Nm. Correa et al., Binding of nitrodiphenylamines to reverse micelles of AOT in n-hexane and carbon tetrachloride: Solvent and substituent effects, J COLL I SC, 208(1), 1998, pp. 96-103
The absorption spectra of N-[2-(trifluoromethyl)-4-nitrophenyl]-4-nitroanil
ine (1), N-[4-nitrophenyl]-4-nitroaniline (2), and N-[2-nitrophenyl]-4-nitr
oaniline (3) were analyzed in reversed micelles of AOT (sodium 1,4-bis (2-e
thylhexyl sulfosuccinate) in n-hexane and carbon tetrachloride. For 1 and 2
the intensity of the band characteristic for the pure solvent decreases as
the AOT concentration increases and a new band develops. This new band is
attributed to the salute bound to the micelle. These changes allowed us to
determine the binding constant (Kb) between these compounds and AOT. Kb at
W-0 = [H2O]/[AOT] = 0 in n-hexane varies from 81 for I to 5092 for 2. Altho
ugh similar trends are observed for carbon tetrachloride, the values of Kb
are smaller than those for n-hexane. The possible salute-solvent interactio
ns of these compounds were analyzed by means of Taft and Kamlet's solvatoch
romic comparison method. The strength of binding is interpreted considering
their hydrogen-bond donor ability as well as their solubility in the pure
solvents. For 1 Kb decreases as W-0 is increased, while fdr 2 no variation
was observed. These effects are discussed in terms of nitrodiphenylamine-wa
ter competition for interfacial binding sites. Moreover, the effect of the
solute size and the presence of the trifluoromethyl group in 1 are importan
t factors to consider in explaining its binding behavior. The spectra of 3
change very little with AOT concentration and only a slight bathochromic sh
ift is observed. Thus, 3 acts as nonhydrogen bond donor solute, merely sens
ing a slight change in the polarity of its microenvironment. (C) 1998 Acade
mic Press.