Showing papers by "Shankar Narayanan published in 2002"

Esterification of salicylic acid over zeolites using dimethyl carbonate

Abstract: The esterification of salicylic acid (SA) using dimethyl carbonate (DMC) is reported for the first time. The reaction is studied in detail over zeolites Hβ, HZSM5 and HY in the temperature region 370–425 K in an autoclave under autogenous pressure. The molar ratio of SA to DMC, the reaction period and the weight of zeolite catalysts are varied. The SA conversion is over 90% for both Hβ and HZSM5 at 423 K. HY is not as effective a catalyst as the other two. Irrespective of the conversion levels the selectivity towards methyl salicylate is greater than 95%. A comparative study on the esterifying ability of DMC and methanol is reported. From the kinetic data, the energy of activation (Ea) for the esterification reaction using DMC over Hβ and HZSM5 is calculated to be 25 and 36 kcal/mol, respectively. A reaction mechanism for the esterification of SA with DMC over zeolites is proposed.

Hydrodechlorination of chlorobenzene on Nb2O5-supported Pd catalysts: Influence of microwave irradiation during preparation on the stability of the catalyst

Abstract: Catalytic hydrodechlorination of chlorobenzene was studied on Pd/Nb2O5 catalysts prepared by the conventional and the microwave heating techniques. The catalysts were characterized by X-ray diffraction (XRD), BET surface area, hydrogen chemisorption and scanning electron microscopy (SEM). The time-on-stream studies reveal that the microwave-irradiated catalyst exhibits better resistance towards deactivation than the conventionally prepared catalyst. Microwave irradiation also seems to be preferable than the high-temperature reduction adopted to increase the particle size. The microwave-irradiated catalyst also shows higher residual activity than the electrically heated catalyst at all reaction temperatures studied. This is attributed to the formation of larger particles of palladium which is in conformity with the basic observation made in the literature that hydrodechlorination is more facile on low-dispersed Pd catalysts.

A novel and environmentally benign selective route for Vitamin K3 synthesis

Abstract: The oxidation of 2-methylnaphthalene was carried out in acetic acid with aqueous hydrogen peroxide. 2-Methyl-1,4-naphthoquinone was obtained in a selectivity of nearly ≥90% at 100 °C for 3 h. The reaction has been studied by varying different parameters like concentration of hydrogen peroxide, strength of acetic acid, molar ratio of 2-methylnaphthalene to hydrogen peroxide, reaction temperature and time. Compared to the conventional preparation of Vitamin K 3 , this method could be economical and ecofriendly as the use of mineral acid and chromium salts are avoided.

The effect of zeolite on the curing of epoxy resin by polyaniline: a kinetic study

Abstract: Polyaniline sulfate-zeolite composite was prepared by emulsion polymerization. Epoxy resin was cured using polyaniline-sulfate salt and various amounts of polyaniline sulfate-zeolite composite. The kinetics of the cure reaction for an epoxy resin based on the diglycidyl ether of bisphenol A (DGEBA) with polyaniline-sulfate and polyaniline sulfate-zeolite composite have been studied using differential scanning calorimetry (DSC) under isothermal and dynamic conditions. Isothermal kinetics analysis was performed using the phenomenological model of Kamal. Dynamic kinetic analysis was performed using Kissinger's method. Copyright © 2002 John Wiley & Sons, Ltd.