Acidity constants of benzidine in aqueous solutions.

Area of Science:

• Analytical Chemistry
• Physical Chemistry

Background:

• Benzidine (Bz) is an aromatic amine with significant industrial applications.
• Understanding its acid-base properties is crucial for environmental and toxicological assessments.

Purpose of the Study:

• To determine the acidity constants (K(a1) and K(a2)) of benzidine in aqueous solutions.
• To characterize the UV-Vis absorption spectra of protonated and neutral benzidine species.
• To establish the relationship between pH, spectral properties, and acidity constants.

Main Methods:

• Potentiometric titration was used to determine acidity constants at 25°C.
• UV-Vis spectrophotometry was employed to record spectra as a function of pH.
• Spectral data were analyzed in conjunction with potentiometric results.

Main Results:

• Acidity constants K(a1) = (1.11 ± 0.08) x 10⁻⁵ and K(a2) = (1.45 ± 0.12) x 10⁻⁴ were determined in water.
• Apparent mixed constants in 0.1M sodium nitrate were K(a1) = (5.37 ± 0.28) x 10⁻⁶ and K(a2) = (1.14 ± 0.09) x 10⁻⁴.
• Absorption spectra of H₂Bz²⁺, HBz⁺, and Bz were obtained with maximal absorption at 247, 273, and 278 nm, respectively.

Conclusions:

• The acidity constants and spectral characteristics of benzidine were precisely determined.
• This provides essential data for the quantification and speciation of benzidine in various chemical systems.
• The findings contribute to a better understanding of benzidine's behavior in aqueous environments.