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Journal of Pharmaceutical Sciences 1994-Feb

Detection and identification of side reactions of halogenated hydrocarbon solvents with amines of pharmaceutical interest by secondary processes to the neutralizations of sulphonphthaleinic dyes with these amines.

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A Hernandez Gainza
R I Konyeaso
R A Asenjo

Keywords

Abstract

The neutralization reactions between amines and diprotic acid dyes in organic solvents generate (dye-, amineH+) and [dye2-, (amineH+)2] ion associates that show two absorption bands in the visible spectrum. An unidentified third absorption band; which appears with a high amine concentration, proves that halogenated hydrocarbon solvents (dichloromethane, chloroform, 1,2-dichloroethane, and carbon tetrachloride) give side reactions with amines (atropine, tropine, quinine, ephedrine, and ajmaline) that generate a quaternary ammonium salt, N-halogenalkylammonium halide ([N(+)-RX,X-]). The molecular weight of the quaternary ammonium salt is the sum of the amine and that of the solvent. The (N(+)-RX,X-) ion associated reacts with [dye2-, (amineH+)2] by substitution reactions, forming (dye2-, amineH+, N(+)-RX) and (dye2-, (N(+)-RX)2] ion associates that justify the third absorption band. The amine-solvent side reactions are of first order with respect to the amine, being very slow processes with rate constant values from 399.4 h-1 (tropine-dichloromethane reaction) to 15.8 h-1 (atropine-1,2- dichloroethane reaction). Rate constants increase with the basicity of the amine measured in the halogenated hydrocarbons employed. Rate constants also increase with a reduction in the number of the halogen atoms present in the halogenated solvent. The new visible absorption band that appears in the amine-dye neutralization gives a quick colorimetric test to bring to light this kind of side reaction in these solvents.

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