Which of the following product(s) may be formed by the reaction of diborane with ammonia?
A
(BN)x
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B
3B2H6⋅2NH3
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C
B3N3H6
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D
B2H6⋅NH3
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Solution
The correct option is CB3N3H6 B2H6+NH3(excess)low temperature−−−−−−−−−→3B2H6.2NH3or[H2B(NH3)2]+[BH4]−
B2H6+NH3(excess)high temperature−−−−−−−−−−−−−−−−−−→Higher temperature (>200oC)(BN)Xboron nitride
B2H6+NH3high temperature(200^oC)−−−−−−−−−−−−−−−−→ratio2NH3:1B2H6B3N3H6borazine
Hence option option A, B and C are correct.
THEORY
Properties :
1. B2H6 is a colourless gas and highly toxic gas with boiling point 180 K.
2. Diborane catches fire spontaneously upon exposure to air. B2H6+3O2⟶B2O3+3H2O ΔcHo=–1976kJmol−1
It burns in oxygen releasing an enormous amount of energy. Most of the higher boranes are also spontaneously flammable in air.
3. Reacts with water to give boric acid B2H6+6H2O⟶2B(OH)3+6H2
Diborane is also hydrolysed by weaker acids (e.g. alcohols) or aqueous alkali B2H6+6ROH⟶2B(OR)3+6H2 B2H6+2KOH+2H2O⟶2KBO2+6H2
4. Diborane undergoes cleavage reactions with Lewis bases(L) to give borane adducts, BH3⋅L B2H6+2NMe3⟶2BH3.NMe3 B2H6+2CO⟶2BH3.CO
4. Reaction with ammonia 3B2H6+6NH3⟶6BH3.NH3 3[H2B(NH3)2]+[BH4]−↓2B3N3H6+12H2(Inorganic benzene
5. Reaction with ammonia B2H6+NH3(excess)low temperature−−−−−−−−−→B2H6.2NH3or[H2B(NH3)2]+[BH4]−
B2H6+NH3(excess)high temperature−−−−−−−−−−−−−−−−−−→Higher temperature (>200oC)(BN)Xboron nitride