B. M. Choudary

Knoevenagel and aldol condensations catalysed by a new diamino-functionalised mesoporous material

Knoevenagel and aldol condensations have been reported by a new diamino-functionalised MCM-41 catalyst synthesised by condensation of the trimethoxysilylpropylethylenediamine on MCM-41. This solid base catalyst is found to be very efficient with reusability for a number of times with consistent activity.

The first example of Michael addition catalysed by modified Mg–Al hydrotalcite

Selective 1,4-additions (Michael reactions) on methyl vinyl ketone, methyl acrylate, simple and substituted chalcones by donors such as nitroalkane, malononitrile, diethylmalonate, cyanoacetamide and thiols were catalysed by solid base, modified Mg-Al hydrotalcite as catalyst in quantitative yields in liquid phase under mild reaction conditions. Products of undesirable side reactions resulting from 1,2-addition, polymerisation and bis-addition are not observed. The work-up procedure is simplified by simple filtration with the use of solid bases.

Catalytic C–C Bond Formation Promoted by Mg–Al–O–t-Bu Hydrotalcite

Abstract Mg–Al–O–t-Bu-hydrotalcite catalyst was found to be an efficient, environmentally attractive and selective solid base catalyst for 1,4 Michael addition. Mg–Al–O–t-Bu hydrotalcite is also effective for simple synthesis of α,β-unsaturated esters and nitriles by condensation of the corresponding activated carboxylic esters or nitriles with various aldehydes by Knoevenagel condensation. These reactions proceeded at room temperature at a greater rate in the presence of Mg–Al–O–t-Bu hydrotalcite than in the presence of any of the other catalysts examined.

Acylation of aromatic ethers with acid anhydrides in the presence of cation-exchanged clays

Abstract Friedel–Crafts acylation of aromatic ethers with acid anhydrides in the presence of mesoporous material, cation-exchanged K10 montmorillonite (M n + – mont., where M n + =Fe 3+ , Zn 2+ , Cu 2+ , Al 3+ and Co 2+ ) was investigated. Fe 3+ - and Zn 2+ -exchanged montmorillonites displayed higher activities ascribed to the synergistic effect of Bronsted and Lewis acidities. Selective acylation is a significant achievement with the formation of 1-acyl-2-methoxynaphthalene, 4-acyl anisole and 4-acyl veratrole from respective aromatic ethers.

Iron pillared clays-efficient catalysts for Friedel-Crafts reactions

Abstract Friedel-Crafts alkylations of aromatic hydrocarbons have been carried out in the presence of a series of clay catalysts originating from K10 montmorillonite and Kunipia. It was found that the iron pillared clays (FePILCs) were the most efficient catalysts producing quantitative conversions with greatly reduced amounts of catalysts in lesser reaction times. Their efficiency is attributed to the higher Fe 3+ contents in the catalysts and the pillaring effect.

Layered double hydroxide fluoride: a novel solid base catalyst for C–C bond formation

LDH-F hydrotalcite catalysts are found to be an efficient, environmentally attractive and selective solid base catalysts for 1,4-Michael addition and also for simple synthesis of α,β-unsaturated esters and nitriles by Knoevenagel condensation. The catalyst displayed unprecedented catalytic activity both in Knoevenagel and Michael reactions under mild liquid phase conditions at a greater rate compared with known solid bases and fluoride catalysts. The present ecofriendly catalyst is a potential alternative to soluble bases.

Mg–Al–O–t-Bu hydrotalcite: a new and efficient heterogeneous catalyst for transesterification

Normal and β-ketoesters have been successfully transesterified with primary, secondary, unsaturated, allylic, cyclic, hindered alcohols and amines by Mg-Al-O-t-Bu hydrotalcite catalyst for the first time affording excellent yields of products at a faster rate under heterogeneous catalysis.

Hydrogenation of acetylenics by Pd-exchanged mesoporous materials

Pd/Si-K10 and Pd/MCM-41 were prepared by exchange in organic media of mesoporous Si modified K10 clay and Na-Al-MCM-41 and the efficiency of these catalysts versus microporous Pd/Y-zeolite is reported in the hydrogenation in the liquid phase of olefins, acetylenes and semi-hydrogenation of acetylenes.

New and ecofriendly options for the production of speciality and fine chemicals

Earlier research efforts in the area of catalysis have focused on large volume, low value products of petroleum and petrochemical industry since the benefits of catalytic processes are enormous in terms of simplification of process technology, atom economy, effluents and finally economy. Fine and specialty chemicals industry with its massive profits realized through huge value addition had endeavored on product innovation. The emerging global competitiveness and public outcry against large amounts of effluents prompted to translate the knowledge of catalytic processes to the fine chemicals industries. In this article, multidirectional efforts towards atom economy, zero emission of effluents and simplification of the processes in the oxidation of olefins, alkenes, alcohols and amines are discussed. Various options encompassing both homogeneous and heterogeneous systems have been explored in the said reactions. The application of microporous and mesoporous heterogeneous catalysts for various oxidations seems to be ideal.

FERROUS SAPONITE FROM THE DECCAN TRAP, INDIA, AND ITS APPLICATION IN ADSORPTION AND REDUCTION OF HEXAVALENT CHROMIUM

Abstract A green-colored clay mineral occurring on the walls of amygdaloidal cavities and along fractures in the Deccan flood basalts at Killari, Maharashtra, India has been identified as iron-rich saponite, with chemical composition (Na0.60K0.04Ca0.47)(Mg2.05Fe2+3.95)(Si6.45Al1.55)O20(OH)4. The XRD data of the Killari sample with d (001) = 1.70 nm and b0 = 0.9275(2) nm conform to that of ferrous saponite. The FTIR spectra show vibrational bands typical of trioctahedral smectites. Differential thermal and thermogravimetric analyses show strong endothermic peaks due to dehydroxylation at 390-420 and 1070-1130 K accompanied by weight losses of 17 and 2.3 wt%. A weak exothermic peak at about 1220 K is also observed. These peaks are characteristic of smectites. 29Si and 27Al MAS NMR studies show that silicon and most of the aluminum in the clay mineral are in fourfold coordination. We have demonstrated for the first time the usefulness of ferrous-saponite in reduction of hexavalent chromium. X-ray photon electron spectroscopic (XPS) studies of the fine clay sample treated with dichromate solution show that this ferrous saponite has the capability of adsorbing and reducing hexavalent chromium to the trivalent state.