• K Rajasekaran

Articles written in Journal of Chemical Sciences

• Guest-host interactions in the cleavage of phenylphenyl acetates by 𝛽-cyclodextrin in alkaline medium

Kinetics of cleavage of phenylphenyl acetates (PPA) and several para-substituted PPAs in basic aqueous sodium carbonate-bicarbonate buffer containing 𝛽-cyclodextrin (CD) have been studied. The reaction exhibits saturation type kinetics and CD accelerates the rate of cleavage by the formation of 1G : 1H inclusion complex. The kinetic results indicate that aryloxy moiety of PPA is included in the hydrophobic cavity of CD. The overall rate constants for the cleavage of the [CD-ester] complex correlate with the Hammett 𝜎-constants and Hansch hydrophobicity parameters 𝜋. At higher concentrations of CD, there is an additional catalysis due to the formation of weak 1G : 2H complex.

• Micellar catalysis in the retro-Knoevenagel reaction of ethyl-𝛼-cyanocinnamates

Kinetics of base catalysed hydrolytic cleavage of ethyl 𝛼-cyanocinnamate (ECC) and several para-substituted ECC have been investigated spectrophotometrically in the presence of anionic surfactant sodium laurylsulphate (NaLS). The rate of cleavage of ECC was retarded by NaLS. The pseudo-first order rate constants, $k_{\text{obs}}$, correlate with the Hammett $\sigma^+_p$ - constants. The $\rho^+$ value (0.86) in aqueous medium is less than $\rho^+$ value (1.11) in 0.02 M NaLS. Kinetic data were analysed by Menger-Portnoy and Piszkiwicz model. The substrate-micelle binding constants, $K_s$, correlate with the Hammett 𝜎-constants and Hansch hydrophobicity constants - 𝜋 of the substituents.

• Guest-host interactions in the alkaline bleaching of triphenylmethane dyes catalysed by 𝛽-cyclodextrin

The rates of alkaline bleaching of triphenylmethane dyes crystal violet (CV), malachite green (MG) and rosaniline (RA) have been measured spectrophotometrically in an aqueous medium at 30°C in the presence of 𝛽-cyclodextrin (CD). At lower concentrations of CD, CV forms productive 1 : 1 (G : H) complex. At higher concentrations of CD, it forms unproductive 1 : 2 (G : H) complex. For the bleaching of MG, CD accelerates or decelerates the rate depending on pH of the medium by forming 1 : 1 (G : H) inclusion complex. Analysis of rate data shows that MG undergoes fading by mixed order process. CD decelerates the water reaction and accelerates hydroxide ion reaction. In the case of RA, both water reaction as well as hydroxide ion reaction are retarded by CD by the formation of inclusion complex.

• # Journal of Chemical Sciences

Volume 134, 2022
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Posted on July 25, 2019