Diboron tetrachloride

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

Diboron tetrachloride

Names
Preferred IUPAC name Diboron tetrachloride
Systematic IUPAC name Tetrachlorodiborane(4)
Identifiers
CAS Number	13701-67-2 Y
3D model (JSmol)	Interactive image
ChemSpider	123068
PubChem CID	139548
UNII	3KKJ90L3I5 Y
CompTox Dashboard (EPA)	DTXSID40160031
InChI InChI=1S/B2Cl4/c3-1(4)2(5)6 Key: LCWVIHDXYOFGEG-UHFFFAOYSA-N InChI=1S/B2Cl4/c3-1(4)2(5)6 Key: LCWVIHDXYOFGEG-UHFFFAOYAN
SMILES ClB(Cl)B(Cl)Cl
Properties
Chemical formula	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)	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⦵)	−468.8 kJ/mol
Related compounds
Related compounds	Diboron tetrafluoride
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa). Infobox references

Synthesis

The modern synthesis involves dechlorination of boron trichloride using copper.^{[2][better source needed]}

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]

Reactions

The compound is used as a reagent for the synthesis of organoboron compounds. For instance, diboron tetrachloride adds to ethylene:^[5]

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]