Experimental correlation between the pKa value of sulfonphthaleins with the nature of the substituents groups.
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.
Balderas-Hernández
Patricia
P
Universidad Autónoma Metropolitana-Iztapalapa, Departamento de Química, Apdo. Postal 55-534, C.P. 09340 México D.F., Mexico.
Ramírez-Silva
María Teresa
MT
Romero-Romo
Mario
M
Palomar-Pardavé
Manuel
M
Roa-Morales
Gabriela
G
Barrera-Diaz
Carlos
C
Rojas-Hernández
Alberto
A
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
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