Esterification of succinic anhydride to di-(p-cresyl) succinate over M n+-montmorillonite clay catalysts

Esterification of succinic anhydride to di-(p-cresyl) succinate over heterogeneous acid clay catalysts is reported. Montmorillonite clay samples exchanged with different cations were prepared and catalytic activity of the resulting materials was investigated in the synthesis of di-(p-cresyl) succinate esters. Among the exchanged clay catalysts, Al3+ and H +-mont were found to be more active for the esterification of succinic anhydride with p-cresol. The activity of Mn+-mont was found to be directly related to the charge to radius ratio of Mn+-ions. The influence of molar ratio of reactants, reaction time, and catalyst amount on the esterification reaction was investigated. The esterification was found to follow the second order rate kinetics and the kinetic parameters such as rate constant (k), equilibrium constant (K) and Gibbs free energy (ÎG°) for the reaction have been determined. The activity of Al3+-mont clay catalyst for the esterification of succinic anhydride with phenol, m-cresol, o-cresol, p-nitrophenol and resorcinol have been studied. Regeneration and reusability of the clay catalyst has also been investigated. © 2004 Elsevier B.V. All rights reserved

Brønsted and Lewis acidity of modified montmorillonite clay catalysts determined by FT-IR spectroscopy

The surface acidity of different modified montmorillonite clay catalysts, Al3+-exchanged montmorillonite (Al3+-Mont) and aluminium pillared montmorillonite (Al-PILC) was determined by DRIFTS (diffuse reflectance Fourier transform infrared spectra) using pyridine as probe molecule. The method involved treating the clay sample directly with pyridine, drying the sample at 120 °C and recording FT-IR spectra in the region 1650 and 1350 cm−1. The spectra obtained showed well resolved absorption bands for Lewis and Brønsted acid sites in the clay catalysts. In order to understand the role of acid sites present on clay catalysts, esterification of propionic acid with p-cresol has been studied. The Brønsted acidity data obtained by FT-IR study for modified montmorillonite clay catalysts correlated well with the catalytic activity in the esterification reaction. Among the modified clay catalysts, Al3+-Mont and H+-Mont clay catalysts showed good activity and Al-PILC showed negligible activity in esterification. The inactivity of Al-PILC catalysts is attributed to the absence of Brønsted acidity

Synthesis of phenylacetates using aluminium-exchanged montmorillonite clay catalyst

Liquid phase esterification of phenylacetic acid with phenol and substituted phenols has been investigated over montmorillonite clay exchanged with H + - Al 3+ - and aluminium polyhydroxy oligomer cations. Among the catalysts studied, Al 3+ - montmorillonite dried at 100°C showed 67 conversion, while the same catalyst dried at 200deg;C showed reduced conversion of 36. Al 3+ - montmorillonite dried at 400°C and montmorillonite exchanged with aluminium polyhydroxy oligomer cations dried at 100°C and calcined at 500°C failed to bring about the reaction. Effects of mole ratio of reactants, reaction period and catalyst amount on yield of the ester and catalyst regeneration are also investigated. Esterification of phenylacetic acid with phenol, cresols, nitrophenols and resorcinol has been carried out in the presence of montmorillonite clay exchanged with H +-ions, Al 3+-ions and polyhydroxy oligomer cations of Al. Na +-montmorillonite (raw clay) was inactive, H +- and Al 3+-montmorillonites, dried at 100°C, showed 52 and 67 conversions to ester, respectively, upon refluxing the phenylacetic acid (20 mmol) and p-cresol (40 mmol) for 6 h. While Al 3+- montmorillonite dried at 200°C showed a conversion of 36 the same catalyst when dried at 400°C showed no conversion. Montmorillonite exchanged with aluminium polyhydroxy oligomers dried at 100°C and calcined at 500°C to get pillared clay (d 0 0 1=17.5 à ) failed to bring about the esterification. Effect of concentration of reactants, amount of catalyst and the reaction time on the yield of p-cresyl phenylacetate has been investigated. The esterification of phenylacetic acid with phenol and substituted phenols like m-cresol, o-cresol, p-nitro phenol and o-nitro phenol showed reduced yield due to steric factors. The activity of the clay catalyst after regeneration has also been studied. © 2004 Published by Elsevier B.V

Abundances of the elements in the solar system

A review of the abundances and condensation temperatures of the elements and their nuclides in the solar nebula and in chondritic meteorites. Abundances of the elements in some neighboring stars are also discussed.Comment: 42 pages, 11 tables, 8 figures, chapter, In Landolt- B\"ornstein, New Series, Vol. VI/4B, Chap. 4.4, J.E. Tr\"umper (ed.), Berlin, Heidelberg, New York: Springer-Verlag, p. 560-63