Tetrachlorodiborane 4 Diboron Tetrachloride

Tetrachlorodiborane(4) was first reported in 1925 by Stock, who prepared the compound by striking an arc between zinc electrodes in liquid boron trichloride.1 Better yields have been obtained by later workers using boron trichloride in the vapor phase and an electrical discharge between mercury2 or copper electrodes..3 However, the rate of formation of tetrachlorodiborane(4) is low, at best about 1.0 g/hr. 

Copper is best evaporated from an alumina crucible of 2-5 mL capacity, resistance heated either by an external molybdenum or tungsten wire spiral or, preferably, by imbedded molybdenum or tungsten wire (See Sec. 11). If the crucible is insulated with a 10-mm layer of a refractory wool, for example, Kaowool (see Sec. 11), a power input of 180-250 W will heat the crucible to 1400° and evaporate the copper. The power required to give the desired rate of evaporation has to be determined for a new crucible by a trial evaporation in the absence of BC13. The volt and amp settings then found should be valid for many runs with the same crucible. An ordinary grade of soft copper rod is satisfactory 

To carry out a preparation of B2C14, the crucible is charged with 12-15 g of 

The boron trichloride can be reused in the experiment with only brief pumping at its melting point to remove excessive amounts of HC1. Traces of B2CU left in the BC13 have no adverse effects in subsequent runs. The reactor should be filled with nitrogen after all volatiles have been pumped out, opened to the air, and quickly put into a fume hood. The residues containing Cu, CuCl, and traces of boron chlorides, may fume slightly in air but they are not pyrophoric. 

in Cryochemistry, M. Moskovits and G. A. Ozin (eds), John Wiley Sons, Inc., New York, 1976, Chap. 3. 

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Diboron Tetrachloride. Tetrachlorodiborane(4) boron chloride. BX), mol wt 163,41, B 13,24%, Cl 86.16%, Prepd by passing gaseous boron trichloride through flow discharge between mercury or copper electrodes Urry cl al, J. Am. Client. Soc. 76, 5293 (1954) Wartik er al, If.org. Syn. 10, 118 (1967) hy passing boron trichloride vapor over boron monoxide at 200 McCloskey et aL, J, Am. Chem Soc. 93, 4750 (1961). Infrared and Raman spectra Linev-sky el al, J. Am Chem. Soc. 7S, 3287 (1953). Review of boron halides Massey, Advan. Inorg. Chem Radiockem 10, 1-152 (1967). 

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