Question

$B( OH )_{3}+ NaOH \rightleftharpoons NaBO _{2}+ Na \left[ B ( OH )_{4}\right]+ H _{2} O$
How can this reaction be made to proceed in forward direction?

• A. addition of cis-$1,2$-diol.
• B. addition of borax.
• C. addition of trans-$1,2$-diol.
• D. addition of $Na _{2} HPO _{4}$.

Answer 1

Answer: (A)

The given reaction is a reversible reaction. The sodium metaborate formed gets hydrolysed to regenerate boron trihydroxide and $NaOH$.
$B( OH )_{3}+ NaOH \rightleftharpoons NaBO _{2}+ Na \left[ B ( OH )_{4}\right]+ H _{2} O$
In the presence of polyhydroxy compounds such as cis-$1, 2$-diol or glycerol, boron trihydroxide forms chelated complex (ring-structure) of higher stability. So on addition of cis-$1,2$- diol, due to the formation of this stable complex, the reaction proceeds in the forward direction.