Diboron tetrachloride
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| Names | |||
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| Preferred IUPAC name
Diboron tetrachloride | |||
| Systematic IUPAC name
Tetrachlorodiborane(4) | |||
| Identifiers | |||
3D model (JSmol)
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PubChem CID
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| UNII | |||
CompTox Dashboard (EPA)
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| Properties | |||
| B2Cl4 | |||
| Molar mass | 163.42 g·mol−1 | ||
| Appearance | colorless liquid | ||
| Density | 1.5 g/cm3 (0 °C) | ||
| Melting point | −92.6 °C (−134.7 °F; 180.6 K) | ||
| Boiling point | 65.5 °C (149.9 °F; 338.6 K) | ||
| Thermochemistry | |||
Heat capacity (C)
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137.7 J/mol K | ||
Std molar
entropy (S⦵298) |
232.3 J/mol K | ||
Std enthalpy of
formation (ΔfH⦵298) |
−523 kJ/mol | ||
Gibbs free energy (ΔfG⦵)
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−468.8 kJ/mol | ||
| Related compounds | |||
Related compounds
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Diboron tetrafluoride | ||
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Diboron tetrachloride is a tetrahalodiborane chemical compound with the formula B2Cl4. It is a colorless liquid.[1]
Synthesis
[edit | edit source]The modern synthesis involves the chlorination of diboron tetrabromide by gallium(III) chloride.[2]
It can also be formed by the electrical discharge procedure of boron trichloride at low temperatures:[1][3]
- BCl3 → BCl2 + Cl
- Cl + Hg (electrode) → Hg2Cl2 or HgCl2
- 2 BCl2 → B2Cl4
The most efficient synthesis technique uses no dechlorinating metal, instead passing radio-frequency AC current through gaseous boron trichloride.[4]
Structure
[edit | edit source]The molecular structure of diboron tetrachloride, B2Cl4, was determined by gas electron diffraction.[5] The molecules have D2d symmetry, i.e. the two planar BBCl2 units are perpendicular to each other (torsion angle Cl-B-B-Cl 90°). The B-B distance is 1.70(4) Å, the B-Cl distance is 1.750(5) Å, the Cl-B-Cl angle is 118.7(3)°. B2Cl4 thus differs significantly from B2F4, which is a planar molecule overall.
Reactions
[edit | edit source]The compound is used as a reagent for the synthesis of organoboron compounds. For instance, diboron tetrachloride adds to ethylene:[6]
- CH2=CH2 + B2Cl4 → Cl2B–CH2–CH2–BCl2
Diboron tetrachloride absorbs hydrogen quickly at room temperature:[3]
- 3 B2Cl4 + 3 H2 → B2H6 + 4 BCl3
With 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.[4]
References
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