Question

Which of the following reactions can be used to prepare diborane?
I) $\ce{BF_3 + LiAlH_4 ->[ether]}$
II) $\ce{BF_3 + NaH ->[450 k]}$
III) $\ce{Na_2B_4O_7 + H_2O -> }$
IV) $\ce{ NaBH_4 + I_2 ->}$

• A. I, II , III
• B. II , III only
• C. III , IV only
• D. I, II , IV

Answer 1

Answer: (D)

Following reactions are used for the preparation of diborane:

$ (I) 4BF_3 + 3Li AlH_4 \ce{->[\text{Diethyl ether}]} \underset{\text{Diborane}}{2B_2H_6} + 3LiF + 3AlF_3$

$(II) 2BF_3 + 6NaH \ce{->[450\,K]} \underset{\text{Diborane}}{B_2H_6} + 6NaF$

(Industrial method)

$(IV) 2NaBH_4 + I_2 \ce{->[\text{DIGLYME}(MeOCH)2CH_2)O_2]}$

$\underset{\text{Diborane}}{B_2H_6} + \underset{\text{(Lab method)}}{2NaI + H_2} \uparrow$

Reaction $(III)$ is used for the preparation of boric acid. i.e.,

$Na_2B_4O_7 + 7H_2O \ce{<=>} 2NaOH + \underset{\text{Boric acid}}{4H_3BO_3}$