Novel and versatile solid superbases derived from magnesium–zirconium composite oxide and their catalytic applications

Zhao, Jin; Xie, Jun; Au, Chak Tong; Yin, Shuang

doi:10.1039/c3ra46559d

Cited by 15 publications

(5 citation statements)

References 36 publications

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“…However, reactions with aliphatic aldehydes and aldehydes with big molecular size are comparatively slower than simple aldehydes showing moderate yield (52–65%, entries 12–13) within 5 h. With diethyl malonate as active methylene compound, the acidity of the acidic protons decreases due to two ester groups, thereby increasing the reaction time for all substrates and giving 70–90% conversion and 100% selectivity within 4–8 h. Polycyclic aromatic aldehydes, such as 1-naphthaldehyde, also reacted efficiently, giving high conversion to the product. It is observed that uncalcined KOH/HT with base strength in the range of 12.7 < H – < 15 shows comparable results to calcined mixed oxide catalyst, i.e., 21 wt % MgO–ZrO 2 and 10.3 wt % K–MgAl(O), having base strength 26.5 ≤ H – < 33.0 (Table , footnotes c and d). This can be understood as high BET surface area of KOH/HT compared to other two made the reaction comparable to each other.…”

Section: Resultsmentioning

confidence: 88%

Comparative Study of Potassium Salt-Loaded MgAl Hydrotalcites for the Knoevenagel Condensation Reaction

et al. 2018

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A series of potassium salt-loaded MgAl hydrotalcites were synthesized by wet impregnation of KNO 3 , KF, KOH, K 2 CO 3 , and KHCO 3 salts over calcined MgAl hydrotalcite (Mg–Al = 3:1). The samples were characterized by X-ray diffraction, Fourier transform infrared, thermogravimetry–differential thermal analysis, scanning electron microscopy, and N 2 absorption–desorption techniques to investigate their structural properties. The results showed formation of well-developed hydrotalcite phase and reconstruction of layered structure after impregnation. The prepared hydrotalcites possess mesopores and micropores having pore diameters in the range of 3.3–4.0 nm and Brunauer–Emmett–Teller surface area 90–207 m 2 g –1 . Base strengths calculated from Hammett indicator method were found increasing after loading salts, where KOH-loaded hydrotalcite showed base strength in the range of 12.7 < H – < 15, which was found to be the preferred catalyst. Subsequently, KOH loading was increased from 10 to 40% (w/w) and catalytic activity was evaluated for the Knoevenagel condensation reaction at room temperature. Density functional theory calculations show that among all of the oxygen atoms present in the hydrotalcite, the O atom attached to the K atom has the highest basic character. In this study, 10% KOH-loaded hydrotalcite showing 99% conversion and 100% selectivity was selected as the preferred catalyst in terms of base strength, stability, and catalytic efficiency.

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Section: Resultsmentioning

confidence: 88%

Comparative Study of Potassium Salt-Loaded MgAl Hydrotalcites for the Knoevenagel Condensation Reaction

et al. 2018

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“…The OH − activated the PS to produce •SO 4 − and •O 2 − , and then •SO 4 − reacted with OH − to yield •OH, which was similar to that of the base-activated persulfate [ 11 ]. As for some contaminants with high acidity constants, superbases may also directly deprotonate them, making them more susceptible to oxidation, especially in the non-aqueous-phase liquid (NAPL) phase [ 13 , 16 ]. The presumed activation mechanism of the bases is shown in Figure 2 .…”

Section: Resultsmentioning

confidence: 99%

“…DCF removal was almost completely suppressed when methanol existed in the solution, indicating that free radicals played dominant roles in the two oxidative systems. The tert-butanol (TBA) reduced the DCF removal ratio by 16.2% and 24.5%, respectively, which indicated that •OH played a more important role than •SO 4 − . The DCF removal ratios after a CuCl 2 addition were 21.3% and 34.8%, respectively, which were slightly lower than those of the control (23.1% and 36.6%), indicating that •O 2 − might exist in the systems.…”

Section: Identification Of Free Radical Speciesmentioning

confidence: 99%

Degradation of Diclofenac by Loaded Solid Superbase-Activated Persulfate

Shi,

Wang,

Gao

et al. 2023

IJMS

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Alkali-activated persulfate (PS) is widely used in situ in chemical oxidation processes; however, studies on the innovation of the alkali activation process are very limited. Two supported solid superbases, namely KNO3/γ-Al2O3 (KAl) and KNO3/SBA-15/MgO (KSM), respectively, were prepared and used to activate persulfate to degrade DCF in this work. The results showed that the superbases elevated the solution pH once added and thus could catalyze persulfate to degrade diclofenac efficiently above pH 10.5. The catalytic efficiency of KAl was close to that of sodium hydroxide, and that of KSM was the highest. The mechanism might be that, in addition to raising the solution pH, some potassium existed as K2O2, which had a strong oxidizing effect and was conducive to DCF removal. Hydroxyl, sulfate and superoxide radicals were all found in the reaction system, among which hydroxyl might play the most important role. The material composition ratio, common anion and humic acid all had some influences on the catalytic efficiency. A total of five intermediates were found in the KSM/PS oxidation system, and six oxidation pathways, which were hydroxylation, dehydrogen, dechlorination, dehydration, decarboxylation, and C-N bond breakage, might be involved in the reaction process. Several highly toxic oxidation products that should be paid attention to were also proposed.

