Current Catalysis - Volume 5, Issue 3, 2016

Background: Specifically, this review includes: (i) a brief overview of basic structure of clay (tetrahedral and octahedral sheet); (ii) types of clays (anionic/ cationic) and their modified forms; (iii) properties of clays such as ion exchange, swelling, intercalation and cation-exchange, acidity; (iv) as well as overview of different clays like montmorillonite clay, pillard clay, organoclay and basic clay with their catalytic applications in various organic transformations. Methods: The objective to write this review was to provide introductory information to those young researchers who are neophytes in the area of clay science and clay catalysis. In the first part of the review, we discussed the basic structure, properties and applications of natural clays. Montmorillonite clay has great importance in the area of catalysis due to their environmental compatibility, low cost, high selectivity, reusability and operational simplicity. Porosity and stability of montmorillonite clay are improved by pillaring, which leads to materials known as pillared clays (PILC). These materials show increased surface area, pore volume, thermal and mechanical stability and, depending on the pillars, improved catalytic activity compared to the parent clays, making them suitable catalysts and adsorbents. Pillaring of clay include the addition of inorganic polycations of nanodimension to the clay interlayer and following thermal initiation. Clay pillaring can be done with a variety of inorganic polycations of Al, Zr, Ti, Cr, Fe etc. Synthesis of these polycations is mostly carried out by controlled hydrolysis of the corresponding metal cations in solutions. The metals incorporated in the pillared clay structure are crucial and make them suitable for a number of different applications, most of them belonging to the named “green chemistry”. This review shows an overview of the different reactions like oxidative cleavage of olefins, allylic oxidation of cyclic and acyclic alkenes, oxidation of phenol, benzylic oxidation of alkyl arenes, hetero-diels–alder reaction, etc. performed using pillared clays as catalysts. The second half of the review covers Organoclays, is an organically modified phyllosilicate, derived from a naturally occurring clay mineral and by exchanging the original interlayer cations from organocations (typically quaternary alkylammonium ions) an organophilic surface is generated, consisting of covalently linked organic moieties. The lamellar structure remains analogous to the parent phyllosilicate. Organoclays are very useful in the removal of oil from water, as a component in paint formulations or as a viscosifier for oil-based drilling fluids. Organoclays have been used in various studies aimed at environmental cleanup application and also utilized as nucleating agents in polymer chemistry. The aromatic pollutants can be remove with the help of organoclays. Clays which are exchanged with hexadecyltrimethylammonium (HDTMA) had shown ability to adsorb benzene, nitrobenzene, chlorobenzene, carbon tetrachloride and trichloroethylene. The review ended with the discussion on properties and various applications of the basic clay i.e. Hydrotalcite, also plays an important role in the area of catalysis not only from an economical viewpoint, but also due to ease of handling, simple separation and reusability. Results: In this review, we discussed the types as well as the properties of different clays (natural or synthetic) along with their basic and important applications to provide a fundamental understanding of clays to the young readers. The interlayer modification of clay generates effective heterogeneous catalytic materials for application in the field of organic synthesis and the catalyst produced with clays are recyclable, which makes them environment friendly. The clay based catalyst synthesis is simple step process as compared to others and it is easily available material. Conclusions: In future, the clay will play important role in the area of organic synthesis due to their physico-chemical properties and it will be helpful to researcher in order to achieve the high selectivity, activity, durability and recyclability in organic transformations.

Background: Ceria (CeO2) is an important catalyst component and support/ carrier and high surface area ceria is extremely useful for increasing catalytic activity in several low temperature applications such as emissions control, water gas shift (WGS), CO oxidation, and VOC combustion/destruction. The highest surface areas reported in the literature using aqueous synthetic routes, in the absence of organic solvents, are in the range of 200–260 m2/g. We report here the preparation of high surface area ceria using three different synthesis methods: 1) dry decomposition of common cerium salts as precursors, 2) precipitation, and 3) soft combustion synthesis. Methods: The three routes were studied using common and readily available cerium precursors, without using expensive templates, surfactants, alcoholic solvents, supercritical drying, or high pressure equipment. We obtained unprecedented high surface areas of >300m2/g by precipitation, after mapping out vast parameter spaces including Ce salt precursor selection, choice of base, pH, method (precipitation at constant pH or titration (pH ramp)), temperature, and aging conditions. We screened more than half of the periodic table and all the rare earth metals from Pr to Lu. Results: For dry decomposition, BET surface areas of ~170 m2/g were obtained from Ce (III) acetate and ~135 m2/g from Ce (III) oxalate and Ce (III) carbonate precursors. Using wet combustion synthesis with aqueous glyoxylic acid and ketoglutaric acid as dispersants we measured ~160 m2/g when starting from Ce (III) acetate but lower surface areas of ~120 m2/g from Ce (III) nitrate. An unprecedented surface area of ~300 m2/g was obtained by precipitation of Ce (IV) nitrate with NMe4OH after a multiparameter optimization using a 64-vessel co-precipitation robotic synthesis station. Supported ceria catalysts were prepared by impregnation with active metals and found to be highly active for the low temperature water gas shift reaction, CO oxidation, and VOC combustion. Conclusion: This work demonstrates the potential to significantly improve conventional inexpensive synthetic routes to high surface area materials with, in many cases, unprecedented high surface areas, by using high throughput mapping of multi-dimensional parameter spaces. It provides practical alternatives to both sol-gel and hydrothermal synthesis methods.

