The stoichiometric balances and absolute stability constants of some amines (atropine, chlorpheniramine and its maleate salt, dextromethorphan hydrobromide, methapyrilene hydrochloride, and quinine and its hydrochloride salt) were determined, using chloroform as the solvent. In chloroform, bromthymol blue was unable to replace the acid part of the amine salts. Nevertheless, the addition of water appears to help this replacement by separating the charges. The absolute stability constant values (between 2.5 X lo4 and 6.0 X lolo) indicate that the compounds formed by reacting amines with bromthymol blue are complexes in nature rather than the salts.
Keyphrases 0 Amine-bromthymol blue complexes-stoichiometric balances, stability constants 0 Bromthymol blue-amine complexes-stoichiometric balances, stability constants 0 Stability constants-amine-bromthymol blue complexes, in chloroform Several methods have been published for the quantitative determination of amines and quaternary ammonium ions, in which the acid dyes form color compounds extractable from the aqueous solution with organic solvents. The color in the organic solvent is measured spectrophotometrically. The work in biology was summarized by Axelrod (l), and a number of applications to pharmaceutical products were summarized by Higuchi and Bodin (2).
Gupta and Cadwallader (3) reported the stoichiometric balance of the thiamine-bromthymol blue complex. Schill (4), Gupta et al. (9, and Hull and Biles (6) reported the partition coefficients or equilibrium constants of these complexes between the aqueous phase and the organic solvent. In the published literature, 'here is little information available regarding the stoi-:hiometric balance, the nature of the reaction, and the stability constants of these complexes. The purpose of this research was to investigate these three properties of some amine-bromthymol blue complexes. The amines tested were: atropine, chlorpheniramine and its maleate salt, dextromethorphan hydrobromide, methapyrilene hydrochloride, and quinine and its hydrochloride salt.