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Question

Which of the following product(s) may be formed by the reaction of diborane with ammonia?

A
(BN)x
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B
3B2H62NH3
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C
B3N3H6
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D
B2H6NH3
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Solution

The correct option is C B3N3H6
B2H6+NH3(excess)low temperature−−−−−−−−3B2H6.2NH3 or [H2B(NH3)2]+[BH4]

B2H6+NH3(excess)high temperature−−−−−−−−−−−−−−−−−Higher temperature (>200oC)(BN)Xboron nitride

B2H6+NH3high temperature(200^oC)−−−−−−−−−−−−−−−ratio 2NH3:1B2H6B3N3H6borazine
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+3O2B2O3+3H2O
ΔcHo=1976 kJmol1
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+6H2O2B(OH)3+6H2
Diborane is also hydrolysed by weaker acids (e.g. alcohols) or aqueous alkali
B2H6+6ROH2B(OR)3+6H2
B2H6+2KOH+2H2O2KBO2+6H2

4. Diborane undergoes cleavage reactions with Lewis bases(L) to give borane adducts, BH3L
B2H6+2NMe32BH3.NMe3
B2H6+2CO2BH3.CO
4. Reaction with ammonia
3B2H6+6NH36BH3.NH3
3[H2B(NH3)2]+[BH4] 2B3N3H6+12H2(Inorganic benzene


5. Reaction with ammonia
B2H6+NH3(excess)low temperature−−−−−−−−B2H6.2NH3 or [H2B(NH3)2]+[BH4]

B2H6+NH3(excess)high temperature−−−−−−−−−−−−−−−−−Higher temperature (>200oC)(BN)Xboron nitride

B2H6+NH3high temperature(200^oC)−−−−−−−−−−−−−−−ratio 2NH3:1B2H6B3N3H6borazine

6. Reduction of diborane can be accomplished with Na or sodium borohydride
2B2H6+2NaNaBH4+NaB3H8
B2H6+NaBH4NaB3H8+H2

7. Li and Na react with B2H6 to give borohydrides.
B2H6+2MHDimethyl ether2M+[BH4]
M=Li, Na



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