SO2 – Am (KOH) – TROPEOLIN OOO – H2O (Am – ETHANOLAMINES, MORPHOLINE) SYSTEMS ACID-BASE PROPERTIES

Abstract

The study of data on acid-base properties of model systems SO2 – KOH – TrOOO – H2O and SO2 – Am – TrOOO – H2O (TrOOO – tropeoline OOO; Am – diethanolamine (DEA), triethanolamine (TEA), N‑methylmonoethanolamine (MMEA) and morpholine (Mf) at 293 K using pH-, spectrophotometry and colorimetry methods are presented. There is a pronounced isosbestic point at 415 nm in the electronic absorption spectra of the systems SO2– Am –TrOOO– H2O (Am = MMEA, MEA and TEA; pH ≤ 7.5; T = 293 K), which indicates the presence of a dynamic equilibrium between ion-molecular forms. According to the width of the absorption spectra, the bases in the region of 2.0 ≤ pH ≤ 8.0 can be arranged in the following row: MEA > Mf > KOH > DEA > TEA > MMEA. The bases can be arranged in the following rows for the effect on optical density at 490 nm: KOH > Mf ≥ MEA > DEA ≥ TEA (at 5.5 ≤ pH < 9.0); KOH = MEA = Mf > DEA = TEA (at pH < 6.0). According to the values of optical density at 360 nm in the region of 2.0 ≤ pH < 8.5, the bases can be arranged in the following row: Mf > KOH ≥ MEA ≥ DEA > MMEA > TEA. The total color difference (ΔE76) and specific color difference (SCD) values were calculated by colorimetric method as a function of pH. The acid–base dissociation constants in the SO2 – Am (KOH) – TrOOO – H2O systems significantly depend on the structure and physicochemical properties of the organic base and differ significantly from those in the HCl (HClO4, H2SO4) – MEA – TrOOO – H2O systems. The interrelation of colorimetric functions was established (total color difference and specific color difference) of SO2 – Am – TrOOO – H2O systems with molar refraction Am, empirical function pKa – lgPow, which combines the basicity and hydrophilicity of Am, formation constants of ammonium sulfites and hydrosulfites, pH- (dpH/dpQSO2), redox- (dЕ/dpQSO2) and conductometric (Dk) titration curves of Am aqueous solutions with gaseous sulfur dioxide.