Dielectric Relaxation of 2-Amino-l-butanol

Abstract

The dielectric relaxation spectrum of the title substance in mixtures with 1,4-dioxane or benzene (pure liquid to moderate mixture ratios) is measured between 5 MHz and 36 GHz at 20°C. The static permittivity is determined over the whole mixture range. The results are discussed in particular with respect to the possibility that different types of hydrogen bonded aggregations may contribute to the main relaxation.The 2-amino-l-butanol molecule offers several hydrogen bonding possibilities. One may expect intramolecular H-bonds as known for similar molecules indicates a correspondingly complex association behaviour by exhibiting a comparably broad main absorption region, which is just the region usually related to self-association, while the high frequency side of the spectrum resembles that normally found with alcohols, its moderate slope indicating subsequent but less intense relaxation contributions. There is no influence of the stereoisomeric composition on the spectrum [3]. It is a question whether the main absorption incorporates overlapping absorptions ascribable to dielectrically distinguishable types of self-association (so that its formal description by discrete spectral components rather than by a continuous distribution of relaxation times would be appropriate). Information in that respect may be gained from the eventual alteration of the relaxation spectrum on dilution of the alcohol by a nonpolar solvent. We have therefore studied the relaxation behaviour and the static dielectric properties of 2-aminol-butanol in mixtures with 1,4-dioxane and benzene.The absorption quantity e"(co) was measured at 10 spot frequencies ranging between 5 MHz and 36 GHz.Reprint requests to Prof. M. Stockhausen, Institut für Physikalische Chemie der Universität, Schloßplatz 4, W-4400 Münster (Germany).The temperature was 20 °C. For reasons of sensitivity the alcohol mole fraction x alc >0.4. The static permittivity e s , on the other hand, was measured over the whole mixture range (x alc >0.01), either at 1.5 kHz (with a Wayne-Kerr B330 bridge) or 5 MHz (with a Wayne-Kerr B 801B bridge), depending on the alcohol content being lower or higher than x alc « 0.4, respectively. The density g, viscosity A/ and refractive index n D were determined in addition.The E" (CO) data (after correction for the conductivity contribution) were fitted by a sum of discrete Debye type spectral components C ; . A minimum number of four components is necessary for satisfactory fits covering the experimental frequency range. Their parameters, i.e. relaxation times T ; and relaxation strengths are represented graphically in Figs, la and 1 b. The relaxation strenghts are normalized to the alcohol concentration, viz. S t c alc /c alc , the asterisk indicating the pure liquid. In Figs. 1 a, b the size of the symbols corresponds roughly to the acceptable variability range of the parameters (only the minor high frequency component C 4 is somewhat less accurately defined). From the static e s data we calculated the apparent dipole moment p app accordin...