Background: Epoxides are useful and important intermediates in pharmaceutical and agrochemical industries. In particular, the opening of epoxides with alcohols is an important transformation for the synthesis of β-alkoxy alcohols which are considered as valuable organic solvents, versatile synthons and intermediates. We have synthesized simple, highly efficient and environment benign catalyst and applied for the ring opening of epoxides with alcohols at room temperature. Methods: All the chemicals were purchased from commercial sources. Solvents used for the chemical synthesis were acquired from commercial sources, were of analytical grade and used without further purification. Thin layer chromatography (Merck Kiesel 60 F254, 0.2 mm thickness) was used to monitor the progress of the reactions and the compounds were purified by silica gel (60-120 mesh) column chromatography. Determination of the purity of the substrate and reaction monitoring were accomplished by GC analysis (Shimadzu GC-2010 Plus) using N2 as a carrier gas and Rtx-5 column (30 m x 0.25 mm x 0.25 mm, Restek, USA). 1H NMR (400 MHz) and 13C NMR (100 MHz) spectra were recorded on Jeol ECX FT-NMR instrument using CDCl3 as solvent and TMS as internal reference. The chemical shift values were expressed on δ scale and the coupling constant (J) in Hz. Results: The quaternary salts of 1-(chloromethyl)-DABCO was synthesised from 1-(chloromethyl)-4- aza-1-azonia-bicyclo[2.2.2]octane tetrafluoroborate and different acids in acetone at 25 °C temperature. These salts were exhibits high catalytic activity for the ring opening of epoxides and gave corresponding β-alkoxy alcohols in good to excellent yields. Styrene oxide and phenyl glycidyl ether gave completely regioselective β-alkoxy alcohol. Conclusion: We have synthesized simple, convenient, highly efficient salts of 1-(chloromethyl)- DABCO and applied as organocatalysts (0.127 mol%) for the regioselective ring opening of epoxides with methanol. Ring opening of styrene oxide with different alcohols to afforded β-alkoxy alcohols in good to excellent yields. The cyclic epoxides gave trans-2-methoxy-cyclic alcohols in excellent yields. The catalyst also catalyzed the less reactive epoxide like glycidyl ethers, epichlorohydrin required a high loading of organocatalyst 3 (2 mol%) to complete the reaction.

Background: A novel one pot protocol has been developed to synthesize polyfunctionalized 4H-pyran derivatives directly from corresponding substituted aldehyde, malononitrile and β-keto ester using a recyclable polystyrene resin functionalized with a piperazine. The significant features of the present protocol are environmental acceptability, operational simplicity, shorter re-action time, high yields, and no chromatographic separation. The polymer catalyst was recovered and reused for four times without a noticeable decrease in the catalyst activity. 04 Methods: All products were characterized using melting point, HRMS, 1H and 13C NMR techniques. Results: The various catalysts were compared with resin bound piperazine under optimized reaction conditions and it was found that resin bound piperazine gave better yield of desired product and it was a recyclable catalyst. Different reaction parameters such as solvent, temperature, time were studied to achieve optimal catalyst performance using resin bound piperazine as a catalytic system. Conclusion: We have demonstrated that resin bound piperazine is an excellent catalyst for the synthesis of 4H-pyran derivatives. The product was isolated by simple filtration process. Also the catalyst was recovered, recycled and reused.

Background: Despite the great attempts to modify the methodology for the synthesis of α-aminonitriles, a vast majority is associated with a variety of drawback. Therefore, the development of an environmentally friendly, inexpensive and effective procedure is still in demand. In order to reach these purposes, we decided to utilize CeO2 nanoparticles as catalyst in the synthesis of α-aminonitriles. Methods: In the present work, an attempt has been made to synthesize a simple method for the preparation of Cerium oxide nanoparticles that can be used as a green, heterogeneous and an effective catalyst for one-pot three component condensation of an amine, aldehyde and trimethylsilyl cyanide in solventless conditions for the expeditious synthesis of α-aminonitriles. Results: A wide range of α-aminonitriles were synthesized by using various aldehydes, ketones and amines with TMCN in the presence of CeO2 nanoparticles at room temperature and solvent free conditions. Ketones and substituted aldehydes with electron-donating and electron-withdrawing groups were efficiently transformed into desired α-aminonitriles. Heterocyclic aldehydes are converted to corresponding products in good yields. Also, the substituted amines reacted in good to excellent yield. In these reactions, separation and purification of products were very easy because CeO2 was not soluble in organic solvents. CeO2 nanoparticles could be recovered and reused for 8 runs without any significant loss of the catalytic activity. Conclusion: In conclusion, we have introduced CeO2 nanoparticles as efficient, mild and safe catalyst for the synthesis of α-aminonitriles by a one-pot three-component condensation of aldehydes or ketones and amines with trimethylsilyl cyanide. As a result, green reaction procedure, short reaction time, simple work-up procedure and high yield of the products are some of the advantages associated with this methodology.

