
TY  - JOUR
A1  - Stunzi, H 
T1  - Derivatives of isatin in aqueous solution. I. Kinetics of ring opening of Isatin-5-sulfonate
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1981
VL  - 34
IS  - 2
SP  - 365
EP  - 371
KW  - 
UR  - https://doi.org/10.1071/CH9810365 
N2  - The reactions of isatin-5-sulfonate anion (si-) which cause a hysteresis in pH titrations were studied by pH-metric and n.m.r, spectroscopic methods. Rapid alkalimetric titrations [I 0.15 M (KNO3),37º] gave the pKa value corresponding to the addition of OH- to si- [pKa(ring) 9.55]. The slow ring opening to the sulfonatoisatate dianion (sia2-) led to a drift of the pH values towards an equilibrium buffer region. Its pKa, value [pKa(eq) 3.44] corresponds to the reaction si-+H2O &#8596; sia 2-+H+ Rapid back-titration gave the pKa value of the ring-opened species Hsia- [pKa(open) c. 1.3]. The rate law for the ring opening d[sia]/dt=k2 [siOH](OH)+k1*[si] was obtained from the rate of change of pH. N-Methylisatin-5-sulfonate behaves analogously. 
ER  -

