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Q.
Hydrogen peroxide is now generally prepared on industrial scale by the
Hydrogen
Solution:
Industrial preparation of $H_2O_2$:
(A) By the electrolysis of $50\%$ $H_2SO_4: 50\% H_2SO_4$ solution is electrolysed at $0^{\circ}$C between $Pt$ electrodes. The per disulphuric acid is formed.
$H_2SO_4 \rightleftharpoons H^+ + HSO_4^-$
At Anode : $2HSO^-_4 \rightarrow H_2S_2O_8 + 2e$
At Cathode : $2H^+ + 2e \rightarrow H_2$
The obtained per disulphuric acid gives $H_2O_2$ on hydrolysis.
$H_2S_2O_8 + 2H_2O \rightleftharpoons H_2O_2 + 2H_2SO_4$
This $H_2O_2$ is separated by distillation at reduced pressure and thus, $30\%$ solution of $H_2O_2$ is obtained.
(B) By the auto-oxidation of $2$-ethyl-anthraquinol (Modem method): Anthraquinol, in a mixture of benzene and $n$-heptanol on treatment with air gives $H_2O_2$ and $2$-ethyl-anthraquinone. This $2$-ethyl-anthraquinone on hydrogenation gives $2$ anthraquinol in presence of $Pd$ catalyst.
It is a cyclic process and it only $H_2$ is consumed, $2$-ethyl-anthraquinone is reobtained during reaction.