Background: Exploiting the twofold nature of ionic liquids as catalyst and reaction media, the synthesis of a library of 5H-benzo[a]phenothiazines has been reported. Firstly, we prepared zinc mercaptides of 2-aminobenzenethiols and 2,3-disubstituted 1,4-napthaquinones which undergo condensation in ionic liquid to generate 5H -benzo[a]phenothiazines. The ionic liquid used was [BMIM][[HSO4] which was recovered and reused for several rounds without appreciable loss in its activity. The structures of all the synthesized compounds were established by IR, 1H-NMR, 13C-NMR spectroscopy and elemental analysis. Methods: We prepared three imidazolium based ionic liquids namely, [BMIM]Br, [BMIM]BF4 and [BMIM][HSO4] and using these ILs synthesized 6,9/6,10-disubstituted 5Hbenzo[ a]phenothiazine-5-one from zinc mercaptides of substituted 2-aminobenzenethiols and 2,3- disubstituted-1,4-napthaquinones. Results: In this paper, 15 different derivatives of 5H-benzo[a]phenothiazine-5-one have been synthesized by reacting zinc mercaptide of 2-amino/2-amino-4-chloro/2-amino-5-nitro/2-amino-5-ethoxy benzenethiols with 2,3-dichloro/3-chloro-2-(2/3/4-substituted anilino)-1,4-napthaquinone in [BMIM]Br, [BMIM]BF4 and [BMIM][HSO4]. Out of the three ILs used [BMIM][HSO4] showed enhanced catalytic activity in terms of product yield and reaction time. This indicates that the catalytic activity of the ionic liquids on the condensation reaction was dependent on the Brønsted acidity of the counter anion. Thus, due to the high Brønsted acidity of hydrogen sulphate counter anion, [BMIM]HSO4 proved to be the most efficient solvent and catalyst for this reaction. The ionic liquid was further recycled and reused for five cycles without any appreciable loss in product yield. Conclusion: In conclusion, an efficient and eco-compatible methodology has been developed for the synthesis of a series of nitrogen and sulphur containing benzo[a]phenothiazines. The significant advantages of this procedure include one-pot, high yields of the products, broad substrate scope, easy work-up procedure and recyclability of the ionic liquid.

Background: Cinnamaldehyde is a valuable raw material in food, perfumery, agrochemical and pharmaceutical industries. Initially, manganate and dichromate ions were used as catalysts for oxidation of cinnamyl alcohols to cinnamaldehyde. But there are several limitations with these methods. Therefore, research is needed to replace the existing method with one which is more practical and feasible for industries. Method: Support material (Zirconia or Titania) was synthesized by ammonolysis, while supported catalysts (0.01%Pt/ZrO2, 0.01%Pd/ZrO2, 0.01%Pt/TiO2, 0.01%Pd/TiO2) were prepared by incipient wetness technique. The samples were characterized by different physicochemical techniques like Scanning Electron Microscopy (SEM), Xray Diffraction (XRD) and Energy Dispersive X-ray Spectroscopy (EDX), and used for the oxidation of cinnamyl alcohol in a batch type reactor. The products were analyzed by GC (PerkinElmer Clarus 580) equipped with FID and column (rtx@-Wax 30m, 0.5mm ID, 0.5nm), using n-nonane as internal standard. Results: The catalysts were tested for the liquid phase oxidation of cinnamyl alcohol to cinnamaldehyde. The effect of various reaction conditions as well as of different solvents on the % conversion was investigated. The maximum conversion of cinnamyl alcohol obtained was 74% with a 71.6% selectivity for cinnamaldehyde in cyclohexane as a solvent under a flow of oxygen gas as oxidant. The catalytic abilities of the catalysts were found to be in the order: 0.01%Pt/ZrO2> 0.01%Pd/ZrO2 > 0.01%Pt/TiO2 > 0.01%Pd/TiO2. The activation energy viz 17.8 kJ/mole, revealed that the reaction is diffusion controlled. Conclusion: In this study, the catalysts (0.01%Pt/ZrO2, 0.01%Pd/ZrO2, 0.01%Pt/TiO2 and 0.01%Pd/TiO2) were synthesized, and evaluated for the oxidation of cinnamyl alcohol to cinnamaldehyde. Although, high catalytic activity was noticed in cyclohexane, but high selectivity was found to occur in toluene. Based on the study, 0.01% Pt/ZrO2 is a promising catalyst for the oxidation of cinnamyl alcohol to cinnamldehyde in toluene.