
TY  - JOUR
A1  - Stunzi, H 
T1  - Derivatives of isatin in aqueous solution. II. Z-E isomerism in isatin &#946;-thiosemicarbazones
JF  - Australian Journal of Chemistry
JO  - Aust. J. Chem.
Y1  - 1981
VL  - 34
IS  - 2
SP  - 373
EP  - 381
KW  - 
UR  - https://doi.org/10.1071/CH9810373 
N2  - The species and reactions of &#946;-thiosemicarbazonoisatin-5-sulfonate (2) which cause hysteresis in pH titrations in aqueous solution [I 0.15 M (KNO3) at 37º] were studied by pH-metric and kinetic examination, and u.v. and n.m.r. (1H and 13C) spectroscopy. In acidic-to-neutral solutions, this compound is stable in the Z configuration (HLZ. Rapid deprotonation gives the species LZ which slowly isomerizes to the E configuration (LE). On fast protonation, the species HLE is obtained with a smaller pKa value than its isomer HLZ--the cause for the observed hysteresis. The pKa values of the species HLZ and HLE (9.92 and 7.41, respectively) were obtained from fast pH titrations. The rate law for the Z-E isomerization was obtained by examination of the variation of pH with time, when addition of base was discontinued. The equilibrium constants for the isomerizations are [HLZ]/[HLE] = 14 and [LE]/[Lz] = 23. Similar results were found for the 1-methyl derivative (3) and for &#946;-semicarbazonoisatin-5-sulfonate (4). 
ER  -