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“…In recent years, an exponential growth in the study of coordination polymers (CPs) is related to their potential applications in gas storage/separation, − sensing, − heterogeneous catalysis, , magnetism, etc. For such applications, important features in CPs are pore/cavity sizes and shapes, , open Lewis acid sites, , and functional organic moieties. − Therefore, their participation in highly efficient catalysis to promote organic transformations with size-, regio-, and stereoselectivity, in a manner similar to inorganic zeolites. ,,− As heterogeneous and recyclable catalysts, many functional CPs have been explored to promote organic reactions, − including alkylation of aromatics, Henry reaction, cyanosilylation of aldehydes, Diels–Alder reaction, transesterification of esters, ring-opening reaction of epoxides, Knoevenagel condensation, − etc. For the synthesis of fine chemicals and pharmaceuticals, one of the most useful C–C bond-forming reactions is between aldehydes and compounds containing active methylene groups, known as Knoevenagel condensation. ,,− This reaction is conventionally catalyzed by bases or Lewis acids and mostly studied in homogeneous systems under conditions with attendant difficulties in catalyst recovery and recycling. , Currently, efforts have resulted in the construction of functional CPs via incorporation of various functional groups, such as −OH, −NH 2 , −CONH–, and...…”

Section: Introductionmentioning

confidence: 94%

Engineering a Nanoscale Primary Amide-Functionalized 2D Coordination Polymer as an Efficient and Recyclable Heterogeneous Catalyst for the Knoevenagel Condensation Reaction

Markad

Khullar

Mandal

2018

ACS Appl. Nano Mater.

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This work reports the design, structural characterization, and catalytic behavior of the first example of primary amide-functionalized coordination polymers (CPs), namely, {[Cd 2 (2-bpbg)(fum) 2 (H 2 O) 2 ]•8.5H 2 O} n (1) (where 2-bpbg = N,N′-bis(2-pyridylmethyl)-1,4-diaminobutane-N,N′-diacetamide and fum = fumarate). CP 1 is synthesized from a one-pot selfassembly of starting materials in methanol under ambient conditions in excellent yield and purity, allowing an easy access to multigram quantities of it within few hours. As an example, CP 1 was used as a highly efficient heterogeneous catalyst in the carbon−carbon bond-forming Knoevenagel condensation reaction for the conversion of benzaldehyde to benzylidene malononitrile. CP 1 possesses both Lewis acidic and Brønsted basic character for the presence of unsaturated metal sites and primary amide groups, respectively, making it a highly competent bifunctional catalyst for such type of reactions. Surprisingly, on the one hand, 100% conversion was observed using only 2 mol % catalyst within 1 h at 27 °C in methanol. On the other hand, 2 mol % and 3 mol % catalyst loadings but without a solvent gives 93% and 100% conversions, respectively, in 1 h at 27 °C. CP 1 is far better than those reported in the literature. To prove the uniqueness and efficiency of the primary amide-based ligand, a similar compound with a pyridyl-based ligand was also synthesized, {[Cd 2 (tpbn)(fum) 2 ]•6H 2 O} n (2) (where tpbn = N′,N′,N″,N″-tetrakis(pyridin-2-ylmethyl)butane-1,4-diamine). With CP 2 under the same catalyst loading and conditions (2 mol %, 27 °C, 1 h), only 28% conversion was observed. This demonstrates that selective heterogeneous catalytic properties of 1 over 2 are due to the presence of the primary amide moieties and open metal sites. Moreover, CP 1 can easily be separated from the reaction mixture and reused for five consecutive cycles without significant loss of its activity. Both 1 and 2 were fully characterized by elemental analysis, infrared spectroscopy, thermogravimetric analysis, and single-crystal and powder X-ray diffraction. These crystallize in the triclinic P1̅ space group, showing their isostructural nature and three-connected, uninodal {6 3 } honeycomb net topology.

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Novel and versatile solid superbases derived from magnesium–zirconium composite oxide and their catalytic applications

Cited by 15 publications

References 36 publications

Comparative Study of Potassium Salt-Loaded MgAl Hydrotalcites for the Knoevenagel Condensation Reaction

Comparative Study of Potassium Salt-Loaded MgAl Hydrotalcites for the Knoevenagel Condensation Reaction

Degradation of Diclofenac by Loaded Solid Superbase-Activated Persulfate

Engineering a Nanoscale Primary Amide-Functionalized 2D Coordination Polymer as an Efficient and Recyclable Heterogeneous Catalyst for the Knoevenagel Condensation Reaction

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