Solid acid-catalyzed dehydration/Beckmann rearrangement of aldoximes: towards high atom efficiency green processes

Rare earth metal ion exchanged (La3+, Ce3+, RE3+) KFAU-Y zeolites were prepared by simple ion-exchange methods and have been characterized using different physico-chemical techniques. In this paper a novel application of solid acid catalysts in the dehydration/ Beckmann rearrangement of aldoximes; benzaldoxime and 4-methoxybenzaldoxime is reported. Dehydration/Beckmann rearrangement reactions of benzaldoxime and 4-methoxybenzaldoxime is carried out in a continuous down flow reactor at 473K. 4-Methoxybenzaldoxime gave both Beckmann rearrangement product (4-methoxyphenylformamide) and dehydration product (4-methoxybenzonitrile) in high overall yields. The difference in behavior of the aldoximes is explained in terms of electronic effects. The production of benzonitrile was near quantitative under heterogeneous reaction conditions. The optimal protocol allows nitriles to be synthesized in good yields through the dehydration of aldoximes. Time on stream studies show a fast decline in the activity of the catalyst due to neutralization of acid sites by the basic reactant and product molecules.

Dehydration of aldoximes on rare earth exchanged (La3+, Ce3+, RE3+, Sm3+) Na–Y zeolites: A facile route for the synthesis of nitriles

Rare earth exchanged Na–Y zeolites, H-mordenite, K-10 montmorillonite clay and amorphous silica-alumina were effectively employed for the continuous synthesis of nitriles. Dehydration of benzaldoxime and 4-methoxybenzaldoxime were carried out on these catalysts at 473 K. Benzonitrile (dehydration product) was obtained in near quantitative yield with benzaldoxime whereas; 4-methoxybenzaldoxime produces both Beckmann rearrangement (4-methoxyphenylformamide) as well as dehydration products (4-methoxy benzonitrile) in quantitative yields. The production of benzonitrile was near quantitative under heterogeneous reaction conditions. The optimal protocol allows nitriles to be synthesized in good yields through the dehydration of aldoximes. Time on stream (TOS) studies show decline in the activity of the catalysts due to neutralization of acid sites by the basic reactant and product molecules and water formed during the dehydration of aldoximes.

Surface Properties and Catalytic Activity of Ferrospinels Containing Cobalt, Nickel and Copper

The present study describes the surface properties and catalytic activities of ferrospinels containing Co, Ni and Cu prepared by the low temperature route. Various physico-chemical methods have been adopted to characterise the systems. The reactions carried out are the Friedel-Crafts benzoylation of aromatics and the cyclohexanol decomposition. We have attempted the sulphate modification of the ferrites and have studied the surface and catalytic properties of the sulphated analogues.The work is presented in six chapters, the last chapter giving the summary and conclusions of the results presented earlier. Our samples prove as potential catalysts for the benzoylation of aromatics , for which truly heterogeneous catalysts are rare. Again , the materials show remarkable dehydration/dehydrogenation activities during cyclohexanol decomposition. There is plenty of scope for research in this field, especially in the development of environmentally benign catalysts for acylation reactions.

Study of cyclohexanol decomposition reaction over the ferrospinels, A1−xCuxFe2O4 (A=Ni or Co and x=0, 0.3, 0.5, 0.7 and 1), prepared by ‘soft’ chemical methods

Preparation of simple and mixed ferrospinels of nickel, cobalt and copper and their sulphated analogues by the room temperature coprecipitation method yielded fine particles with high surface areas. Study of the vapour phase decomposition of cyclohexanol at 300 °C over all the ferrospinel systems showed very good conversions yielding cyclohexene by dehydration and/or cyclohexanone by dehydrogenation, as the major products. Sulphation very much enhanced the dehydration activity over all the samples. A good correlation was obtained between the dehydration activities of the simple ferrites and their weak plus medium strength acidities (usually of the Brφnsted type) determined independently by the n-butylamine adsorption and ammonia-TPD methods. Mixed ferrites containing copper showed a general decrease in acidities and a drastic decrease in dehydration activities. There was no general correlation between the basicity parameters obtained by electron donor studies and the ratio of dehydrogenation to dehydration activities. There was a leap in the dehydrogenation activities in the case of all the ferrospinel samples containing copper. Along with the basic properties, the redox properties of copper ion have been invoked to account for this added activity.