ELECTRONIC ABSORPTION SPECTRA OF ION PARIS COMPOSED OF SUBSTITUTED AMINE PICRATES IN ACETONITRILE

The spectra of the undissociated forms of triethylammonium, 2,4-lutidinium, pyridinium, and anilinium picrates in acetonitrile are shifted to shorter wavelengths as compared to the spectrum of the picrate ion. In order to calculate these spectra from the over-all spectra of 0.01 M amine picrate (BHA) solutions, the ionic dissociation constants JPbha and formation constants Kd-BHA were determined and found equal to 4.4 × 10-3 and 6 × 109 for triethylammonium, 3.6 × 10-3 and 2 × 105 for lutidinium, 3.0 × 10-3 and 6 × 3 for pyridinium, and 1.1 × 10-3 and 4 × 102 for anilinium picrates, respectively. The wavelength of maximum absorption and the absorbance index at λmax were 373 mμ and 1.92 × 104 5for picrate ion, respectively, and for the undissociated picrates in the order mentioned 356 and 1.8 × 104, 347 and 1.85 × 104, 346 and 1.74 × 104, and 348 and 1.5 × 104. It is concluded that the undissociated forms of the picrates are present mainly as ion pairs, except anilinium picrate, 20 % of which may be present in a molecular form. Qualitative confirmation of this conclusion was derived from infrared spectra. Homoconjugation constants, [B2H+]/[BH+][B], were estimated equal to 0 for triethylammonium, 8 for lutidinium, 7 for pyridinium, and 4 for anilinium from spectrophotometric data in picrate solutions containing excess base. © 1968, American Chemical Society. All rights reserved.