p-Block Elements-I 1 Question 8
8. $\mathrm{B}(\mathrm{OH}){3}+\mathrm{NaOH} \rightleftharpoons \mathrm{NaBO}{2}+\mathrm{Na}\left[\mathrm{B}(\mathrm{OH}){4}\right]+\mathrm{H}{2} \mathrm{O}$
How can this reaction is made to proceed in forward direction?
(2006, 3M)
(a) Addition of cis 1, 2-diol
(b) Addition of borax
(c) Addition of trans 1, 2-diol
(d) Addition of $\mathrm{Na}{2} \mathrm{HPO}{4}$
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Answer:
Correct Answer: 8. (a)
Solution:
- Orthoboric acid is a very weak acid, direct neutralisation does not complete. However, addition of cis-diol allow the reaction to go to completion by forming a stable complex with $\left[\mathrm{B}(\mathrm{OH})_{4}\right]^{-}$as:
$$ \underset{\mathrm{HO}>\mathrm{BO} \backslash \mathrm{OH}+2 \underset{\mathrm{CH}{2}-\mathrm{OH}}{\mathrm{H}{\backslash} \mathrm{CH}{2}-\mathrm{OH}} \longrightarrow}{\underset{\mathrm{H}{2} \mathrm{C}-\mathrm{O}}{\mathrm{H}{2} \mathrm{C}-\mathrm{O}}>\mathrm{B} \backslash \mathrm{O}-\mathrm{CH}{2}+2 \mathrm{H}_{2} \mathrm{O}} $$
