A Polarographic Investigation of the Pseudo Acid Properties of Nitroparaffins¹

Abstract

The nitroparaffins have long been recognized as pseudo acids. They dissolve in alkaline solution through the formation of salts according to the equation This neutralization is a relatively slow process and the rates of neutralization by different bases have been investigated by Maron and La Mer3 and more recently by P e a r~o n .~ In both investigations the reaction rate was followed conductometrically.De Vries and Ivett5 reported that the wave heights for the reduction of nitroparaffins were proportional to the concentration of the nitroparaffin when 0.05 mo1a.r sulfuric acid was used as the supporting electrol.yte but that this relationship was not linear when 0.05 molar sodium sulfate was used in place of sulfuric acid. When sodium sulfate was used as the supporting electrolyte the @H increased as the reduction progressed because hydrogen ions were used up in the reduction process. This increase in @H caused a shift in the equilibrium between the normal and aci-forms of the nitroparaffin in favor of the aci-form which was not reducible a t the dropping mercury cathode. As the concentration of the nitroparaffin was increased the pH became still greater resulting in still more of the aci-nitroparaffin being formed and consequently the wave height was not proportional to concentration. The nitroparaffins could not be reduced in 0.1 N sodium hydroxide or 0.1 N tetramethylammonium hydroxide. This investiga-R-CHzNOz -t OH-+ R-CH-NO2-+ Hz0(1) Presented before the Division

Molecular Size Effects in the Kinetics of the Electroreduction of Nitroalkanes on Mercury

“…As long as the limiting current is diffusion controlled (d E~/d pH)= (d E/d pH)i,C' Results given in the literature over a wide range of pH (2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12) indicate that the reaction order changes with pH in an S shaped manner [19]. It approaches zero in both acid and alkali and has a value close to unity near the inflection point.…”

“…In acid media only the first wave can be observed. The disappearance of both waves in alkaline media is explained by the formation of the aci-form R, R 2CHN02 --+ R , R 2 C = NOOH, which cannot be reduced in the same potential region [2,3].…”

Polarographic Study of Lower Nitroparaffins in Nonalkaline Media

“…That the type and strength of supporting electrolyte used in polarographic work involving the nitroparaffins have a decided effect on their half-wave potentials can readily be seen by comparing the results presented in this paper with those of Petru (10) and Miller eí al. (9). Solutions used by the former were mentioned at the beginning of this paper.…”

“…A polarographic method for estimating the amount of nitromethane in air has recently been developed (11), but here again unbuffered solutions were used. The pseudo acid properties of some nitroparaffins, including the determination of rates of nitro-aci tautomerism in buffered alkaline solutions, have been polarographically investigated (9). The only other study of the polarographic reduction of nitroparaffins in buffered solutions has been that of Petru (10), using 30% methanol solutions in Britton-Robinson buffers (2).…”

A Polarographic Study of Nitro Compounds

“…This small diffusion current was assigned to the equilibrium state between the reducible nitro compound and the non-reducible anion or '-form which existed at the pH used. The rates of conversion of nitroparaffins and the positions of the equilibria were studied rather thoroughly by Miller, et al (3).…”