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Micellar effects on the alkaline hydrolysis of isatin and its derivatives

Al-Ayed, Abdullah S., Ali, Mohd. Sajid, Al-Lohedan, Hamad A., Al-Sulaim, Adel M., Issa, Zuheir A., Kabir-ud-Din,
Journal of colloid and interface science 2011 v.357 no.2 pp. 393-399
alkaline hydrolysis, hydrophobicity, ion exchange, micelles, models, sodium chloride, sodium dodecyl sulfate, sodium hydroxide, surfactants, ultraviolet-visible spectroscopy
Herein we have investigated the hydrolysis of 1H-indol-2,3-dione (isatin, I) and its derivatives of different hydrophobicities, viz. N-dimethylaminomethyl indol-2,3-dione (II), N-morpholinomethyl indol-2,3-dione (III), N-pipridinomethyl indol-2,3-dione (IV), N-heptylaminomethyl indol-2,3-dione (V), N-dodecylaminomethyl indol-2,3-dione (VI), N-hexylanilinomethyl indol-2,3-dione (VII), N-decylanilinomethyl indol-2,3-dione (VIII), and N-hexadecylanilinomethyl indol-2,3-dione (IX), in the presence of an excess amount of sodium hydroxide. All the isatin derivatives were synthesized in the laboratory. The progress of the reactions was studied by exploiting UV–visible spectrophotometry. The observed rate constant, kw, increases linearly on increasing the hydroxide ion concentration, indicating first-order dependence on [OH⁻]. The effects of surfactants, cationic (cetyltrimethylammonium chloride, CTACl), and anionic (sodium dodecyl sulfate, SDS) were also investigated. The rate of reaction increased on increasing the concentration of CTACl and, after reaching a maximum, it started decreasing. Conversely, anionic micelles of SDS inhibited the rate of hydrolysis of isatin and its derivatives. The results of the effect of CTACl were analyzed using a pseudophase ion-exchange model while the inhibition by SDS was analyzed using a simple Menger–Portnoy model. The effects of added salts, such as NaBr, NaCl, and (CH₃)₄NBr, were also seen on the isatin hydrolysis. It was found that the addition of salts decreased the rate enhancement efficiency of the CTACl.