Manabu Ohira

Raman and infrared spectra of polyaniline

Abstract The structure of polyaniline has been determined by Raman and infrared spectroscopy. The polyaniline prepared by the chemical or electrochemical oxidation of aniline in acidic media consists of reduced repeat units [−C 6 H 4 NHC 6 H 4 NH−] and protonated oxidized repeat units [−C 6 H 4 NC 6 H 4 N + H−]. A − or [−C 6 H 4 N + HC 6 H 4 N + H−]. 2A − , where A − is a dopant. Alkali treatment dedopes the protonated oxidized repeat units, while electrochemical reduction converts the oxidized repeat units to the reduced repeat units. The highly reduced polyaniline is sensitive to air and the reduced repeat units are changed to the oxidized repeat units [−C 6 H 4 NC 6 H 4 N−] by exposure to air.

THERMODYNAMIC STUDY OF THE AGGREGATION OF AZO DYES CONTAINING TWO TRIFLUOROMETHYL GROUPS IN AQUEOUS SOLUTIONS

The aggregation behaviour of azo dyes containing two trifluoromethyl groups, sodium 5-(3,5-bistrifluoromethyl-phenylazo)-6-hydroxynaphthalene-2-sulfonate, 1, and disodium 4-(3,5-bistrifluoromethylphenylazo)-3-hydroxy-naphthalene-2,7-disulfonate, 3, in aqueous solutions has been investigated by 19F NMR and visible absorption spectroscopy. The visible absorption spectra of the corresponding azo dyes containing two methyl groups, sodium 5-(3,5-dimethylphenylazo)-6-hydroxynaphthalene-2-sulfonate, 2, and disodium 4-(3,5-dimethylphenylazo)-3-hydroxynaphthalene-2,7-disulfonate, 4, in aqueous solutions have also been measured. From the visible absorption spectra, the aggregation number has been estimated to be 2 for all the dyes in the concentration region under examination (1 × 10–5 to 1 × 10–3 mol dm–3) and the aggregation constants have been calculated, the temperature dependence of which led to the determination of the thermodynamic parameters. Consequently, the substituents in the dyes affected entropically the aggregation processes. The aqueous solutions of 1 at concentrations greater than 5 × 10–3 mol dm–3 became gelatinous while those of 2, 3 and 4 did not. 19F NMR spectra have been recorded to elucidate the behaviour of 1 and 3 at the higher concentrations. The 19F NMR spectra of both dyes consisted of one singlet whose shapes did not change with dye concentration. The fluorine signals exhibited a progressive shift to higher and lower magnetic field with increasing dye concentration for 1 and 3, respectively. From this concentration dependence, the aggregation constants and the differences in the chemical shifts between the dye monomers and aggregates have been estimated. The aggregation constants determined by 19F NMR were in fair agreement with those calculated using visible absorption spectra. Furthermore, the differences in the chemical shifts between the dye monomers and aggregates have given important information concerning the relative spatial location between a fluorine atom and an adjacent aromatic ring.

Gelation of an aqueous fluorinated dye solution

The gelation of aqueous solutions of sodium 1-(3,5-bistrifluoromethylphenylazo)-2-hydroxy-6-naphthalenesulfonate is investigated by means of 19F NMR spectroscopy.

Introduction of a trifluoromethyl group into sodium 1-phenylazo-2-hydroxy-5-benzenesulfonate

Abstract The syntheses of sodium 1-(2-trifluoromethylphenylazo)-2-hydroxy-5-benzenesulfonate, sodium 1-(3-trifluoromethylphenylazo)-2-hydroxy-5-benzenesulfonate, and sodium 1-(4-trifluoromethylphenylazo)-2-hydroxy-5-ben-zenesulfonate is reported and the solubility of these dyes in water was found to be dependent on the position of the trifluoromethyl group. Derivatives containing a methyl group could not be prepared, showing that the coupling reaction is affected by the substituent of the diazotized aniline derivatives. The extinction coefficients of the aqueous dye solutions did not change within the concentration range 1 × 10 −5 to 1 × 10 −3 mol dm −3 , which suggests that the dyes do not aggregate at these dye concentrations. The sorption behavior of the dyes by a nylon 6 film was investigated and compared with that of the fluorinated derivatives of sodium 1-phenylazo-2-hydroxy-6-naphthalenesulfonate. The intrinsic binding constants for the former dyes were found to be much smaller than those for the latter dyes.

pH Indicator with dual 19F NMR and VIS responses

A pH indicator, sodium 1-(4-N,N-dimethylaminophenylazo)-2-trifluoromethyl-4-benzenesulfonate, has been prepared, which makes it possible to measure using two kinds of spectroscopy, i.e.19F NMR and VIS spectroscopy.