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Direct and alternating current polarography of nitrobenzene in aqueous solutions and in acetonitrile Kleinerman, Marcos Yusim


The polarographic reduction of nitrobenzene in aqueous buffered solutions, and that of nitrobenzene and o-nitrophenol in anhydrous acetonitrile was investigated. Alternating current polarography was: used in addition to "conventional” polarography for the work done with aqueous solutions. Non-reducible surface-active agents, e. g. Triton X-100, split the d. c. waves of nitrobenzene in basic and neutral solutions, in two parts, the total current remaining nearly the same as in absence of the surface-active agent. The a. c. wave corresponding to the first step of the split d. c. wave becomes larger as the d. c. wave becomes smaller with increasing concentration of the surface-active agent. A limiting ratio of 1:3 is obtained for the heights of the two resulting d. c. waves in basic solution in presence of sufficient amount of the surface-active agent, and the height of the a. c. wave corresponding to the first d. c. step reaches its maximum value. In acid solution no splitting occurs, but the d. c. wave is shifted to more negative potentials. The a. c. wave does not become larger. The results are interpreted by postulating a mechanism for the reduction of nitrobenzene involving the initial formation of the semi-quinone PhNO, whose stability toward further reduction increases with the pH of the solution and with the concentration of the surface-active agent. The latter hinders the reduction of the semi-quinone by forming a film at the mercury/solution interface by adsorption. Application of Delahay's theory of irreversible polarographic waves is made, and some of its shortcomings are discussed. In anhydrous acetonitrile nitrobenzene and o-nitrophenol are reduced stepwise, and their behaviour resembles that of nitrobenzene and several other aromatic nitro-compounds in aqueous basic solution in presence of surface-active substances.

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