reagent for the Synthesis of Organo-boron Compounds. I. The Reaction of Diboron Tetrachloride with Ethylene. Journal of the American Chemical Society. 76. 21. 1954. 5299–5301. 0002-7863. 10.1021/ja01650a011.
5. Urry. Grant. Wartik. Thomas. Moore. R. E.. Schlesinger. H. I.. The Preparation and Some of the Properties of Diboron Tetrachloride, B₂Cl₄. Journal of the American Chemical Society. 76. 21. 1954. 5293–5298. 0002-7863. 10.1021/ja01650a010.