Question

Which of the following reaction takes place at cathode in electro chemical manufacture of adiponitrile from acrylonitrile?

(a) H2O →2H^++\(\frac{1}{2}\) O2+ 2e^–

(b) 2CH2=CHCN+2H2 O+2e^–→NC – (CH2)4 – CN

(c) 2CH2=CHCN+2H2 O+2e^–→NC – (CH2)4 – CN+2OH^–

(d) 2CH2=CHCN+2H2 O→NC – (CH2)4 – CN+\(\frac{1}{2}\) O2

This question was addressed to me during a job interview.

The above asked question is from Inorganic Chemical in division Inorganic Chemical Industries of Chemical Technology

Answer 1

Correct option is (c) 2CH2=CHCN+2H2 O+2e^–→NC – (CH2)4 – CN+2OH^–

To explain I would say: Reaction H2O →2H^++\(\frac{1}{2}\) O2+ 2e^– takes place at anode since it is an oxidation reaction. In the reaction 2CH2=CHCN+2H2O + 2e^– → NC-(CH2)4-CN, charge is unbalanced. Reaction  2CH2=CHCN+2H2O+2e^–→NC-(CH2)4-CN+2OH^– takes place at cathode.