- 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
-
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.
- Gainza,Konyeaso,Asenjo
-
p. 226 - 232
(2007/10/02)
-
- Substitution reactions of benzethonium chloride with ion associates of bromocresol green - quinine and bromophenol blue - quinine in dichlormethane
-
An excess concentration of base quinine (Q) reacts with a sulphonphthalein diacidic dye XH2, (bromocresol green, BCGH2, or bromophenol blue, BPBH2) in dichlormethane solution to form an ion associate (X(2-)(QH21+)2) of stoichiometry 1:2 (dye:amine).Benzethonium chloride (CIB) reacts with the 1:2 ion associate to form an ion associate (QH1+,X2-,B1+) and quinine hydrochloride ClQH(1+).This substitution reaction is a chemical equilibrium with formation constants of 1.50+/-0.67, 1.64+/-0.54, 1.07+/-0.29, 1.04+/-0.20, and 0.84+/-0.26 for BCG and 1.86+/-0.59, 1.47+/-0.23, 1.40+/-0.65, 1.13+/-0.37, and 1.11+/-0.27 for BPB at 283.16, 288.16, 293.16, 298.16, and 303.16 K respectively.The thermodynamic parameters determined by van't Hoff's equation are ΔH0 = -21.766+/-7.482 kJmol-1, ΔS0 = -73+/-51 Jmol-1K-1, and ΔG0 = -1.134+/-0.972 kJmol-1 for BCG and ΔH0 = -18.678+/-7.482 kJmol-1, ΔS0 = -61+/-26 Jmol-1K-1, ΔG0 = -0.916+/-0.401 kJmol-1 for BPB (ΔG0 at 293.16K; and ΔH0 and ΔS0 determined in the range 283-303K). Key words: bromocresol green-quinine-benzetonium, ion associate mixture, bromophenol blue-quinine-benzethonium, equilibrium constants, thermodynamic parameters.
- Gainza, Alberto Hernandez,Konyeaso, Roy Ikemefula
-
p. 937 - 944
(2007/10/02)
-
- Antiglaucoma agents
-
Pharmaceutical compositions and a method for reducing intraocular pressure by topically applying a carboxyalkyl dipeptide are disclosed.
- -
-
-
- Antiglaucoma agents
-
Pharmaceutical compositions and a method for reducing intraocular pressure by topically applying a carboxyalkyl dipeptide are disclosed.
- -
-
-