Green and Sustainable Tandem Catalytic Approach for Fine-Chemicals Synthesis Using Octahedral MnO₂ Molecular Sieve: Catalytic Activity versus Method of Catalyst Synthesis

Abstract

Octahedral MnO 2 molecular sieve (OMS) was prepared using hydrothermal synthesis route in the absence and in the presence of urea. OMS was also prepared by solvent free method.Catalysts were characterized by the complementary combination of X-ray diffraction, N 2adsorption, scanning electron microscope, UV-visible spectroscopy, thermo gravimetric analysis, and NH 3 & CO 2 temperature programmed desorption techniques. Catalysts were investigated in the oxidation of benzyl alcohols, hydration of aromatic/heterocyclic nitrile and condensation reactions (Knoevenagel and Aldol). Furthermore, applicability of the catalyst was extended in one-pot tandem conversion of benzyl alcohol to 2-benzylidenemalononitrile, (E)-chalcone, and 2,3-dihydro-1,5-benzothiazepine. 2-Benzylidenemalononitrile and (E)-chalcone were prepared by two steps tandem reactions from benzyl alcohol, whereas 2,3-dihydro-1,5-benzothiazepine was prepared by three steps tandem reaction from benzyl alcohol. Recycling study show that no significant decrease in the catalytic activity was observed even after five recycles. To the best of our knowledge, this is the first report, which shows that OMS materials obtained using different synthesis methods exhibited significant difference in the catalytic activity in the above mentioned reactions. flask fitted with a condenser. Product was filtered, washed with deionised water, and dried at 120 C for 8-10 h. Material is designated as OMS-2 (Yield = 80%). Synthesis of OMS-2 by solvent free methodOMS-2 was prepared under solvent free condition by following the reported procedure. 33 In a typical synthesis, 2.37 g KMnO 4 (0.06 mol) and 5.51 g (0.09 mol) of Mn(Ac) 2 .4H 2 O were mixed and grounded in a mortar. The mixed powder was kept in a Teflon lined autoclave at 120C for 12 h. The resulting black product was thoroughly washed with deionised water to remove any ions which may remain in the product, and dried at 120C for 8-10 h. Material is designated as OMS-2-SF (Yield = 56 %). Hydrothermal synthesis of OMS-2 using urea 8 mmol of KMnO 4 (1.26 g) was dissolved in 20 mL of deionised water. 28 mmol urea (1.68 g) was added (in 15 minutes) to the solution and the reaction mixture was stirred for 30 minutes at ambient condition. After 30 min, resulting solution was added drop wise to a vigorously stirred mixture of MnSO 4 .H 2 O (10.5 mmol, 1.77 g in 6 mL water) and conc. HNO 3 (0.6 mL). The reaction mixture was refluxed for 24 h in a round bottom glass flask fitted with a condenser. Product was filtered, washed with deionised water, and dried at 120C for 8-10 h. OMS-2 material prepared with urea is designated as OMS-2-U (Yield = 99 %). Catalyst characterizations X-ray diffraction (XRD) patterns were recorded in the 2θ range of 5-80° with a scan speed of 2°/min on a PANalytical X'PERT PRO diffractometer using Cu Kα radiation (λ=0.1542 nm, 40 kV, 40 mA) and a proportional counter detector. Nitrogen adsorption measurements were performed at -200C by Quantachrome Instruments, Autosorb-IQ volumetric adsorption analyzer....

Simple Synthesis of TiO2/MnOx Composite with Enhanced Performances as Anode Materials for Li-Ion Battery

“…One of the promising candidates, MnO2, has attracted a lot of research attentions, due to a large theoretical capacity of 1232 mAh/g, relatively low thermodynamic equilibrium voltage and electromotive force [4] as well as rich resources on earth and environmental friendliness [5][6][7][8][9][10]. In these several decades, a wide range of MnO2 materials with different crystallographic structures are prepared in the literature including α, β, γ and δ phases which are classified on the basis of MnO6 octahedral building blocks [11]. However, most of the transition metal oxides including MnO2 have the following problems including: (1) large volume expansion and contraction during charge and discharge processes resulting in pulverization of the particles as well as electrode films [12,13] and (2) intrinsically low electrical and ionic conductivity [14], both of which lead to unsatisfactory performances.…”

Bicatalytic Multistep Reactions En Route to the One‐Pot Total Synthesis of Complex Molecules: Easy Access to Chromene and 1,2‐Dihydroquinoline Derivatives from Simple Substrates

“…Conveniently, tandem/domino processes could be triggered the introduction of an electrophilic carbonyl function. Multicatalytic processes based on an oxidation as the first step involved for example a Cu-TEMPO/peptide catalysis, [10] a Pd NPs-catalysed oxidation/supported amine-catalysed aldolisation, [11] TPAP/NMO-catalysed oxidation/prolinol derivative-catalysed conjugated addition, oxidation/Knoevenagel condensation catalysed by octahedral MnO2 molecular sieve, [12] or oxidation/Biginelli condensation in mechanochemical conditions, [13] for example. Recently, the one-pot synthesis of flavones was proposed catalysed by Au NPs supported on LDH (Layered Double Hydroxide) for which transient alcohols formed upon an aldol reaction were oxidised and further cyclised.…”

Efficient Synthesis of α,β‐Unsaturated Ketones from Primary Alcohols and Ketones over Mg2+‐Modified NiGa Hydrotalcites

“…Acetophenone is a common substrate in the investigation for the oxidation/aldol condensation tandem reaction. To our delight, excellent conversion and a high 88.9% isolated yield of the corresponding chalcone could be obtained under the present catalytic system (Table , entry 12), higher than MnO 2 molecular sieve . In contrast to dione, cyclohexanone and cycloheptanone gave excellent yield of the condensation products (Table , entries 13 and 14), further elucidating the existence of the steric hindrance.…”

“…Urea TiN nanoparticle was found to be active catalyst only in the reaction between benzyl alcohol and acetophenone . In the same reaction, octahedral MnO 2 could give a high 92.3% conversion of benzyl alcohol with a 84.9% selectivity of E‐chalcone . Recently, Zhang et al, have found that CeO 2 could accelerate the oxidative C–C coupling of ketones and primary alcohols to produce α, β ‐unsaturated ketones without base additives .…”