Question

What is Tollen's reagent? Write the chemical equation of its reaction with glucose.

Hint:

Tollen's tests for \(-\)CHO groups; glucose is reducing and gives a bright silver mirror due to \(\mathrm{Ag^+ \rightarrow Ag^0}\).

Answer 1

Tollen's reagent: Ammoniacal silver nitrate containing the complex ion \([\mathrm{Ag(NH_3)_2}]^+\) (often represented as \([\mathrm{Ag(NH_3)_2}]\mathrm{OH}\)); it oxidises aldehydes to carboxylates giving a silver mirror.
With glucose:
\[ \mathrm{C_6H_{12}O_6} + 2\,[\mathrm{Ag(NH_3)_2}]^+ + 3\,\mathrm{OH^-} \longrightarrow \mathrm{C_6H_{11}O_6^-} + 2\,\mathrm{Ag(s)} + 4\,\mathrm{NH_3} + 2\,\mathrm{H_2O} \] On acidification: \(\mathrm{C_6H_{11}O_6^- \rightarrow C_6H_{12}O_7}\) (gluconic acid).