Visible and Ultraviolet Absorption Spectra of 1,3,5-Trinitrobenzene in Water in the Presence of Sodium Hydroxide

Abstract

Abstract (1) Absorption spectra of the colored solutions of 1,3,5-trinitrobenzene and various concentrations of sodium hydroxide in water have been measured at 25°C. The colored solution shows absorption bands at 260, 300 and 440∼500mμ. The absorbances of the visible absorption bands increase below the sodium hydroxide concentration, about 0.6 n, but decrease above the sodium hydroxide concentration, as the concentration of sodium hydroxide increases. On the other hand, the 260 and 300 mμ bands, observed above the sodium hydroxide concentration, about 0.4 n, increase their absorbances with an increase in concentration of sodium hydroxide. These lead to the suggestion that the visible absorption bands are due to [Trinitrobenzene·OH]− and the 260 and 300 mμ bands are due to [Trinitrobenzene·2OH]2−. (2) Below the sodium hydroxide concentration, about 0.6 n, Benesi and Hildebrand’s equation holds for the colored solutions, giving an equilibrium constant of 2.7 for the reaction between trinitrobenzene and hydroxyl ion in water at 25°C. (3) On keeping the colored solution to stand for long hours, the 260 and 300 mμ bands and the visible absorption bands decrease their absorbances, while an absorption band appears at about 350 mμ. (4) When an aqueous solution of hydrochloric acid is added into the colored solution with a high concentration of sodium hydroxide, the absorbances of the visible absorption bands increase. The 260 mμ band and the visible absorption bands disappear by adding a solution of hydrochloric acid, enough to neutralize the sodium hydroxide contained in the solution. By the addition of acids, [Trinitrobenzene·OH]− and [Trinitrobenzene·2OH] 2− seem to change into trinitrobenzne reversibly.