Pyrolysis of diborane

G in the presence of a catalytic amount of a Lewis base such as dimethylether, (GH2)20. In addition to the gas-phase pyrolysis of diborane, can be prepared by a solution-phase process developed at Union Garbide Gorp. Decaborane is a key intermediate in the preparation of many carboranes and metaHa derivatives. As of this writing, this important compound is not manufactured on a large scale in the western world and is in short supply. Prices for decaborane in 1991 were up to 10,000/kg. 

Boron is also obtained by the pyrolysis of diborane. Only moderate temperature is required (400-900°C) with a pressure up to 1 atm [6][7]... 

At about the same time, the pyrolysis of diborane was studied by Bragg et al.88 in the temperature range 90-130 °C. These workers again used a static system (reaction vessel volume 212 cm3) and followed the conversion both by measurement of pressure increase and by determination of the amount of hydrogen formed. The system was also examined by mass spectrometric analysis. The empirical rate law was found to be... 

Diborane. Se. Vol 2, p B253-R, under Boron Hydrides and p B255-L, under Boron Hydride Fuels. See also the following addnl Refs Refs 1) F.R. Price, JACS 72, 5361-65 (1950) 8e CA 45, 2755(1951)(First 8e 2nd pressure limits of espln of Diborane-Oxygen tnixts) 2) R.P. Clarke R.N. Pease, JACS 73, 2132-34(1951) 8s CA 45, 7418(1951) (Kinetics of pyrolysis of Diborane) 3) J-K-Bragg et al, JACS 73, 2134-40(1951) 8s CA 45, 7418(l951)(Kinetics of pyrolysis of Diborane) 4) A.T. Whatley 8s R.N. Pease, JACS 76, 1997-99(1954) 8s CA 48. 8543(1954) (Thermal expln of Diborane-oxygen mixts)... 

In the decade after 1951, when the ecurliest kinetic studies (27, 52) established that the ratedetermining step in the pyrolysis of diborane is of order 1.5 and has an activation energy of approximately 27 kcal mole , further detailed investigations of the mechanism of interconversion of the boranes were reported by various workers (46, 143, 226, 227, 266, 267), of whom Riley Schaeffer may be singled out for special mention. Since then further publications have been so numerous that only a brief summary can be given here. In nearly every case the mechanistic conclusions are based on the assumption that the initial step is a reversible one, namely. 

Figure 2. The first products of pyrolysis of diborane at 111°C gas-chromatogram peak areas plotted against time (after Borer et al., Ref. 26).

Plasma dissociation of gaseous B2H6 leads to the formation of BH2, which may be observed by intracavity laser spectroscopy. The observations, however, do not establish whether the BH2 is formed directly from B2H6 or results solely from secondary chemistry [6]. Pyrolysis studies have not answered this question, although a recent computational study has probed the early stages of B2H6 pyrolysis using many-body perturbation theory (MBPT) and the coupled-cluster approximation. The study considers two elementary processes which are viewed as key steps in the pyrolysis of diborane [7] ... 

The first reported synthesis of catalyst-free boron nanoribbons was in the year 2004 by Xu et al. a-Tetragonal, single-crystal growth of boron nanoribbons was observed via this low-temperature (630-750°C) and low-pressure (200 mTorr) pyrolysis of diborane gas. A puffy ball like growth was found on the silicon substrate at the aforanentioned tanperature zone of the furnace (Figure 20.8a). The SEM and TEM studies disclosed the typical width of the nanoribbons to be about 800-3200 nm and thickness about 15-20 nm (Figure 20.8b). 

FIGURE 20.8 SEM image of boron nanoribbons formed through (a) pyrolysis of diborane gas ( puffy ball ) (b) pyrolysis of diborane gas ( grass-like ) (Adapted from Xu, T. T. et al., Nano Lett., 2004, 4, 963-968.) and (c) the chemical vapor deposition method. (Adapted from Jash, P. and Trenary, M. Journal of Physics Conference Series, 2009,176, 012011(1-11).)... 

Croft (26) has obtained high-purity boron films by pyrolysis of diborane. 

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