POLAROGRAPHIC HALF-WAVE POTENTIALS OF SOME Β-Nitrostyrenes AND RELATED COMPOUNDS

Abstract

The polarographic half-wave potentials of a number of 8-nitrostyrenes, p-nitropropenylbenzenes, and p-nitrobutenylbenze~les havc been determined in aqueous ethanolic solution a t an apparent pH of 6.54. A linear relationship exists between these values and Ilammett sigma constants, but not with their ultraviolet absorption maxima or with their dipole moments.The polarographic wave of 11 diethyl benzaln~alonates, under the same conditions, was masked by the hydrogen wave.Nitro groups are reducible a t the dropping-mercury cathode, and their half-\\rave depend upon the solvent%nd upon ~vhether it is a n isolated or an aro~natic llitro group. Holleck and Ja~lllalcoudalcis (2) state that the nitro group of ,&nitrostyrene sho\vs some properties characteristic of the above tn-o classes.In an acid rnediunl nitroalkanes exhibit 011ly one polarographic wave, which varies little with PI-I (-0.75 to -0.89 V over a range of 3 pIH units) ; a t PI-I 4.3 a second \\rave starts a t -1.5 V which is obscured by the hydrogen wave (1). In an alkaline medium the diffusion current of the nitroallcanes falls with time because of equilibration with the non-reducible aci-form (1). Reduction of the nitro group a t the dropping-mercury electrode is an irreversible, four-electron process which leads to the respective hydroxylamine. The second wave, a t more negative potentials, involves the reduction of the alkylhydroxylammonium ion to the al1;ylamnlonium ion and is a t\vo-electron process (I).Aromatic nitro compounds, except for the o-and p-nitroanilines, the o-and p-nitrophenols, and the o-and 9-dinitrobenzenes, behave siinilarly, except that the half-wave changes linearly with pH over a t least part of the pH scale. At pH < 5 nitrobenzene gives two waves involving four electrons and two electrons to give the respective -phenylhydroxyla~~~ine and The exceptions noted above are abnormal, because the resulting phenylhydroxylamine can lose water t o give a reducible quinonoid structure (1, 3). Illtroduction of one or two methyl groups into the benzene ring has little effect upon the half-wave potential of the nitrobenzene unless the two methyl groups are both ortho to the nitro group (see Table 11); when the half-\\rave potential is shifted to lllore negative values (I). Such effects are noted when the functional group, such as nitro, can -undergo a marlied meso~llerisn~ with the aromatic ring, and \\rhen both the functional group and the ortho substitrlents are bulky (1,4). The nitro group then should, and does, behave more like an aliphatic nitro group toward polarographic reduction (I). I t has been stated (4) that differences in the half-wave potentials of ortho-and para-substituted ~nembers of this series give an insight into the nature and extent of certain types of ortho 'Issued as Szifield Teclmical Paper No. 319,

Polarographic half-wave potentials and ultraviolet absorption spectra of some conjugated heteroenoid compounds

“…Half-wave potentials were obtained for the terephthalylidene derivatives of some active methylene compounds, 2 (Table VI). The tetracarbethoxy compound (2) has a half-wave potential much less negative than that of diethyl benzalmalonate (11) (E+ 2 -1.4 V) (9), and even less than that of diethyl cinnamylidenemalonate (3). This is not the case for the related meta isomer of 2 (E+ 2 -1.4 V).…”

“…This note discusses the effect of phenyl substituents, and non-aqueous media has been examined by and Marciszewski (6) has reduced methyl 1-methylbutylidenecyanoacetate. In this work, the reduction of these compounds (7,s) was carried out under conditions similar to those used by Silver and Holmes (9). In all but a few cases single waves were obtained (Tables I and 11).…”

Organic polarography

“…Correlations involving polarographic data have been described. Data for 7-nitro-p-terphenyl and related compounds were correlated to charge transfer frequencies and parameters arising from elementary molecular orbital theory (469); for m-, p-, and o-substituted nitrobenzenes to Hammett values (482); and for ß-nitrostyrene, ß-nitropropenylbenzene, and ß-nitrobutenylbenzene de-rivatives to Hammett values (1183). Correlations to UV absorption maxima or dipole moments were not successful in the latter studies.…”

Synthesis and chemical reactions of some conjugated heteroenoid compounds

“…The methods of synthesis of these compounds, their melting and (or) boiling points, and their analytical figures, where necessary, are listed in Tables I-XXIX.2 The compounds listed in the individual tables are summarized in Table XXXIV ring and with changes in the A and B groups. This led to an in vitro study of the rates of reaction of these compounds with potassium cyanide and with the nucleophilic models n-butanethio13 and n-butylamine (I), and to the determination of their halfwave potentials (2), partition coefficients (3), and ultraviolet, infrared, and nuclear magnetic resonance spectral properties. This work has shed some light not only on the mode of action of these compounds but also on the effects of steric factors upon their biological actisties.…”