a_bab
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Boron tribromide?
What would be the best way of reducing BBr3 to elementary boron?
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bbartlog
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Reduction with hydrogen at elevated temperature. Sounds tricky, methinks you would need a nice tube furnace (with semi-disposable tube since your
boron would end up deposited on it), multiple gas flow regulators including one that could handle the tribromide, and some sort of multi-stage
cooler/condenser/gas capture stage to deal with the HBr and unreacted tribromide. Unless this were a project you'd be attempting for its own sake I'd
just keep the BBr3 (useful in its own right) and order the boron.
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a_bab
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Oh, but I don't plan to do the reduction.
I know BBr3 is very toxic, besides I will never have my hands on it. I was just wondering how is used in electronic semiconductors (pre-deposition).
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JohnWW
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BBr3 (and similarly BCl3) is too valuable as a reagent to be simply reduced in bulk to B, although its reduction to a finely-divided form of B may
make it a useful intermediate in the production of "doped" high-band-gap diamond semiconductors (which are still largely experimental and costly). It
could be used to make organoboron compounds by reaction with Grignard reagents; and to make covalent esters of boric acid by reaction with alcohols or
phenols. Production of acyl bromides (which could then be used in acylations) by reaction with carboxylic acids, and some organic bromination
reactions, are also possibilities.
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not_important
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Reducing a mixture of H2 and BBr3 on a hot W or Ta filament is one way of getting high purity crystalline boron.
However for semiconductor doping the boron halides or B2H6 are used as such, low pressure gas phase generally diluted with inert gas. and/or H2. It
doesn't take much, dopant levels are generally in the range of one dopant atom per 10<sup>4</sup> to 10<sup>8</sup> atoms of
Si or Ge.
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