Determination of pK(a)'s for thymol blue in aqueous medium: evidence of dimer formation.
Formation constants for recrystallized thymol blue were determined in water, using the SQUAD and SUPERQUAD programs. The best model correlating spectrophotometric, potentiometric and conductimetric data was fitted with the dissociation of HL(-)=L(2-)+H(+)-log K=8.918+/-0.070 and H(3)L(2)(-)=2L(2-)+3H(+)-log K=29.806+/-0.133 with the SUPERQUAD program at variable low ionic strength (1.5x10(-4)-3.0x10(-4) M); and HL=L(2-)+H(+)-log K=8.9+/-0.000, H(3)L(2)(-) =2L(2-)+3H(+)-log K=30.730+/-0.032, H(4)L(2)=2L(2-)+4H(+)-log K=32.106+/-0.033 with SQUAD at 1.1 M ionic strength.
Balderas-Hernández
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Departamento de Quimica, Universidad Autónoma Metropolitana-Iztapalapa, Apdo. Postal 55-534, C.P. 09340, México D.F., Mexico; Facultad de Estudios Superiores Cuautitlán, U.N.A.M, Sección de Quimica Analitica, Av. Quetzalcóatl s/n Cuautitlán Izcalli, Estado de México, C.P. 54740, Mexico.
Ramírez
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MT
Rojas-Hernández
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Gutiérrez
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