Magnetic core–shell titanium dioxide nanoparticles as an efficient catalyst for domino Knoevenagel–Michael-cyclocondensation reaction of malononitrile, various aldehydes and dimedone

Abstract

Fe3O4@SiO2@TiO2 efficiently catalysed the preparation of tetrahydrobenzo[b]pyrans by a one-pot three component reaction of aldehydes, dimedone and malononitrile at 100 °C under solvent-free conditions.

Preparation of 1,2,4,5‐tetrasubstituted imidazoles over magnetic core–shell titanium dioxide nanoparticles

“…As an example, calculations for the strongest diffraction line of 25.3° give an FWHM of 0.0157°, a crystallite size of the catalyst of ca 9 nm via the Scherrer equation ( D = Kλ /( β cos θ )) and an interplanar distance of 0.3548 nm (using the same strongest diffraction line at 25.3°) was calculated via the Bragg equation: dhkl = λ /(2sin θ ) ( λ is the wavelength of Cu radiation, 0.154178 nm). Crystallite sizes as obtained from the various diffraction lines using the Scherrer equation are found to be in the nanometre range (7.5–11.6 nm) …”

“…Fe 3 O 4 @SiO 2 @TiO 2 were synthesized by the reaction of nano‐Fe 3 O 4 with tetraethyl orthosilicate and tetrabutyl titanate successively according to previous literature (Fig. ) …”

“…1). [30,31] The X-ray diffraction (XRD) pattern of the catalyst (Fe 3 O 4 @SiO 2 @TiO 2 ) was obtained in the range of 5-70°( Fig. 2).…”

Design and identification of nano‐Mg‐[4‐methoxy phenyl‐salicylaldimine–methyl‐pyranopyrzole] Cl2 and its catalytic application on the preparation of 1‐(α‐aminoalkyl)‐2‐naphthols

“…One‐pot multi‐component reactions are important in organic chemistry because of the ability of them to prepare the related products from the reaction between three or more starting materials in one step without the creation of side products and atomic waste. Short reaction time, high efficiency, simplicity, easy work up and the lack of the need to isolate the generated intermediates during the reaction are significant advantages of these reactions …”

Silica-coated magnetic NiFe2O4 nanoparticles-supported H3PW12O40; synthesis, preparation, and application as an efficient, magnetic, green catalyst for one-pot synthesis of tetrahydrobenzo[b]pyran and pyrano[2,3-c]pyrazole derivatives

“…Catalysts used for one-pot, three-component reactions include piperidine [21], hexadecyltrimethyl ammonium bromide (HTMAB) [22], sodium bromide [23], ionic liquids [24][25][26][27][28][29], tetramethylammonium hydroxide [30], diammonium hydrogen phosphate [31], organocatalysts [32], sodium selenite [33], tetrabutylammonium bromide (TBAB) [34,35], polyaniline-silica gel [36], alum [KAl(SO 4 ) 2 Á12H 2 O] [37], rare earth perfluorooctanoates, e.g. Re(PFO) 3 [38], Caro's acid [39], amines or amino acids [40], potassium phosphate [41], PPA-SiO 2 [42], microwave irradiation [43], BF 3 ÁOEt 2 [44], magnetic core-shell titanium dioxide nanoparticles (Fe 3 O 4 @SiO 2 @TiO 2 ) [45], NH 4 H 2 PO 4 -Al 2 O 3 [46], DABCO-EtOH [47], TPPA [48], t-BuOK-t-BuOH [49], L-proline under ultrasound irradiation [50], and silica coated magnetitepolyoxometalate nanoparticles (Fe 3 O 4 @SiO 2 @NH-NH 2 -H 3 PW 12 O 40 ) [51]. Many of these methods suffer from one or more limitations, for example low yields, use of expensive reagents, long reaction times, tedious work-up procedures, and cooccurrence of several side reactions.…”