title: Experimental correlation between the pKa value of sulfonphthaleins with the nature of the substituents groups.
abstract: This work presents the results obtained from a spectrophotometry study performed on some indicators of the sulfonphtaleins like phenol red (PR), thymol blue (TB), bromothymol blue (BTB), xylenol orange (XO) and methylthymol blue (MTB). During the first stage the acidity constants of some of the indicators were determined using the data from spectrophotometry, potentiometry and with the use of the software SQUAD. These were as follows: for the equilibrium 2H+BTB<-->H(2)BTB, log beta(2)=15.069+/-0.046 and for H+BTB<-->HBTB, log beta(1)=8.311+/-0.044. For the XO and the MTB five values were calculated for each, namely, for MTB: log beta(5)=42.035, log beta(4)=38.567+/-0.058, log beta(3)=32.257+/-0.057, log beta(2)=23.785+/-0.057, and log beta(1)=12.974+/-0.045 while for XO: log beta(5)=40.120+/-0.102, log beta(4)=35.158+/-0.062, log beta(3)=29.102+/-0.053, log beta(2)=21.237+/-0.044, and log beta(1)=11.682+/-0.044. During the second stage, a study was conducted on the effect of the substituents present in the indicators to determine the effect of different functional groups on the pK(a) value corresponding to the last indicator's dissociation.
authors: Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Química, Apdo. Postal 55-534, C.P. 09340 México D.F., Mexico.
authors: Patricia
authors: P
authors: Balderas-Hernández
authors: María Teresa
authors: MT
authors: Ramírez-Silva
authors: Mario
authors: M
authors: Romero-Romo
authors: Manuel
authors: M
authors: Palomar-Pardavé
authors: Gabriela
authors: G
authors: Roa-Morales
authors: Carlos
authors: C
authors: Barrera-Diaz
authors: Alberto
authors: A
authors: Rojas-Hernández
mesh_terms: D001979:Bromthymol Blue / Q000031:analogs & derivatives / Q000737:chemistry; D003198:Computer Simulation; D006863:Hydrogen-Ion Concentration; D007202:Indicators and Reagents / Q000737:chemistry*; D008956:Models, Chemical; D010636:Phenols; D010637:Phenolsulfonphthalein / Q000737:chemistry; D011522:Protons; D013056:Spectrophotometry, Ultraviolet; D013454:Sulfoxides; D013944:Thymolphthalein / Q000031:analogs & derivatives / Q000737:chemistry; D014992:Xylenes / Q000737:chemistry
chemical_list: D007202:Indicators and Reagents; D010636:Phenols; D011522:Protons; D013454:Sulfoxides; D014992:Xylenes; C002074:methylthymol blue; C013713:thymol blue; D010637:Phenolsulfonphthalein; C016833:xylenol orange; D001979:Bromthymol Blue; D013944:Thymolphthalein