Diboron tetrachloride

With apparatus and procedures of the type to be described, diboron tetrachloride production rates approaching 1.0 g./hour may be anticipated with a new reactor tube. Yields decrease with aging, but relatively long service with a production rate no lower than 0.20 to 0.50 g./hour can generally be relied upon. 

Since boron trichloride reacts with many lubricants to form hydrogen chloride, the diboron tetrachloride synthesis is carried out in a grease-free system. A mercury float-valve vacuum system4 depicted in Fig. 15 is employed here. The U-traps have a capacity of 50 ml. without plugging and tubes A and B have... 

Liquid diboron tetrachloride decomposes relatively rapidly at room temperature, quickly turning from colorless to dark red in the process. The decomposition rate is insignificant at —80°, and this temperature is recommended for long-term storage. 

Although thermally rather unstable at room temperature, liquid diboron tetrachloride decomposes relatively slowly at temperatures below 0°. In the gas phase, the substance may be exposed to ambient temperatures for periods as long as 5 to 10 minutes without the risk of appreciable deterioration. The colorless substance melts5 at —93.0° and its vapor pressures in the interval —63.5 to 22.5° are given by the equation 3... 

Owing to its extreme reactivity, diboron tetrachloride must always be handled in dry oxygen-free apparatus. Sudden exposure to air has been known to result in detonation. 

Feeney, Holliday, and Marsden reported that when diboron tetrachloride and isobutene were mixed in a molar ratio of approximately 1 2, without solvent at -78°, the isobutene was polymerised to a rubbery polymer. It is likely that adventitious water, or a reaction product of water and the B2C14, was the co-catalyst in this reaction [39]. 

Bromodiborane, 0159 l-Bromopentaborane(9), 0186 Chlorodiborane, 0160 B-Ch lorodimcthy laminodiboranc, 0962 Diboron tetrachloride, 0161 Diboron tetrafluoride, 0162 l,2-Dibromopentaborane(9), 0187 Iododiborane, 0165 Tetraboron tetrachloride, 0179 See related non-metal halides, non-metal hydrides... 

Di[bis(trifluoromethyl)phosphido]mercury, 1371 f Diborane(6), 0166a Diboron oxide, 0169 Diboron tetrachloride, 0161 Diboron tetrafluoride, 0162 Dibromine pentoxide, 0276 Dibromine trioxide, see Bromine bromate, 0275 Dibromoacetylene, 0579... 

Chloro-l,2,4-triselenadiazolium chloride, 4083 Chlorotetrafluorophosphorane, 3981 Diboron tetrachloride, 0161... 

B2C14 diboron tetrachloride (not BC12 boron(II) chloride)... 

The stereospecific cis-addition of diboron tetrachloride to alkynes and alkenes (37) may be interpreted as an interaction of the empty 7r-orbitals of the boron atoms with the 7r-orbital of the organic species. According to this picture, boron-boron bond breaking would lag behind boron-carbon bond formation. The transition state is a 4 + 2 Hiickel aromatic ( .=0), and thermal addition is allowed. If bond making and breaking were synchronous, this four-center reaction would be more like the <7-77 exchange reactions, which we shall discuss later. With regard to (37), there is a discrepant case in which an apparent trans addition of diboron tetrachloride to cyclopentadiene has been found (Saha et al., 1967). 

Holliday, A. K F. J. Marsden, and A. G. Massey The Reactions of Diboron Tetrachloride with Some Nitrogen-Containing Donor Molecules. J. Chem. Soc. 3348 (1961). 

Figure 5-23 Reactions of boron trihalides and diboron tetrachloride.

Diboron tetrachloride is obtained via electric discharge through BC13 in the presence of copper or mercury. In an important reaction, B2CLi readily adds across C=C double bonds to form bis(dichloroboiyl) products that can in turn be used to synthesize a variety of species (Fig. 5-23). 

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