Title: The mechanisms of thermal decomposition of diborane and of interconversion of the boranes
Abstract: Most previously proposed mechanisms for the pyrolysis of diborane rest on the assumed symmetric dissociation B2H6 ⇌ 2BH3, which as an equilibrium has never been observed. On exhaustive re-examination the existing evidence strongly implies that (under ordinary conditions) the initial act of decomposition is neither symmetric nor asymmetric fission, but 2B2H6 → BH3 + B3H9, followed so rapidly by BH3 + B2H6 → B3H9 that a measurable concentration of BH3 never builds up. The straight pyrolyses of B2H6, B4H10 and B5H11, the effect of H2 on the decomposition of each compound, the B2H6B4H10, B2H6B5H11 and B2H6B5H9 co-pyrolyses, the interconversion of the boranes and their behaviour in D and 10B isotope-exchange studies are all explained on the basis of a single unified mechanism as far as the appearance of B10H14. The paradox arising from an apparent conflict in the evidence regarding the first isolable intermediate in the pyrolysis of diborane, whether B4H10 or B5H11, is resolved in favour of the former. Interconversion reactions occur by the exchange of BH or BH3 (but never BH2) groups, or, in the case of hydrogen-rich species of formula type (BH)n(BH3)3, by splitting off BH3 molecules. Intermediates participate in condensation reactions in which normally H2 is released, but B3H9 appears to be the only species involved that splits off H2 spontaneously at moderate temperatures.
Publication Year: 1970
Publication Date: 1970-04-01
Language: en
Type: article
Indexed In: ['crossref']
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Cited By Count: 40
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