Discussion
The major product formed from the reaction between B2H6 and two equivalents of NH3 at 300 ℃ is
Answer: D
At 300 ℃ the product is borazine, (HBNH)3.
Diborane and ammonia first combine at low temperature, but on heating the adduct loses hydrogen and the B-N units close into a six-membered ring of alternating boron and nitrogen atoms, the 'inorganic benzene':
\[ \begin{aligned} &3\text{B}_{2}\text{H}_{6} + 6\text{NH}_{3} \\ &\rightarrow 2\text{B}_{3}\text{N}_{3}\text{H}_{6} + 12\text{H}_{2} \end{aligned} \]
The ratio of one diborane to two ammonia is exactly the one this equation uses.
The other options are species met at low temperature. Diborane and ammonia in the cold give the ionic diammoniate of diborane, formed by unsymmetrical cleavage of the B-H-B bridges; ammonia borane, BH3·NH3, is the simple Lewis adduct; and [NH4]+[BH4]− is a salt-like hydride. All of these lose hydrogen on heating, and at 300 ℃ that dehydrogenation ends in the borazine ring.
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